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Daylight, Energy
and Indoor Climate
Basic Book
Daylight, Energy and Indoor Climate Basic Book
Version 3.0 – 2014
VAS 455232-071 0 © 2014 VELUX GROUP. ® VELUX AND TH E VELUX LOGO ARE REGIS TERED TRADEMA RKS USED UNDER LICEN SE BY THE VELUX GROUP.
Content
Contents
Preface 3
Introduction 5
1 Daylight 9
1.1 Daylight 11
1.2 Daylighting 14
1.3 Daylighting quality 16
1.3.1 Visual needs 16
1.3.2 Non-visual effects of light 19
1.4 Benefits of daylight 25
1.4.1 Human benefits 25
1.4.2 Energy savings for electric lighting 29
1.4.3 Environmental benefits 31
1.5 Parameters influencing daylighting performance 32
1.5.1 Climate 32
1.5.2 Latitude 34
1.5.3 Obstructions and reflections on site 36
1.5.4 Building design 38
1.5.5 Windows and skylights 43
1.5.6 Sun tunnels 47
1.6 Daylight with roof windows, flat-roof windows and modular skylights 48
1.6.1 Impact of three window configurations on daylight conditions 48
1.6.2 Effects of roof windows in Solhuset kindergarten 51
1.6.3 Effects of adding flat-roof windows and modular skylights
to a former town hall, now a kindergarten 53
1.6.4 Effects of roof windows in Green Lighthouse 55
1.6.5 Effects of roof windows when renovating school buildings 56
1.6.6 Effect of roof windows in MH2020 Sunlighthouse 59
1.6.7 Effect of roof windows in the renovation of residential buildings 62
1.7 Daylight calculations and measurements 66
1.7.1 Illuminance 66
1.7.2 Luminance 68
1.7.3 Daylight factor 70
1.7.4 Daylight autonomy 73
1.7.5 Useful daylight illuminance (UDI) 74
1.8 Daylight simulation tools 75
1.9 Daylight requirements in building codes 79
1.9.1 Building Codes 80
1.9.2 The European Committee for Standardization, CEN 81
1.9.3 The International Organization for Standardization, ISO 81
1.9.4 Design Guidelines 82
2 Ventilation 83
2.1 Indoor Air Quality 85
2.1.1 How to achieve good indoor air quality 85
2.1.2 Indoor air quality indicators 89
2.1.3 Health 91
2.1.4 Increased airtightness requires occupant action 93
2.1.5 Mental performance and indoor air quality 97
2.2 Ventilation and ventilation systems 98
2.2.1 Natural ventilation 98
2.2.2 Mechanical ventilation 100
2.2.3 Hybrid ventilation 101
2.2.4 Demand-controlled ventilation 105
2.3 Fresh air from outside 106
2.4 Natural ventilation with roof windows 108
2.4.1 Driving forces of natural ventilation 108
2.4.2 Background ventilation with VELUX ventilation flap 112
2.4.3 Airing 114
2.4.4 Optimal winter ventilation strategy for existing buildings 117
2.4.5 Summer ventilation 117
2.4.6 Automatic window opening with VELUX roof windows 118
2.5 Ventilation of different building types 119
2.5.1 Renovation of residential buildings 119
2.5.2 New residential buildings 12 1
2.5.3 Schools and kindergartens 124
2.5.4 Commercial buildings 124
2.6 Tools and calculation methods 126
2.6.1 VELUX Energy and Indoor Climate Visualizer 127
2.7 Building codes and standards 129
3 Thermal comfort 133
3.1 How to achieve thermal comfort 135
3.1.1 Thermal discomfort 136
3.1.2 Parameters influencing thermal comfort 138
3.1.3 The preference for variation in temperature 139
3.1.4 Adaptation to a warm climate 139
3.2 Health impacts of the thermal environment 141
3.2.1 Heat strokes 141
3.2.2 Effect of uniform temperature indoors 141
3.2.3 Sleep quality 1 41
3.3 Productivity and learning 142
3.4 Thermal comfort with roof windows and solar shading 144
3.4.1 Blinds and shutters 144
3.4.2 Ventilative cooling 148
3.4.3 Night cooling 153
3.4.4 Automatic control 156
3.5 Building types and climate 159
3.5.1 Renovation of residential buildings 159
3.5.2 New residential buildings 159
3.5.3 Low-energy buildings 159
3.5.4 Schools and kindergartens 160
3.5.5 Commercial buildings 160
3.5.6 Effect of climate change and urban heat islands 161
3.6 Evaluation methods 166
3.6.1 Parameters 166
3.6.2 Evaluation of an existing building 167
3.6.3 Tools and calculation methods for evaluation during
the design phase 167
3.6.4 Regulation and standards on thermal comfort 169
4 Acoustics 171
4.1 Noise or sound 17 3
4.1.1 Technical description of noise or sound 176
4.2 Good acoustic environments 178
4.3 Indoor noise 179
4.3.1 General 179
4.3.2 Bedroom, living room and kitchen 179
4.3.3 Mechanical equipment 180
4.4 Outdoor noise 18 1
4.4.1 General 18 1
4.4.2 Parameters affecting outdoor noise level 181
4.4.3 Traffic noise 181
4.4.4 Rain noise 184
4.4.5 Heavy noise (aircraft, trains, trucks) 184
4.5 Evaluation and measurements 186
4.5.1 General aspects 186
4.5.2 Sound insulation 186
4.5.3 Measurement of sound insulation according
to European standards 187
4.6 Acoustics requirements in building codes 190
5 Energy 191
5.1 Energy 193
5.2 Energy sources 193
5.3 Energy terminology 195
5.4 Energy use in buildings 196
5.4.1 Primary energy vs. net energy 197
5.5 Window systems 199
5.5.1 U value 199
5.5.2 g value 200
5.5.3 Energy balance 200
5.6 Energy performance of different building types 204
5.6.1 Energy aspects of daylight 204
5.6.2 Energy aspects of ventilation 208
5.6.3 Energy aspects of solar shading 209
5.6.4 Building energy performance in cold climates 209
5.6.5 Building energy performance in warm climates 21 0
5.6.6 Consequences of future requirements
for better energy performance 21 1
5.7 Renewable solar energy supply 21 4
5.7.1 Solar thermal system 216
5.7.2 Photovoltaic system (PV) 21 8
5.8 Index 222
6 Environment 223
6.1 Life Cycle Assessments 225
6.1.1 LCA 225
6.1.2 Other parameters of life cycle assessments 227
6.2 The European methodology for assessing sustainability of buildings 228
6.2.1 Framework 228
6.3 Assessments of buildings 229
6.3.1 Active House 229
6.3.2 BREEAM 231
6.3.3 German Sustainable Building Council (DGNB) 2 31
6.3.4 French Haute Qualité Environemetn (HQE) 231
6.3.5 LEED 231
6.3.6 Passive House 232
6.3.7 Green Building Councils 232
6.4 Assessment of construction Products 232
6.4.1 Construction products and Environmental Product
Declarations Active House 232
6.4.2 Other Environmental Performance Declarations (EPDs) 233
6.5 Overview of EU legislation 234
6.5.1 Construction Products Regulation (CPR) 234
6.5.2 Registration, Evaluation and Authorisation
of Chemicals (REACH) 234
6.5.3 Restriction of Hazardous Substances(RoHS) 235
6.5.4 Battery Directive 235
6.5.5 Waste of Electrical and Electronic Equipment (WEEE) 235
6.6 Index 236
References 237
Glossary 257
1 VELUX
Preface
2 PREFACE 3 VELUX
Preface
Daylight, Energy and Indoor Climate
at the heart of the VELUX brand
Daylight and fresh air have been at the
core of our business since the company
was founded in 1942. By bringing day-
light and fresh air into people's homes,
the VELUX Group has helped to create
spaces of high quality and to increase
the health and well-being of the occu-
pants.
The benefits of VELUX products are
more important today than ever before.
Health and well-being constitute one
of the most important agendas of the
future, and a sharper focus on energy
savings must not be allowed to over-
shadow the indoor climate.
A good indoor climate, with generous
daylight levels and provision of fresh
air from outside, is the key to making
homes, offices, kindergartens and
schools healthy places to live and work
in. Our health and well-being are essen-
tial parameters to the quality of our
lives; but we spend an excessive
amount of time inside buildings – and
the air that we breathe and the daylight
we are exposed to have a great impact
on those parameters. In recent years,
much of the debate on sustainable ar-
chitecture – and the public discourse on
sustainability as a whole – has focused
on energy, CO² emissions and the effi-
cient use of material resources. These
are all vitally important issues for our
survival on this planet; but they are only
three of a whole spectrum of issues fac-
ing us as human beings living in the built
environment. Because health and well-
being are paramount to all of us, the
primary goal for sustainable homes and
urban areas should be to preserve those
precious benefits for the people who
live in them.
Why this Daylight, Energy and
Indoor Climate Book?
With this book, we aim to share our in-
sight and knowledge by giving specific
advice and concrete documentation on
the effects and benefits of VELUX
products in buildings. When creating
new buildings – as well as renovating
existing ones – the specific solutions
need to be considered in a holistic per-
spective , with usage, personal needs,
function, location, orientation, building
geometry and window configuration
playing very important roles.
4 PREFACE 5 VELUX
Daylight, Energy and Indoor Climate Basic Book
3rd edition December 2014
Issued by
VELUX Knowledge Centre for Daylight, Energy and Indoor Climate (DEIC)
Editorial team:
Per Arnold Andersen, per.a.andersen@velux.com
Karsten Duer, karsten.duer@velux.com
Peter Foldbjerg, peter.foldbjerg@velux.com
Nicolas Roy, nicolas.roy@velux.com
Jens Christoffersen, jens.christoffersen@velux.com
Thorbjørn Færing Asmussen, thorbjorn.asmussen@velux.com
Karsten Andersen, karsten.andersen@velux.com
Christoffer Plesner, christoffer.plesner@velux.com
Marie Helms Rasmussen, marie.helmsrasmussen@velux.com
Frank Hansen, frank.hansen@velux.com
Responsible editor:
Per Arnold Andersen, per.a.andersen@velux.com
Find more information on www.velux.com
Introduction
Indoor climate in a historical
perspective
Daylight and ventilation by windows
are inseparably connected to indoor
climate. Indoor climate encompasses
all the elements: temperature, humidity,
lighting, air quality, ventilation and
noise levels in the habitable structure.
We spend most of our time indoors.
Yet the indoor environment is discussed
much less than the outdoor environ-
ment. The presumption is that we are
safe indoors. Buildings provide shelter,
warmth, shade and security; but they
often deprive us of fresh air, natural
light and ventilation.
The positive health effect of light, in
this case of sunlight, was acknowl-
edged by the Egyptians, ancient Greeks
and Romans, each of whom worshipped
their own sun god. Much later, at the
beginning of the 1900s, sunlight as a
healer was put to practical use. Sanato-
ria were built to administer light therapy
for people suffering from skin diseases
and other ailments.
The importance of the indoor environ-
ment, and of indoor air quality in par-
ticular, was recognised as early as the
first century BC. However, it was not
until the early decades of the twentieth
century that the first relations between
parameters describing heat, lighting
and sound in buildings and human
needs were established. In fact, the last
hundred years have seen much effort
put into management of the indoor
environment, with the goal of creating
healthy and comfortable conditions for
the people living, working and recreat-
ing in them.
In the late 19th century, the environ-
mental factor ‘thermal comfort’ was
introduced as being part of the overall
concept of indoor comfort. It was rec-
ognised that poorly ventilated rooms,
besides being responsible for poor air
quality, could also result in unwanted
thermal effects through both tempera-
ture and humidity.
Although we spend most of our time in-
doors, we are still “outdoor animals”
(Baker N, 2009). The forces that have
selected the genes of contemporary
man are found in the plains, forests and
mountains, not in centrally heated bed-
rooms or ergonomically designed work-
stations. We have adapted to the indoor
life, but our gene code is still defined for
outdoor life. Sick building syndrome,
winter depressions, asthma and aller-
gies are symptoms linked to the quality
of the indoor environment in terms of
our biological needs. It is imperative
that buildings and spaces where we
spend much of our time are designed
with those needs in mind; going back
to nature, with natural ventilation and
natural lighting.
6 PREFACE 7 VELUX
How to evaluate the quality of
the indoor climate?
There are no general methods that
encompass everything in a formula or
a single number. There are several
indicators for how we can support our
biological and physiological needs;
ventilation rate for natural ventilation,
daylight levels to be achieved, solar
radiation exposure levels, comfortable
temperature levels, relative humidity
levels, sound levels and so on. The chap-
ters of this book will explain the individ-
ual indicators and offer advice on spe-
cific levels that should be achieved to
create a good indoor climate.
It is, however, just as important to
evaluate the indoor environment with
our senses; do we feel well indoors?
Human factors, including physiology,
perception, preferences, and behaviour
make every individual a very accurate
sensor. The indoor environment is more
than the sum of its parts, and its
assessment has to start with human
beings.
Indoor climate and health
The human senses, “windows of the
soul” (Bluyssen, 2010), are basically the
instruments we have to report or indi-
cate whether we feel comfortable in
the indoor environment and how we
feel our health is affected by it. We
judge the indoor environment by its
acceptability with respect to heat, cold,
smell, noise, darkness, flickering light
and other factors. But in terms of
health effects, it is not just the human
senses that are involved, but the whole
body and its systems. Indoor environ-
mental stressors that can cause dis-
comfort and adverse health effects
comprise both environmental and
psychosocial factors, such as working
and personal relationships. However,
the greatest impact on our health from
the indoor environment comes from the
availability and quality of daylight and
fresh air.
The prevalence of diseases like allergies
and asthma is increasing rapidly. This
trend is attributed to changes in the
indoor environment, but there is still
limited understanding of the specific
causes. Presently, the only solid conclu-
sion is that humid buildings are a cause.
Sunlight is a natural anti-depressant
that helps us synchronise with the
natural rhythm of life, and direct sun-
light and high daylight exposure levels
are shown to be effective in preventing
winter depressions.
Indoor climate and energy
consumption
The focus on energy savings is an in-
creasing challenge to existing building
stock as well as new and future build-
ings, as energy consumption is believed
to result in climate changes. It is, how-
ever, important to remember that all
energy in buildings is used to serve peo-
ple’s needs, comfort and well-being.
The VELUX Group considers Sustainable
Living as a way of making the changes
to limit the environmental impact at
home, without compromising on the
quality of the indoor environment.
Optimal use of daylight, natural ventila-
tion during summertime, and intelli-
gently controlled solar shading are all
examples of technologies that – in com-
bination with intelligent building design
– can be used to reduce the energy con-
sumption of new and existing buildings.
It is all about the sun; without solar
radiation there would be no light, no
wind, no heat, no life. And the solar ra-
diation reaching the earth is far larger
than the sum of energy needed. Solar
energy is often viewed as a set of niche
applications with a useful but limited po-
tential.
However, it is the only supply-side energy
solution that is both large enough and
acceptable enough to sustain the plan-
et’s long-term requirements; available
solar energy exceeds the world´s annual
energy consumption by a factor of
1 500 (Perez, 2009). Fossil fuels like oil
and coal alone could fulfil our energy
needs for another three or four genera-
tions, but would do so at a considerable
environmental cost (Perez, 2009).
Environment
The production, disposal and lifetime
use of VELUX products potentially im-
pact the environment in other ways
than through climate change, and ma-
terials like wood, glass and aluminium
should be used with environmental im-
pact in mind. The VELUX Group uses
Life Cycle Assessment to evaluate the
impact of its products on the environ-
ment.
9 VELUX
Daylight
10 DAY LI GH T 11 VELUX
» There is no substitute for daylight «
0500 1000 1500 2000
Wavelength [nm]
Flux [W]
VisibleIRUV
380
2500
780
Figure 1 .1 Diagram of the elec tromagnetic spe ctrum showing the lo cation
of the visibl e spectrum.
Daylight
Daylight has been used for centuries as the
primary source of light in interiors and has
been an implicit part of architecture for as
long as buildings have existed. Not only does
it replace electric light during daytime,
reducing energy use for lighting, it also influ-
ences both heating and cooling loads, which
makes it an important parameter of an energy-
efficient design. Additionally, recent research
has proved that daylight provides an array of
health and comfort benefits that make it
essential for buildings’ occupants.
1.1 Daylight
Daylight is described as the combina-
tion of all direct and indirect light ori-
ginating from the sun during daytime.
Of the total solar energy received on
the surface of the earth, 40% is visible
radiation and the rest is ultraviolet
(UV) and infrared (IR) wavelengths,
as shown in Figure 1.1.
Daylight availability outside varies for
different locations due to different sun
paths and sky conditions through the
course of the day, the season and the
year. Put simply, the amount of light on
the ground depends on the solar eleva-
tion; the higher the sun, the greater the
illuminance on the ground. Daylight lev-
els vary significantly on horizontal and
vertical surfaces by time of day and
season, directly related to the local sun
paths and sky conditions.
While certain electric light sources can
be constructed to match a certain
spectrum of daylight closely, none have
been made that mimic the variation in
the light spectrum that occurs with
daylight at different times, in different
seasons, and under different weather
conditions (Boyce et al., 2003).
12 DAYLIGHT 13 VELUX
Figure 1 .2 Spectral com position of four typ ical light source s – daylight (upper page 10), halog en
(lower page 10), fluorescen t (upper pa ge 11), and LED (lower pag e 11). Measureme nts made by
John Mardaljevic.
!
Remember
Of the solar energy received on the surface of the earth, 40% is visible light
and the rest is ultraviolet (UV) and infrared (IR) wavelengths.
No electric light source can mimic the qualities of daylight.
300
0.0
0.2
0.4
0.6
0.8
1.0
400 500 600 700 800
Wavelength [nm]
Spectral Power [norm]
Daylight
CCT 6459
CRI 98
300
0.0
0.2
0.4
0.6
0.8
1.0
400 500 600 700 800
Wavelength [nm]
Spectral Power [norm]
Fluorescent
CCT 4022
CRI 83
Daylight
300
0.0
0.2
0.4
0.6
0.8
1.0
400 500 600 700 800
Wavelength [nm]
Spectral Power [norm]
Halogen
CCT 2680
CRI 93
Daylight
300
0.0
0.2
0.4
0.6
0.8
1.0
400 500 600 700 800
Wavelength [nm]
Spectral Power [norm]
LED
CCT 7014
CRI 78
Daylight
14 DAY LI GH T 15 VELUX
1.2 Daylighting
Daylighting describes the controlled use
of natural light in and around buildings
(Reinhart, 2014). It is the practice of
placing windows, or other transparent
media and reflective surfaces so that-
natural light provides effective internal
illumination during the day. Successful
daylighting requires design considera-
tions at all stages of the building design
process, from site planning to architec-
tural, interior and lighting design.
Daylight in buildings is composed of a
mix – direct sunlight, diffuse skylight,
and light reflected from the ground and
surrounding elements. Daylighting design
needs to consider orientation and build-
ing site characteristics, facade and roof
characteristics, size and placement of
window openings, glazing and shading
systems, and geometry and reflectance
of interior surfaces. Good daylighting
design ensures adequate light during
daytime.
Some basic characteristics of daylight
outdoors:
• Direct sunlight is characterised by
very high intensity and constant
movement. The illuminance produced
on the surface of the earth may ex-
ceed 100 000 lux. The brightness of
direct sunlight varies by season, time
of day, location and sky conditions.
In a sunny climate, thoughtful archi-
tectural design is required, with
careful management of allowance,
diffusing, shading and reflecting.
• Skylight is characterised by sunlight
scattered by the atmosphere and
clouds, resulting in soft, diffuse light.
The illuminance level produced by an
Figure 1 .3 The compone nts of daylight.
overcast sky may reach 10 000 lux in
the winter and as high as around
30 000 lux on a bright overcast day
in the summer. In a cloudy climate, the
diffuse sky is often the main source of
useful daylight.
• Reflected light is characterised by
light (sunlight and skylight) that is
reflected from the ground: terrain,
trees, vegetation, neighbouring build-
ings etc. The surface reflectance of
the surroundings will influence the
total amount of reflected light
reaching the building facade. In some
dense building situations, the light
reflected from the ground and sur-
roundings can be a major conributory
part of daylight provisions indoors.
The goals of room daylighting are to
adequately illuminate visual tasks, to
create an attractive visual environment,
to save electrical energy and to provide
the light needed for our biological
needs. A good luminous environment is
simultaneously comfortable, pleasant,
relevant, and appropriate for its intended
uses and users (Lam, 1977).
Daylighting systems can be simple:
from combining window design with
appropriate internal and external
shading (e.g. external awning blind and
internal Venetian blind) – to systems
designed to redirect sunlight or skylight
to areas where it is required (e.g. sun
tunnels). More advanced systems can
be designed to track the sun or passively
control the direction of sunlight and
skylight.
Daylighting is inseparably linked to the
energy demand and indoor climate of a
building. The size and placement of
glazing should be determined together
with the total energy use of the building
and specific requirements for daylighting.
!
Remember
Daylight in buildings is composed of a mix – direct sunlight, diffuse skylight
and light reflected from the ground and surrounding elements.
Light from the sun is intense and directional.
Light from the sky is soft and diffuse.
Light reflected from the ground can often account for 15% or more of the
total daylight reaching a building facade.
Direct
sunlight
Reflected
light
Skylight
» Good quality lighting should include lighting for health, in
parallel with meeting the other needs of people who will occupy
the space «
16 DAY LI GH T 17 VELUX
1.3 Daylighting quality
The design of well-lit environments re-
quires an understanding of the function
and capabilities of the visual system, in-
sight into visual perception, knowledge
of the basic properties of light, and oth-
er factors such as health issues (CIE,
2004a-b, LRC, 2003). These include
knowledge of our visual system about
adaptation (the eye’s adjustments to
ambient light levels), spectral (colour)
characteristics, composition of diffuse
and direct light, brightness contrast or
luminance gradient and more. They also
include knowledge of our circadian
(non-visual) system about factors such
as appropriate light signals during the
day and darkness at night (to maintain
circadian rhythms), the intensity of light
and the time of day when it is applied,
as well as its spectral characteristics.
1.3.1 Visual needs
We have traditionally concentrated our
design work on creating lighting condi-
tions that are suitable for the visual
tasks performed in a room and that
simultaneously meet individual needs.
Attention needs to be given to both our
central vision (illumination of an object)
and our peripheral vision (illumination
of the surroundings). Peripheral vision
contributes to an impression of the sur-
roundings in which we find ourselves –
space dimensions and shape, ambience,
materials and light distribution. In the
design phases this is supported by
appropriate placement and sizing of
windows to achieve an intelligent bal-
ance between the intensity of light,
its location and direction.
Visual comfort
The light in a room should neither
restrain nor impede our ability to see,
thus allowing us, at all times, easily to
orientate ourselves and move freely
around in the rooms and the building.
If the lighting of a space is unsuitable
or inadequate, and makes it difficult to
see properly, it will influence our perfor-
mance (the visual system), as well as
affect our health (the circadian system)
and personal well-being (the perceptual
system). It can result in unnecessary
eye strain and give rise to symptoms
such as eye irritation, fatigue and head-
ache. Lighting conditions that can
cause these symptoms are poor bright-
ness and contrast, high luminance
differences and flickering.
A good daylighting design will provide
large amounts of glare-free light; a poor
daylighting design, on the other hand,
will provide either inadequate amounts
of light - so that electric lighting has to
be used frequently - or large amounts of
light, together with glare (Boyce et al.,
2003). Furthermore, our daily life con-
sists of changing visual tasks, with simi-
larly changing demands on the lighting
provided.
» A daylit space is primarily lit with natural light and
combines high occupant satisfaction with the visual and
thermal environment, with low overall energy use for lighting,
heating and cooling «
The light variation within our field of
view can influence visual comfort and
performance. For good visibility, some
degree of uniformity of light is desira-
ble. Poor visibility and visual discom-
fort, such as glare, may occur if the eye
is forced to adapt too quickly to a wide
range of light levels.
Too high or too low contrast can also
result in tiredness, headaches and dis-
comfort. Although there are no specific
guidelines for dwellings, it is believed
that luminance variations of around
10:1 are suitable for daylighting design.
Generally speaking, the human eye can
accept greater luminance variations
when spaces are lit by daylight than
when they are artificially lit.
The sensation of glare can occur when
luminance variations exceed 20:1 to
40:1 (Rea, 2000). In the event of glare,
the eye adapts to the high level of the
glare source, which makes it hard to
perceive details in the now too-dark
work area. Glare from daylight may be
caused by several potential sources
such as the sun, bright sky and clouds,
and surfaces reflecting the sun.
There are three main types of glare:
• Disability glare – the effect of scat-
tered light in the eye whereby visibili-
ty and visual performance are re-
duced. This occurs when glare
sources of high luminance (e.g. sun
or specular reflection of the sun) are
in the field of view. In daylit interiors,
it is often found that discomfort glare
is reported before disability glare be-
comes an issue.
• Discomfort glare – defined as an irri-
tating or distracting, but not neces-
sarily impairing, effect. So in most
cases, the perceived magnitude of
discomfort glare is lower than for dis-
ability glare. Discomfort glare indoors
is influenced by the full visual environ-
ment, including windows, reflections
(especially specular), external sur-
roundings and/or interior surfaces.
Discomfort glare may cause later
side- or after effects in the form of
headaches or fatigue.
• Reflections or veiling glare – reflec-
tions on display screens or other task
materials (e.g. paper) reduce the con-
trast between background and fore-
ground for the visual task and thus
reduce readability. Reflections occur
when bright light sources (e.g. win-
dows) are in the reflected field of
view of the screen.
To reduce the occurrence of glare, shad-
ing devices should be employed. Figure
1.5 below shows a situation where glare
is controlled by external solar shading
(awning blind). Shading devices such as
Venetian blinds, awnings, vertical blinds
and roller blinds are suitable for this
purpose, but the specific material char-
acteristics should be taken into consid-
eration. A movable or retractable de-
18 VELUX VELUX 19
vice can be individually adjusted, while
fixed devices may need additional
shading devices to support individual
requirements for glare protection.
Windows located in more than one ori-
entation, or in the roof, could adequately
maintain daylight illumination for the
visual tasks and provide a view to the
outside, rather than being shaded to
control potential glare sources.
Daylight availability
The primary target in the daylighting of
buildings has generally been to provide
adequate light levels in the room and on
the work plane, so that daylight is the
main, or only, source of light (autono-
mous) during daytime. Several metrics
address daylight availability for a task
and/or a space, and an important as-
pect of daylight is to understand that it
is variable: it varies with the seasons of
the year, the time of day, and the
weather. For this reason, metrics for
daylight availability calculations are often
based on relative rather than absolute
values. This is usually defined in terms
of the relationship between the light
available at different positions inside
with that available outside (e.g. the
daylight factor, DF).
The absolute levels of illuminance that
are needed for a particular visual task
will depend on the character of the task
and the visual environment where it is
performed. As an example, the Char-
tered Institution of Building Services
Engineers, CIBSE (CIBSE, 2006), rec-
ommends the following light levels.
See section 1.7.1.
• 100 lux for interiors where visual
tasks is movement and casual seeing
without perception of detail.
!
Remember
Daylight should provide enough light in the room and on the work plane to be
the main, or only, source of light during daytime.
Occupants can accept greater luminance variations in spaces lit by daylight
than if artificially lit.
Luminance variations of around 10:1 are suitable for daylighting design.
The sensation of glare can occur when luminance variations exceed 20:1 to 40:1.
• 300 lux for interiors where visual
tasks are moderately easy.
• 500 lux for interiors where visual
tasks are moderately difficult and
colour judgment may be required, e.g.
general offices, kitchens.
• 1 000 lux for interiors where visual
tasks are very difficult, requiring
small details to be perceived.
Requirements for daylighting have yet
to be defined in terms of specific illumi-
nance levels, but there is enough evi-
dence in literature to indicate that illu-
minances in the range of 100 to 3 000
lux are likely to result in significant re-
duction of electric lighting usage
(Mardaljevic, 2008).
View
Meeting the need for contact with the
outside living environment is an impor-
tant psychological aspect linked to day-
lighting (Robbins, 1986). The provision
of daylight alone is not enough to satis-
fy user desires for views. Windows pro-
vide contact with the outside, supply
information of orientation, give experi-
ence of weather changes and allow us
to follow the passage of time over the
day.
A view that includes layers of sky, city
or landscape, and ground (Boyce et al.,
2003), could counteract tiring monoto-
ny and help relieve the feeling of being
closed in. The size and position of win-
dow systems need to be considered
carefully in relation to the eye level of
the building occupants.
1.3.2 Non-visual effects of light
Daylight has a wide range of influences
on humans that go far beyond our need
for vision. We often refer to this as the
non-visual effects of light. When we
speak about health, balance and physio-
logical regulation, we are referring to
the functions of the body’s major health
keepers: the nervous system and the
endocrine system. These major control
centres of the body are directly stimu-
» Our body uses light as it uses food and water, as a nutrient for
metabolic processes «
Figure 1 .5 Luminance map of a task area
showing sun p atches causing gla re.
Luminan ce map of task area sh owing glare
control with external solar shading.
Log. (c d/m2)
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© PHOTOLUX
20 DAY LI GH T 21 VELUX
06:00
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Cortisol level Melatonin level
Figure 1.6 Production of the hormones melatonin and cortisol (Brainard, 2002).
lated and regulated by light (Edwards
and Torcellini, 2002) by a specific sub-
type of retinal ganglion cells – ipRGCs -
intrinsically photosensitive retinal gan-
glion cells. Together with our visual
system, these ganglion cells in the eye
are sensitive to light.
Circadian rhythms
Many aspects of human physiology and
behaviour are dominated by 24-hour
rhythms that have a major impact on
our health and well-being. They control
sleep/wake cycles, alertness and per-
formance patterns, core body tempera-
ture rhythms, as well as the production
of the hormones melatonin and cortisol
(Pechacek et al., 2008). These daily
rhythms are called circadian rhythms
and their regulation depends very much
on the environment we live in. The dy-
namic variation of light, both daily and
seasonally, is a critical factor in setting
and maintaining our 24-hour daily
rhythms – our circadian rhythms –
which, in-turn, play a key role in the
regulation of the sleep/wake cycle.
Sleep disruption has been linked to poor
cognitive function, stress, depression,
poor social interaction, metabolic and
cardiovascular disease, increased sus-
ceptibility to infection - and even cancer.
An appropriate light signal during the
day and darkness at night are therefore
critical in maintaining key aspects of
our overall health (Circadian House,
2013).
For example, in order to align our body
clock, morning light is the most impor-
tant signal for entrainment. Light in the
morning also increases our levels of
alertness, allowing increased perfor-
mance at the beginning of the day.
Whereas reduced light levels in the
evening promote sleep at night. There
are other external time markers but
daylight’s characteristic light/dark
variation, continuity and spectral com-
position are excellent synchronisers of
our circadian rhythm. It is now evident
that daylight is not just a stimulus for
vision, but acts as a key element in the
regulation of many areas of human
health. Figure 1.6 shows the production
rhythms of the hormones melatonin
and cortisol.
Biological functions of light
How our biology responds to light inten-
sity, duration, timing, and spectrum is
highly complex and varies greatly be-
tween our visual and circadian systems.
All these characteristics are used as a
first step towards prescriptions of
healthy lighting in buildings (Veitch,
2002). Inadequate light exposure can
disrupt normal circadian rhythms and
have a negative effect on human per-
formance, alertness, health and safety.
We know that outdoor daily light expo-
sure allows us to regulate our sleep/
wake timing and levels of alertness.
But the reality is that we spend we
spend 90% of our time indoors (Klepeis,
2001; Leech, 2002; Schweizer, 2007),
where we are exposed to relatively low
light levels of a limited spectral range,
and where the patterns of light and
darkness occur at irregular intervals.
Preliminary evidence suggests that low
light exposure is associated with dimin-
ished health and well-being and can
lead to reduced sleep quality, depressed
mood, lack of energy and impaired so-
cial relations.
Light intensity
Most people are able to read and work
with a daily light level of 500 lux, but
one hour’s exposure to 500 lux may not
be enough to trigger the circadian
rhythm (intensity). In a study by Mard-
aljevic et al. (2012), a case with and
without roof windows is investigated to
determine the effect of light intensity.
The case with only facade windows
shows that the degree of light intensity
is greatest for those viewpoints/direc-
tions located closest to and directed to-
wards the window. The case with roof
windows shows a greater intensity for
all locations in the room, and with less
of a preference for those views directed
towards the window. This illustrate the
importance of using daylight as a key
source of light required for effective
suppression of melatonin, since the
magnitude needed could be of the order
of 1 000 lux depending on the spectrum.
As another example, a study conducted
in San Diego during a temperate and
sunny period showed that, when awake,
22 DAY LI GHT 23 VELUX
the average person spent 4% of each
24 hours in illumination greater than
1 000 lx (on average 130 min), and more
than 50% of the time in illuminance
levels from 0.1 to 100 lx (Espiritu et al.,
1994); the people with the shortest
daily exposure time to high light levels
(above 1 000 lx) reported the lowest
mood.
Other light exposure investigations
show a similar trend. We know day-
lighting can provide much higher levels
of illumination than electric lighting,
and can help significantly to increase
the light dose received by people spend-
ing most of their time indoors. In sup-
port of this, a large Finnish epidemio-
logical study found that health-related
quality of life was higher for people re-
porting higher interior light levels (Gri-
maldi et al., 2008).
Duration and timing
The visual system reacts to and pro-
cesses light impulses in a fraction of a
second, whilst the biological clock
needs minutes or hours (duration).
This means that both the illuminance at
the eye and the duration of exposure
are important to the effect of light on
our circadian system. The time of day at
which light is registered on the retina
also has a clearly different effect on the
visual system and circadian rhythm
(timing). Exposure to intense light in the
morning can reset the biological clock
to an earlier time (“get up earlier”),
whilst in the evening, it sets it to a later
time (“get up later”). This is, in essence,
the syndrome of jetlag, caused by a
conflict between the biological time of
day and the geographical time of day.
The visual system reacts identically
whatever the time of day.
Specific requirements for different age
groups also need to be taken into ac-
count. Adolescent and young adults
have a somewhat delayed biological
clock and need more light in the morn-
ing (bedroom, breakfast room, class-
room, etc.), whereas older people have a
biological clock that has shifted earlier
(often resulting in falling asleep in the
evening and waking up early in the
morning) (Wirz-Justice and Fournier,
2010).
Spectrum
Daylight is recognised as having the
highest levels of light needed for the bi-
ological functions (Hathaway et al.,
1992) compared with typical electric
light sources.
The light that is important to our circa-
dian rhythm (C(λ)) is different from the
light that is important to our visual sys-
tem (V(λ)) because of the spectral dif-
ference in the light sensitivity of the in-
dividual photoreceptors (spectrum).
The circadian system (C(λ)) is most
affected by the wavelength region 446
to 488 nm, whereas the visual system
(V(λ)) is most affected by the wave-
» We need more light at the right time and the right kind «
length around 555 nm, as shown in fig-
ure 1.7. Figures 1.1. and 1.2 presented
earlier show that the spectral composi-
tion of daylight is much richer in these
regions of the electromagnetic spec-
trum than typical electric light sources.
!
Remember
People in modern societies do not receive enough light on a daily basis and
need to be exposed to higher levels of illumination for longer durations.
We need a daily daylight exposure, because daylight is rich in the spectrum
to which the non-visual system is most sensitive.
Healthy light is linked to healthy darkness.
380
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650
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Special power distribution [-]
Visible
V(λ)C(λ)
0%
20%
40%
60%
80%
100%
Figure 1 .7 Circadian (C(λ)) and vis ual (V(λ)) systems' r esponse to light (Pe chacek et al., 2008).
24 DAY LI GH T 25 VELUX
» People perform better in daylight environments «
1.4 Benefits of daylight
1.4.1 Human benefits
We know that appropriate light signals
during the day and darkness at night
are critical in maintaining key aspects
of our overall health. In order to align
our body clock, morning light is the
most important signal for entrainment.
Light in the morning also increases our
levels of alertness, allowing increased
performance at the beginning of the
day. From mid-morning to early even-
ing, high levels of daylight, allow us to
regulate our sleep/wake timing and lev-
els of alertness; whereas reduced light
levels in the evening and a dark room
with blackout promote sleep at night.
The inability to provide building occu-
pants with a good overall lighting envi-
ronment can have subsequent impact
on health and place a substantial bur-
den on the individual, society and the
broader economy.
Performance and productivity
Bright lighting is generally believed to
make people more alert, and well-daylit
spaces are generally perceived by occu-
pants to be “better" than dim gloomy
ones (Mardaljevic et al., 2012). Day-
lighting has been associated with im-
proved mood, enhanced morale, less fa-
tigue, and reduced eyestrain (Robbins,
1986). Many studies show that the per-
formance and productivity of workers
in office, industrial, and retail environ-
ments can increase with the quality of
light. Companies have recorded an in-
crease in productivity of their employ-
ees of about 15% after moving to a new
building with better daylight conditions.
which resulted in considerable financial
gains (Edwards and Torcellini, 2002).
Another study demonstrated that
greater satisfaction with lighting condi-
tions (both daylight and electric light-
ing) contributed to environmental satis-
faction, which, in turn, led to greater job
satisfaction (Veitch et al., 2008).
Studies also show that daylit environ-
ments lead to more effective learning.
It was found that students in class-
rooms with the most window area or
daylighting produced 7% to 18% higher
scores on the standardised tests than
those with the least window area or
daylight (Heschong, 2002).
Benefits of higher light dose
We have no evidence for “what is the
necessary light dose?”, but we do have
clear indication that the light dose
needed is higher than interior light lev-
els prescribed by electric lighting in
standards and regulations. Studies sug-
gest that higher doses would leave peo-
ple with a feeling of being more positive
about life (Espiritu et al., 1994), while
social interactions immediately follow-
ing exposure to over 1 000 lx were
more co-operative and less quarrel-
some (Aan het Rot et al., 2008).
Maison Air e t Lumière, France.
26 DAY LI GH T 27 VELUX
» In domestic buildings, health requirements suggest that
higher levels of daylight than are currently used are desirable.
This gives scope for energy savings «
User satisfaction
Windows are highly valued by office
workers (Edwards and Torcellini,
2002). Surveys have shown that more
than 60% of office workers would like
direct sunlight in their offices in least
one season of the year (Christoffersen,
1999) and believe that working under
natural daylight is better for their
health and well-being than electric light-
ing (Lighting Research Center, 2014).
Employees working in offices highly
value access to a window - indeed, they
value it more than privacy in their office
(Wotton, 1983). Several studies have
shown that people prefer daylight to
artificial lighting at work. This is often
linked to daylight’s dynamic variation of
intensity, colour and direction and the
positive effect these have on our expe-
rience and mood (Christoffersen, 1999;
Veitch, 2003). Canadian studies show
that there is a general perception that
daylight should be the primary light
source for the sake of our health and
well-being (Veitch, 1993, 1996).
A few studies in dwellings show that
natural light is the single most impor-
tant attribute in a home, with over
60% of respondents ranking it as im-
portant (Finlay, 2012). A WHO survey
involving eight cities across Europe,
showed that individuals who report in-
adequate natural light in their homes
have a greater risk of depression and
falls (Brown, 2011).
Benefits of view
Building interiors should be designed
in a way that permits the human need
to be linked to the natural environment
to be satisfied by minimising overshad-
owing and allowing distant views
(Wirz-Justice, 2010). A natural view is
preferred to a view towards man-made
environment, and a wide and distant
view is appreciated more than a narrow
and near view. A diverse and dynamic
view is more interesting than a monoto-
nous view. The content of the view can
influence rental or cost price of hotels,
dwellings and office buildings (Kim and
Wineman, 2005). A view to to nature
may have a positive influence on peo-
ple’s sense of well-being (Kaplan,
2001), better subjective health (Kaplan,
1993), higher environmental satisfac-
tion (Newsham et al., 2009), better
mood (Grinde and Grindal Patil, 2009),
reduced health problems (Heschong
Mahone Group, 2003), job satisfaction,
recovery of surgical patients (Ulrich,
1984), stressful experiences (Ulrich et
al., 1991), and seating preference
(Wang and Boubekri, 2010, 2011). A
study by Ariës et al. (2010) shows that
views in offices independently judged
to be more attractive were associated
with reduced discomfort and, through
the discomfort effect, with better sleep
quality.
CarbonLight Homes
28 DAY LI GH T 29 VELUX
Impact of daylight in hospital rooms
There is some evidence that daylight
exposure can affect post-operative out-
comes in patients and, consequently,
that daylight should be a consideration
in hospital design. Ulrich (1984) report-
ed that hospital patients with a view of
green spaces, as opposed to those with
a view of a blank brick wall, recovered
more quickly from surgery and required
less post-operative pain medication.
Beauchemin and Hays (1998) found
that patients on the sunnier side of a
cardiac intensive care ward showed
lower mortality rates than those on the
less-sunny side. Another study deter-
mined that sunlight exposure was asso-
ciated with both improved subjective
assessment of the patients and also re-
duced levels of analgesic medication
routinely administered to control post-
operative pain (Walch et al., 2005). The
importance of the amount of daylight in
a patient's room indicates an impact on
patients' length of stay; coronary artery
bypass graft surgery patients' length of
stay in hospital was reduced by 7.3
hours per 100 lx increase of daylight
(Joarder and Price, 2013).
Prevention of Seasonal Affective
Disorder (SAD)
Seasonal Affective Disorder is a depres-
sion-related illness linked to the availa-
bility and change of outdoor light in the
winter. Reports suggest that 0.4% to
9.7% of the world's population may suf-
fer from SAD, with up to three times
that number having signs of the afflic-
tion (called sub-syndromal SAD (or
S-SAD) without being classified as a
major depression (primarily in Northern
America and Northern Europe) (Rosen,
et al., 1990). Light therapy with expo-
sure levels at the eye of between 2500
lux (for 2 hours) or 10 000 lux (for 30
minutes) has shown to be an effective
cure against SAD (Sloane, 2008). Expo-
sure to daylight outdoors (~ 1000 lux)
can also reduce SAD symptoms (Wirz-
Justice et al., 1996). So, as seasonal
mood disturbance is relatively common,
the amount of daylight in our homes or
workplaces can be of considerable sig-
nificance – though the effective value
of daylight will depend on the architec-
tural design of a room and the facade
(Pechacek et al., 2008). Light therapy
can also be used to treat other depres-
sion-related symptoms (e.g. non-season-
al depression, premenstrual, bulimia).
1.4.2 Energy savings for electric
lighting
Another benefit of using daylighting for
ambient and/or task illuminance in a
space is that it can save energy by re-
ducing the need for electric lighting.
Several studies in office buildings have
recorded the energy savings for electric
lighting from using daylight in the range
of 20-60% (Galasiu, 2007), but it de-
pends on the lighting control system
used, how well the space is daylit during
occupied hours and the intended func-
tions of the space. If no control system
is installed, the occupant entering a
space will often switch on the electric
lights. Quite why occupants switch on
or off the office lights is not always ob-
vious, but it is even less obvious in a do-
mestic setting, where demand for light
is typically driven by human needs and
wishes.
In non-domestic buildings, official rec-
ommended illumination levels are de-
fined for the spaces they illuminate.
They are dependent on the type of
space to be lit and the functions within
it, and are based on both the functional
efficiency of anticipated tasks per-
formed in the spaces and visual comfort
(IEA, 2006). Typically guidelines and
recommendations for light levels exist
for communal residential buildings but
not for single-family houses.
Estimation of savings potential in do-
mestic buildings requires a user profile,
and models for switching on/off the
lights. In a study by Mardaljevic et al.
(2012), the French RT 2005 model was
used. They analysed the potential for in-
creased daylight provision for a house
with or without skylight to save electric
lighting energy at eight European loca-
tions. The study shows that increased
daylight is estimated to reduce the
need for artificial lighting by 16-20%,
depending on the location and orienta-
tion of the house. See section 1.6.6
In LichtAktiv Haus in Germany,
the electric lighting used in the kitchen
and living room shows a significant
tendency of being affected by the inte-
rior daylight level; the lights are
typically switched on before sunrise
and after sunset. There is a reasonable
correlation between high daylight level
and switching probability, while outside
weather, day of the week has less impact
(e.g. family with children).
» When properly selected and installed, an energy-efficient
skylight can help minimise your heating, cooling and lighting
costs «
30 DAYLIGHT 31 VELUX
0
500
1.000
1.500
2.000
2.500
3.000
3.500
5.500
Final energy consumption (TWh)
1995 2000 2005 2010 2015 2020 2025 2030
Residential Outdoor stationary Industrial Commercial
4.000
4.500
5.000
Figure 1 .10 LichtAktiv Haus. Temporal ma p of lighting use in the ki tchen (2012), showing time
of sunrise ( blue) and sunset (red). Lighting use an d sunrise/sunset de pends on local tim e, which
account s for Daylight Saving Time (DST).
Figure 1 .11 Global elec tricity consumpt ion for lighting with current soci o-economic trends and
policies i s projected to rise . The actual growt h will depend on deman d for artificial light and the
effic iency of lighting tec hnologies, jus t two of the factors in fluencing increased consu mption
(IEA, 2006).
Global lighting electricity
Electric Light Kitchen
2
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24
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20
18
16
14
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10
8
6
4
The IEA publication Light's Labours
Lost suggests that policies to encour-
age better use of daylight typically
implement the following measures to
encourage savings potential from the
use of daylight:
• Implemented daylight-saving time
(DST) and sometimes double DST.
• Acknowledging credit for daylight
measures in building codes.
• Supported R&D and dissemination of
daylighting practices and technologies.
• Labelling and certification of windows.
1.4.3 Environmental benefits
Increasing use of natural resources,
such as daylight and air, in our buildings,
through constructive use of windows in
the facades and roofs, can influence our
dependency on fossil fuels as well as re-
duce combustion of greenhouse gases.
Lighting is one of the largest consumers
of electricity and one of the biggest
causes of energy-related greenhouse
gas emissions. The amount of electrici-
ty consumed by lighting is almost the
same as that produced from all gas-
fired generation and about 15% more
than that produced by either hydro or
nuclear power. Indoor illumination of
tertiary-sector buildings uses the larg-
est proportion of lighting electrical en-
ergy, comprising as much as the resi-
dential and industrial sectors combined.
On average, lighting accounts for 34%
of tertiary-sector electricity consump-
tion and 14% of residential consump-
tion in OECD countries. In non-OECD
countries these shares are usually higher.
(IEA, 2006)
!
Remember
Daylit environments facilitate better performance, productivity and learning.
Light therapy with exposure levels at the eye of between 2500 lux (for 2
hours) and 10 000 lux (for 30 minutes) has shown to be an effective cure for
SAD and other depression-related symptoms.
» Electricity used for artificial lighting is a significant cause
of a building’s CO2 cost: in offices, it can be 30% of the total.
This is why good daylighting is so important to sustainable
architecture «
32 DAY LI GH T 33 VELUX
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Log. (c d/m2)
1) Figure 1 .13 Luminanc e map of a clear sunny
sky. The imag e above describes a clear sky
luminanc e distribution. U nder clear sky con di-
tions, the sky lumina nce is about ten time s
brighte r at the horizon than the zenith. In addi -
tion to the sky luminanc e is the sun luminance .
The sun acts as a dynami c light source of
very high intensity.
3) Figure 1. 15 Luminance ma p of an overcast
sky. The imag e above describes a n overcast
sky lumin ance distribution. Under pe rfect over-
cast sk y conditions, t he sky luminance is
the same i n all orientations , and the zenith is
about three times bri ghter than the horizon.
2) Figure 1 .14 Luminance map of an intermedi-
ate sky. The im age above describe s an interme-
diate sky luminance dis tribution. In this p ar-
ticular ca se, the sun energ y has been scattered
by the clouds, which results in a softer transi-
tion betwe en the very intens e luminance of the
sun and the l uminance of the sky. It is p ossible
to obser ve that the clouds (illumi nated by the
sun) have higher luminance values than the sky.
1.5 Parameters influencing
daylighting performance
1.5.1 Climate
The prevailing climatic conditions of a
building site define the overall precondi-
tions for the daylighting design in terms
of sunlight availability, visual comfort,
thermal comfort and energy perfor-
mance. Figures 1.13 to 1.15 show the
effect of climatic conditions on the sky
luminous distribution and intensity.
Figure 1 .12 Frequency of weat her in % for three dif ferent European cities.
0
10
20
30
40
50
60
70
Weather, Frequency in %
Clear Intermediate Overcast
Oslo Paris Rome
Example
The char ts below show an overview of the monthly sky condi tions for 3 European locations :
Rome, Paris and Oslo. With in working hours (8-17 ), cumulat ive data of daylight availability show
that a horizo ntal illuminance of 10 k lx might be available for 6 0 to 85 % of working hour s and
20 klx for around 30% of wor king hours. By co ntrast, the global illuminan ce (total of sunlight
and skylight) varies si gnificantly wit h latitude. A global horizontal illuminance of 30 k lx is
exceeded for 35% of working hours (8-17) in Oslo, but 65% of the t ime in Rome.
34 DAYLIGHT 35 VELUX
1.5.2 Latitude
The latitude of a building site deter-
mines the solar altitude for a given time
of day and year. The summer and winter
solar altitude properties for a specific
location are important design inputs for
the control of direct solar radiation. Lat-
itude will also determine the length of
daytime and solar availability at differ-
ent seasons of the year. Maximum and
minim solar elevation will depend on the
latitude of the site; on moving away
from the equator towards north or
south, the difference between summer
and winter becomes greater as lati-
tudes increase. Figure 1.16 show the
difference in outdoor illuminance be-
tween northern and southern European
locations.
The highest peak of global illuminance
is during the summer (for the northern
hemisphere), when the sun is at its
highest level, and about two and a half
times greater than the lowest peak
during the winter, when the sun is at
its lowest level.
Figure 1 .16 Global illuminance in north ern and souther n European locati ons.
Global Illuminance – Kiruna, Sweden (67.85°N)
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4
Global Illuminance – Ro me, Italy (41.90°N)
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36 DAYLIGHT 37 VELUX
Figure 1 .18 Component s of view – facade window situation.
Example
The followin g figure show the ef fect of ob-
struction on daylight ava ilability in a simple
room with a ve rtical facade window, and the
effec t of adding a flat-roof win dow to deliver
daylight deeper into the o bstructed roo m. The
result s show that obstruc tion can greatly af-
fect the a mount of daylight that will reach the
building in terior, and how adding an uno b-
structed window on the roof can provi de much
more daylight.
Figure 1 .19 Comparison of dayli ght levels in a room withou t (left) and with ex ternal obstruction
(centre and right).
DF 2.07% Average DF 1.03% Average DF 3.24%
Median DF 1.05% Median DF 0.58% Median DF 2 .96%
Uniformity Dmin/Dav 0.18 Uniformity Dmin/Dav 0.22 Uniformity Dmin/Dav 0.41
1.5.3 Obstructions and reflections
on site
External reflections and obstructions
from surrounding elements on the
building site (buildings, vegetation,
ground surface etc.) will influence the
amount of daylight reaching the interior
of a building.
Roof windows and skylights are gener-
ally less affected by obstructions from
sand and have more generous views to
the sky than facade windows, as illus-
trated in Figures 1.17 and 1.18.
Figure 1 .17 Component s of view – roof window situation.
Clear sk y view
Obstructed view
Clear sk y view
Obstructed view
39 VELUX38 VELUX
Figure 1 .20 Luminance and daylight factor simulations o f scenario 1.
1) Situatio n with 10% glazing to floor area
ratio (facade window only).
The resu lts from scenar io 1 show that a 10% glazing t o floor area ratio will o nly achieve a DF of 2%
a few metre s from the facade an d leave the back of the roo m with very low light levels . Even
though th e average DF of the room is e qual to 1.9%, only a sma ll work plane area achieve s values
above 2%, a nd only one of the thre e workplaces repr esented can be c onsidered daylit.
Example: daylight in deep buildings
The simulations below dem onstrate the daylig ht performanc e of a deep room
with three differen t window configurations inst alled.
Room dimen sions: 8m (d) x 4m (w) x 3m (h)
Pane visual transmittance (τv): 0.78
Surfac e reflectanc e: 0.35 (floor), 0.66 (wall), 0.90 (ceilin g)
1.5.4 Building design
Geometry
The geometry of a building influences
its capacity to deliver adequate levels
of daylight to the interior. When the
building is deep, daylighting solely by
facade windows has its limitations. No
matter how much glass there is in the
facade, it will only be possible to
achieve an adequate daylight distribu-
tion (DF > 2%) a few metres from the
facade, as shown in Figures 1.20 and
1.21.
Measures like light shelves and reflective
ceilings can improve the light distribu-
tion from the facade slightly, but these
solutions are often associated with vis-
ual discomfort. The most effective way
to bring daylight deeper into buildings is
to use light from the roof with products
like VELUX roof windows and sun tun-
nels.
40 DAYLIGHT 41 VELUX
2) Situation w ith 30% glazing to floor area ratio (facade window o nly).
The results from scenario 2 show tha t a 30% glazing to floor area ratio will achieve a DF facad e
of 2% approx imately 4.5 metres f rom the facade. T he DF average is equal to 5. 1%, but it i s highly
non-u niform and not well dist ributed over the work plane area, wi th very high values n ear the
window and low v alues at the back, a luminous environment likely to cause visual discom fort and
glare. In th is scenario, two of the three workp laces represen ted can be considered daylit.
3) Situation wi th 20% glazing to flo or area ratio (11% fac ade window + 9% roof win dow).
The results from scenario 3 show tha t a combination of facade and roof win dows with a 20%
glazing to f loor area ratio provides gener ous and useful DF levels over the entire wor k plane, with
an aver age DF of 6.4%. T he results demo nstrate that the u se of roof windows mea ns better day-
lighting perfo rmance and a luminous environment not as likely to c ause glare and visual discom-
fort . In this scenario , all of the three workp laces represen ted can be conside red well daylit.
Simulations perfor med with the VELUX Daylig ht Visualizer. CVP VELUX roof w indows are used in
scenario 3.
Figure 1 .21 Luminance an d daylight factor simulations of scenario 2. Figure 1 .22 Luminance an d daylight factor simulations of scen ario 3.
42 DAY LI GH T 43 VELUX
Fig ure 1. 23 Lumi nance simulations s howing the effe ct of surface ref lectance on d aylight levels.
Material properties
The colour and reflectance of room sur-
faces are part of the lighting system.
Dark surfaces reflect less light than
bright surfaces, and the result is likely
to be an unsatisfactory luminous envi-
ronment in which there is little indirect
or reflected light. Bright vertical surfac-
es inside the room are generally pre-
ferred to dark ones, but shading devices
used to control sunlight should use
darker materials in order to limit the risk
of glare (e.g. grey awning blinds).
Figure 1 .24 A diagram showing th e sun's paths on the wint er solstice (shor test day),
the equin ox (day and nigh t almost equal) an d the summer sols tice (longest d ay).
1.5.5 Windows and skylights
Orientation
The orientation of windows influences
the availability and qualities of daylight
in the interior. In the northern hemi-
sphere, light coming from the north is
mainly composed of diffuse skylight
and provides the interior with a func-
tional and comfortable light that is
pretty stable throughout the day.
Light coming from south, east and west
orientations will, in many cases, provide
the interior with direct sunlight and
light levels that vary significantly
throughout the day as the sun pursues
its course around Earth.
Note that roof windows and skylights
installed in low-pitched roofs and flat
roofs are likely to receive direct sun-
light.
Average DF 6.41% Average DF 5.60% Average DF 5.24%
Median DF 4.68% Median DF 3.86% Median DF 3.49%
Uniformity Dmin/Dav 0.33 Uniformit y Dmin/Dav 0.21 Uniformity Dmin/Dav 0.31
Floor (0.70) Floor (0.30) Floor (0.15)
Wall (0.85) Wall (0.50) Wall (0.30)
Ceiling (0.85) Ceiling (0.70) Ceiling (0.30)
44 DAYLIGHT 45 VELUX
» It is impossible to “optimise” buildings for good daylighting
performance with static glazing alone, since daylight intensity
varies dramatically «
Interior shading, Venetian blind
Interior shading, pleated Blind
Exterior shading, roller shutter
Exterior shading , awning blind
Figure 1.25 Different shading solutions.
Glazing dimensions
The amount of daylight entering a room
is linked to the total glazing area of win-
dows in that room.
Glazing transmittance
The amount of daylight transmitted
through a window pane is reduced by
the number of glass layers it has to pen-
etrate. As a rule of thumb, double glaz-
ing (with no coating) lets in approx.
80% of the light, while triple glazing
(with no coating) lets in approx. 70%
of the light (compared to an open win-
dow). Coloured or coated glass can re-
duce the visible transmittance of a win-
dow pane to values as low as 20% and
significantly modify the spectral quality
of the transmitted light, as well as the
perception of surface colours in the in-
terior.
Shading
Shading and sunscreening are just as
important to good daylighting perfor-
mance as the window itself. Pleated
blinds and Venetian blinds can be used
to adjust the amount of daylight enter-
ing spaces and to reduce window lumi-
nance to control glare. The Venetian
blind can also be used to redirect the
light into the room.
The most efficient shading solution to
prevent direct solar radiation into the
building is to use external shading. Ex-
amples of external shadings are roller
shutters and awning blinds. A dark grey
screen (VELUX awning blind 5060) will
reduce the illuminance and luminance
levels significantly to a level where the
risk of glare is avoided.
!
Remember
As a rule of thumb, double-layer glazing transmits approx. 80% of the light
and triple-layer glazing transmits approx. 70% of the light.
Coloured or coated glass can reduce the visible transmittance of a window
pane to values as low as 20%.
46 DAYLIGHT 47 VELUX
Position
The positioning of windows will influ-
ence the distribution of daylight in the
room and determine the amount of
'useful' daylight. Window position
should also take into account the rela-
tion between the view to the outside
and the eye level of the occupants.
Linings
The geometry and depth of window lin-
ings will influence the amount of day-
light entering the room and can be used
to soften the luminance transition be-
tween the high luminance values of the
window and the surfaces of the room.
Example
The figu re below shows the eff ect of differen t window position in an at tic with four roof win -
dows. The r esults show that the average DF value s vary in the room, but not as much a s median
DF values , which are a better represent ation of the useful a mount of daylight in the room. It is
also wort h noting the effec t of window placement on the uniformity of daylight in t he room and
taking i t into consideratio n in the building desig n and window layout.
Average DF 5.63% Average DF 4.45% Average DF 5.88%
Median DF 3.88% Median DF 1.60% Median DF 2.94%
Uniformity Dmin/Dav 0.22 Uniformity Dmin/Dav 0.06 Uniformity Dmin/Dav 0.14
1.5.6 Sun tunnels
Orientation
Orientation is a crucial factor influenc-
ing Sun Tunnel's performance. These
products are intended to transport in-
tense sunlight - to diffuse it into useful
daylight in deep areas of buildings or ar-
eas where a window is not necessary
but daylight is wanted. Sun Tunnels
should be oriented to maximise their ex-
posure to direct sunlight.
Length and configuration
The length of a Sun Tunnel influences
the number of inter-reflections needed
for sunlight to reach the interior of a
room. While shorter Sun Tunnels will
deliver more light, the very high reflec-
tiveness of the metal material used in
them allow sunlight to be efficiently
transported over long distances - up to
6m. Rigid Sun Tunnels will deliver more
light than flexible Sun Tunnels.
Dimensions
The amount of daylight entering a room
from Sun Tunnels is linked to the dimen-
sions of the product.
Diffuser transmittance
The transmittance and optical proper-
ties of the diffuser influence both the
amount and distribution of daylight
from Sun Tunnels. As the name suggest,
the diffuser takes the direct sunlight
coming down the Sun Tunnel and dif-
fuses it to achieve a good distribution
of daylight in the room.
Figure 1 .26 Diagram showing su nlight
transpo rt in Sun Tunnels.
48 DAYLIGHT 49 VELUX
1.6 Daylight with roof
windows, flat-roof windows
and modular skylights
1.6.1 Impact of three window
configurations on daylight conditions
Under similar conditions, roof windows
are shown to provide at least twice as
much light as vertical windows of the
same size, and three times more light
as dormers of the same size, illustrated
in Figure 1.27. The roof window also
provides a larger variation of light levels,
which increases the visual interest of
the room (Johnsen et al., 2006).
» Roof windows and skylights deliver significantly more light
than vertical and dormer windows «
Figure 1 .27 Compariso n of daylight factor levels a long the depth of the r oom.
0
2
4
6
8
10
Distance from window wall (m)
0
Daylight factor (%)
0.5 1.0 1.5 2.0 2.5 3.0
Roof window
Vertical window Dormer window
In addition to providing more daylight,
roof windows are also shown to give
higher wall luminance than dormer and
facade windows, which results in a
softer transition between the high lumi-
nance of the window pane and the adja-
cent wall, and thus reduces the risk of
glare. The figure above shows the dif-
ference between the perceived glare
from a facade, dormer and roof window.
Vertical Dormer Roof
Figure 1 .28 Fish-eye rend ering of view toward the window wall under s unny sky conditio ns in De-
cember at n oon. The images sh ow that the sunlight com es directly into th e field of view in all
three ca ses. For the roof window, however, the sunlight s eems to cause les s glare.
50 DAY LIGHT 51 VELUX
1.6.2 Effects of roof windows in
Solhuset kindergarten
The architect firm Christensen & Co
Architects (CCO) used daylight factor
simulations to validate and optimise
daylight conditions in this kindergarten
project.
The daylight factor simulation of the ini-
tial design showed areas of the building
where the light levels were not suffi-
cient, such as the gymnastics room lo-
cated in the central part and the dining
room facing east (e.g. 5% DF instead of
2% DF). By contrast, it also showed
high light levels in certain areas that
could be used to optimise daylight levels
throughout the building.
According to the architect, the position
and design of the window linings has
been optimised in the final design to
achieve optimal daylight conditions in
all key areas of the building, and to pro-
mote a more rational solution in terms
of ceiling construction. The daylight
factor simulation of the final design,
shown in the figure below, shows a
significant improvement on the results
obtained with the initial design.
Figure 1 .30 Daylight factor simulation of t he initial design (lef t) and final design
(right) of Solhuset kindergarten.
Solhuset kindergarten.
52 DAY LI GH T 53 VELUX
Figure 1 .32 Daylight factor rendering o f Drømmebakken kindergar ten project in Denmark.
Drømmebakken kindergarten.
1.6.3 Effects of adding flat-roof windows
and modular skylights to a former town
hall, now a kindergarten
Daylight is the perfect material for reno-
vation and indoor climate improve-
ments of existing building structures.
Improving daylight conditions can help
significantly to revitalise the use of a
space and to improve the comfort and
well-being of the occupants.
This kindergarten project was a former
town hall and had a flat roof with no
windows or skylights before the inter-
vention. CASA architects used VELUX
Modular Skylights and flat-roof win-
dows to add daylight in the project’s key
areas and provide children with bright
interior spaces.
54 DAYLIGHT 55 VELUX
Daylight performance with roof windows
Figure 1 .34 Daylight fact or renderings of Gr een Lighthouse c omparing
daylight performan ce with and without ro of windows.
Second floorFirst floor
3.0%
3.0%
1.8%
Ground floor
Daylight Factor %
9.0
7.8
6.6
5.4
4.2
3.0
1.8
0.6
3.0%
1.8%
Daylight performance without roof windows
Second floorFirst floorGround floor
Daylight Factor %
9.0
7.8
6.6
5.4
4.2
3.0
1.8
0.6
Daylight Factor %
9.0
7.8
6.6
5.4
4.2
3.0
1.8
0.6
Daylight Factor %
9.0
7.8
6.6
5.4
4.2
3.0
1.8
0.6
Daylight Factor %
9.0
7.8
6.6
5.4
4.2
3.0
1.8
0.6
Daylight Factor %
9.0
7.8
6.6
5.4
4.2
3.0
1.8
0.6
4.2%
1.8%
1.8%
4.2%
9.0%
7.8%
3.0%
7.8%
5.4%
4.2%
4.2%
Green Lighthouse.
1.6.4 Effect of roof windows in Green
Lighthouse
The daylight performance of Green
Lighthouse, a VELUX 2020 Model
Home, has been evaluated with daylight
factor simulations. In order to show the
effect of VELUX roof windows, a com-
parison of the daylight conditions with
and without the use of roof windows
was performed.
The results, presented in Figure 1.34,
show that the roof windows deliver
high levels of daylight to the second
floor’s lounge area, providing the occu-
pants with a healthy, strongly daylit in-
door environment, and with contact to
the sky.
The results also show that the use of
roof windows contributes to raising
daylight levels on the lower floors sub-
stantially via the bright atrium space,
and results in a better distribution of
daylight on all floors by balancing the
light coming from the facade windows.
56 DAYLIGHT 57 VELUX
Langebjerg School. Figure 1.37 Daylight factor simulation after renovation.
» New classrooms with more, and better distributed daylight «
1.6.5 Effect of roof windows when ren-
ovating school buildings
The effect of adding roof windows in
Langebjerg School was evaluated with
daylight factor simulations comparing
the daylight performance before and
after renovation, in which four roof
windows were added to each class-
room, as well as in the circulation areas.
Figure 1.36 shows the daylight factor
results obtained with the initial design
in which the classrooms have two roof
windows. The simulation results show
that classrooms had average DF levels
of around 3.0%-3.4%, with the excep-
tion of one room that had an average
DF of 1.5%.
The daylight factor levels obtained for
the new proposal of the school are
shown in figure 1.37. The addition of 3
to 4 roof windows in each class room
results in reach higher DF levels ranging
between 4,4% and 5,3%, but most
importantly they help achieve a much
better distribution in the individual
classrooms to ensure that each student
desk receives adequate levels of day-
light and reduce the contrast in the
daylight levels of the room.
Figure 1.36 Daylight factor simulation before renovation.
58 DAYLIGHT 59 VELUX
Mangler
Figure 1 .39 Section view of a l uminance render ing showing daylight dis tribution in false colour
(left) an d photo-realis tic (right).
1.6.6 Effect of roof windows in
MH2020 Sunlighthouse
VELUX Roof windows are used to deliv-
er daylight both on the ground floor and
first floor of Sunlighthouse, as shown in
Figure 1.39. Daylight factor renderings
of the ground floor and first floor show
that all the main living areas of the
house have generous levels of daylight
above 5% DF, see figure 1.40. The anal-
ysis also show that the house and its oc-
cupants will benefit from bright circula-
tion areas under the roof window on the
first floor and around the courtyard on
the ground floor.
Sunlighthouse.
60 DAYLIGHT 61 VELUX
Figure 1 .41 Temporal map of e lectric lighting u sage in Sunlighthouse. The blue line represents the
time of sunr ise, and the red line t he time of sunset.
Electric Light Kitchen
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The building monitoring report of Sun-
lighthouse also demonstrates the effect
of the good daylight conditions, with
very few hours in the year when electric
lighting was used during daytime. The
figure below shows electric lighting us-
age in the kitchen space from January
to November.
Green Lighthouse.
Figure 1 .40 Daylight factor re ndering of Sunlighthouse ground floor (lef t) and first fl oor (right).
62 DAY LI GH T 63 VELUX
Figure 1 .44 Impact of adding r oof windows on energy s avings for lighting .
DEU-Hamburg
ESP-Madrid
FRA-Paris
GBR-London
ITA-Roma
POL-Warsaw
RUS-Moscow
SWE-Ostersund
Energy savings for lighting
0
20
40
80
60
120
100
140
Saving [kWh/yr]
North-facingWest-facing South-facing East-facing
The higher levels of daylight increase
the number of hours when electric
lighting will not be needed, which, in
turn, results in significant energy sav-
ings for lighting. The figure below
shows energy savings in the area of 100
KWh/yr across all climates and orienta-
tions tested (Mardaljevic et al., 2012).
The study also investigated the impact
of adding roof windows on the amount
of daylight received at eye level at spe-
cific periods of the day and night in or-
der to evaluate the non-visual of effects
of light. Figure 1.45 shows the results
obtained for the living room in Rome.
Each circle represents a specific view
position with four view directions and
three time periods.
The results showed significant increas-
es for potential non-visual effects of
daylight with the addition of roof win-
dows: a 25% increase in the morning
period and a 45% increase in the after-
noon period. Similar increases in perfor-
mance were seen in all rooms and
across all climates and orientations
tested.
1.6.7 Effect of roof windows in the ren-
ovation of residential buildings
A recent study investigating the effect
of adding roof windows to a single-fam-
ily house has shown that roof windows
and better daylight conditions can be
tied to several positive outcomes, and
this in all climates in Europe.
First and foremost, the addition of roof
windows led to a marked increase in
the amount of daylight and its occur-
rence in levels in the key UDI autono-
mous range of 300-3 000 lux. The fig-
ure below shows increases of daylight
provision in the range of 40% from the
addition of roof windows to the kitchen
space across all climates and orienta-
tions tested (Mardaljevic et al., 2012).
Figure 1 .43 Impact of adding roof windows on the oc currence of daylight levels in the rang e
300-3000 lux.
0
20
40
60
80
100
DEU-Hamburg
% yr [08h20h]
ESP-Madrid
FRA-Paris
GBR-London
ITA-Roma
POL-Warsaw
RUS-Moscow
SWE-Ostersund
UDI auto: 300 < E < 3000 lux
North-facingWest-facing South-facing East-facing
64 DAYLIGHT 65 VELUX
Figure 1 .45 Impac t of adding roof windows on the potentia l for non-visual ef fects of daylight fo r
multiple p ositions, view direc tions and time of day.
Period MED AVG MAX MIN
06.00-10.00 58 % 54 % 81 % 21 %
10.00-18.00 73 % 67 % 89 % 35 %
18.00-06.00 1 % 1 % 5 % 0 %
Period MED AVG MAX MIN
06.00-10.00 33 % 38 % 80 % 7 %
10.00-18.00 29 % 42 % 89 % 10 %
18.00-06.00 0 % 0 % 5 % 0 %
020 40 60 80 100
N-VE Potn [%]
020 40 60 80 100
N-VE Potn [%]
66 DAYLIGHT 67 VELUX
!
Remember
Illuminance (lux) is the measure of the amount of light received on a surface.
It is the measure of light currently used by most performance indicators to
determine daylight availability in the interior. Figure 1 .48 Illuminance renderings of Maison Air et Lumiè re.
Typical illuminance values:
Direct sunlight 100,000 lux
Diffuse skylight 3,000-18,000 lux
Minimum levels for tasks and activities:
Residential rooms 200-500 lux
Classrooms (general) 300-500 lux
Workspace lighting 200-500 lux
Figure 1.47. Luxmeter.
Figure 1.46. Illuminance diagram.
1.7 Daylight calculations
and measurements
1.7.1 Illuminance
Illuminance is the measure of the
amount of light received on a surface.
It is typically expressed in lux (lm/m²).
Illuminance levels can be measured with
a luxmeter, shown in Figure 1.47, or
predicted through the use of computer
simulations with recognised and vali-
dated software (e.g. VELUX Daylight
Visualizer). Figure 1.48 shows an example
of an illuminance rendering. Illuminance
is the measure of light currently used by
most performance indicators to deter-
mine daylight availability in the interior.
68 DAYLIGHT 69 VELUX
1.7.2 Luminance
Luminance is the measure of the
amount of light reflected or emitted
from a surface. It is typically expressed
in cd/m².
Luminance levels can be measured with
a luminance meter, shown in Figure
1.51, or through the use of high dynamic
range (HDR) imaging techniques to-
gether with a digital camera and lumi-
nance mapping software (e.g. Pho-
tolux), example shown in Figure 1.52.
Luminance levels can be predicted
through the use of computer simula-
tions with recognised and validated
software (e.g. VELUX Daylight Visualiz-
er). Figure 1.53 shows an example of a
luminance rendering. Luminance is the
measure of light used to evaluate visual
comfort and glare in the interior.
Figure 1 .50. Cool pix cam era and fisheye lens
used to create luminance maps.
Figure 1 .51. Luminanc e meter.
Figure 1.49. Luminance diagram.
Figure 1 .52 Luminance map showing the dist ribution of luminan ce values in Atika, a con cept
house by VELUX, under over cast sky cond itions.
Typical luminance values:
Solar disk at noon 1,600,000,000 cd/m2
Solar disk at horizon 600,000 cd/m2
Frosted bulb (60 W) 120,000 cd/m2
T8 cool white fluorescent 11,000 cd/m2
Average clear sky 8,000 cd/m2
Average cloudy sky 2,000 cd/m2
Figure 1.53 Luminance renderings of Maison Air et Lumière.
!
Remember
Luminance (cd/m2) is the measure of the amount of light reflected or emitted
from a surface.
It is the measure of light used to evaluate visual comfort and glare in
the interior.
70 DAY LI GH T 71 VELUX
internal (lux)
external (lux)
Sensor
Sensor
internal (lux)
external (lux)
Sensor
Sensor
internal (lux)
external (lux)
Sensor
Sensor
Figure 1 .54 Drawing show ing the values mea sured by the dayligh t factor metho d (simultaneous r eading
of the internal and external (unobstructed) horizontal illuminance levels).
1.7.3 Daylight factor
Daylight factor (DF) is a daylight availa-
bility metric that expresses – as a per-
centage – the amount of daylight avail-
able inside a room (on a work plane)
compared to the amount of unobstruct-
ed daylight available outside under
overcast sky conditions (Hopkins,
1963).
The key building properties that deter-
mine the magnitude and distribution of
the daylight factor in a space are
(Mardaljevic, J. (2012)):
• The size, distribution, location and
transmission properties of the facade
and roof windows.
• The size and configuration of the
space.
• The reflective properties of the inter-
nal and external surfaces.
• The degree to which external struc-
tures obscure the view of the sky.
The higher the DF, the more daylight is
available in the room. Rooms with an
average DF of 2% or more can be con-
sidered daylit, but electric lighting may
still be needed to perform visual tasks.
A room will appear strongly daylit
when the average DF is 5% or more, in
which case electric lighting will most
likely not be used during daytime (CIB-
SE, 2002).
Measurement grid
In most cases, daylight factor levels in
rooms are measured at work plane
height (e.g. 0.85m above the floor),
leaving a 0.5m border from the walls
around the perimeter of the work plane,
as shown in Figure 1.55.
0 2 4 6 8 10
Figure 1 .55 Daylight fac tor (DF) simulati on in a classroom b efore (left) and a fter (right) ren ovation,
includin g a 0.5m perimete r from the walls arou nd the work plane.
Average DF 2.75% Average DF 5.06%
Median DF 2.30% Median DF 4.09%
Uniformity Dmin/Dav 0.15 Uniformity Dmin/Dav 0.49
Climate-based daylight factor
The amount of daylight in a building’s
interior depends on the availability of
natural light outside at that location, as
well as the properties of the building
spaces and its surroundings. The evalu-
ation of daylight performance should,
therefore, take account of the availability
of daylight on site in addition to the
properties of the space (CIE, 1970).
Using recorded climatic data (outdoor
diffuse illuminance), we can determine
what DF levels will be needed to reach
the target illuminance level over a given
period of the year. The example below
shows how the target DF is determined
from climate data to achieve daylight
levels of 300 lux for 50% of the year.
72 VELUX VELUX 73
Figure 1 .57 Daylight autono my (DA) simulation in a clas sroom before (lef t) and after (right)
renovatio n, including a 0.5m perimeter fr om the walls around the wo rk plane.
1.7.4 Daylight autonomy
Daylight autonomy (DA) is a daylight
availability metric that corresponds to
the percentage of the occupied time
when the target illuminance at a point
in a space is met by daylight (Reinhart,
2001).
A target illuminance of 300 lux and a
threshold DA of 50%, meaning 50% of
the time daylight levels are above the
target illuminance, are values that are
currently promoted in the Illuminating
Engineering Society of North America
(IESNA, 2013), see section 1.9.4.
020 40 60 80 100
Avera ge DA300 59% Ave rage DA 300 82%
Mean DA300 63% Mean DA300 82%
Uniformity Dmin/Dav 0.14 Uniformity Dmin/Dav 0.83
Figure 1 .56 Cumulative cur ves of available external diffu se horizontal illum inance for Oslo
(Norway), Par is (France) and Rome (Ita ly).
City Internal lux External lux DT %
Oslo 300 12 000 2,5%
Paris 300 15 700 1,9 %
Rome 300 19 20 0 1,6%
DT = =
EInternal 300 lux · 100%
EExternal 15 700 lux = 1 ,9%
74 DAY LI GH T 75 VELUX
Figure 1 .58 Useful daylight illuminance (U DI) simulation in a clas sroom before (lef t) and after
(right) renovation, inclu ding a 0.5m perimeter from the walls around the wor k plane.
Figure 1 .59 Luminance rendering of Sun lightHouse shown with photo-realistic an d false
colour images
1.7.5 Useful daylight illuminance (UDI)
Useful daylight illuminance (UDI) is a
daylight availability metric that corre-
sponds to the percentage of the occu-
pied time when a target range of illumi-
nances at a point in a space is met by
daylight.
Daylight illuminances in the range 100
to 300 lux are considered effective
either as the sole source of illumination
or in conjunction with artificial lighting.
Daylight illuminances in the range 300
to around 3 000 lux are often perceived
as desirable (Mardaljevic et al, 2012).
Recent examples in school daylighting
design in the UK have led to recommen-
dations to achieve UDI in the range 100-
3 000 lux for 80% of occupancy hours.
1.8 Daylight simulation tools
Daylighting simulation tools make it
possible to evaluate the quantity and
distribution of daylight in a room, while
taking into account key influential pa-
rameters such as window placement,
building geometry, external obstruction,
interior divisions and material proper-
ties.
Most CAD visualisation programs used
today are capable of generating images
that look realistic, but they do not pro-
vide information about the quantity and
quality of daylight in the rooms. Simula-
tion tools like Daylight Visualizer enable
professionals to make informed deci-
sions about daylight performance and
building design, and get an accurate im-
pression of the appearance of daylight
in the rooms. Figure 1.59 below shows a
luminance rendering with photo-realistic
and false colour images.
Example
Avera ge UDI100-3000 83% Ave rage UDI 100-3000 88%
Mean UDI100-3000 85% Mean UDI100-3000 90%
Uniformity Dmin/Dav 0.61 Uniformity Dmin/Dav 0.58
020 40 60 80 100
76 DAY LI GH T 77 VELUX
VELUX Daylight Visualizer
VELUX Daylight Visualizer is a profes-
sional and validated simulation tool for
the analysis of daylight conditions in
buildings. It is intended to promote the
use of daylight in buildings and to aid
professionals by predicting and docu-
menting daylight levels and the appear-
ance of a space prior to realisation of
the building design. The program’s sim-
ple user interface makes it accessible,
quick and easy-to-use.
Figure 1 .60 Section views of a luminance rendering showing the effe cts of VELUX Modula r Sky-
lights in t he atrium space of an of fice building.
Figure 1 .61 Screenshots of VELUX
Daylight Visualizer output viewer
showing a daylight factor re ndering
(top), an illuminance rendering (left)
and a lumina nce rendering in fa lse
colour (right).
78 DAY LI GHT 79 VELUX
1.9 Daylight requirements
in building codes
There are very few (or no) daylighting
requirements or recommendations in
existing standards and building regula-
tions that are enforceable by law in any
country.
The VELUX Group is working to have
windows recognised as sources of illu-
mination and sun provision in buildings;
we are promoting healthy indoor envi-
ronments and helping to reduce the
electricity used for lighting. Our goal is
for daylighting to be specifically men-
tioned and considered in building stand-
ards and regulations, together with
specific performance criteria for all
main living areas and activity zones of
a building. Three key points that we
believe should be taken into account,
when daylight requirements are imple-
mented in national legislation:
• Daylight should be used as primary
light source in buildings in daytime
and fulfil both our visual and non-
visual (biological) needs.
• We recommend levels of minimum
300 lux for most of the room area by
meeting a target climate-based day-
light factor and 500 lux for areas
where productive work is performed.
See section 1.7.3
• We recommend that national renova-
tion strategies should address the
importance of always improving day-
light conditions when renovating a
building.
The recommended prescriptive demands
that compare window area with day-
light factor as equally valid methods of
achieving adequate daylight conditions
have their limitations.
As an example, a study by Aarhus
School of Engineering investigated the
influence of window size, placement
and other parameters on the distribu-
tion of daylight in a room. The window
size in the 23 different models is, in all
cases, in accordance with the present
(10% glass area to floor area) and fu-
ture Danish demands for glass area to
floor area (15%). The study compared
the recommended requirements for
daylight in commercial buildings – a
daylight factor of 2% on the work plane
(present Danish building regulations),
and an average daylight factor in the
room of 3% (suggested requirements
in the 2020 standard).
The calculations show that if shading
from external surroundings or common
facade design is included, then only 9 of
the 23 models meet a daylight factor of
more than 2%, and only 3 models meet
an average daylight factor of more than
3%, corresponding to future recom-
mended requirements in Danish build-
ing legislation.
Key features
• Any project, any scale
Daylight Visualizer can be used to
evaluate daylight conditions in any
type of project, including residential,
commercial and industrial projects of
any scale.
• Photo-realistic and false colour images
Visualise and quantify the amount
and distribution of daylight (luminance,
illuminance and daylight factor) in
buildings with false colour and photo-
realistic images.
• Daylight factor calculations
Daylight factor (DF) is a one-step
simulation - the most commonly used
performance indicator to evaluate
daylight availability in buildings.
• Results report
A report can be generated of simula-
tion results, presenting the daylight
performance by zone for each room/
space in the building. Results include
average, median, minimum, maximum
and uniformity values for each zone.
• Create/import projects
Use the embedded modelling tool to
generate 3D models in which roof and
facade windows can be freely inser ted.
Or simply import 3D models directly
from your CAD program Autocad,
Revit, SketchUp, Archicad and more)
with the following supported 3D file
formats DWG, DXF, SKP and OBJ.
• Fast and accurate
Daylight Visualizer is a validated
daylighting simulation tool based on
state-of-the-art rendering technology
capable of simulating the complex
character of daylight in building inte-
riors.
For more information about VELUX
Daylight Visualizer, please visit the
official website http://viz.velux.com.
80 DAY LIGHT 81 VELUX
1.9.2 The European Committee for
Standardization, CEN
In several European Standards involving
daylight, the general benefits of day-
light tend to be explained as follow:
• The design illuminance levels needed
to enable people to perform visual
tasks efficiently and accurately shall
be obtained by means of daylight,
electric light or a combination of
both.
• Windows are strongly favoured in
buildings for the daylight they deliver,
and for the visual contact they pro-
vide with the outside environment.
It is important to ensure windows do
not cause visual or thermal discom-
fort, or loss of privacy.
• Potential energy savings by using
daylight
• Light is important to people’s health
and well-being.
In EN 12464-1:2011, the importance of
daylight is taken into account and re-
quirements for lighting are generally
applicable whether it is provided by
daylight, artificial lighting or a combina-
tion of both. EN 12464-1:2011 specifies
requirements for most indoor work
places in terms of quantity and quality
of illumination. At present, only EN
15193-1 (Energy performance of build-
ings – Energy requirements for lighting)
provides detailed considerations of the
effect of daylight on the lighting energy
demand (monthly and annual), and day-
light availability classification as a func-
tion of the daylight factor. A new stand-
ard for daylighting of buildings that will
define metrics used for the evaluation
of daylighting conditions and give
methods of calculation that can be ap-
plied to all spaces is under preparation.
1.9.3 The International Organization for
Standardization, ISO
Several ISO working groups include
daylight as an element in their work
groups. At present, one standard (ISO,
2014a) applies to calculations methods
for daylight in both existing buildings
and the design of new and renovated
buildings.
1.9.1 Building Codes
Legislation related to daylighting has
historically been defined by one or more
of the following criteria: window or
glazing area in relation to the room area
or facade area; quantity of daylight by
daylight factor in a point in the room or
as an average daylight factor of the
room area; sunlight provision for a spe-
cific day or season; and a view to the
outside environment (Boubekri, 2004):
• Requirements for windows and their
glazing area in relation to room area
or facade area. It is important to
stress that legislation that mandates
a minimum ratio of glazing area can-
not be considered as daylight legisla-
tion, since it does not translate the
actual daylight presence inside the
room or building; it does not consider
factors such as outside boundary
conditions, building overhangs, per-
manent shading, glass configuration
or transmittance.
• The quantity of indoor illumination
inside a room. Levels for daylighting
are generally described as preferred
or recommended - either by specific
illuminance (lux) levels on a work-
plane or by daylight factor (DF). Day-
light factor is the most recognised
performance indicator used to speci-
fy daylight conditions in buildings.
The advantage of the DF method is
that it is quick to calculate, and can
be used in the early design process.
It enables the validation of the quan-
tity, uniformity and spatial distribu-
tion of diffuse daylight in rooms,
giving architects and designers what
they need to make informed decisions.
• The provision of sunlight and its du-
ration. This type of legislation, usually
referred to as “solar zoning legisla-
tion”, attempts to guarantee building
occupants access to sunlight for a
predetermined period of time during
the day, season and year. Considera-
tions of sunlight access and its dura-
tion will influence the decision on ori-
entation, the disposition of rooms and
their windows, selection of solar
shading devices and consideration of
the surroundings. In countries such as
Japan and China, solar zoning relates
to public health, safety and welfare.
• A view to the outside environment
provides buildings' occupants with
information about orientation, and
weather and times changes through-
out the day. This kind of legislation
calls attention to window sill-height,
glazing width (or the sum of widths
for all windows) as a fraction of
facade area, and type of glazing
material used.
» The EU Workplace (Health, Safety and Welfare) Regulations
(1992) requires that “Every workplace shall have suitable and
sufficient lighting” and that this lighting “shall, as far as is
reasonably practicable, be by natural light” «
82 DAY LI GH T
1.9.4 Design Guidelines
Several independent authorities publish
guidance material and set the criteria
for best practice in the profession.
These are the Chartered Institution of
Building Services Engineers (CIBSE),
UK and the Illuminating Engineering
Society of North America (IESNA),
USA. As an example, CIBSE has pub-
lished its Lighting Guides on Daylighting
and window design, and IESNA has
published a standard on approved
method: IES Spatial Daylight Autonomy
(SDA) and Annual Sunlight Exposure
(ASE) (IESNA, 2013), which describes a
new suite of metrics of daylighting per-
formance in an existing buildings and
new designs, from concept to construc-
tion documents.
Several established and much-used
methods of assessing, rating, and certi-
fying the sustainability of buildings,
such as LEED (Leadership in Energy and
Environmental Design), BREEAM
(Building Research Establishment Envi-
ronmental Assessment Methodology),
and DGNB (Deutsche Gesellschaft für
nachhaltiges Bauen), make recommen-
dations for daylight as part of their as-
sessment schemes. Overall, daylight
factor is the most common indicator in
most of them, but the calculation meth-
ods and benchmarks are different.
Apart from daylight factor as an indica-
tor, a view to the outside, glare control,
and illuminance levels are frequently
used parameters for describing visual
comfort.
• BREEAM states that “. . . at least
80% of floor area in occupied spaces
has an average daylight factor of 2%
or more”. In domestic buildings, it
states “... Kitchens achieve a mini-
mum daylight factor of at least 2%;
living rooms, dining rooms and stud-
ies achieve a minimum average day-
light factor of at least 1.5%, and
80% of the working plane should
receive direct light from the sky”.
• LEED states that “. . . through com-
puter simulation that the applicable
spaces achieve daylight illuminance
levels of a minimum of 25 foot-candles
(fc) (270 lux) and a maximum of 500
fc (5400 lux) in a clear sky condition
on September 21 at 9 a.m. and 3 p.m.
Areas with illuminance levels below
or above the range do not comply.
However, designs that incorporate
view-preserving automated shades
for glare control may demonstrate
compliance for only the minimum
25 fc (270 lux) illuminance
level".
• DGNB states that “. . . 50% of the us-
able area throughout a building has a
DF (> 3% very good, > 2% medium,
> 1% slight, < 1% none)”; “. . .based on
simulation, the daylight in perma-
nently used work areas (3%≤ DF very
good, 2,5%≤ DF < 3% medium, 2%
≤ DF < 2,5% slight, DF < 2% none)”.
83 VELUX
Ventilation
84 VENTILATION 85 VELUX
Ventilation
The purpose of ventilation is to freshen up
the air inside buildings in order to achieve
and maintain good air quality and thermal
comfort. Ventilation also has important
psychological aspects, which can be
illustrated by the feeling of being in control,
having odour management and creating
a link to nature.
2.1 Indoor Air Quality
2.1.1 How to achieve good indoor air
quality
As we spend 90% of our time indoors,
it is crucial to understand what the
quality of the indoor air we breathe is.
Indoor air quality is influenced by the
generation of pollutants indoors but
also depends on the outdoor air around