Review of Active and Passive Daylighting Technologies for Sustainable Building

Abstract

According to the International Energy Agency, nearly 20% of worldwide electricity is used up by lighting. This is equal to the total electricity nuclear power generates. Thus, it is needy to explore new technologies for direct use of sunlight via integrating daylight system to the building, which is cost-saving, environment-friendly, and a green solution rather than indirect conversion of electricity to lighting even from renewable sources. In this paper, we present a review on the existing technologies of daylighting systems up to date and how they can provide lighting in a building interior via collection and distribution of sunlight. Our review is a comprehensive study to embrace both passive daylighting system with stationary design and active daylighting system equipped with sun tracking. The economic feasibility, general challenges, and prospects of daylighting systems are also discussed to understand the existing problems that hinder the extensive deployment of daylighting systems. In conclusion, more research works are needed in improving the technological development of a daylighting system so that it is more affordable, environment-friendly, less energy-intensive, and easy to install and gives uniform illumination for the effective application in both commercial building and residential houses.

Full text

Review Article
Review of Active and Passive Daylighting Technologies for
Sustainable Building
Nneka Obianuju Onubogu ,
1
Kok-Keong Chong ,
1
and Ming-Hui Tan
2
1
Lee Kong Chian Faculty of Engineering and Science, Universiti Tunku Abdul Rahman, Bandar Sungai Long, 43000 Kajang,
Selangor, Malaysia
2
Faculty of Engineering and Green Technology, Universiti Tunku Abdul Rahman, Jalan Universiti Bandar Barat,
31900 Kampar, Malaysia
Correspondence should be addressed to Kok-Keong Chong; chongkk@utar.edu.my
Received 23 June 2021; Revised 13 September 2021; Accepted 5 October 2021; Published 26 October 2021
Academic Editor: K. R. Justin Thomas
Copyright © 2021 Nneka Obianuju Onubogu et al. This is an open access article distributed under the Creative Commons
Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work
is properly cited.
According to the International Energy Agency, nearly 20% of worldwide electricity is used up by lighting. This is equal to the total
electricity nuclear power generates. Thus, it is needy to explore new technologies for direct use of sunlight via integrating
daylight system to the building, which is cost-saving, environment-friendly, and a green solution rather than indirect
conversion of electricity to lighting even from renewable sources. In this paper, we present a review on the existing
technologies of daylighting systems up to date and how they can provide lighting in a building interior via collection and
distribution of sunlight. Our review is a comprehensive study to embrace both passive daylighting system with stationary
design and active daylighting system equipped with sun tracking. The economic feasibility, general challenges, and
prospects of daylighting systems are also discussed to understand the existing problems that hinder the extensive
deployment of daylighting systems. In conclusion, more research works are needed in improving the technological
development of a daylighting system so that it is more affordable, environment-friendly, less energy-intensive, and easy to
install and gives uniform illumination for the effective application in both commercial building and residential houses.
1. Introduction
The major purpose of both natural and artificial lights is to
provide good and comfortable visibility for indoor and out-
door activities throughout the day regardless of weather con-
ditions [1]. Daylighting is an introduction of natural light
into an indoor environment to reduce the energy consump-
tion by artificial light sources in the building [2, 3]. The
amount and quality of illumination enable our indoor activ-
ities to be carried out effectively especially during nighttime,
which is important to increase productivity and improve
quality of life. From the various literature, it has been discov-
ered that artificial lighting consumes as high as 40% of the
annual building energy consumption, which is one of the
major challenges for achieving the United Nations sustain-
able development goals [4]. The sun is a clean, abundant,
and sustainable energy source, which is also the most funda-
mental source of renewable energies amongst others on the
earth [2]. For residential and commercial buildings, solar
energy can be harnessed without deteriorating our natural
resources to provide heat, light, cooling (air-conditioning),
and electricity. We can directly harvest solar energy as day-
light to illuminate the indoor environment without energy
conversion loss, which can indirectly minimize energy wast-
age [5]. Daylighting system is an already existing and fast-
growing technology, which is designed to collect and distrib-
ute sunlight for effective internal illumination of a building,
hence contributing to its sustainability [4, 6–8]. A sustain-
able building is designed in such a way that it conserves or
advances the quality of life with positive influences on the
climate and natural environment, where the natural
resources can be preserved over a long period of time. Sus-
tainability in a building design should never be disregarded,
and it is crucial to bring a long-term impact to humans for
Hindawi
International Journal of Photoenergy
Volume 2021, Article ID 8802691, 27 pages
https://doi.org/10.1155/2021/8802691

the fast urbanization process recently in the world [9]. Irre-
spective of other constituents of a sustainable building, inte-
gration of daylighting system into the building architectural
design cannot be overlooked as it is the most sustainable and
healthy way of providing natural illumination inside the
building. Also, most passive daylighting systems perform
two functions of providing daylight and ventilation simulta-
neously for achieving the target of low-energy or green
building.
The visible range of photonic energy from the sun can be
extracted by using either a passive daylighting system that is
associated with the building structure or an active daylight-
ing system. Figure 1 illustrates a general idea of the two
designs [10]. The differences between passive and active day-
lighting systems are well defined by how sunlight is captured
and disseminated. In a passive daylighting system, static and
nontracking designs are adopted for collecting, reflecting,
and distributing the sunrays into the interior of a building,
which includes the application of windows, sliding glass
doors, static waveguide, and skylights. In an active daylight-
ing system, sunlight is collected by a combination of optical
and mechanical devices with a sun-tracking mechanism that
actively tracks the sun and distributes daylight into the
building’s interior via waveguide [11, 12].
The advantage of an active daylighting system is its
tracking devices, which makes it effective as daylighting
commences from the very early morning to the late evening
as compared to stationary passive daylighting systems. The
disadvantage is that the active daylighting system incurs
high initial installation cost associated with maintenance
and operational costs in the future [13]. Three major merits
of adopting passive daylighting in sustainable building
design include affordability, stress-free installation, and styl-
ishness in design [14]. The prominent benefits as indicated
by Kubba are as follows [1]:
(1) At a very affordable cost, it can easily be recon-
structed into completely built structures or even into
an ongoing construction
(2) The air indoor is of better quality as forced air mech-
anisms are eliminated using a daylighting system
(3) In passive daylighting, minimum system mainte-
nance is required as there is no mechanical device
unlike in the active daylighting system
(4) Economized or eradicated cooling and heating costs
since passive daylighting pays dividends over the
lifespan of a structure
It has been observed by expert architects of passive solar
designs that the design of buildings with passive daylighting
systems costs a bit more than buildings made of only con-
crete blocks and bricks but saves money on a long-term
basis. The challenges of integrating passive daylighting in
sustainable building designs are the following:
(1) During the selection of building materials for houses
with passive daylighting especially window glass,
costly mistakes might be made as it is a difficult task
to choose the accurate glass for the design. Selection
of the accurate glass is dependent on the location
(north, south, east, or west) of the glass in the build-
ing and the weather condition of the area of the
building location
(2) Daylighting and heat are closely associated. The use
of daylighting in the summer or countries with warm
climate all year round can cause a rise in the amount
of energy consumed by the air-conditioning system
(3) Inappropriate design of a passive daylighting system
can cause glare on items and appliances at home
such as furniture, television, fridge, and computers.
Thus, the arrangement of things in the home
requires cautious planning [15]
In this paper, various kinds of daylighting systems will
be reviewed under two major headings: “passive daylighting
systems”which are the basic types of daylighting systems
where sometimes waveguide is applied to increase the pene-
tration of daylight and “active daylighting systems”which
are advanced daylighting technologies consisted of a solar
collector with sun-tracking system and waveguide is neces-
sary for daylight distribution.
2. Technical Description of Passive
Daylighting Systems
A passive daylighting system is mostly installed in buildings
with inadequate openings from walls and is constructed such
that natural light from the sun can pass through horizontal
surfaces or rooftops of the building and into the interiors
[16]. Nevertheless, the panic over the swift reduction of
energy resources and the environmental effects of their uses
has preceded designers to reimplement passive daylighting
methods in buildings to lessen the energy consumption for
lighting [17]. Passive daylighting systems include tubular
daylight, louvers, skylights, roof windows, sloped glazing,
soda pop bottle solar light, windows, light reflectors and
shelves, and sawtooth roofs [18–38]. Table 1 shows a sum-
mary of various designs of passive daylighting systems
encompassing the design configuration, critical problems,
Tracking
solar
collector
Passive
Active
Window
(glass)
Figure 1: Active versus passive daylighting system.
2 International Journal of Photoenergy

Table 1: Summary of the various studies in passive daylighting system.
Reference Category Design
configuration Picture/drawing Critical problem of the technique Possible research work that
can be done in the future
Wikipedia [21]
Skylights
Fixed unit
skylight
(1) Skylights can only be fixed on the roof
of the building or residential house
(2) It has limited illumination area that
only covers certain distance from the
window, glazing, glass, etc.
(3) It has other associated problems of
daylighting including visual comfort,
uncontrollable brightness, and heat
(4) It can only be fixed at the top floor of
the building
More research works are
required for improving
illumination, visual comfort,
brightness, and control of the
heat inside the building.
Wikipedia [21] Operable
skylight
Wikipedia [21] Retractable
skylight
Retractable
skylights
Open area
3International Journal of Photoenergy

Table 1: Continued.
Reference Category Design
configuration Picture/drawing Critical problem of the technique Possible research work that
can be done in the future
https://vedantfacade
.com/sky-lights-3/
[25]; Cuce and Riffat
[26]
Sloped glazing
Livingstone [29]
Straight and
splayed
skylight
Straight skylight Splayed skylight
https://www.pinterest
.com/pin/
54887689184732372/
[36]
Roof
Sawtooth roof
Soda pop
bottle solar ligh
Roof monitor
and clerestory
Sawtooth roof
Light reectors
and shelves
Conventional
side window
https://www.aiche
.org/chenected/2011/
09/soda-bottle-solar-
light-bulb [30]
Soda pop
bottle solar
light
This method is usually applied to the
rural areas experiencing poverty. The
associated problems include potential rain
water leaking into the house especially
when there is heavy rain with strong
wind. Also, the durability and reliability
of the soda pop bottle cannot be
guaranteed.
It cannot be implemented to the modern
house or building where the distance
between the roof and ceiling are larger
than the length of the soda pop bottle.
More research works are
required for improving
illumination, visual comfort,
brightness, and control of the
heat inside the building.
Shi and Chew [31]
Windows
Conventional
windows
(1) It can only be fixed to peripheral wall
of the building
(2) It has limited illumination area that
only covers certain distance from the
window, glazing, glass, etc.
(3) The associated problem of daylighting
via windows include visual discomfort,
uncontrollable brightness, and heat
More research works are
required for improving
illumination, visual comfort,
brightness, and control of the
heat inside the building.
Omer [33], Shi and
Chew [31]
Clerestory
windows
Boubekri [34];
Berardi and Anaraki
[35]
Light
reflectors and
shelves
4 International Journal of Photoenergy

Table 1: Continued.
Reference Category Design
configuration Picture/drawing Critical problem of the technique Possible research work that
can be done in the future
Shi and Chew [31];
Boubekri [34] Louver system Glass at the
buildings’
exterior
Louvers in the
buildings’ interior
Kapsis et al. [38];
Shen and
Tzempelikos [39]
Façade
Daylight section
(higher level)
Viewing section
(middle level)
Slide up and down
Spandrel
(lower level)
Ikuzwe and Sebitosi
[37]
Skylights
Passive
zenithal light
pipe
Light pipe
Conventional
side window
The optical loss increases with the
number of light reflection in the light
pipe.
Tube transmission efficiency is low at low
sun altitude angle (during morning and
afternoon period). Since there is no
tracking system, the skylight element can
only accept the sunlight with the incident
angle less than acceptance angle of light
pipe, where the sun reaches certain
altitude angle.
More research works are
required for increasing the
acceptance angle and
reducing the number of light
reflection within the pipe.
Paroncini et al. [22]
Tubular
daylighting
device (TDD)
or light pipe
5International Journal of Photoenergy

Table 1: Continued.
Reference Category Design
configuration Picture/drawing Critical problem of the technique Possible research work that
can be done in the future
Earp et al. (2004)
1
[40]; Wang et al. [41];
Earp et al. (2004)
2
[42]
Luminescent
solar
concentrators
(LSC)
The LSC can only guide the light in the
designated direction.
It has high optical loss due to absorption
and scattering inside the LSC material.
The design uses total internal reflection to
guide the sunlight and is highly
dependent on the sun position that varies
throughout the day.
More research works are
required for increasing the
acceptance angle and
transmission efficiency.
6 International Journal of Photoenergy

and future research exploration. The critical problems are
the views of the authors based on the compilation of multi-
ple in-depth reviews of articles and their research experi-
ences in the relevant subject.
2.1. Skylights. Skylights, including light conveying fenestra-
tion that makes a portion or the complete roof of the space
of a building, are normally used to give a visual view of the
outdoor surroundings for inhabitants inside as well as to
allow illumination from the sunlight into the building via
top lighting. Skylights are usually installed mainly on the
highest floor of a multistory building or on the roof of a
single-story building [20]. The type of material skylights
are made of can have a significant impact on the quality of
the daylight and also the energy efficiency of the building.
Popular glazing materials used for skylights embrace several
types of glass and plastics with a wide range of colors and
thicknesses. Dome-shaped, pitched, and flat panel skylights
are usually positioned on the same level as the roof of the
building. One main part of skylight designs are light wells.
Light wells guide the light through the building’s roof and
ceiling by controlling the daylight it receives before it gets
into the building interiors. The light well is designed such
that it concurrently distributes light and shields the viewer
from very bright sunlight [13]. Below are various types of
skylights but not limited to the following examples:
(1) Fixed unit skylight: this skylight has no ventilation
and has a structural perimeter frame supporting
the light-transmitting portion that is built from glass
or plastic [21]
(2) Tubular daylighting device (TDD) or light pipe: this
is a fixed unit skylight element mounted on the roof,
which receives sunlight and distributes it through a
light conveying optical conduit to a light diffusing
element. This system collects and passes sunlight
through a 0.254 m to 0.5588 m roof-mounted dome
[21]. The dome captures the sunlight and redirects
the light rays into an aluminum tubing system for
dispersion into the building through multiple specu-
lar reflections [22, 23]. The size of the dome is
dependent on the size of the building and is made
from acrylic or polycarbonate for the aim of blocking
ultraviolent rays
(3) Retractable skylight: this type of skylight consists of a
retractable window frame or a set of retractable win-
dow frames installed on top of a roof. When the win-
dow frame is controlled, it rolls offthe frame on a set
of tracks so that the inner part of the building where
it is fixed can completely open to the outdoors for
direct daylight or ventilation. They operate on a
motorized cable system and can be controlled to
retract up and down or left and right [21]
(4) Operable skylight: this skylight design is also named
a venting skylight or a roof window if it is accessible
to the inhabitants of the house. Its appearance is like
that of a single-window frame, which is hinged at the
top and is opened a few inches towards the top direc-
tion to allow air circulation and more daylight. Man-
ually operable skylight sometimes has a hand-
operated latch, which can be used to open it to a cer-
tain level and completely close [24]
(5) Sloped glazing: in sloped glazing, a single assembly
contains several infill panels in a framing system
and is generally designed for a specific project and
fixed in sections [25]. There are many types of glaz-
ing commonly used in residential windows, i.e., sin-
gle clear glass, single glazing with gray tint, double
clear glass, double glazing with gray tint, double glaz-
ing with selective tint, double glazing with low emis-
sivity (Low-E), and triple glazing with Low-E [26,
27]. When daylighting and energy saving need to
be considered simultaneously, selecting a window
glazing becomes complicated [28]
(6) Straight and splayed skylight: these two designs
allow daylight to enter a building from the roof.
The dissimilarity between these two designs is that
the splayed skylight design disperses the light more
broadly in the building as compared to the straight
skylight design. On the other hand, the spacing
between the straight skylights is closer as compared
to the splayed skylight to provide the same amount
of illumination [29]
2.2. Soda Pop Bottle Solar Light. This is the most inexpensive
and easiest way to obtain light in a dark room and is com-
monly found in rural homes where there is never any elec-
tricity [30]. A plastic coke bottle (preferably one and a half
liters’size) made of polycarbonate is filled with water and
some amount of liquid bleach to stop algae from growing
in the bottle. It is then sealed with a cover and pushed half-
way through a circular cut (with an exact diameter as the
bottle) on a steel sheet, which holds the bottle in place to
prevent it from slipping. It is then firmly fixed into a hole
made in a corrugated iron roof and a sealant is applied
around the hole to prevent rainwater from getting in. When
the sun shines directly on the coke bottle, it illuminates the
room.
2.3. Conventional Windows. Windows attached to the walls
of a building is the most popular way to allow daylight into
a building. Based on the weather condition and latitude of
the building location, windows fixed at several orientations
are usually combined to give a sufficient mix of light for
the building. Increasing the number of windows and their
size is the best approach to achieve more daylight in a build-
ing [31]. The amount of sunlight obtainable from a window
can be enhanced in three diverse ways; (1) the first method is
by inclining the sides of window openings such that the inte-
rior opening is bigger than the exterior opening so that more
sunlight can be obtained in the room. (2) The second
method is by installing the window nearby a light-colored
wall so that the sunlight can reflect better. (3) The third
method is by using an enormous light-colored windowsill
to project sunlight into the room [32]. It is essential to
7
International Journal of Photoenergy

choose the proper type and grade of glass for windows since
it can have an impact on the light transmitted through the
windows. The weakness of this daylighting system is that
some buildings do not have sufficient area to fix window
openings and the installed windows cannot spontaneously
regulate the daylight when the sunlight is excessive to make
the occupants comfortable [31].
2.4. Clerestory Windows. These are vertically placed high
windows or a combination of windows above eye level.
The clerestory roof windows, also known as high-level glaz-
ing because of their location are vertical or tilted openings
projecting up from the roof plane [33]. They can be used
to give access to diffuse daylight from the north in the north-
ern hemisphere that uniformly illuminates a room. In addi-
tion, clerestory windows shine on interior wall surfaces
painted with white or with a light color to enhance illumina-
tion in the room. It is a very brilliant way to admit natural
light and fresh air to the inner spaces of a building coupled
with its aesthetic characteristics.
2.5. Light Reflectors and Shelves. This is a mechanism used to
redirect sunlight to the back of the room by reflecting it away
from the ceiling [34]. Light reflectors and shelves can be reg-
ulated manually and are seldom used these days since a mix-
ture of other methods, both artificial and natural, is now in
existence. Nevertheless, it is still used in some areas where
artificial light alone does not provide enough illumination.
The incorporation of light shelves can advance the quality
of daylighting close to the windows while the useful daylight
illuminance (UDI) level at the back of the room reduces
slightly [35]. They give an effect gotten by placing a white
or reflective metal light shelf outside the window. During
the summer season, a projecting eave shields the windows
from direct sunlight. The light shelf projects farther than
the shadow formed by the eave, and sunlight is reflected in
the upward direction by the light shelves to illuminate the
ceiling. The reflective illumination from the ceiling will
reduce shadows and in so doing reduce the need for univer-
sal illumination. Light shelves also decrease the amount of
heat entering the room via the window.
2.6. Louver System. This system receives the sunlight falling
in front of the room and redirects it to the back of the room.
With this system, the daylight level in the front room can be
reduced while improving the illuminance level at the rear of
the room [34]. There are two types of designs for the louver
system which are static and dynamic. The dynamic type of
louver system operates dynamically by following the sun
position and has better performance as compared to the
static type, but calibration and algorithms are needed to
adjust the sun illumination required by the building as well
as the heating and cooling requirements [31].
2.7. Sawtooth Roof. This type of roof can be seen in older fac-
tories where it uses a group of vertical roof glasses facing
away from the equator corner of the building to collect dif-
fused light. It is split apart by sloped roof elements. A por-
tion of the glass support structure is angled, opaque, and
well protected with a cool roof for insulation and a shiny
barrier. This roof can be used to uniformly illuminate a large
room while decreasing the impact on the building's overall
height [36].
2.8. Passive Zenithal Light Pipe. Ikuzwe and Sebitosi pro-
posed a novel solution called the passive zenithal light pipe
for improving interior daylighting in existing schools located
in the rural area of South Africa [37]. The passive zenithal
light pipe is a system that can collect, transport, and distrib-
ute illuminance from the sun over extended distances in a
building. It consists of a top plexiglass dome, which collects
sunlight and reflects it down a pipe via numerous mirror-
like reflections with the diffuser fixed at the bottommost part
of the tube, typically to the ceiling, for distributing the day-
light into the inner parts of the room. The light pipe’s per-
formance was tested by means of a plexiglass dome,
mirrored pipe, and a polycarbonate prismatic diffuser, which
has shown that a plexiglass dome has 90% sunlight capturing
capacity on sunny days and 70% on cloudy days. From the
experiments conducted on the diffuser, results showed that
the polycarbonate prismatic diffuser can deliver better uni-
form spatial light distribution during cloudy days in com-
parison to the distribution during sunny days. They
improved the efficiency of the passive light pipe from 178
lux to 350 lux as was needed inside the classroom based on
the principle of edge ray by using a nonimaging optical col-
limator [37].
2.9. Façade. Kapsis et al. studied a bottom-to-top motorized
roller shade having configurable automated control installed
in office spaces as a means of implementing the idea of a
basic three-section facade [38]. This concept is a potential
method for integrating daylighting into facade design.
Enhanced glass facade design may increase the use of day-
light and yield major savings in electricity consumption of
lighting [39]. In the three-section facade design, the lower
level of the facade is opaque, the middle level is transparent
for viewing, and the upper level directs the daylight into the
building space. In other words, the bottom-up shade is actu-
ally a roller shade operating from top to bottom such that
the bottom of the window is covered while daylight enters
from the upper section of the window to the room as illus-
trated in Table 1. A remote control can be used to open or
close the motorized shades whenever it is needed. From
the study, in the parts of the room where electric lighting
is needed as they are further away from the façade, the
bottom-up shade gives 46% higher Daylight Autonomy
(DA) as it allows natural light from the sun to go in via
the upper level of the facade and further into the room for
illumination thus decreasing the energy consumed for elec-
tric lighting by 21-41% annually [38].
Similarly, Shen and Tzempelikos examined the balance
between daylighting and energy consumed in small secluded
offices having one external facade with internal roller shades
while considering the properties of glazing and shading and
their control, size of the window, climate, and orientation in
an incorporated daylighting method. Various analyses were
carried out to show that north windows can permit enough
daylight into the building for all locations with more than
8 International Journal of Photoenergy

30% window-to-wall ratios. East windows perform better for
the other orientation because, during the morning hours, the
shades would close for a short while in comparison to the
south and west facades. They noted that DA rises based on
window area and shading and glazing transmittance
depending on climatic factors [39].
2.10. Luminescent Solar Concentrators (LSCs). Earp at al.
proposed luminescent solar concentrators (LSCs) with three
different colored fluorescent dyes (a pile of pink, green, and
purple LSCs) to give a concentrated nearly white source of
light that is coupled into polymer sheets to transport sun-
light in the range of 10 m [40]. The concentrated light is
transported by polymer light guide sheets that are flexible
clear polymethylmethacrylate (PMMA) light guides rather
than optical fibers as the light from LSCs is not a pointolite.
Fluorescent dyes captivate and emit light isotopically in
which the emitted light is greatly concentrated along the col-
lector edges via total internal reflection. The narrow flexible
polymer light guides are an extension of the collector, which
guides the daylight into the building. It was noted that the
main aim of the daylighting applications of LSC is the
light-to-light efficiency, which is governed by the eye’s spec-
tral sensitivity. Light-to-light efficiency is the ratio of output
to input luminous flux [41]. In their prototype, a collector
area of 1:2m×0:135 m has shown that indirect solar inten-
sity of 100,000 lux can convey 1000 lm of nearly white light
having a 6% light-to-light efficiency and luminous efficacy
of 311 lm/W. They noticed that some light loss was triggered
by surface defects including excessive adhesive and nonuni-
formity in flatness that can be avoided by the careful produc-
tion of LSC. Besides, further concentrating the light
eliminated by the LSC into a pointolite just to be able to con-
vey it via optical fibers to a secluded place in a building is an
energy-inefficient process. To overcome these problems, the
fluorescent fiber solar concentrator (FSSC) system was pro-
posed by Wang et al. [41]. However, Earp et al. defended
that LSCs do not need a sun-tracking system, and their light
output is easily coupled without any added optics and the
LSC system appears to be the well-suited solar collector for
use with bendable solid light guides [42]. Optimization of
the design parameters can lead to adequate illumination of
a room from the concentrated light. The advantage of LSCs
compared to other daylighting systems is that they accept
diffused and reflected sunlight and so require simple or no
tracking devices.
3. Active Daylighting System
Numerous solar concentrators and highly efficient light cou-
plers are essential for sufficient sunlight collection for indoor
illumination. To save power consumption on electrical light-
ing, daylight can be provided for the interior of a building
via sunlight focused by a solar concentrator and guided by
a bundle of optical fibers. Active daylighting system with a
solar concentrator requires a precise sun-tracking system
to achieve high optical efficiency for daylight collection and
distribution. Therefore, we can categorize the active day-
lighting systems under two major headings: single-axis
tracking system and dual-axis tracking system [43]. Table 2
is a summary of several designs of active daylighting sys-
tems, including the optical design configuration, tracking
system, and waveguide design, key findings, and the critical
problems of the technologies from the perspective of the
authors based on the compilation of multiple in-depth
reviews of articles and their research experiences in the rele-
vant subject.
3.1. Active Daylighting System with Single-Axis Tracking
System. Active daylighting systems attached to single-axis
trackers only have a single degree of rotational freedom to
track the sun. It usually tracks the change of sun position
due to the hour angle, but it is not designed to follow the sea-
sonal change of the earth’s equatorial plane with respect to
the sun position [44]. This active daylighting system is an
intermediate solution, which is simpler than the dual-axis
tracking system but more complicated than passive daylight-
ing system.
3.1.1. Linear Fresnel. Ullah and Shin proposed a new method
for the linear Fresnel lens as shown in Figure 2 [45]. At the
capturing stage, daylight was uniformly distributed to
increase the efficiency of the system, and direct sunlight
was focused via the linear Fresnel lens. The focused sunlight
then went into and out of a collimating lens of which the col-
limated sunlight was guided by the optical fibers. Achieving
a high concentration of light with the linear Fresnel lens was
essential; hence, a popular nonimaging optical component
called the trough compound parabolic concentrator (CPC)
was introduced just before the optical fibers [45]. Also, silica
optical fibers (SOFs) placed before plastic optical fibers
(POFs) were used to distribute sunlight to each floor with
small losses and less heat. Most existing linear Fresnel day-
lighting systems have some difficulties such as low accuracy
in design, installation, and routing of hardware [46]. Tripa-
nagnostopoulos et al. also discussed the application of a lin-
ear Fresnel lens to control the illumination of a building
interior space due to its ability to segregate the beam and
the diffuse solar radiation [47].
3.1.2. Parabolic Trough. Ullah and Shin proposed an
approach of an active daylighting system by using a para-
bolic trough where sunlight was captured by the parabolic
trough, focused towards a parabolic reflector, and directed
into a multistory building through the optical fibers (POFs)
[45]. Similar to the linear Fresnel system, to attain a very
high concentration of light with the parabolic trough, a
trough CPC was introduced before the optical fibers as
shown in Figure 3 [45]. The advantage of their proposed sys-
tem is just like that of the linear Fresnel system: it is expand-
able and simply requires a tracking module having one axis.
POFs are ideal in daylighting systems as they are low-cost,
bendable, durable, and suitable for complicated wiring in
buildings. The disadvantage of their proposed system is that
the uniformity of light inside the building is not yet achiev-
able and SOFs are quite costly.
3.2. Active Daylighting System with Dual-Axis Sun-Tracking
System. Active daylighting system attached to a dual-axis
9International Journal of Photoenergy

Table 2: Summary of the various studies in active daylighting systems.
Reference Optical design configuration Tracking
system Waveguide design Analysis type Key findings Critical problem of the technique Possible future research
Ullah and Shin
[45]
Linear Fresnel lens coupled to a
plano-concave collimating lens
and then to trough of compound
parabolic concentrator before
focusing sunlight onto linear
array of optical fibers
Single-
axis
tracking
Silica optical fibers
before plastic optical
fibers to reduce the
heat problem for
distributing sunlight
to each floor with
small losses
Theoretical
modelling
using
LightTools
(1) This hybrid system combines
sunlight and LED light with
electric lighting controls to
achieve the required illumination
levels at all times. Electric lighting
power consumption is saved
since an average illuminance of
500 lx is maintained
(2) The simulated efficiency of
the daylighting system is better
than that of traditional lighting
systems based on the average
illuminance in the room interior
and on the illumination quality of
the system through combining
daylight and LED light
(3) Advantages: both design
configurations are expandable
and require only a single-axis
tracking module
(4) Disadvantages: for both
designs, light uniformity is not
achieved in the building interior
and silica optical fiber is
expensive
Due to single-axis tracking, linear
reflectors encounter edge effect
where some of the optical fibers
are unable to receive the sunlight
when the declination angle of the
sun varies throughout the year.
Tracking accuracy can affect the
effectiveness of the daylighting
system.
Thermal issue for the optical
fibers is a concern in this design.
More practical data is needed for
long-term observation on
thermal stress and cycling effects
to the optical fibers for durability
and reliability test.
More study is required on the
performance of the system when
the sun is not at the normal
direction of the concentrator.
The impact of tracking accuracy
on the performance.
Detailed analysis for the
durability and reliability of the
system is required.
Ullah and Shin
[45]
Parabolic trough coupled to a
parabolic reflector and then to
trough of compound parabolic
concentrator before focusing
onto linear array of optical fibers
Single-
axis
tracking
Ullah and Shin
[46]
Ullah and Shin
[49]
Point-focused Fresnel lens
coupled to a plano-concave lens
and to a bundle of optical fibers
Dual-axis
tracking
Silica optical fibers
coupled to plastic
optical fibers for
distributing sunlight
to the building with
small losses
Theoretical
modelling
using
LightTools
and
experimental
study
(1) Improved illumination levels
can be attained via a combination
of sunlight and LED light, as
compared to the traditional
lighting systems
(2) The quantity of optical fibers
in the bundle should be carefully
chosen based on the surface area
of the concentrator
(3) More than 500 lx illuminance
can be delivered uniformly to
different parts of the building
Tracking accuracy can affect the
effectiveness of the daylighting
system.
Thermal issue of optical fibers is
a concern in this design. More
practical data is needed for long-
term observation on thermal
stress and cycling effects to the
optical fibers for durability and
reliability test.
The impact of tracking accuracy
on the performance
Detailed analysis for the
reliability and durability of the
system is required.
10 International Journal of Photoenergy

Table 2: Continued.
Reference Optical design configuration Tracking
system Waveguide design Analysis type Key findings Critical problem of the technique Possible future research
Muhs [50]
Parabolic dish concentrator
coupled to secondary faceted cold
mirrors that divide the solar
irradiance into visible and
infrared spectrums while
allowing only visible light to be
reflected and focused into large
core PMMA optical fibers. The
solar irradiance in the infrared
spectrum is used for electricity
generation.
Dual-axis
tracking
Large core plastic
optical fibers
System-level
design,
preliminary
performance,
and cost
evaluation
(1) Challenges such as cost,
spatial and temporal variability,
surplus illumination, glare, and
energy efficiency encountered by
most passive daylighting systems
can be eased with the use of
hybrid solar lighting
(2) The estimated total system
cost is ~$3000 for a 2 m2
collector, illuminating about 12
luminaires covering nearly
1000 ft2 of floor space. This
means that installation cost is
~$3/ft2 with less than $2/Wp
peak performance
(3) The payback period of this
daylighting system can be less
than 5 years
There is a significant empty space
on the receiver not filling up with
the aperture of the optical fiber.
This causes low packing factor
with serious optical loss for the
system.
Thermal issue of optical fibers is
a concern in this design. More
practical data is required for
long-term observation on
thermal stress and cycling effects
to the optical fibers for durability
and reliability test.
More detailed study can be done
to analyze the solar flux
distribution produced by the
parabolic dish concentrator and
the entrance aperture of optical
fibers must be optimized to
increase the packing factor for
receiving maximum concentrated
sunlight.
Han et al. [51]
Fresnel lens fixed on a dual-axis
tracker to focus sunlight which is
transmitted via optical fiber
Dual-axis
tracking Plastic optical fibers
Experimental
analysis and
photometric
analysis
(1) Continuous illumination was
realized on the task plane during
the day and at low solar altitudes
(2) With the use of a light source
having a correlated color
temperature (CCT) of 5000 K in
combination with sunlight, very
bright daylight is delivered from
a luminaire coupled to the optical
fiber cable
(3) Consumption of electric
energy for indoor lighting in
buildings could be drastically
decreased by the hybrid system
(4) This daylighting system can
be used to achieve electric energy
savings of 174 kWh when the
luminous efficacy of the LED
lamp is 17 lm/W and operation
duration is 8 h/day for 110 days
in a year
Tracking accuracy can affect the
effectiveness of the daylighting
system.
Transmission efficiency of the
fiber is 65%, and the total optical
losses are not fully studied.
The illumination distribution is
not uniform.
The system can be made more
cost effective by the use of electric
lamps that has higher luminous
efficacy together with an electric
light placed closer to the diffuser
[50].
11International Journal of Photoenergy

Table 2: Continued.
Reference Optical design configuration Tracking
system Waveguide design Analysis type Key findings Critical problem of the technique Possible future research
Pham et al.
[52]
Convergent linear Fresnel lens
collects sunlight, while the
divergent linear Fresnel lens
transmits the light.
Dual-axis
tracking
Divergent linear
Fresnel lens
Theoretical
modelling
using
MATLAB
and
LightTools
(1) A high uniformity can be
achieved via the daylighting
systems’collector and
transmitter. All the grooves of the
Fresnel lens uniformly distribute
the sunlight over the receiver
such that the entire lens also
uniformly distributes sunlight
over the receiver
(2) From simulation results,
efficiency of ~80% with a
tolerance of ~0.60 and a
concentration ratio of 340 times
can be achieved from the
collector
(3) High uniformity of more than
90% is attained from the
divergent linear Fresnel lens
Overheating issue on the optic
fiber is a concern due to high
solar concentration ratio of 340
suns.
The acceptance angle of the
newly designed optical system is
0.60
°
at which the solar power
received by the system drops to
90%.
More detailed analyses can be
carried out related to the use of
plate beam splitter (PBS) to
convey more than 85% of the
visible light to the optical fibers
and reflect higher than 90% IR
wavelength for other
applications.
A study on the optical losses of
silica optical fibers (SOFs)
combined to plastic optical fibers
(POFs) can be performed.
Ullah and Shin
[46]
Convex parabolic reflector
coupled to concave parabolic
reflector and then to a bundle of
optical fibers
Dual-axis
tracking
Silica optical fibers
before plastic optical
fibers to reduce the
heat problem for
distributing sunlight
to the building with
minimum losses
Experiments
and
theoretical
modelling
using
LightTools
(1) With the use of a large
sunlight collecting system, more
sunlight can be directed into the
optical fibers
(2) More than 500 lx uniform
illuminance can be sent into the
building
Tracking accuracy can affect the
effectiveness of the daylighting
system.
Thermal issue of optical fibers is
a concern in this design. More
practical data is needed for long-
term observation on thermal
stress and cycling effects to the
optical fibers for durability and
reliability test.
Packing factor issue of optical
fibers at the receiver should be
optimized.
More research study can be
carried out to reduce the poor
packing factor of round optical
fibers. The rectangular glass
optical fibers proposed by Aslian
et al. can be adopted in this
design, but more analysis is
required [66].
12 International Journal of Photoenergy

Table 2: Continued.
Reference Optical design configuration Tracking
system Waveguide design Analysis type Key findings Critical problem of the technique Possible future research
Schlegel et al.
[53]
Parabolic dish concentrator
coupled to faceted cold mirrors
that is capable of dividing the
solar irradiance into visible and
infrared spectrum and allows
visible light to be reflected and
focused to large core PMMA
optical fibers.
Dual-axis
tracking Plastic optical fibers
Theoretical
modelling
using
TRNSYS
transient
simulation
program
(1) The study considered an
office building model attached
with hybrid lighting. The yearly
energy impact on lighting,
cooling, and heating loads was
considered in their simulation
which was carried out in six
localities in the United States
(2) Based on a 10-year profit
return period, the capital of the
hybrid systems cost $2410 in
Honolulu, HI, and $1995 in
Tucson, AZ; and the hybrid
lighting systems in these two
cities performed best
(3) The best economic place to
mount a hybrid lighting system
was found to be Honolulu, HI,
with Tucson, AZ, being the best
place in continental United States
There is a significant empty space
on the receiver not filling up with
the aperture of the optical fiber.
This causes low packing factor
with serious optical loss for the
system.
Performance optimization can be
carried out to improve the overall
efficiency and hence decrease the
system overall cost.
Sapia [54]
Primary parabolic collector
(PPC) coupled to a secondary
collector (SOE), both covered
with a very reflective surface in
the visible range but transparent
in the near-infrared range (cold
mirror) and then to a bundle of
optical fibers
Dual-axis
tracking Plastic optical fibers MATLAB
simulation
(1) A substitute electrical lighting
operation period of 12 h for 320
days in a year is expected of this
daylighting system
(2) The photovoltaic conversion
of sunlight to electricity and then
to light for daylighting can be
avoided by use of this sunlight
addressing system
(3) The prorated overall cost of
the entire system is USD 6538 for
a collective area of 4.48 m2
There is a significant empty space
on the receiver not filling up with
the aperture of the optical fiber,
which causes low packing factor
with serious optical loss for the
system.
The overall efficiency of the
system is only 21%.
13International Journal of Photoenergy

Table 2: Continued.
Reference Optical design configuration Tracking
system Waveguide design Analysis type Key findings Critical problem of the technique Possible future research
Ullah and Shin
[5]
Heliostats direct sunlight towards
the focusing mirror and from
there to the mirror light pipe.
Dual-axis
tracking Mirror light pipe
Theoretical
modelling
and analysis
(1) To achieve high illumination
in the interior of building, the
mirror light pipe was coated with
prismatic optical lighting film
and multilayered optical film and
was made in a cylindrical way to
attain uniform illumination
(2) Advantages of this
daylighting system include
affordability, manageability, the
simplicity of design, the
applicability of quick
manufacturing, and expansion to
produce large-scale system
The light intensity at different
floors is different: occupants at
the highest floor may suffer high
light intensity while the
occupants at the lowest floor may
suffer due to low light intensity.
Study carried out is only
theoretical where the practical
implementation of the whole
system is not considered
carefully. The design is
complicated as it involves the
control of heliostat fields to
accurately focus the sunlight onto
the central receiver.
For the heliostats in the array, we
need to take into consideration
the shadowing and blocking
effects between the heliostats.
More detailed research is
required to integrate with light
control system in each floor and
to ensure that the light intensity
in each floor is about the same.
More studies can be done to
optimize layout design of the
heliostats to consider the land
area usage and blocking and
shadowing effects.
Tsangrassoulis
et al. [54];
Kristensen [56]
Heliostat with concentrating
Fresnel lens connected to a large
core liquid fiber optic cable
coupled to a luminaire in a
windowless room
Dual-axis
tracking
Liquid fiber and
ordinary PMMA
fibers
Theoretical
and
experimental
analysis
(1) As a complementary source
of lighting, a metal Halide
projector with a 150 W BLV lamp
and a Schott projector with a
150 W MH lamp are positioned
together with the heliostat and
two backup T5 fluorescent lamps
embedded in the luminaire
(2) The daylighting system
integrated with efficient artificial
lighting controls can reduce
electrical energy consumption by
50–75% in commercial buildings
[55]
The transmission efficiency of the
proposed liquid optical fiber is
low, which is only 3.4%.
The brightness of MH lamps can
be reduced using continuous or
two-level dimming. However, the
highest dimming range is roughly
30% of the rated lamp power.
The problems associated with the
dimming of the MH lamps
include decrease in efficiency and
reduced lifetime of the lamp by
90%.
More research should be carried
out to increase the efficiency of
the liquid optical fiber system.
More studies are needed for the
flux control dimming system and
the light sources connected
externally.
La Forêt
Engineering
Co. Ltd. [57]
Himawari lens focusing unit and
optical fiber devices
Dual-axis
tracking
Very pure quartz
glass optic fiber cable
conveys the visible
rays with very little
loss.
Theoretical
and
experimental
analysis
(1) The major benefit of this
system is that furniture carpets,
rugs, and artwork would not fade
and thus are safe
(2) As Himawari products
contain only a little amount of
infrared radiation, there would be
no interference with room
temperature or air conditioning
systems
The solar concentration ratio is
10,000 suns. Thus, they use
highly pure quartz glass fiber to
transmit the concentrated
sunlight.
More research works on the
thermal effect under ultrahigh
solar concentration ratio on the
highly pure quartz glass fiber
cable are required.
14 International Journal of Photoenergy

Table 2: Continued.
Reference Optical design configuration Tracking
system Waveguide design Analysis type Key findings Critical problem of the technique Possible future research
Chen et al. [58] Himawari system Dual-axis
tracking Plastic optical fibers
Theoretical
and
experimental
analysis
(1) The system can meet the
lighting necessity at the
horizontal work plane based on
the visual performance in the
office and also provide the
circadian system entrainment
which is the nonvisual effect of
lighting at the same time
(2) There is a great chance of
achieving a suitable level of
circadian light at a workspace with
no window via the application of
the fiberopticsdaylightingsystem
(FODS) in northern China
(3)Incomparisonwithusual
artificial lighting systems,
circadian light can be delivered
more efficiently via this
daylighting system
(4) This is the first study examining
the FODS nonvisual performance
Anormalwindowmaystillbe
preferable to occupants in a
building compared to the FODS.
Since the FODS have a narrow
beam light intensity distributor, it
must be used with a unique
luminaire for indoor lighting
dispersal. More so, balancing the
illuminance levels and light
uniformity of the illumination from
the luminaire at horizontal and
vertical planes might be difficult.
Even though the FODS system has
great merits for the wellbeing and
health of the inhabitants, it has a
higher cost of installation
compared to the regular artificial
lighting system.
The FODS was only tested in the
northern part of China. If used in a
different location and climate, there
is a high chance of occurrence of
unidentified problems.
The photometric properties of
the indoor luminaire can be
improved upon.
An improved luminaire reflector
design having proper light
intensity.
Distribution might lead to an
increase in the lighting
performance of the FODS in terms
of visual and nonvisual activities.
To analyze the performance of the
FODS via subjective assessment,
experiment should be conducted
in a real office with a human.
Song et al. [59]
Multiple concentrating lenses for
focusing sunlight to the plastic
optical fibers
Dual-axis
tracking Plastic optical fibers
Theoretical
and
experimental
analysis
(1) 34% system transmission
efficiency has been obtained via
experiment, considering both the
attenuation ratio of the optical
fibers and the light transmittance
of the lens
(2) The tracking system is very
good with a precision of 0.1
°
to
accommodate the focusing at
2500 suns
(3) The total internal reflection
angle is ±30
°
, and experimental
results showed that larger
incident angles result in greater
attenuation
(4) The benefit of this system is the
provision of light to dim rooms or
underpasses while preventing or
reducing the transmission of
energetic particles and infrared (IR)
and ultraviolent (UV) rays, thereby
reducing the amount of electrical
power consumption for air-
conditioning systems
Tracking accuracy can affect the
effectiveness of the daylighting
system as less than 0.1
°
sun-
tracking error gives less than 20%
output luminous flux loss.
The illumination inside the room
is not well distributed.
More research can be carried out
to include an optical funnel as the
secondary concentrator to reduce
the impact of sun-tracking error.
More studies are needed to
improve the uniformity of
illumination distribution.
15International Journal of Photoenergy

Table 2: Continued.
Reference Optical design configuration Tracking
system Waveguide design Analysis type Key findings Critical problem of the technique Possible future research
Khosravi et al.
[60]
A combination of passive and
active optical components:
sunlight redirectors to redirect
sunlight at a predetermined angle
to the exterior facades of the
building. The redirectors redirect
sunlight such that the entire
façade is bathed by sunlight and
dispersed uniformly to multiple
floors. A portion of the sunlight
at each floor is captured,
concentrated, and recollimated
by the concentrator (lens and an
enclosure containing a separate
lens and mirror assembly) fixed
on the facade of the building. The
light coming from the
concentrator is fed to the light
guides.
Dual-axis
tracking
Hollow rectangular
pipe
Theoretical
modelling
(1) With this daylighting system,
uniform illumination can be
provided in the building most of
the time
(2) The efficiency of the
concentrator as it refers to the
ratio of output light to the light
that strikes the lens assembly is
found to be 95%
(3) Simulation result showed that
about 77% of light can be gotten
from the light pipe; 3% will
return to the entrance of the pipe
and exit the pipe, while materials
in the pipe will absorb 20%
(4) Overall system efficiency is
calculated to be 30%
(5) This daylighting system can
only perform under direct
sunlight as it cannot focus
diffused light; hence,
complementary electrical lighting
is essential during overcast sky
conditions
For high solar altitude angle,
large portion of the sunlight can
pass between the slats rather than
interacting with them which
causes the intensity of captured
sunlight to be reduced.
More research works are needed
to decrease the optical losses due
to the change of sun position.
Moving mechanism to track the
sun position can be implemented.
Kim and Kim
[61]
The first mirror is a circular-
shaped aluminized glass that
tracks the sun and reflects
sunlight to a flat or concave
secondary reflecting mirror.
Dual-axis
tracking
Mirror sunlighting
system with
secondary reflecting
concave or flat mirror
Experimental
analysis
Experiments were conducted
during clear and overcast sky
conditions. The performance of
the system was measured in
terms of illuminance and sunlight
illumination ratio. Results
showed that with the mirror
sunlighting system, the
illuminance level in a
semiunderground space can be
improved by eleven times with
the use of a flat secondary
reflective mirror and fifteen times
with the use of a concave
secondary mirror. Thus, the
concave secondary mirror was
preferable.
Each optical daylighting system
can only be applied to a single
floor of a building.
The mirror sunlighting may
cause glaring and visual
discomfort.
The illumination inside the room
is not uniform, and it is unable to
illuminate a room without
window.
More research works can be
conducted to improve the visual
comfort and uniformity of indoor
illumination via diffuser.
16 International Journal of Photoenergy

Table 2: Continued.
Reference Optical design configuration Tracking
system Waveguide design Analysis type Key findings Critical problem of the technique Possible future research
Chong et al.
[62]; Onubogu
[63]; Obianuju
and Chong
[64]; Onubogu
et al. (2019)
[65]
80 primary facet mirrors coupled
to 20 secondary facet mirrors and
to densely packed plastic optical
fibers for daylight distribution
Dual-axis
tracking Plastic optical fibers
Theoretical
modelling
using
LightTools
and
experimental
study
(1) The equivalent power
conversion efficiency of the
prototype 2S-NISC was found to
be 22% based on 170 W input
solar power
(2) The proposed 2S-NISC
daylighting system having an
optimized 4 m2 collective area
was projected to cost USD
1231.20, which is cheaper than
most active daylighting systems
(3) Taking a 4% interest rate and
a 2% fuel inflation into
consideration, a total profit
period of 6.1 years was estimated.
This is practical as the active
daylighting system has a lifetime
of at least 15 years
The sun-tracking error may cause
a significant drop in efficiency.
The current design is not suitable
for mass production because each
facet mirror is aligned for its own
predefined tilted angle.
More research works can be
conducted to design the solar
concentrator via 3D printing
method or mould casting the
geometry of the concentrator.
17International Journal of Photoenergy

tracker has two degrees of rotational freedom, which is capa-
ble of perfect alignment to the sun at all times to achieve
maximum optical performance throughout the year [48].
Conveyance of uniform sunlight to areas such as the base-
ment, storerooms, windowless rooms, and various floor
areas was mentioned to be possible via an active daylighting
system [46].
3.2.1. Fresnel Lens. Ullah and Shin proposed a uniformly
illuminated daylighting system for the interior of a building
by using a point-focused Fresnel lens coupled to a light pipe
or a bundle of fibers [46, 49]. A Fresnel lens having a con-
stant pitch of 0.5 mm was employed for the Fresnel lens day-
lighting system as illustrated in Figure 4 [49]. For the Fresnel
lens daylighting system, a plano-concave lens is employed to
yield collimated light which illuminates the entrance aper-
ture of the optical fibers uniformly [46, 49]. POF with a large
core diameter was selected for distributing the daylight as it
has favorable features as listed in Section 3.1.2. Since POFs
cannot withstand the high intensity of sunlight, SOFs were
introduced before the POFs to absorb some heat first. Also,
index matching gel was employed to lessen losses caused
by the air gap in between the SOF and the POF [49].
Muhs described a similar type of Fresnel lens daylighting
system incorporated with a dual-axis tracking solar concen-
trator scheme which utilizes Fresnel lenses to directly focus
sunlight to the entrance of a series of optical fiber [50].
Han et al. have developed an active daylighting system
that uses a Fresnel lens placed on a two-axis tracker to track
and receive sunlight and then transmit it via optical fiber
cables where continuous illumination is achieved by sup-
porting the light from the sunlight with artificial light as
required [51].
Pham et al. presented a daylighting system with a new
design of a linear Fresnel lens that can achieve high unifor-
mity. Each groove of the lens uniformly disseminates sun-
light over the receiver in such a way that the entire lens
also disseminates sunlight over the receiver uniformly [52].
In their design, the collector or receiver is built with a con-
vergent linear Fresnel lens, whereas the divergent linear
Fresnel lens is used in fabricating the distributor. They also
mentioned that the two linear Fresnel lenses are built at right
angles to each other and orthogonal to the incoming bundle
of sun rays.
3.2.2. Parabolic Dish/Mirror. Ullah and Shin proposed an
efficient approach with a parabolic mirror for the fiber-
based daylighting system as shown in Figure 5 [46]. Here,
a parabolic mirror captured and focused sunlight on a sec-
ondary mirror that subsequently illuminated the optical
fiber bundles uniformly. Features of the parabolic mirror
include a small f/Dratio, a high concentration ratio, and a
big aperture area to get the most of the sunlight captured.
Concave and convex parabolic reflectors were employed to
yield collimated light. For the purpose of rotating the light-
Incoming sunlight
Linear fresnel
lens
Collimating lens +
trough CPC
Linear array of plastic
optical bers
Optical ber
bundles
Support pillars
Figure 2: Front view of the physical layout of linear Fresnel lens daylighting system by introducing the trough compound parabolic
concentrator (CPC) before the optical fibers (source: adapted from [45]).
Incoming sunlight
Parabolic
reector
Trough CPC (on top)+
Parabolic trough (below)
Linear array of plastic
optical bers
Optical ber bundles
Support pilla
r
2
1
3
Figure 3: Front view of the physical layout of parabolic trough daylighting system by introducing the trough compound parabolic
concentrator (CPC) before the optical fibers (source: adapted from [45]).
18 International Journal of Photoenergy

collecting components to the sun, a two-axis sun-tracking
device was included in the daylighting system. The circular
shape organization of the bundle of optical fibers enabled
maximum sunlight to be received.
Similarly, Muhs and Schlegel et al. studied a combined
hybrid lighting system using a parabolic dish concentrator
with dual-axis tracking as shown in Figure 6 [50, 53]. Schle-
gel et al. mentioned that their hybrid lighting systems had an
outstanding performance in Honolulu, HI, and Tucson, AZ,
mitigating their systems’capital costs of $2410 and $1995
per module, with a 10-year profit period [53]. Muhs listed
the five major elements of the integrated hybrid lighting sys-
tem which are sunlight and electric lamps as the light
sources, sunlight collection and tracking systems, light dis-
semination systems, hybrid lighting control systems, and
the hybrid luminaires [50]. The direct normal irradiance
gathered by the two-axis tracking concentrator was reflected
to a secondary element that is capable of dividing the solar
irradiance into two spectrums: visible and infrared. The sec-
ondary element consists of eight faceted cold mirrors that
only permit the reflection of visible light which is focused
into large core PMMA optical fibers that transport the sun-
light into parts of the building where it is needed [53].
Sapia presented a daylighting system comprising a pri-
mary parabolic collector (PPC) covered with a very reflective
film and a secondary collector (SOE) with a very reflective
surface in the visible range but transparent in the near-
infrared range (cold mirror). This daylighting system design
resembles that of Figure 6. The secondary collector reflects
the solar irradiance towards the top of the bundles of optical
fibers with only the visible part. After the light travels for
approximately 10 m through the fibers, it arrives at the tubu-
lar diffusing components in the luminaries [54].
3.2.3. Heliostat Field. Ullah and Shin proposed an inexpen-
sive idea of a solar tower daylighting system to distribute
sunlight to each floor of a multiple-story building by means
of collecting, directing and disseminating sunlight through
the heliostats, mirror light pipe, and light guide as shown
in Figure 7 [5]. The heliostats with circular plane mirror
having a diameter of 0.7 m each were organized in circular
arcs of radii at 1.5 m, 2.5 m, 3.5 m, and 4.5 m at one corner
of the mirror light pipe. Each heliostat is operated with a
two-axis sun-tracking system to track the sun at all times
during the day. The focusing mirror of 1 m diameter was
mounted at 0.5 m above the mirror light pipe. Each heliostat
directed sunlight to the focusing mirror. The focusing mir-
ror made an angle of 10.12
°
relative to the ground axis and
was structured to insert the light into the mirror light pipe
that was then conveyed and distributed to each floor of the
building via a directing mirror. Five floors of 50 m
2
area each
were illuminated with thirteen heliostats. To attain very
good illumination in the buildings’interior, the mirror light
pipe was coated with prismatic optical lighting film and mul-
tilayered optical film and was built in a cylindrical form to
attain uniform illumination. They claimed that the system
had numerous advantages such as affordability, manageabil-
ity, simplicity of design, the applicability of quick
manufacturing, and expansion to produce a large-scale sys-
tem. However, the study is still in the stage of theoretical
modelling and analysis.
Tsangrassoulis et al. presented a prototype of a hybrid
lighting system (the heliostat-liquid fiber optic lighting sys-
tem) that conveys daylight from a heliostat with a concen-
trating Fresnel lens to a luminaire in a room without
window, via a large core liquid optic fiber [55]. The system
was called the Universal Fiber Optic (UFO) system, which
Incoming sun rays
Plano-concave
lens
Sun-tracking
module
Support pillar
Silica optic ber
Index
matching
Plastic optic ber
Figure 4: Physical layout of Fresnel lens daylighting system
showing ray-tracing and sun-tracking module (source: adapted
from [46]).
Incoming sun rays
Concave parabolic
reector
Sun-tracking
module
Support pillar
Silica optic ber
Index
matching
Plastic optic ber
Convex parabolic
reector
Figure 5: Physical layout of the parabolic mirror daylighting
system showing ray-tracing and sun-tracking module (source:
adapted from [46]).
Secondary collector
with cold mirrors
Primary parabolic
collector
Bundles of optical
ber
Figure 6: Hybrid lighting prototype showing the secondary
collector with eight faceted cold mirrors (source: adapted from
[53]).
19International Journal of Photoenergy

was mounted on the highest roof of the University of Ath-
ens, Physics Department building, during the 2002 summer.
The modules of the UFO system embrace a heliostat to cap-
ture the sun with the Fresnel lens of 1 m diameter of which
the light goes through the fiber optic cables consisting of liq-
uid fiber and ordinary PMMA fibers. As a complementary
source of lighting, a metal Halide projector with a 150 W
BLV lamp and a Schott projector with a 150 W MH lamp
is positioned together with the heliostat and two backup
T5 fluorescent lamps embedded in the luminaire. The day-
lighting system integrated with efficient artificial lighting
controls can reduce electrical energy consumption by 50–
75% in commercial buildings [56].
3.2.4. Himawari. La Forêt Engineering Co. Ltd. introduced a
commercial Himawari system consisting of a lens focusing
unit and optical fiber devices with a sun-tracking system
[57]. They have two types of products, which are 36 Lens
Himawari XD-100S/36AS capable of supplying daylight to
6 terminals and 12 Lens Himawari XD-50S/12AS capable
of supplying daylight to 2 terminals. To compute the sun’s
position and alter its angle, the Himawari system has a
built-in sun sensor, an interior clock device, and a micropro-
cessor. After the sun sets, it shuts down and resets its posi-
tion to get prepared for the subsequent sunrise. At the
focal point of the lens, an inlet end of an optical fiber cable
is fixed in which light is focused via a Fresnel lens and only
visible light goes into the optical fibers. A very pure quartz
glass fiber cable conveys the visible rays with negligible loss.
The major benefit of this system is that furniture carpets,
rugs, and fade artwork would not fade and thus are safe.
As Himawari products contain only a little magnitude of
infrared radiation, they would not interfere with room tem-
perature or air conditioning systems. Figure 8 shows the
schematic diagram of the front view of the Himawari solar
lighting system.
Chen et al. studied the potential of the Himawari system
to give occupants appropriate lighting to aid visual functions
and attain the circadian system entrainment in a particular
office in Beijing, China [58]. They mentioned that the system
can meet the lighting necessity at the horizontal work plane
based on the visual performance of the occupants’in the
office and also provide the circadian system entrainment
which is the nonvisual effect of lighting at the same time.
3.2.5. Multiple Concentrating Lens System. Another active
daylighting system called “double-axis sun-tracking and
concentrating system”consisting of multiple concentrating
lenses was suggested and developed by Song et al. [59]. This
daylighting system consists of plastic optical fibers, two-axis
sun-tracking technology, and lenses for focusing and trans-
mitting sunlight as shown in Figure 9. The entrance of the
fiber is 2 mm in diameter, and light is focused on a 2 mm
diameter spot which is directly on top of the entrance face
of the fiber. Considering both the attenuation ratio of the
optical fibers and the light transmission power of the lens,
the transmission efficiency of the system was calculated as
34% via experiment. They made a very good tracking system
of 0.1
°
precision to accommodate the system focusing level
at 2500 suns. The system is comprised of two feedback cir-
cles, namely, coarse and fine adjustments, via an angle
encoder and a special photodiode array accordingly. The
advantage of this system is that it can provide light to dark
rooms or underpasses by preventing or reducing the dissem-
ination of infrared rays (IR), ultraviolet (UV) rays, and ener-
getic particles thus reducing the amount of electrical power
consumption for air-conditioning systems [59]. The total
internal reflection angle was ±30
°
, and their experimental
results showed that the outcome of greater incident angles
is greater attenuation.
3.2.6. Core Sunlighting System. Khosravi et al. presented and
described a novel approach to daylighting called core sun-
lighting system (CSLS), which is consisted of active and pas-
sive optical modules to collect sunlight outside multifloor
buildings and then transfer the sunlight to the dark parts
of the building [60]. In the new approach, sunlight redirec-
tors that redirect sunlight at a predetermined angle to the
exterior facades of the building were mounted at the roof
level all around the building. The redirectors redirect sun-
light such that the entire façade was bathed by sunlight
and dispersed uniformly amongst multiple floors. A portion
Direct sunlight
Heliostats with
circular plane mirrors
Mirror light pipe
Focusing mirror
Figure 7: Conceptual design of solar tower heliostat array daylighting system for the illumination of multifloor buildings via mirror light
pipe (source: adapted from [5]).
20 International Journal of Photoenergy

of the sunlight at each floor was captured, concentrated, and
recollimated by the concentrator components mounted on
the facade of the building. The concentrator consisted of
the lens and an enclosure containing a separate lens and
mirror assembly. The light coming from the concentrator
was fed into the light guides and was then dispersed to the
core of the building efficiently. In the new design, sunlight
was captured from all sides, and therefore, it was stress-
free to transport uniform light to every part of the building
either small or large. To achieve high efficiency at high solar
altitudes, the vertical array of mirrors was replaced by a new
rotating redirector unit that can operate in two modes based
on the solar elevation [60].
3.2.7. Mirror Sunlighting System. Kim and Kim proposed a
mirror sunlighting system consisting of two optical systems
in which the first mirror is fixed on top the roof of the build-
ing in the northern hemisphere to guide the sunlight
through the building's core and to distribute the sunlight
via a secondary mirror reflector network to the areas inside
the building [61]. Their system had an 80 cm diameter clear
dome, double reflecting mirrors, a base, a tracking mecha-
nism, and an activator. The roof dome made of a see-
through acrylic covered with an ultraviolet shield material
was used to protect the initial reflecting mirror as shown
in Figure 10 and also ensure the transmittance of the sun
remains high. The primary mirror was designed with alumi-
nized glass having a circular shape of 75 cm diameter and
2.5 mm thickness since it was meant to track the sun, receive
the sunlight, and maintain high reflectance and durability.
The secondary reflecting mirror was made either flat or con-
cave for improving the adaptability to receive reflected sun-
light from the primary mirror reflector. For performance
evaluation, the mirror sunlighting system was positioned
on the rooftop of a four-story building in South Korea, and
on the first floor of the same building, a secondary mirror
was fixed ahead of the opening in a room to direct sunlight
to the inner part of the room. Experiments were conducted
during clear and overcast sky conditions, and the perfor-
mance of the system was measured in terms of illuminance
and sunlight illumination ratio. Results showed that with
the mirror sunlighting system, the illuminance level in a
semiunderground space can be improved by eleven times
with the use of a flat secondary reflective mirror and fifteen
times with the use of a concave secondary mirror. Conse-
quently, the concave secondary mirror was preferable for
the mirror sunlighting system [61].
3.2.8. Two-Stage Nonimaging Solar Concentrator. Majority
of the optical fiber daylighting systems are costly and easily
affected by pointing error and have a complex optical design
in which many stages of focusing devices are required to
reduce the nonuniformity of concentrated sunlight. To solve
the above-mentioned issues, Chong et al. proposed an alter-
native active daylighting system with a two-stage nonima-
ging solar concentrator (2S-NISC) incited by their earlier
research work in nonimaging optics as shown in Figure 11
[62–65]. The prototype 2S-NISC is made up of 80 pieces of
5 cm by 5 cm primary facet mirrors, 20 pieces of 8 cm by
8 cm secondary facet mirrors, and compactly packed POFs
as a daylight delivery system. The equivalent power conver-
sion efficiency of the prototype 2S-NISC was found to be
22% based on 170 W input solar power. For economic anal-
ysis, the proposed 2S-NISC daylighting system having an
optimized 4 m
2
collective area was projected to cost USD
1231.20. Taking a 4% interest rate and a 2% fuel inflation
into consideration, the total profit period of 6.1 years was
estimated. This is practical as the active daylighting system
has a lifetime of at least 15 years.
4. Waveguide of Daylight as Light
Transporting System
The waveguide of daylight, embracing optical fiber, light
pipe, light tubes, etc., plays an important role to transport
and distribute the collected daylight deep inside the building.
For an active daylighting system, a waveguide is purposely
designed to guide the daylight for a long distance in the
building especially to reach the room without a window.
For a passive daylighting system, a waveguide is only
designed for a certain application with a short distance
Himawari lens
Figure 8: Himawari solar lighting system (source: adapted from
[57]).
Concentrator
Sun positioning
device Reducing gears
Stepper motor
for altitude
Stepper motor
(inside) for azimuth
Angular
transducer
Figure 9: Active daylighting system consisted of dual-axis sun-
tracking and concentrating system (source: adapted from [59]).
21International Journal of Photoenergy

transmission inside a room in which the transmission effi-
ciency is not as good as an active daylighting system.
4.1. Solar Pipe or Sunpipe. Solar pipe or sunpipe, as it is nor-
mally called and trademarked by Solatube, has several other
names trademarked by various manufacturers which include
light pipes, solar tunnels, sun tubes, light tubes, sunlight
tubes, daylight pipes, and light tunnels. This type of wave-
guide has been in existence for approximately 4000 years,
which was first used by the Egyptians to send light to the
center of the pyramid via mirrors and light shafts. For
instance, a passive daylighting system consists of a top col-
lector as a skylight dome, reflective pipe tube, and an emitter
mounted inside the room to be lit. The passive daylighting
system reflects sunlight and normal daylight via an alumi-
num pipe with a pure silver base mirror finish. The light pipe
is sealed using a clear ultraviolent stabilized polycarbonate
top dome to avoid dust. The light uniformly spreads into
the room under the sun pipe through a smooth opaque fin-
ish or plain opal diffuser located at the ceiling of the room.
Kocifaj et al. highlighted that for the light tube to be highly
efficient, it must be targeted directly to the sun [23].
4.2. Fluorescent Fiber Solar Concentrator (FFSC). Wang et al.
proposed a fluorescent fiber solar concentrator (FFSC) consist-
ing of an optical fiber-based solar concentrator with a PMMA
plate and 150 pieces of 1 m long and 2 mm diameter three-
colored (green, red, and yellow) fluorescent fibers [41]. The
material of these fluorescent fibers is acrylic with embedded
quantum dots and there are 150 pieces of fluorescent fibers
evenly inserted into 1200 × 1200 mm PMMA plate with 2 mm
space in between two fibers. An aluminum brushing connects
each fluorescent fiber at the edges of the FFSC plate with a
10 m long and 2 mm diameter PMMA clear optical fiber and
fixed by a kind of ultraviolent glue. The concentrated light
was transported through the clear optical fiber to a remote dark
room. The FFSC has great prospective in remote interior day-
lighting for application in building integration and can also be
applied in underground areas of buildings such as car parks
during the daytime. This deviceproduceslightthathasthe
same color as direct sunlight. Wang et al. emphasized that irre-
spective of the advantages, a limitation was faced during their
research which was the deficiency in the fluorescent fiber mar-
ket because only fluorescent fiber of 2mm diameter was avail-
able and supplied [67].
4.3. Air-Clad Optical Rod Daylighting System. Shao and Cal-
low presented a novel static tubular daylighting device com-
posed of a set of light rods used in conveying light from
outside a building to areas with low illumination or dark
rooms within a building in Singapore [66, 68]. This device
called an air-clad optical rod daylighting system can receive
light passively similar to a light pipe and conveys light via
total internal reflection with high productivity like a fiber
optic cable having a small diameter. The light rod is a very
polished rod-shaped piece of optical clarity PMMA and
can be built into most existing buildings without the need
for structural adjustment as they are suitably small with a
diameter of 50 mm. It is manufacture d from optical quality
polymer and clad by air. In this design, the total internal
reflection uses the refraction of light at the boundary
between two surfaces having dissimilar refractive indexes
by covering a core material with a higher refractive index
with that of a lower refractive index. The air surrounding
the rod served as an ultralow refractive index cladding,
which led to a 180-degree total acceptance angle obtained
theoretically that is needed for a full, static collection of sky-
light all day. Test results showed that these rods have a light
transmittance equivalent to light pipe with an aspect ratio
six times smaller. To investigate the performance, Shao
and Callow compared the rod with a well-established day-
lighting technology: 300 mm diameter Monodraught Sun-
pipe called a light pipe, in which both work using the same
principles and perform about the same function. It was real-
ized that the same transmittance efficiency and diffuser-
surface illuminance of the light pipe is now available in a
more compact system, which is an advantage. On the other
hand, the ends of the rods are quite eye-catching and would
deliver a very good lighting effect with reduced glare. Light
pipes would be selected over the rods if the building enve-
lope permits the installation of light pipes. In contrast, if
the building fabric has limitations on the size of the device
or where a rare visual effect is needed, the rods are advanta-
geous [68, 69].
4.4. Rectangular Glass Optical Fiber. Aslian et al. proposed
the application of glass optical fibers having a rectangular
cross-section in a combined concentrator photovoltaic and
daylight system [70]. The use of rectangular glass optical
fiber (RGOF) can give better efficiency in coupling and light
power transmission compared to that of round fibers, as a
bundle of RGOFs is more tightly packed with very minimum
gaps between the fibers. Results of their simulation showed a
good match between the distribution of output flux and the
solar cell dimensions for the case of RGOF, which is the
same as the higher coupling efficiency of RGOF.
5. Economic Feasibility of Active and Passive
Daylighting Systems
When approaching the issue regarding the economic feasi-
bility of daylighting technologies, the first predicament faced
is the initial investment cost between the daylighting system
and the conventional lighting system. Conventionally, the
major considerations of an economic feasibility study for
Transparent roof
dome
First reecting mirror
Figure 10: Mirror sunlighting system showing the first reflecting
mirror (source: adapted from [61]).
22 International Journal of Photoenergy

daylighting systems embrace capital investment cost and
operation, and maintenance costs, which can be quantified
easily [71]. The real value of daylighting cannot be only
rated on electricity saving as there are other long-term ben-
efits such as natural lighting, low-energy building, sustain-
able lifestyle, and reducing greenhouse gas emission.
For active daylighting systems, Chong et al. conducted a
reasonable analysis based on various designs of active day-
lighting systems with single-axis and double-axis trackers
[62]. The study only considered the costs of the solar con-
centrator and sun-tracking system without waveguide and
building fitting for illuminating daylight. The costs are
USD 600-800 per m
2
for linear focusing concentrator such
as parabolic trough and linear Fresnel lens with single-axis
tracking, while the costs are as high as USD 1500-1882 per
m
2
for point focus parabolic reflector and Fresnel lens with
two-axis tracking.
For passive daylighting system, the initial capital invest-
ment will be lower than that of active daylighting system
because it does not require a solar concentrator with a
sun-tracking system. Instead, the illumination control sys-
tem is essential for both active and passive daylighting sys-
tems, which is important to sense the available daylight
and then control the illuminance level of the artificial lights
by dimming or turning offthe electric lights to achieve
energy saving. Li et al. analyzed the cost of integrating
hybrid semitransparent photovoltaic and daylighting system
to the office building in which the simple monetary payback
of just around 15 years was estimated considering electricity
tariff, chiller plant cost, and CO
2
trading in the calcula-
tion [72].
For maintenance cost, both active and passive daylight-
ing systems require a regular basis of cleaning to ensure
the optimal performance of the system. Hence, the cleaning
cost can be considered the most dominant factor in the
maintenance of both daylighting systems [73]. Additionally,
active daylighting system requires extra maintenance costs
for the tracking mechanism such as equipment service and
repair cost. For the operation cost, the active daylighting sys-
tem requires electricity to operate the motor and control
devices of the sun-tracking system. Since passive daylighting
does not require any electricity to function, the operating
cost can be negligible.
Besides the aforementioned cost analyses, some
researchers also included factors that are more difficult to
identify and quantify in the feasibility study such as building
heating and cooling saving, green building index, carbon tax
savings, CO
2
trading, and the effect of daylight on human
wellbeing in their cost-benefit analysis [71, 72, 74].
In 2009, Li et al. have performed the cost analysis of
lighting and daylighting schemes in Hong Kong by installing
energy-efficient lighting together with dimming control in a
Chinese restaurant [75]. By taking into account all the cost
factors, the simple payback period and internal rate of return
are 2.8 years and 26%, respectively. Kirankumar et al. stud-
ied the cost-saving of a triple-glazing system with different
configurations of reflective glasses to achieve payback period
ranging between 2.1 years and 4.5 years [76]. In 2016, Fon-
toynont et al. conducted the economic analysis of different
daylighting strategies for a standard French office building
to include moving service spaces to the periphery, increasing
ceiling height, and adding lightwells of various shapes. The
minimum payback period of the investment is 41 years
based only on savings on lighting electricity, but the benefits
should be beyond the electricity-saving that include occu-
pants’well-being, safety increase of an electrical blackout,
high rental and resell value [77]. In the same year, Mayhoub
and Papamichael conducted a cost-benefit analysis for build-
ing core sunlighting system (BCSS) by varying electricity
cost, electricity-saving, initial cost, and cleaning cost [73].
Their study concluded that the increment of electricity has
a significant impact on the reduction of the payback period
of the BCSS. They also stated that the BCSS is unlikely to
achieve a positive economic performance if the energy sav-
ing of the system is less than 50%. From the above literature,
it can be concluded that the payback period of daylighting
system is location-dependent due to different local weather
conditions (external illumination level), local electricity tar-
iff, and, labor cost.
The vision of daylighting must not be restricted within
the worthiness of investment in a short-term monetary ben-
efit but towards the aim of decarbonization for a long-term
Mirror
assembly set
Facet
mirror
Secondary concentrator
with secondary facet
mirrors
Primary concentrator
with primary facet
mirrors
Figure 11: Active daylighting system consisted of two-stage nonimaging solar concentrator (2S-NISC) (source: adapted from [63]).
23International Journal of Photoenergy

impact. It is also necessary to consider the quality of the
visual environment contributed to the occupant satisfaction
and psychophysiological wellbeing through a connection to
the outdoors and support for circadian rhythms [78]. From
the environmental point of view, greenhouse gases such as
CO
2
,SO
2
, and NO
x
emission from power generation are
one of the main causes of air pollution which are threatening
the health of human beings. The energy saved from daylight-
ing can reduce the usage of fossil fuel and greenhouse gas
emission to the environment to provide a greener and
cleaner planet earth for us and our future generation [75].
6. General Challenges and Prospects of
Daylighting Systems
Even though daylighting systems are known for their bene-
fits, some challenges still need to be overcome before they
can be widely deployed to reduce electricity consumption
for building lighting. By gathering various technological
and economic issues of daylighting systems, the challenges
are listed and discussed as the following [41, 45]:
(1) Most active daylighting systems are still expensive to
install because the whole system design is complicated
including solar collectors/concentrators, light trans-
mission systems, and electronic control systems.
Hence, it needs a large initial capital investment for
the hardware and software based on the width of the
roof space, which is the reason why many people are
still discouraged from installing active daylighting sys-
tems, especially for residential houses
(2) Solar energy is intermittent and not available at night. A
hybrid system must be built to complement a situation
when solar irradiance is low or not available during
nighttime in which the daylighting system is required
to couple with a conventional lighting system. The direct
component of solar irradiance can illuminate a space
more effectively and efficiently in both active and passive
daylighting systems. Moreover, a cloudy day with a high
diffuse component of solar irradiance can greatly reduce
the performance of daylighting. As a result, the con-
sumer should consider the cost of daylighting on top of
the existing artificial lighting in the architectural design
of the house, and a control system with sensors is also
necessary for managing the hybrid lighting systems
(3) Passive daylighting systems have various limitations
including the extra brightness gotten from the daily
and annual movement of the sun, heat, the limited
penetration depth inside the house, and blocking
by nearby buildings. Furthermore, the architectural
design of the house also affects the harnessing of pas-
sive daylighting in which solar irradiance usually
does not reach some areas of the house such as an
intermediate room without a window, dining area,
and basement. To overcome this issue, the passive
daylighting systems require additional investment
in light pipes for guiding the daylight deep into the
house but it still encounters difficulty in network dis-
tribution of light pipes or waveguides by considering
the bending angle of the waveguide. A large bending
angle can cause significant optical loss of daylight
transported via waveguide based on the total internal
reflection principle and subsequently suffers lighting
energy losses. Therefore, an appropriate study is
required on a case-by-case basis due to the location
and orientation of the house, proximity to tall build-
ings, etc.
(4) The solar radiation varies with latitude, longitude,
local weather conditions, and geographical land-
scape, which makes the availability of sunlight with
the regional locations change significantly according
to seasons. During winter in some countries, the
sunrays collected by solar collectors are not sufficient
to meet the day-to-day daylighting needs. Hence, a
supplementary source of power must be used, lead-
ing to extra costs
(5) Solar concentrators in an active daylighting system
must be equipped with a sun-tracking system at a
reasonably high accuracy during daily operation.
The sun-tracking system is crucial to align the sun-
light parallel with the central axis of the solar con-
centrator for the purpose of focusing and
transmitting the sunlight through the waveguide. It
is essential that the acceptance angle of the solar con-
centrator be larger than that of the pointing error of
the sun-tracking system to achieve high optical effi-
ciency of the solar concentrator. Consequently, the
performance of the sun-tracking system determines
the performance of the daylighting system
(6) Active and passive daylighting systems can be a
source of glare and radiate heat to the inhabitants
while providing illumination to the building, which
can make them uncomfortable and affect their eyes.
A house inhabitant who exposes his eyes to a bright
patch of daylight, either direct or reflected, will need
time to readjust his eyesight to see at lower light
levels. Regular eye adaptation caused by these issues
can negatively affect the eye leading to an eye defect.
Thus, daylighting control is very important to make
available enough illumination while keeping unnec-
essary heat gain to a minimum
(7) If the location of a daylighting system is within or
around a shaded area, its performance will be poor
because shade has a negative effect on solar collectors.
Shades and solar daylighting systems cannot coexist
together even though some manufacturers claim that
their daylighting systems are shade tolerant
The purpose of our review article is to review the various
existing configurations of passive and active daylighting sys-
tems, which can lead to a more sustainable configuration in
the future. Some critical findings and future scopes of studies
based on the articles reviewed are listed as follows:
24 International Journal of Photoenergy

(i) Smart home technology will be getting more popu-
lar in the future; hence, the integration of daylight-
ing systems into a smart controller for artificial
lighting systems can save unnecessary electricity
bills during the daytime. More research works can
be carried out to analyze the economic feasibility
and environmental impact on future smart homes
with the integration of daylighting systems
(ii) Artificial intelligence software can be developed for
designing active and passive daylighting systems
into the architectural design of buildings and resi-
dential houses. The artificial intelligence software
must be able to simulate the daily and annual illu-
mination pattern inside the house by considering
various factors including local weather data, geo-
graphical location of the subject, and nearby objects
such as trees, buildings, and hills
(iii) Comprehensive research works on the various
impacts of integrating daylighting systems into the
building including heat effect, the initial capital cost
of investment and return of investment, daylight
illumination pattern from a window, and comfort-
ability of daylight during different times must be
put into consideration
(iv) Material research is another aspect to accelerate the
deployment of a passive daylighting system into the
building. Referring to an article in Nature, Korgel com-
mented that the advancement in electrochromic win-
dow materials, which change color and/or
transparency when subjected to an electric field, can
revolutionize the design of new window glass by regu-
lating the heating and lighting requirements of build-
ings by responding to environmental changes [79].
Not long ago, in 2017, Davy et al. fabricated a new
organic solar cell made of hexabenzocoronene (cHBC)
derivatives in a laboratory at Princeton University har-
vesting near-ultraviolet photons to fulfill the unmet
requirement of powering smart windows to allow day-
light by significantly reducing heat and hence saving
about 40% in an average building’senergycosts[80].
Definitely, this is just one part of material science to
show the advancement of new material to influence
the deployment of daylight in the building
Through the review of the technologies and designs of
the existing daylighting systems, we can know what has been
done so far and the niche areas required for further research
and development. For sustainable development and energy
efficiency of buildings, there is still room for exploration to
increase the utilization of daylight. As part of a sustainable
building design, daylight deployment should be considered
in the early stages of a building project development [81].
7. Conclusion
As lighting consumes as high as 40% of the annual building
energy consumption, we have presented a comprehensive
review on both the active and passive daylighting systems
for achieving sustainable buildings. The economic feasibility
has been analyzed in detail where the initial investment cost
is considered high by taking into account electricity saving
alone, while the integrating of daylighting system into the
architecture of the building can bring long-term impact for
a sustainable building including occupants’well-being, natu-
ral lighting, low-energy building, sustainable lifestyle, and
reducing greenhouse gas emission. In general, the challenges
of daylighting systems are also discussed to understand the
existing problems hindering the extensive implementation
of daylighting system in the building. More research works
should be encouraged in developing better and more creative
designs of daylighting systems for sustainable buildings that
are affordable, easy to install, environment-friendly, less
energy-intensive, comfortable, and capable of providing uni-
form illumination. In a view of long-term impact, United
Nations Sustainable Development Goals and the govern-
ment policy are important factors to increase awareness
and to encourage the adoption of daylighting systems for
achieving sustainable buildings.
Data Availability
The numerical data used to support the findings of this
study are included within the article.
Conflicts of Interest
The authors have no conflicts of interest to declare.
Acknowledgments
The authors would like to express their gratitude to the Min-
istry of Energy, Green Technology and Water (AAIBE Trust
Fund) with vote account 4356/001. Besides, the authors
would also like to express their gratitude to UTAR Strategic
Research Fund 2018 with project number IPSR/RMC/U-
TARSRF/PROJECT 2018-C1/001 (vote account 6274/011)
for the financial support.
References
[1] S. Kubba, Handbook of Green Building Design and Construc-
tion, Elsevier/Butterworth-Heinemann, Amsterdam, 2017.
[2] A. M. Omer, “Green energies and the environment,”Renew-
able and Sustainable Energy Reviews, vol. 12, pp. 1789–1821,
2008.
[3] M. S. Alrubaih, M. F. M. Zain, M. A. Alghoul, N. L. N. Ibrahim,
M. A. Shameri, and O. Elayeb, “Research and development on
aspects of daylighting fundamentals,”Renewable and Sustain-
able Energy Reviews, vol. 21, pp. 494–505, 2013.
[4] M. Krarti, P. M. Erickson, and T. C. Hillman, “A simplified
method to estimate energy savings of artificial lighting use
from daylighting,”Building and Environment, vol. 40,
pp. 747–754, 2005.
[5] I. Ullah and S. Shin, “Concept of solar tower for daylighting in
multi-floor buildings,”vol. 1, pp. 2–7, 2013.
25International Journal of Photoenergy

[6] F. C. Winkelmann and S. Selkowitz, “Daylighting simulation
in the DOE-2 building energy analysis program,”Energy and
Buildings, vol. 8, pp. 271–286, 1985.
[7] D. Phillips, Daylighting: Natural Light in Architecture, Archi-
tectural Press, Elsevier, Oxford, 2004.
[8] E. C. Castanheira, H. A. Souza, and M. Z. Fortes, “Influence of
natural and artificial light on structured steel buildings,”
Renewable and Sustainable Energy Reviews, vol. 48, pp. 392–
398, 2015.
[9] Y. W. Lim and M. H. Ahmad, “Daylighting as a sustainable
approach for high-rise offices in tropics,”International Journal
of Real Estate Studies, vol. 8, pp. 30–42, 2013.
[10] J. C. McVeigh, Sun Power: An Introduction to the Applications
of Solar Energy, Pergamon, Oxford, 1983.
[11] F. Sharp, D. Lindsey, J. Dols, and J. Coker, “The use and envi-
ronmental impact of daylighting,”Journal of Cleaner Produc-
tion, vol. 85, pp. 462–471, 2014.
[12] T. Huang, H. Hocheng, T. Chou, and W. Yang, “Bring free
light to buildings: overview of daylighting system,”in Mate-
rials and Processes for energy, A. Mendez-Vilas, Ed., pp. 639–
648, Formatex Research Center, Spain, 2013.
[13] D. L. DiLaura, K. W. Houser, R. G. Mistrick, and G. R. Steffy,
Illuminating Engineering Society: The Lighting Handbook. Ref-
erence and Application, 10th edition10th edition, , 2011.
[14] P. Lotfabadi, “Analyzing passive solar strategies in the case of
high-rise building,”Renewable and Sustainable Energy
Reviews, vol. 52, pp. 1340–1353, 2015.
[15] “Encyclopedia of Alternative Energy: The Worlds of David
Darling,”August 2020, (http://www.daviddarling.info/
encyclopedia/P/AE_passive_solar_design.html).
[16] K. M. Al-Obaidi, M. Ismail, and A. M. Abdul Rahman, “A
study of the impact of environmental loads that penetrate a
passive skylight roofing system in Malaysian buildings,”Fron-
tiers of architectural research, vol. 3, pp. 178–191, 2014.
[17] A. Zain-Ahmed, K. Sopian, M. Y. H. Othman, A. A. M. Sayigh,
and P. N. Surendran, “Daylighting as a passive solar design
strategy in tropical buildings: a case study of Malaysia,”Energy
Conversion and Management, vol. 43, pp. 1725–1736, 2002.
[18] C. Ciugudeanu and D. Beu, “Passive tubular daylight guidance
system survey,”Procedia Technology, vol. 22, pp. 690–696,
2016.
[19] I. L. Wong, “A review of daylighting design and implementa-
tion in buildings,”Renewable and Sustainable Energy Reviews,
vol. 74, pp. 959–968, 2017.
[20] E. J. Gago, T. Muneer, M. Knez, and H. Koster, “Natural light
controls and guides in buildings. Energy saving for electrical
lighting, reduction of cooling load,”Renewable and Sustain-
able Energy Reviews, vol. 41, pp. 1–13, 2015.
[21] Wikipedia. SkylightSeptember 2020, https://en.wikipedia.org/
wiki/Skylight.
[22] M. Paroncini, B. Calcagni, and F. Corvaro, “Monitoring of a
light-pipe system,”Solar Energy, vol. 81, pp. 1180–1186, 2007.
[23] M. Kocifaj, F. Kundracik, S. Darula, and R. Kittler, “Availabil-
ity of luminous flux below a bended light-pipe: design model-
ling under optimal daylight conditions,”Solar Energy, vol. 86,
pp. 2753–2761, 2012.
[24] Orange County Skylights, “Skylight guide,”September 2020,
https://ocskylights.com/skylight-guide/.
[25] Vedant façade designer, “Skylights,”September 2020, https://
vedantfacade.com/sky-lights-3/.
[26] E. Cuce and S. B. Riffat, “A state-of-the-art review on innova-
tive glazing technologies,”Renewable and Sustainable Energy
Reviews, vol. 41, pp. 695–714, 2015.
[27] B. P. Jelle, A. Hynd, A. Gustavsen, D. Arasteh, H. Goudey, and
R. Hart, “Fenestration of today and tomorrow: a state-of-the-
art review and future research opportunities,”Solar Energy
Materials & Solar Cells, vol. 96, pp. 1–28, 2011.
[28] W. J. Hee, M. A. Alghoul, B. Bakhtyar et al., “The role of win-
dow glazing on daylighting and energy saving in buildings,”
Renewable and Sustainable Energy Reviews, vol. 42, pp. 323–
343, 2015.
[29] J. Livingston, Designing with Light: The Art, Science and Prac-
tice of Architectural Lighting Design, John Wiley & Sons, Inc.,
Hoboken, New Jersey, 2014.
[30] “The global home of chemical engineers. From soda bottle to
solar lightbulb,”October 2020, https://www.aiche.org/
chenected/2011/09/soda-bottle-solar-light-bulb.
[31] L. Shi and M. Chew, “A review on sustainable design of renew-
able energy systems,”Renewable and Sustainable Energy
Reviews, vol. 16, pp. 192–207, 2012.
[32] D. Booth, J. Booth, and P. Boyles, “Building for energy inde-
pendence: sun/earth buffering and superinsulation,”Commu-
nity Builders, 1983.
[33] A. M. Omer, “Focus on low carbon technologies: the positive
solution,”Renewable and Sustainable Energy Reviews, vol. 12,
pp. 2331–2357, 2008.
[34] M. Boubekri, “Daylighting Strategies,”in Daylighting architec-
ture and health, pp. 111–126, Elsevier, 2008.
[35] U. Berardi and H. K. Anaraki, “Analysis of the impact of light
shelves on the useful daylight illuminance in office buildings in
Toronto,”Energy Procedia, vol. 78, pp. 1793–1798, 2015.
[36] “Pinterest. Section Design - eLADwiki,”October 20, 2020,
https://www.pinterest.com/pin/54887689184732372/.
[37] A. Ikuzwe and A. B. Sebitosi, “A novel design of a daylighting
system for a classroom in rural South Africa,”Solar Energy,
vol. 76, pp. 359–368, 2004.
[38] K. Kapsis, A. Tzempelikos, A. K. Athienitis, and R. G. Zmeureanu,
“Daylighting performance evaluation of a bottom-up motorized
roller shade,”Solar Energy,vol.84,pp.2120–2131, 2010.
[39] H. Shen and A. Tzempelikos, “Daylighting and energy analysis
of private offices with automated interior roller shades,”Solar
Energy, vol. 86, pp. 681–704, 2012.
[40] A. A. Earp, G. B. Smith, J. Franklin, and P. D. Swift, “Optimi-
sation of a three-colour luminescent solar concentrator day-
lighting system,”Solar Energy Materials and Solar Cells,
vol. 84, pp. 411–426, 2004.
[41] C. Wang, H. Abdul-Rahman, and S. P. Rao, “Daylighting can
be fluorescent: development of a fibre solar concentrator and
test for its indoor illumination,”Energy and Buildings,
vol. 42, pp. 717–727, 2010.
[42] A. A. Earp, G. B. Smith, P. D. Swift, and J. Franklin, “Maximiz-
ing the light output of a luminescent solar concentrator,”Solar
Energy, vol. 76, pp. 655–667, 2004.
[43] F. Muhammad-sukki, R. Ramirez-iniguez, S. G. Mcmeekin,
B. G. Stewart, and B. Clive, “Solar concentrators,”Interna-
tional Journal of Applied Science, vol. 1, pp. 1–15, 2010.
[44] J. Zafrullah, Tracking Solar Concentrators, Springer, Heidel-
berg, London, 2013.
[45] I. Ullah and S. Shin, “Highly concentrated optical fibre-based
daylighting systems for multi-floor office buildings,”Energy
and Buildings, vol. 72, pp. 246–261, 2014.
26 International Journal of Photoenergy

[46] I. Ullah and S. Shin, “Uniformly illuminated efficient daylight-
ing system,”Smart Grid Renew Energy, vol. 4, pp. 161–166,
2013.
[47] Y. Tripanagnostopoulos, C. Siabekou, and J. K. Tonui, “The
Fresnel lens concept for solar control of buildings,”Solar
Energy, vol. 81, pp. 661–675, 2007.
[48] H. Mousazadeh, A. Keyhani, A. Javadi, H. Mobli, K. Abrinia,
and A. Sharifi,“A review of principle and sun-tracking
methods for maximizing solar systems output,”Renewable
and Sustainable Energy Reviews, vol. 13, pp. 1800–1818, 2009.
[49] I. Ullah and S. Shin, “Development of optical fiber-based day-
lighting system with uniform illumination,”Journal of the
Optical Society of Korea, vol. 16, pp. 247–255, 2012.
[50] J. Muhs, Design and Analysis of Hybrid Solar Lighting and Full-
Spectrum Solar Energy Systems, American Solar Energy
Society’s, Madison, Wisconsin, 2000.
[51] H. J. Han, M. U. Mehmood, R. Ahmed et al., “An advanced
lighting system combining solar and an artificial light source
for constant illumination and energy saving in buildings,”
Energy and Building, vol. 203, article 109404, 2019.
[52] T. T. Pham, N. H. Vu, and S. Shin, “Daylighting system based
on novel design of linear Fresnel lens,”Buildings, vol. 7, p. 92,
2017.
[53] G. O. Schlegel, F. W. Burkholder, S. A. Klien, W. A. Beckman,
B. D. Wood, and J. D. Muhs, “Analysis of a full spectrum
hybrid lighting system,”Solar Energy, vol. 76, pp. 359–368,
2004.
[54] C. Sapia, “Daylighting in buildings: developments of sunlight
addressing by optical fiber,”Solar Energy, vol. 89, pp. 113–
121, 2013.
[55] A. Tsangrassoulis, L. Doulos, M. Santamouris et al., “On the
energy efficiency of a prototype hybrid daylighting system,”
Solar Energy,vol. 79, pp. 56–64, 2005.
[56] P. E. Kristensen, “Daylighting technologies in non-domestic
buildings,”International Journal of Sol Energy, vol. 15,
pp. 55–67, 1994.
[57] Himawari-http://net.co.jp. Himawari Solar Lighting System,La
Foret Engineering Co., Ltd, 2015, October 27, 2020, https://
www.himawari-net.co.jp/e_page-index01.html.
[58] X. Chen, X. Zhang, and J. Du, “The potential of circadian light-
ing in office buildings using a fibre optics daylighting system in
Beijing,”Building and Environment, vol. 182, pp. 107–118,
2020.
[59] J. Song, Y. Zhu, Z. Jin, and Y. Yang, “Daylighting system via
fibers based on two-stage sun-tracking model,”Solar Energy,
vol. 108, pp. 331–339, 2014.
[60] S. Khosravi, M. A. Mossman, and L. A. Whitehead, “Core sun-
lighting system, a new approach to daylighting in buildings,”
Energy Procedia, vol. 57, pp. 1951–1960, 2014.
[61] J. K. Kim and G. Kim, “Overview and new developments in
optical daylighting systems for building a healthy indoor envi-
ronment,”Building and Environment, vol. 45, pp. 256–269,
2010.
[62] K. K. Chong, N. O. Onubogu, T. K. Yew, C. W. Wong, and
W. C. Tan, “Design and construction of active daylighting sys-
tem using two-stage non-imaging solar concentrator,”Applied
Energy, vol. 207, pp. 45–60, 2017.
[63] N. O. Onubogu, “Wide acceptance angle optical fiber-based
daylighting system using two-stage reflective non-imaging
solar concentrator,”Master of Engineering Science Thesis, Uni-
versiti Tunku Abdul Rahman, Malaysia, 2017.
[64] O. N. Obianuju and K. K. Chong, “High acceptance angle opti-
cal fiber based daylighting system using two-stage reflective
non-imaging dish concentrator,”Energy Procedia, vol. 105,
pp. 498–504, 2017.
[65] N. O. Onubogu, K. K. Chong, C. W. Wong, T. K. Yew, and
B. H. Lim, “Optical characterization of two-stage non-
imaging solar concentrator for active daylighting system,”
Solar Energy, vol. 185, pp. 24–33, 2019.
[66] J. M. Callow and L. Shao, “Air-clad optical rod daylighting sys-
tem,”Lighting Research & Technology, vol. 35, pp. 31–38, 2003.
[67] C. Wang, H. Abdul-Rahman, and S. P. Rao, “Development and
testing of a fluorescent fibre solar concentrator for remote daylight-
ing,”Journal of Energy Engineering, vol. 136, no. 3, pp. 76–86, 2010.
[68] L. Shao and J. M. Callow, “Daylighting performance of optical
rods,”Solar Energy, vol. 75, pp. 439–445, 2003.
[69] J. M. Callow and L. Shao, “Performance of air-clad optical rod
daylighting system. Right Light 5,”in Proceedings of the 5th
International Conference on Energy Efficient Lighting, pp. 20–
31, Nice, France, May 2002.
[70] A. Aslian, K. K. Chong, S. H. Tavassoli, C. J. Tan, and O. B.
Hazave, “Rectangular glass optical fiber for transmitting sun-
light in a hybrid concentrator photovoltaic and daylighting
system,”International Journal of Photoenergy, vol. 2020, Arti-
cle ID 8813688, 2020.
[71] M. Mayhoub and D. Carter, “The costs and benefits of using
daylight guidance to light office buildings,”Building and Envi-
ronment, vol. 46, no. 3, pp. 698–710, 2011.
[72] D. H. Li, T. N. T. Lam, W. W. H. Chan, and A. H. L. Mak,
“Energy and cost analysis of semi-transparent photovoltaic in
office buildings,”Applied Energy,vol.86,no.5,pp.722–729, 2009.
[73] M. Mayhoub and K. Papamichael, “Cost/benefit analysis for
building core sunlighting systems,”Energy and Buildings,
vol. 118, pp. 37–45, 2016.
[74] A. Bakshi and J. A. Jakubiec, A simple cost-benefit estimation
for daylighting design and analysis during the design process
in Building Simulation, 2011.
[75] D. H. Li, A. H. Mak, W. W. Chan, and C. C. Cheng, “Predict-
ing energy saving and life-cycle cost analysis for lighting and
daylighting schemes,”International Journal of Green Energy,
vol. 6, no. 4, pp. 359–370, 2009.
[76] K. Gorantla, S. Shaik, K. J. Kontoleon, D. Mazzeo, V. R.
Maduru, and S. V. Shaik, “Sustainable reflective triple glazing
design strategies: spectral characteristics, air-conditioning cost
savings, daylight factors, and payback periods,”Journal of
Building Engineering, vol. 42, p. 103089, 2021.
[77] M. Fontoynont, K. Ramananarivo, T. Soreze, G. Fernez, and
K. G. Skov, “Economic feasibility of maximising daylighting
of a standard office building with efficient electric lighting,”
Energy and Buildings, vol. 110, pp. 435–442, 2016.
[78] M. Andersen, “Unweaving the human response in daylighting
design,”Building and Environment, vol. 91, pp. 101–117, 2015.
[79] B. Korgel, “Composite for smarter windows,”Nature, vol. 500,
pp. 278-279, 2013.
[80] N. C. Davy, M. Sezen-Edmonds, J. Gao et al., “Pairing of near-
ultraviolet solar cells with electrochromic windows for smart
management of the solar spectrum,”Nature Energy, vol. 2,
p. 17104, 2017.
[81] F. Jalaei and A. Jrade, “Integrating building information
modelling (BIM) and LEED system at the conceptual design
stage of sustainable buildings,”Sustainable Cities and Society,
vol. 18, pp. 95–107, 2015.
27International Journal of Photoenergy