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Should We Re-think Regulations and Standards for Lighting at Workplaces? A Practice Review on Existing Lighting Recommendations



Nowadays lighting projects often include temporal variations of the light, both spectrally and in terms of intensity to consider non-visual effects of light on people. However, as of today there are no specific regulations. Compliance with common lighting standards that address visual aspects of light, often means that only little non-visually effective light reaches the eye. In this practice review we confront existing regulations and standards on visual lighting aspects with new recommendations on non-visual aspects and highlight conflicts among them. We conclude with lighting recommendations that address both aspects.
published: 13 May 2021
doi: 10.3389/fpsyt.2021.652161
Frontiers in Psychiatry | 1May 2021 | Volume 12 | Article 652161
Edited by:
Shadab Rahman,
Harvard Medical School,
United States
Reviewed by:
Ljiljana Udovicic,
Federal Institute for Occupational
Safety and Health, Germany
Cosmin Ticleanu,
Building Research Establishment,
United Kingdom
Kevin William Houser,
Oregon State University,
United States
Oliver Stefani
Specialty section:
This article was submitted to
Sleep Disorders,
a section of the journal
Frontiers in Psychiatry
Received: 11 January 2021
Accepted: 14 April 2021
Published: 13 May 2021
Stefani O and Cajochen C (2021)
Should We Re-think Regulations and
Standards for Lighting at Workplaces?
A Practice Review on Existing Lighting
Front. Psychiatry 12:652161.
doi: 10.3389/fpsyt.2021.652161
Should We Re-think Regulations and
Standards for Lighting at
Workplaces? A Practice Review on
Existing Lighting Recommendations
Oliver Stefani 1,2
*and Christian Cajochen 1,2
1Centre for Chronobiology, Psychiatric Hospital of the University of Basel, Basel, Switzerland, 2Transfaculty Research
Platform Molecular and Cognitive Neurosciences (MCN), University of Basel, Basel, Switzerland
Nowadays lighting projects often include temporal variations of the light, both spectrally
and in terms of intensity to consider non-visual effects of light on people. However, as
of today there are no specific regulations. Compliance with common lighting standards
that address visual aspects of light, often means that only little non-visually effective
light reaches the eye. In this practice review we confront existing regulations and
standards on visual lighting aspects with new recommendations on non-visual aspects
and highlight conflicts among them. We conclude with lighting recommendations that
address both aspects.
Keywords: lighting, workplace, standards, circadian rhythms, non-image forming effects of light
The advent of electric lighting made it possible to decouple working hours by means of shift work
from times when daylight was available. Concomitant to alterations in working hours, sleep-wake
times are very often irregular in shift workers thereby impacting on the endogenous circadian
timing system with negative health consequences (1). Light as the principal synchronizer (i.e.,
Zeitgeber) of human circadian rhythms, is “seen” during the biological night while at work, which
might lead to circadian rhythms disturbance such as shift work sleep disorder (SWD). SWD is
a circadian rhythm sleep disorder characterized by insomnia and excessive sleepiness affecting
people whose work hours typically occur during the habitual sleep period (1). In particular light
with high proportions of short wavelengths in the blue spectral range in the evening and at night
suppress the secretion of the night hormone melatonin, a marker of circadian rhythmicity in
humans. Additionally to negative light effects during the night, low illuminances during the day
can destabilize circadian rhythms (2).
Continuously disturbing the entrainment of endogenous circadian rhythms with external
diurnal Zeitgeber rhythms with can weaken the regenerative ability of the organism (3,4). Night
work is associated with negative consequences for somatic and mental health (5) and persistent
desynchronization of endogenous rhythms limits cognitive performance (6). Thus, with the
increase in flexible working times, innovative lighting concepts that take particular account of
non-visual lighting effects become particularly important.
With the increased time spent in buildings, the length of time during which people are exposed
to high amounts of daylight decreases. Although, lighting standards for workplaces ensure that
we can see well, specifications for artificial lighting correspond to twilight conditions outdoors (7).
500 lx of artificial light indoors corresponds to 0.5% of the light on a cloudless day. Measurements
Stefani and Cajochen Practice Review on Existing Lighting Recommendations
at workplaces have shown that workers are usually exposed to
illuminance of only 100 lx for more than 50% of the day (8),
which fall far below the recent recommendation of daylight
illuminance exposure (9).
Where life safety is threatened (e.g., in emergency situations
like building fires) interior lighting projects must comply with
requirements imposed by regulations regarding minimum
levels of illuminance. Different regions of the world approach
regulations, recommended practices, and standards differently.
For the design and operation of workplaces, the German
“Technical Rules for Workplaces” (ASR) for example, reflect
the state of the art for occupational medicine, occupational
hygiene, as well as other reliable ergonomic findings for
setting up and operating workplaces. According to the German
Workplace Ordinance, workplaces must receive as much
daylight as possible and be equipped with artificial lighting
that is appropriate for the safety and health protection of
employees. The Technical Rules for Workplaces ASR A3.4
(10) “Lighting” specify the requirements of the Workplaces
Ordinance for setting up and operating the lighting in
workplaces as well as the requirements for glare protection
when exposed to sunlight. In Germany for example, an artificial
lighting system for workplaces must meet requirements
concerning illuminance, limitation of glare, color rendering,
flickering, or pulsation as well as shadows. DGUV Informative
Publication 215-210 “Natural and Artificial Lighting of
Workplaces” of the German Social Accident Insurance (DGUV)
offers also assistance to employers in implementing the
ASR A3.4 “Lighting.”
Standards differ from regulations. In general, lighting
professionals are expected to appraise each design situation
and develop criteria for illuminance, color rendering quality,
uniformity, correlated color temperature (CCT) etc., that are
appropriate for a project, and although, there is no obligation to
comply to standards, they provide valuable guidance. Workplace
lighting in particular should consider these standards. One
example is the German DIN EN 12464-1:2011-08 (11). This
standard specifies the planning principles for lighting systems,
but does not specify the requirements for the safety and
health protection of employees at work. This standard gives
illuminance recommendations for the task area, the immediate
surroundings, background area, and for walls and ceilings.
In a new draft (prEN 12464-1:2019), higher illuminances are
recommended in order to allow for adjustments. In the new
draft, the horizontal illuminance of 500 lx for workplaces e.g.,
is now specified as a minimum requirement. A higher value
(1000 lx) is specified, which is to be used e.g., in rooms with
elderly persons with lower eyesight. The demands on lighting
quality are determined by the visual tasks that the human eye
has to master. The classic quality features of lighting can be
divided into three basic quality features, which are weighted
differently depending on the use of the room and the desired
appearance: Visualization, visual comfort, and visual ambience.
The following applies:
Visual performance is influenced by the illuminance and the
limitation of direct and reflected glare.
Good color rendering and a harmonious brightness
distribution ensure visual comfort.
Visual ambience is determined by CCT, light direction, and
modeling (i.e., the distribution of light and shadows).
Good lighting systems are also characterized by energy efficiency.
However, according to DIN EN 12464-1 (11), the quality of light
should not be reduced for lower energy consumption.
The purpose of the Swiss SIA 2024 (12) is to standardize
assumptions about room usage, in particular about personal
occupancy, and equipment usage. These assumptions should
be applied in calculations and verifications according to the
standards of energy and building services engineering if there is
no more accurate information available. The requirements are
regarded as standard values for the design of plants or factories
in an early planning phase. Finally, typical values are given
for power and energy requirements in the areas of appliances,
lighting, ventilation, etc.,
Further, important features are flicker-free lighting and the
possibility of changing brightness and CCT. Luminaires that are
too bright in the field of view can cause glare. Therefore, light
sources must be shielded in a suitable way. Glare is a complex
topic that cannot be discussed in rigorous detail in this work.
Other work, such as the DIN EN 12464-1 should be referred to.
When working with PC screens, care should be taken that
the luminance ratio between the working field and its immediate
surroundings is no greater than 3:1. The luminance ratio between
the work surface and the more distant surfaces should not
exceed 10:1. Due to higher luminances and improved anti-
reflective coatings, modern PC screens can tolerate much higher
environmental luminance levels than their predecessors. DIN
EN 12464-1 describes the permissible limit values for avoiding
reflected glare. For screens with a luminance of L 200
cd/m2luminances of up to 1500 cd/m2are permissible for
luminaires. For monitors with a monitor luminance L >200
cd/m2(typical for offices with good to very good daylight supply
and correspondingly adapted flat screens) luminance values of up
to 3000 cd/m2are permissible. The ambient contrast ratio (A-
CR) is a key metric to achieve a high image quality of displays
when considering bright ambient lighting (13). While OLED
(organic light-emitting device) based displays exhibit several
attractive features, such as self-emission, high brightness, and a
high contrast ratio, when operated under bright ambient light,
most of the incident light is reflected and decreases the A-CR
which makes the application under high illuminances difficult.
Today there are several methods to eliminate reflected ambient
light in OLEDs (e.g., by a circular polarizer or a destructive
interference layer). A-CR is generally defined as
ACR =Lon +Lambient ·RL
Loff +Lambient ·RL
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Stefani and Cajochen Practice Review on Existing Lighting Recommendations
where Lon (Loff ) represents the on-state (off-state) luminance
value of an LCD or OLED, and Lambient is ambient luminance
(14). RLis the luminous reflectance of the display panel.
For a balanced luminance in the room all surfaces must be
taken into account. Surface luminances can be determined by the
reflectance of the surfaces and the illuminance on the surfaces.
According to DIN EN 12464-1 recommended reflectances are:
ceiling: 0.7 to 0.9
walls: 0.5 to 0.8
floor: 0.2 to 0.4
Regarding good color rendering it is commonly recommended
to have a CRI of Ra >80. We have recently found evidence for
positive effects of a high CRI (Ra 97 vs. 80) on visual comfort,
daytime wakefulness, well-being, and nighttime sleep (15). A
newer and better system for evaluating a light source’s color
rendering property is IES TM-30-15. The fidelity index and the
gamut index of IES TM-30-15 of the LED causing the before
mentioned positive effects were Rf.97 and Rg.101, respectively,
and for the poorer performing LED it was Rf.81 and Rg.94.
Without shadows objects are only two-dimensional images.
Only the correct distribution of light and shadow guarantees
that faces and gestures, surfaces, and structures can be easily
recognized (11). A pleasant lighting climate is created when
people, architecture, and room furniture are illuminated in
such a way that shapes and surface structures are clearly
visible. Distances can be easily estimated and orientation
in the room is made easier. Good visual communication
requires that faces are easily and quickly recognized. In
areas where good visual communication is important, for
example in offices and meeting areas, DIN EN 12464-1
recommends a higher average cylindrical illuminance of 150 lx.
The cylindrical illuminance is the average of all vertical light
on an imaginary cylinder. DIN EN 12464-1 cites “modeling”
as an important quality feature for the perception of people
and objects. Modeling is the relationship between cylindrical
and horizontal illuminance and should be between 0.30
and 0.60.
The international WELL Building Institute (16) aims for
advancing health and well-being in buildings. It also provides
recommendations for lighting to support visual acuity and is
mainly based on the American National Standards Institute
(ANSI) and Illuminating Engineering Society (IES) RP-1-20 (17)
standard and on the standard of the Ontario Ministry of Labour,
Computer Ergonomics: Workstation Layout and Lighting (18).
At workstations or desks requirements are met when
1. The ambient lighting system is able to maintain an average
light intensity of 215 lx or more, measured on the horizontal
work plane. The lights may be dimmed in the presence of
daylight, but they should be able to independently achieve
these levels.
2. The ambient lighting system is zoned in independently
controlled banks no larger than 46.5 m² or 20% of open floor
area of the room (whichever is larger).
3. If average ambient light is below 300 lx, task lights providing
300 to 500 lx at the work surface are available upon request.
The American National Standards Institute and Illuminating
Engineering Society of North America. RP-1-20 provides
recommended luminance ratios for offices:
1. Luminance ratios should not exceed 3:1 between a paper task
and an adjacent visual display terminal.
2. For ceiling luminance ratios, 10:1 is the maximum
acceptable ratio.
3. Luminance ratios should not exceed 10:1 between a task and a
remote surface.
In the latest version of the WELL v2 pilot (Q1 2021) it is
recommended that indoor spaces should comply with one
of the lighting reference guidelines (IES Lighting Handbook
10th Edition, EN 12464-1: 2011, ISO 8995-1:2002(E) (CIE S
008/E:2001), or GB50034-2013).
It is only known since 2002 that the human eye has a third
photoreceptor for processing ambient light in addition to the
two classical photoreceptor types, the rods, and cones (19,20).
Effects of visible radiation, which are mainly controlled by this
newly discovered photoreceptor, but make a minor contribution
to classical visual information processing, are also called non-
visual light effects. Berson and colleagues reported that those
ganglion cells containing the photopigment melanopsin project
almost exclusively to the nucleus suprachiasmaticus (SCN), the
central pacemaker driving circadian rhythms. They are also
able to transmit light signals into the cortex without the help
of the classical photoreceptors. Thus, these ganglion cells have
been termed “intrinsically photosensitive retinal ganglion cells
(ipRGC)” with melanopsin maximally sensitive to visible short-
wave radiation (21).
Provencio et al. (22) reported that a coarsely resolved network
of photosensitive ganglion cells extends over the retina of mice,
which has the task of detecting brightness. Later, it was found that
these melanopsin-containing ganglion cells are distributed not
only in the fovea but also over the entire retina with a density of
3–5 cells/mm² and have their maximum concentration of 20–25
cells/mm² in the area surrounding the fovea (20,23). IpRGCs are
not evenly distributed across the retina but have a higher density
in the lower half so that light that falls into the eye from above
and impinges the lower half of the retina suppresses the nocturnal
release of melatonin more than light from below (24,25).
While blue-enriched light can contribute to increased
alertness, especially in the evening and at night, nocturnal
exposure to light reduces melatonin secretion. Melatonin
secretion is especially reduced by light at night if people are
exposed to only a low dose of light during the day (26). Today,
people often live their lives in isolation from their natural
environment with a high risk to develop circadian disorders
(27). Severe circadian disturbances are found in people who are
forced to chronically change their lifestyle by adapting their sleep-
wake schedules to the imposed work schedules (e.g., rotating
shift workers) (1). A milder form of circadian disorder occurs
in many people due to too short night’s sleep on working days
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and a delayed onset and prolonged duration of sleep on non-
working days. Over 80% of people in western industrialized
countries show this altered sleep behavior and that nightly
sleep on non-working days is delayed by an average of 90
min (28).
Since circadian rhythms only have an approximate period
length of 24 h, they require daily synchronization with the
environment (29,30). The rotation of the earth and thus the
regular light-dark change is the most important environmental
signal for the synchronization of circadian rhythms (31).
For the interpretation of ambient brightness, photoreceptors
continuously calculate the intensity, and spectral composition
of the light entering our eyes (32). Thus, when light with
increased short-wave radiation enters the eye, ipRGCs signal
a bright phase of day to the SCN. In addition, the times of
change from dark to light phase and vice versa (i.e., dawn
and dusk) provide a crucial input for the SCN and the
synchronization of circadian rhythms with the environment
(31,33,34). Bright white light at night can shift the
circadian phase backward by up to 3 h in the next 24-h
cycle. In contrast, early morning exposure to light can shift
the circadian phase forward by up to 2 h in the next 24-h
cycle (35,36).
Some studies document acute effects of bright light on the
subjective feeling of alertness at night and during usual sleep
periods (3739), before falling asleep (40) and immediately
after waking up in the morning (41,42) but also during
daytime (43). Although, most of these studies compare very low
illuminances (5–50 lx) with high illuminances (1,000–5,000 lx)
of fluorescent white light, alerting effects were estimated to
occur already at around 100 lx during the night and at 500 lx
during the evening. Thus, there is evidence, that subjective
wakefulness due to bright light can basically occur at any
time of the day. Other research with objective measures
has so far only been able to prove a wakefulness inducing
effect of bright light at night (44) and results of studies
conducted during the day provided inconsistent results (43,
45,46), possibly due to smaller differences in the light levels
compared. Nevertheless, bright light during the day makes
the circadian system less sensitive to nocturnal light (26,47
49). Although the protocols of these studies differ from each
other, illuminances that were compared during the day were
significantly different from each other (i.e., at least 10-fold
up to 400-fold different). A dark phase of several hours can
increase sensitivity to light. Thus, early morning exposure to light
immediately after awakening (i.e., after several hours of nightly
sleep in darkness) can phase advance the circadian phase by
1–3 h (50,51).
In many cases, the alerting effect of light, especially in the
evening and at night, is also associated with an increase in
attention and working memory performance (41,52). Non-
visual effects also include the mood enhancing effect of bright
light (5355), with required light doses being around 2500
lx-h. There is also evidence that the current mood reflects
a person’s level of alertness and the immediate effect of
bright light on mood is mediated by the wakefulness inducing
effect (56).
Considering our experience with around 100 years of electric
lighting, people have been exposed to this artificial creation 5,000
times shorter than to the light at night from fire. The first
evidence for the use of handcrafted light sources comes from
archaeological findings from around 500,000 years ago. Fire was
used as a source of light at night, but life and work still depended
on daylight. Daylight is perhaps the purest form of human centric
lighting since our eyes have had several million times longer to
optimize to daylight than to LEDs. It is therefore reasonable to
assert, from the evolutionary standpoint, that human eyes, and
behavior are not yet optimized to electric light.
New lighting technologies that try to mimic continuously
changing CCT and illuminance of sunlight according to the
time of day are often termed HCL (Human Centric Lighting).
According to manufacturers of these lighting technologies,
it is possible to provide people indoors with artificial light
similar to daylight in such a way that they can benefit from
the beneficial effects natural daylight would provide. These
include increased alertness, concentration, and performance. A
publication summarizing the benefits of HCL on humans shows
that it has sound motivations (57). The authors conclude that
“bright days and dark nights are a good starting point,” and
suggest that apart from electric lighting, architecture should
be driven by daylight design principles. A conclusion that we
support. Since HCL is increasingly being promoted and used
for work places or private homes due to their postulated effects,
the Swiss State Secretariat for Economic Affairs (SECO), and
the Federal Office of Public Health (FOPH) have commissioned
the Centre for Chronobiology at the University of Basel to
evaluate scientific literature on HCL (58). The central question
was whether this light can influence physiological, cognitive,
or subjective effects in humans, i.e., the effects perceived by
humans themselves.
The Basel study (58) has shown that only a few studies have
investigated whether HCL can influence the above mentioned
effects. Therefore, the University of Basel has extended the
assessment and additionally evaluated studies on physiological,
cognitive, or subjective effects of artificial light that affects people
during the day during office hours (from 7:00 a.m. to 5:00 p.m.)
but does not continuously adapt to the properties of daylight. A
total of 45 studies met the inclusion criteria. On the basis of these
studies, it was possible to check for 33 different effect variables
whether they depend on the light intensity and CCT of artificial
light that affects people during the day.
The Basel study (58) shows that neither the light intensity
nor CCT significantly influence physiological parameters such as
pulse rate and brain waves during normal office hours. In the case
of cognitive effects, however, it was shown that light intensity
and CCT had an influence on the reaction time of people. In
addition, the spectrum of light influences the accuracy with
which people solve tasks. In the subjective effects, light intensity
and light spectrum had an influence on the concentration,
tiredness and drowsiness perceived by the persons themselves.
Overall, however, the observed effect strengths of the light effect
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Stefani and Cajochen Practice Review on Existing Lighting Recommendations
during office hours were rather small. Nevertheless, the authors
of the study come to the conclusion that high light intensity
and higher CCT during daytime hours are advantageous in
artificially illuminated interiors, even if these advantages are only
evident in cognitive and subjective effects but not in physiological
parameters. During the night, the effects of higher CCT are more
prominent even in field studies. While blue-enriched white light
sources can adjust circadian rhythm to night-shiftwork, reduce
sleepiness, and enhance cognitive performance of night-shift
workers (59) this concept should be applied cautiously and only
if workers must work very concentrated (e.g., in control rooms).
While there are numerous studies providing evidence of non-
visual effects of light during the evening and at night, results
might not be translatable to the day. In line with the Basel study
(58), a literature review on daytime non-visual effects of light
on alertness (60) concludes that the present literature provides
inconclusive results on alerting effects of light during daytime,
particularly for objective measures and correlates of alertness.
The authors suggest that the alerting potential of exposure to
more intense white light should still be investigated. Another
systematic review assessed effects of light on alertness and mood
in daytime workers (61). Although, they conclude that light with
a high CCT may improve alertness during the day, they suggest
that additional studies are still needed because all findings are
based on low-quality evidence.
Impacts of two dynamic LED lighting concepts with
illuminance and CCT gradually decreasing between 1:30 p.m.
and 5 p.m. were investigated on its effects on sleep and well-
being (62). In one setting illuminance changed from 700 to 500 lx
and CCT from 6000 to 3500 K, in the other from 500 to 300 lx,
and CCT from 5000 to 3000 K. The settings were compared
to static light (500 lx, 5000 K and 300 lx, 4000 K). A significant
increase in subjective alertness was observed at 1 p.m., indicating
a potential solution to reduce the subjective sleepiness in the
afternoon. On the other hand, a significant decrease in perceived
sleep quality and sleep duration was reported after subjects
were exposed to dynamic lighting. No significant differences
were observed for mental stress, productivity, visual comfort, or
perceived naturalness.
A different approach with custom-built desktop luminaires
intended to support office occupants’ entrainment while
supporting their alertness during the day. The luminaires
were designed to deliver three lighting interventions. First
saturated blue light (455 nm, 50 lx) in the morning (6–12 a.m.),
Then polychromatic white (6500 K, 200 lx) light at midday
(12 a.m.1:30 p.m.) provided a smooth transition from the first
to the third intervention. The third intervention was saturated
red light (634 nm, 50 lx) in the afternoon (1:30–5 p.m.). In their
results the authors observed advances in sleep start and sleep end
times and hence they suggest that the participants were better
entrained to the local 24-h light dark cycle while at the same time
reporting increased subjective alertness in the afternoon with red
light (63).
The effect of dynamic light during shift work on the quality
of sleep and melatonin secretion was examined with staff of an
Intensive Care Unit (ICU) and compared with staff from a similar
ICU with standard light (64). CCT controlled ceiling luminaires
with light tubes (2700 and 6500 K) and indirect lighting with
RGBW lights “to imitate the reflection of the sun” were used
but no information about the spectral characteristics is reported.
The light changed color and intensity. The nightlight between 10
p.m. and 5 a.m. was dim (68 lx), and short-wavelength depleted
causing the light to appear “unnaturally red.” Between 5 and
6 a.m., the light gradually changed to a daylight scenario (525 lx).
In the afternoon from 3 p.m. light levels decreased. Between
8 and 10 p.m. a change occurred “toward a mix of primarily
red, green, and white.” Since no precise spectral measurements
are available but only RGB percentages it is difficult to replicate
the lighting conditions. Nevertheless, the intervention group
reported to be more rested and assessed their condition on
awakening as better than the control group. The study, however,
found no significant differences in sleep efficiency and melatonin
levels. Subjectively, nurses from the intervention group assessed
their sleep as more effective than participants from the control
group. In a different field study, bright fluorescent lighting
(1500–2000 lx) when compared to standard lighting (300 lx) in
hospitals decreased sleepiness of ICU nurses working a 10-h
night shift (65).
In a field experiment, effects of dynamic lighting on office
workers were tested (66). In the dynamic lighting condition,
employees experienced a gradually changing lighting scenario
(changing twice a day between 8 and 12 a.m. and 1:30 and 4 p.m.
from 700 to 500 lx and 4700 to 3000 K). The static condition
provided an illuminance of 500 lx and CCT of 3000 K While
employees were more satisfied with the dynamic lighting there
were no significant differences for need for recovery, vitality,
alertness, headache and eyestrain, mental health, sleep quality, or
subjective performance.
Under strictly controlled laboratory conditions, we examined
whether dynamic light across the day influences cognitive
performance, visual comfort, melatonin secretion, sleepiness,
and sleep (67). Volunteers either woke up with static daylight
LED (100 lx at the pillow and 4000 K, melEDI 69 lx) or with a
dynamic daylight LED that changed CCT (2700–5000 K) and
intensity (0–100 lx at the pillow, melEDI 0.4–76 lx) across the
day (daylight here refers to the spectral characteristics of the
Toshiba TRI-R LED). Participants underwent a 49-h laboratory
protocol. They spent the first 5-h in the evening under standard
lighting, followed by an 8-h nocturnal “baseline” sleep episode
at habitual bedtimes. Thereafter, they spent a scheduled 16-h
waking day under one of the lighting conditions. Following a
8-h nocturnal “treatment” sleep episode, the volunteers spent
another 12 h either under static or dynamic light. Horizontal
illuminance at desk height ranged, depending on the position,
between 150 and 650 lux, which corresponds to standard office
lighting. Under dynamic light, evening melatonin levels were less
suppressed 1.5 h prior to usual bedtime, and participants felt less
vigilant in the evening compared to static light. Sleep latency
was significantly shorter compared to the static light condition
while sleep structure, sleep quality, cognitive performance,
and visual comfort did not significantly change. These results
support the recommendation of using blue-depleted light and
low illuminances in the late evening, which can be achieved
by a dynamically changing LED solution. Since illuminance
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Stefani and Cajochen Practice Review on Existing Lighting Recommendations
decreased to around 1 lx, this lighting concept can only be
applied in domestic areas but if concentration at work in the
late evening and at night is required, this lighting concept would
be counterproductive.
To date, only a few field studies investigated the influence
of dynamic lighting solutions during shift work. A field study
surveying the state of subjective alertness and fatigue in 542
employees during three-shift work (8 h working shifts) in
ongoing production operations compared dynamic light with a
static lighting condition (68). In a first round, 256 respondents
evaluated the static lighting concept by completing a structured
questionnaire. In a second round, 287 respondents commented
on the alternating lighting concept. Fourty one percent of the
participants who experienced the alternating lighting concept
took part in the survey on the static lighting concept. They
worked in three shifts (morning, late, and night) for 8 h each.
The alternating lighting concept featured a high horizontal
illuminance on the workplace (850 lx) and a high CCT (5300 K)
during daytime. The resulting vertical illuminance at eye height
was 237 lx (melEDI 164 lx) and CRI was Ra 77. During nighttime,
a reduced illuminance (580 lx) with low CCT (3400 K) and CRI
of Ra 85 was deployed. This resulted in a vertical illuminance
of 158 lx (melEDI 71 lx) at eye height. Illuminance and CCT
changed gradually between 5 and 8 p.m. and between 5 and
9 a.m. This setting was compared to the static lighting condition
(horizontal at the workplace 760 lx, vertical at the eye 210 lx
(melEDI 128 lx), 4600 K, CRI Ra 82). All participants assessed
specific lighting characteristics (such as CCT, brightness, color
rendering, appeal) using a seven-point Likert scale. No significant
differences were found between the participants’ rating of the
characteristics surveyed in terms of alternating and static lighting
conditions. The transitions from day to night conditions and
vice versa had no disturbing effect on the participants’ rating of
the lighting criteria surveyed (p>0.05). Thus, it was concluded
that shift workers accepted the alternating lighting system.
In addition, there were no significant differences in alertness
and fatigue between the early and late shifts for both lighting
conditions. This survey indicated the potential usefulness of a
dynamic lighting solution for shift-work without major impact
on the worker’s alertness and fatigue level. However, objective
measures such as salivary melatonin levels, and reaction time
measures to assess vigilant attention are clearly mandatory for
future studies to test the usefulness of dynamic lighting solutions
in shift work environments.
With the goal to provide adequate light for visual tasks while
lessening disruption of the human circadian system, Moore-
Ede et al. (69) derived a spectral sensitivity curve with a peak
at 477 nm and a full-width half-maximum of 438 to 493 nm.
While there are other products commercially available that notch
the spectrum in the melanopsin region, they specifically call it
“steadystate circadian potency spectral sensitivity” and suggest
that it “permits the development of spectrally engineered LED
light sources to minimize circadian disruption and address the
health risks of light exposure at night in our 24/7 society, by
alternating between daytime circadian stimulatory white light
spectra and nocturnal circadian protective white light spectra.”
They further suggest, that it could provide attractive and energy-
efficient white electric light that minimizes circadian disruption
if violet LED dies with peak wavelengths of 410 to 420 nm
replace the typical 450 nm blue peak emissions of conventional
LEDs. Since short-wavelength light is known to have alerting-,
performance-, and mood enhancing properties (70,71), they
suggest that this light at night could be used to reduce human
error, without the risk of circadian disruption and health
disorders. The alerting effect of short-wavelength light could be
retained because there is evidence by a single study that the
alerting effects of 420 nm violet light are even greater than 440
or 470 nm blue light (72).
In an approach to mimic certain aspects of daylight (i.e., direct
warm sunlight and diffuse cool skylight), Aalborg University
proposed a combination of directional task lighting and diffuse
ambient lighting, with respective intensities and CCTs to create
naturally perceived luminous variations. Such lighting concepts
mimicking the combination of light from the sun and sky date
back to 1952 (73). Aalborg University conducted a pilot study
with four participants that worked for 4 months in such static
and dynamic lighting. Visual comfort, perceived atmosphere,
and work engagement were evaluated with interviews and
questionnaires. The tentative results indicate that dynamic
lighting has a positive effect on visual comfort, perceived
atmosphere, and work engagement compared to static lighting
(74). Another study (75) from the same author investigated
the quality of light in an office after adding ceiling-mounted
spotlights to traditional diffuse ceiling panels with the intention
to complement the directionality of the natural daylight inflow
from windows. The visual light quality and perceived atmosphere
of the office environment was tested with 30 volunteers through
questionnaires, reaction cards and semi-structured interviews.
The authors report: “The direct flow of light is recommended
to be more than 15% of the total illuminance at the work-plane
to provide the distinct visual appearance of modeling and a
cozier atmosphere, which is preferable for socializing, and <45%
to avoid glare and high contrast for visual tasks. Direct warm
and diffuse cool lighting were perceived as the most natural but
were not always preferred. There is a slight preference for cooler
ambient lighting in clear sky situations and warmer ambient
lighting in overcast situations. Strong individual preferences for
combinations of color temperatures was identified. . . .”
Effects on well-being and motivation by changing light
distribution were investigated by Fleischer (76) in 2001. Lighting
consisted of luminaires that slowly changed between direct and
indirect light. The ratio between direct and indirect lighting
was changed according to the time of the day or to weather
conditions. It was shown that pleasure rises with higher
illuminance and a large indirect component. This might be due
to a “sky-like” impression of the bright ceiling. The preference
for a large indirect component was also found by Houser et al.
(77) who report a subtle overall preference, when the indirect
contribution to horizontal illuminance was 60% or greater.
With an increase of the direct component and an increase of
illuminance arousal rises. The direct component results in a
darker ceiling but brighter desk. Apparently this contradicts the
findings of (23) and (25) that find higher sensitivity of ipRGCs
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for light coming from above. The results of Fleischer, however,
may not be explained by NIF effects (by ipRGCs) but solely by
visual effects.
From a non-visual and circadian perspective, compliance with
the above-mentioned standards cannot guarantee that enough
biological active light reaches the eye (78). Some studies (45,79,
80) report that corneal illuminance levels of at least 1000 lx for
several hours are necessary to achieve non-visual effects during
the day. Many of these studies investigated the effects of light
therapy in the morning while others also found effects with
illuminances ranging from 1000 to 1700 lx during various normal
office hours (when compared to 165–200 lx). Thus, lighting
standards addressing visual aspects are currently not designed to
account for non-visual light effects during the day.
Today, an evaluation of the non-visual effectiveness of
radiation is based on a radiometric characterization of the
radiation entering the eye, and the corneally measured spectral
irradiance is weighted with the spectral sensitivity of all five
photoreceptors and referenced to the spectrum D65 (standard
illuminant) (81). The International Standard of the International
Commission on Illumination (CIE) CIE S 026:2018 (82) “CIE
System for Metrology of Optical Radiation for ipRGC-Influenced
Responses to Light” defines spectral sensitivity functions,
quantities, and metrics to describe the ability of optical radiation
to stimulate each of the five photoreceptor types (S-cone, M-
cone, L-cone, rhodopsin, and melanopsin). This standard also
denotes a quantity named the “melanopic equivalent daylight
illuminance” (melanopic EDI or melEDI), that is expressed in
Lux. The melanopic EDI of a light condition expresses how much
daylight results in the same melanopic irradiance as the test light
condition. Nowadays lighting projects often include temporal
variations of the light, both spectrally and in terms of intensity.
Lighting projects that consider the possible effects of changing
light on people, try to optimize well-being. However, as of today
there are no specific regulations. Recommended practices sprout
everywhere but experts in the field criticize them.
Seven examples for recommendations for circadian lighting
are (in alphabetical order):
1. Chartered Institution of Building Services Engineers (CIBSE)
and Building Research establishment (BRE) Research Insight
Circadian lighting (83).
2. CIE S 026:2018 (82) “CIE System for Metrology of Optical
Radiation for ipRGC-Influenced Responses to Light.”
3. DGUV 215-210 “Non-visual Effects of Light on Humans”
4. DIN SPEC 67600:2013-04 (85) (technical report) “Biologically
Effective Lighting - Planning Recommendations.”
5. Recommendations for Healthy Daytime, Evening, and Night-
Time Indoor Light Exposure (9).
6. UL DG 24480 (86) “Design Guideline for Promoting
Circadian Entrainment with Light for Day-Active People.”
and the update WELL v2 pilot (87).
CIBSE and BRE Research Insight Circadian
Based on a literature review (83) and their results from a field-
study they suggest these tentative recommendations:
1. “From mid-morning until early afternoon, use higher than
normal levels of light with increased blue light. Current high
color temperature light sources such as LEDs and some types
of fluorescent light give high outputs of blue light. There is still
scope to tailor their spectra further in the future to fit the peak
response of the ipRGC sensors in the eye and maximize their
circadian impact.
2. Toward the end of the day, dim the lighting (while retaining
enough light to meet visual task recommendations) and lower
its color temperature (“warmer,” redder light, similar to that
in a domestic setting). There is also future scope to alter the
spectrum of existing LEDs to give very low circadian stimulus
in the evening or at night. Even warm white LEDs often have a
small peak of blue light which can stimulate the ipRGCs.
3. Maximize reflected light from room surfaces by using light
fittings with an upward light component, and “wall washing”
to illuminate the walls directly. This will give more light to
people facing the walls.
4. As light levels will be higher than normal for part of the day,
use high quality fittings to minimize glare and avoid all flicker.
Have a balanced visual environment, for example by avoiding
very light-colored desks.
5. Vary the lighting gradually, to avoid disturbing the occupants.
Controls need to be reliable.
6. People vary in their preferences for lighting; conventional
good practice is to offer individual control but this can negate
the circadian effects. There is no obvious way round this.
7. Explain to the occupants what the lighting system is doing and
the purpose of varying the lighting.”
CIE S 026:201861 “CIE System for
Metrology of Optical Radiation for
ipRGC-Influenced Responses to Light”
CIE recommends to spend adequate time outdoors during the
day since it is associated with better health and well-being and
also recommends to not restrict daylight within indoor settings.
Although, no specific quantities are given, CIE recommends a
high melEDI during the day to support alertness, the circadian
rhythm, and good sleep during the night in a position statement
on Non-Visual Effect of Light. During the evening and at night a
low melEDI facilitates sleep initiation and consolidation (88).
DGUV 215-210 “Non-visual Effects of Light
on Humans”
This DGUV (German statutory accident insurance) information
brochure (84) provides advice on hazards to safety and health
at work, how they can be avoided and how opportunities
for maintaining health can be exploited with modern lighting
concepts. Since scientific knowledge about the non-visual effects
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Stefani and Cajochen Practice Review on Existing Lighting Recommendations
of light on humans is not yet complete, as the brochure says,
it is not yet possible to derive any generally valid quantitative
statements regarding non-visual effects, for example numerical
values for illuminance or CCT. This brochure gives the advice
that daylight should be used first and foremost. For this reason,
workplaces should preferably be located close to windows. The
better the inner clock is synchronized by daylight, the less
sensitive it is to disturbing factors, such as artificial light in
the evening. Only if little daylight is available at workplaces,
bright artificial lighting or lighting with high blue components
should be used as a supplement during the day. Light sources
with high CCTs are usually favorable for this purpose. This light
can achieve similar non-visual lighting effects as daylight, but
cannot replace it. In the evening, bright light and light with
high blue components should be avoided. This should be done
at least 2 h before the usual start of sleep. During this time,
the light should primarily illuminate the work surface relevant
to the visual task and not fall directly into the eye. Looking
directly into the light source and at very brightly illuminated
surfaces should be avoided. When working on a computer, tablet
or smartphone, special blue light filter programs (e.g., flux, Night
Shift or other manufacturer-specific blue light filter apps) should
be used at least 2 h before the usual start of sleep. Furthermore,
advice is given, that during the day, bright walls, and ceilings
should enhance the non-visual effects through indirect light
components. In the evening, the necessary brightness at the
workplace should be limited. The lower indirect share of light on
the ceiling and walls should reduce non-visual effects.
DIN SPEC 67600:2013-04 “Biologically
Effective Illumination - Design Guidelines”
The German DIN SPEC 67600:2013-04 “Biologically effective
illumination - Design guidelines” recommends: Illuminance at
the eye 250 lx at CCT =8000 K or Illuminance at the eye
290 lx at CCT =6500 K. The Commission for Occupational
Health and Safety and Standardization (KAN) (represents
occupational health and safety interests in the standardization
process) criticizes (89):
“Contents of the already published DIN SPEC 67600:2013-04
(technical report) “Biologically Effective Lighting - Planning
Recommendations” are partly based on insufficiently secured
findings, therefore a misinterpretation during its application
cannot be excluded . . . the planning recommendations of DIN
SPEC 67600 (technical report) do not form a secure basis for
the implementation of the Technical Regulation for Lighting ASR
A3.4 in operation.”
CIBSE and BRE concluded in a literature review: “The
existing recommendations in DIN SPEC 67600 should be treated
with caution.”
Recommendations for Healthy Daytime,
Evening, and Night-Time Indoor Light
A recent publication (9) from experts in lighting,
neurophysiological photometry and sleep and circadian
research provides an expert consensus for healthy daytime
and evening/night-time light environments. They come to the
conclusion that “Throughout the daytime, the recommended
minimum melEDI is 250 lx at the eye measured in the vertical
plane at 1.2 m height (i.e., vertical illuminance at eye level when
seated). If available, daylight should be used in the first instance
to meet these levels. If additional electrical lighting is required,
the polychromatic white light should ideally have a spectrum
that, like natural daylight, is enriched in shorter wavelengths
close to the peak of the melanopic action spectrum. During the
evening and at home, Brown et al. (9) recommend to reduce
melEDI to around 10 lx at least 3 h before bedtime. During sleep
the recommended maximum melEDI is 1 lx.
UL DG 2448022 “Design Guideline for
Promoting Circadian Entrainment With
Light for Day-Active People”
UL DG 2448022 “Design Guideline for Promoting Circadian
Entrainment with Light for Day-Active People” recommends:
“The amount of light equivalent to that after 1 h of exposure,
capable of suppressing the production of melatonin at night by
30 per cent . . . should be continuously available at the occupant’s
eyes for a minimum of 2 h during the daytime.” This would
translate into a vertical illuminance at the eye of about 350 lx for
warm light (CCT <3000 K) and 200 lx for cool light (CCT >
5000 K) sources. Here the question arises, how a suppression of
melatonin at night relates to a measure of light during the day.
UL DG 2448022 is commented by the IES (90) as follows:
“It is important to note that UL Design Guideline 24480 is not a
consensus (ANSI) document. The IES maintains the position that
any Recommended Practice related to light and health should be a
consensus document developed through an accredited American
National Standards Institute process. Without the full rigor of
an ANSI approved Standard, non-consensus based information
cannot be deemed to have been fully vetted and lacks the authority
to provide public guidance regarding means or methods that
affect public health. The IES urges the lighting industry to exercise
caution when considering a non-consensus document for design,
application, product qualification or regulatory purposes.”
The Well Standard and Well v2 Pilot
The WELL standard recommends for melanopic light intensity at
work areas: “Light models or light calculations demonstrate that
at least one of the following requirements is met”:
1. At 75% or more of workstations, at least 200 equivalent
melanopic lx (EML) is present, measured on the vertical plane
facing forward, 1.2 m above finished floor (to simulate the view
of the occupant). This light level may incorporate daylight, and
is present for at least the hours between 9:00 a.m. and 1:00 p.m.
for every day of the year.
2. For all workstations, electric lights provide maintained
illuminance on the vertical plane facing forward (to simulate
the view of the occupant) of 150 EML or greater.
The newer WELL v2 pilot recommends these levels for all spaces
(at least 150 EML) and adds the corresponding EDI value (136
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Stefani and Cajochen Practice Review on Existing Lighting Recommendations
melEDI). In case that 218 melEDI or more are achieved, the space
would achieve a better score in a system based on points. These
light levels vertical plane at the eye should be achieved at least
between the hours of 9 a.m. and 1 p.m. and may be lowered after
8 p.m. at night.
CIBSE and BRE concluded in a literature review (91): “The
existing recommendations in the WELL Building Standard should
be treated with caution.”
The circadian timing system in humans is genetically timed
in such way that we are active and awake during daytime
and inactive and asleep during the night (i.e., diurnal species).
Thus, during the biological night the hormone melatonin is
actively secreted in a circadian fashion usually peaking 2–3 h
after habitual bedtime. As melatonin is important for many
physiological processes in the human body (e.g., antioxidant
and regulating sleep-wake timing), its secretion should not be
suppressed or altered in the evening and at night by light.
Avoiding light at night during shift work, however, is rather
difficult, especially if workers need to be fully concentrated. Thus,
ideal lighting conditions during night shifts is always a trade-off
between optimal light for visual tasks, safety, alertness, and well-
being and optimal light for non-visual effects avoiding circadian
phase shifts and melatonin suppression.
Exposure to brighter light and light with high proportions
of short wavelengths in the blue spectral range during the day
can improve subjective alertness, concentration, the reaction
time, and accuracy with which individuals solve tasks. It reduces
tiredness and drowsiness and helps to maintain circadian
rhythms and improve sleep quality as compared to darker and
blue depleted light. Physiological measures (e.g., EEG), however,
are less likely to be affected by light during the day, most probably
related to the fact that we are a diurnal species. The pathway
of light for affecting circadian rhythms, sleep-wake behavior,
alertness and well-being in individuals is predominantly expected
to be through the eye and the stimulation of ipRGCs, which
then send signals to the suprachiasmatic nucleus (SCN) and
other areas in the brain implicated in the regulation of
different neurobehavioral domains. Therefore, it can be assumed
that melEDI is a suitable measure for predicting melatonin
suppression and other non-visual effects in humans. A precise
quantity of melEDI to trigger these effects however is difficult to
determine and may depend on the output domain (e.g., alertness,
melatonin, sleep, circadian phase shifts etc.,) one is interested
in. Based on the expert consensus (9) mentioned above, we
recommend to aim for 250 lx melEDI during usual daytime office
hours (in the vertical plane at 1.2 m height) for everyone working
inside buildings, even if this requires more energy.
Notably, luminous efficacy is calculated in Lumens per Watt
because Lumens are based on visual brightness perception
(V lambda curve). Non-visual aspects, however, should be
considered too. Non-visual effects have a different spectral
sensitivity curve compared to the visual perception of brightness
and are therefore not considered in the common calculation
of energy efficiency; therefore, we would recommend not only
considering Lumens per Watt as a measure for luminous efficacy
but also a measure that considers “non-visual luminous efficacy”
during the day (e.g., melanopic EDI per Watt). When light is
capable to reinforce normal circadian patterns of alertness during
the day and sleep at night, studies have either used very high light
levels (approximately 1000 lx) or strongly blue enriched light
(CCT 17000 K). Notably, most field studies have not controlled
for the position of individuals within a room and hence for their
precise light exposure levels at the eye.
A lighting concept that reduces melatonin suppression during
the night while still allowing for high concentration would be
ideal. Since melatonin suppression is mainly linked to the melEDI
(92,93) and not necessarily to CCT, metameric light sources that
reduce melatonin suppression could be an innovative solution
(94). By optimizing the light spectrum metamerically, daytime
alertness could also be improved (95). Additionally, the light
distribution could be changed between night and day. Since
direct light increases arousal (76) and iPRGCs are probably more
sensitive to indirect light from the ceiling (25), these factors could
be considered in the lighting design for day and night. Following
existing guidelines to avoid glare and yet achieving a high amount
of melEDIs at workplaces during the day could be achieved by
three workarounds:
1. Optimizing the spectrum by using light sources with a
relatively high melEDI (and a high CRI).
2. Optimizing vertical illuminances at the eye by optimizing
the light distribution (also considering the reflection of
surrounding surfaces. Optimized lighting design can provide
higher light levels at the eye (vertical illuminances) for the
same horizontal illuminance. Often, downwards oriented
lighting from ceiling mounted luminaires intended for rooms
with PC screen result in relatively low vertical illuminances.
To achieve higher vertical illuminance and hence more light at
the eyes, suspended or floor standing luminaires with indirect
light distribution (that direct light onto the ceiling) and “wall
washing” luminaires can be used. Additional white vertical
elements can increase vertical illuminances.
3. Since the melanopsin-containing ganglion cells in the eye are
distributed over a large area of the retina, it can be assumed
that the non-visual effect of light is greatest when light comes
from a large-area source. In nature, this light comes from the
sky. If only a small area of the retina is illuminated, as is the
case with the directional light of a spot, a weaker non-visual
effect is assumed.
During the evening we share the opinion with Brown and
colleagues (9) of reducing melEDI to around 10 lx, of course, only
if no safety-relevant activities have to be carried out (i.e., at home
before bedtime).
The original contributions presented in the study are included
in the article/supplementary material, further inquiries can be
directed to the corresponding author/s.
Frontiers in Psychiatry | 9May 2021 | Volume 12 | Article 652161
Stefani and Cajochen Practice Review on Existing Lighting Recommendations
OS wrote the main manuscript text. CC provided
critical review of and revisions to the manuscript. All
authors contributed to the article and approved the
submitted version.
OS disclosed receipt of the following financial support for the
research, authorship, and/or publication of this article. The study
was partly supported by Schweizerische Bundesbahnen AG,
(SBB), Switzerland.
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Conflict of Interest: The authors declare the following potential conflicts of
interest with respect to the research, authorship, and/or publication of this article:
OS is listed as an inventor on the following patents: US8646939B2—Display system
having circadian effect on humans; DE102010047207B4—Projection system and
method for projecting image content; US8994292B2—Adaptive lighting system;
WO2006013041A1—Projection device, and filter thereof; WO2016092112A1—
Method for the selective adjustment of a desired brightness and/or color of a
specific spatial area, and data processing device thereof. OS is a member of the
Daylight Academy. OS has had the following commercial interests in the last
four years (2017–20) related to lighting: Investigator-initiated research grants
from Derungs, Audi, VW, Porsche, Festo, ZDF, Toshiba, and SBB; Speaker fees
for invited seminars from Merck, Fraunhofer, Firalux, and Selux. CC has had
the following commercial interests in the last four years (2017–2020) related
to lighting: honoraria, travel, accommodation and/or meals for invited keynote
lectures, conference presentations or teaching from Toshiba Materials, Velux,
Firalux, Lighting Europe, Electrosuisse, Novartis, Roche, Elite, Servier, and WIR
Bank. CC is a member of the Daylight Academy.
Copyright © 2021 Stefani and Cajochen. This is an open-access article distributed
under the terms of the Creative Commons Attribution License (CC BY). The use,
distribution or reproduction in other forums is permitted, provided the original
author(s) and the copyright owner(s) are credited and that the original publication
in this journal is cited, in accordance with accepted academic practice. No use,
distribution or reproduction is permitted which does not comply with these terms.
Frontiers in Psychiatry | 12 May 2021 | Volume 12 | Article 652161
... The current "Hygienic standard for day lighting and artificial lighting for middle and elementary school" issued by the Ministry of Health of the People's Republic of China [25] pointed out that the CRI of the classroom lighting source should not be less than 80, especially in professional classrooms such as art, chemistry, and handicrafts, which affects the correct identification of the color of the object prevents the object from displaying its color truly, will cause vision problems such as color blindness and color weakness over time. The white LEDs mainly use blue chip (450-455 nm) and yellow phosphor to generate white light in common [26][27][28] . This method will directly lead to the phenomenon of low CRI and uneven color space distribution, even arise the blue light hazards due to the blue light dominance [29] . ...
Aim: To compare the damage of light-emitting diodes (LEDs) with different color rendering indexes (CRIs) to the ocular surface and retina of rats. Methods: Totally 20 Sprague-Dawley (SD) rats were randomly divided into four groups: the first group was normal control group without any intervention, other three groups were exposed by LEDs with low (LED-L), medium (LED-M), and high (LED-H) CRI respectively for 12h a day, continuously for 4wk. The changes in tear secretion (Schirmer I test, SIt), tear film break-up time (BUT), and corneal fluorescein sodium staining (CFS) scores were compared at different times (1d before experiment, 2 and 4wk after the experiment). The histopathological changes of rat lacrimal gland and retina were observed at 4wk, and the expressions of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in lacrimal gland were detected by immunofluorescence method. Results: With the increase of light exposed time, the CFS value of each light exposed group continued to increase, and the BUT and SIt scores continued to decrease, which were different from the control group, and the differences between the light exposed groups were statistically significant. Hematoxylin-eosin (HE) results showed that the lacrimal glands of each exposed group were seen varying degrees of acinar atrophy, vacuole distribution, increasing of eosinophil granules, etc.; the retina showed obvious reduction of photoreceptor cell layer and changes in retinal thickness; LED-L group has the most significant change in all tests. Immunofluorescence suggested that the positive expressions of TNF-α and IL-6 in the lacrimal glands of each exposed group were higher than those of the control group. Conclusion: LED exposure for 4wk can cause the pathological changes of lacrimal gland and retina of rats, and increase the expression of TNF-α and IL-6 in lacrimal gland, the degree of damage is negatively correlated with the CRI.
... More globally, the impact of the visual and non-visual effects of light on human activity is gaining importance nowadays, giving rise to the human-centric lighting concept [66] and recommendations such as adapting light environments throughout the day [67]. ...
Full-text available
Most living organisms in both the plant and animal kingdoms have evolved processes to stay in tune with the alternation of day and night, and to optimize their physiology as a function of light supply. In mammals, a circadian clock relying on feedback loops between key transcription factors will thus control the temporally regulated pattern of expression of most genes. Modern ways of life have highly altered the synchronization of human activities with their circadian clocks. This review discusses the links between an altered circadian clock and the rise of pathologies. We then sum up the proofs of concept advocating for the integration of circadian clock considerations in chronotherapy for health care, medicine, and pharmacotherapy. Finally, we discuss the current challenges that circadian biology must face and the tools to address them.
... Such systems should support circadian entrainment by dynamically changing the intensity and Correlated Colour Temperature (CCT) of lighting [29]. While there is not yet robust evidence that integrative lighting as designed today may support circadian entrainment in any real-life application [29][30][31], occupants do appreciate the dynamicity of integrative lighting [32]. ...
This article concerns a field study about the use of non-invasive manual lighting and shading control to save energy in listed buildings. The system was chosen to limit cabling and masonry work. The test room consists of an individual office located in a historical building in Southern Italy. The room was retrofitted with two roller shades (semi-transparent and blackout) and six LED-based pendants provided with step-dimming and three Correlated Colour Temperature options. Shading and lighting could be remotely controlled from the desk by six subjects who took part in the test for two weeks each. Behavioural interventions and a set back to default setting at the end of the working day were adopted to improve the test subjects’ energy behaviour. The results show that energy for lighting could be reduced between 15% to 71% compared to European benchmark, with wide range accounting for variability of individual preference and weather conditions. The savings are due to the computer-based work, the communication and engagement campaign, as well as the default settings. The findings suggest that simple manually controlled systems are energy and economic viable solution for listed buildings, since the system accommodates users’ needs, and proper training is provided to the users.
... For instance, the epochs succession 1,1,1,0,1,20,3,0,0 forms the sequence of segments: 1=(1,1,1), 2=(0), 3= (1,20,3), 4= (0,0) and those epochs have external positions 1,2, 3,4,5,6,7,8,9 in the succession of epochs and internal positions 1,2,3,1,1,2,3,1,2 inside the zero/non zero segments. ...
Full-text available
Abstract Background The Author's interest is to apply physiological recordings for real-life, long-term and unsupervised monitoring as a complement to telemedicine and home care. This means the search for parameters that will be used to alert when some kind of support will be needed. To this end, the Author has recorded and published an appropriate Motionwatch8 dataset and this article continues to explore some of its basic characteristics in preparation for its analysis. Content The Author claims that Motionwatch8 data, both acceleration and light, are recorded as a succession of samples, but the zero threshold levels of the device imply a segmentation of the data from 2 events: crossing the zero thresholds upwards and downwards. The paper describes those segments and uses a simple numerical example to show some some of their features, such as their circadian rhythms. Finally, we propose a data model that allows the evaluation of Motionwatch8's light data, which are often co-recorded along with acceleration. Conclusion The examples suggest that, at least for some parameters, using the segment lengths or the sum and average of their Count/Lux values provides the same information. The pairs of segments and intervals used in the examples are easy to calculate, their relationship to device measurements is intuitive and they provide a useful guideline, but the sequence of segments is open to a variety of analysis methodologies to be explored. The proposed type of data model may allow some use of the light data measured by the Motionwatch8. This paper concludes the basic exploration of the dataset and future work is to find suitable parameters for home care.
... In closing this section, we note that a number of other recommendations relevant to physiological and neurobehavioural effects of light have been proposed in recent years, including some guidelines and specifications by commercial (for-profit) entities (reviewed in [57]). Unlike these previous suggestions, the present recommendations are both built around an SIcomplaint, internationally accepted and validated measurement system and are supported by expert scientific consensus, features recognised as critical by established industry regulatory and standardisation bodies [58,59]. ...
Full-text available
Ocular light exposure has important influences on human health and well-being through modulation of circadian rhythms and sleep, as well as neuroendocrine and cognitive functions. Prevailing patterns of light exposure do not optimally engage these actions for many individuals, but advances in our understanding of the underpinning mechanisms and emerging lighting technologies now present opportunities to adjust lighting to promote optimal physical and mental health and performance. A newly developed, international standard provides a SI-compliant way of quantifying the influence of light on the intrinsically photosensitive, melanopsin-expressing, retinal neurons that mediate these effects. The present report provides recommendations for lighting, based on an expert scientific consensus and expressed in an easily measured quantity (melanopic equivalent daylight illuminance (melaponic EDI)) defined within this standard. The recommendations are supported by detailed analysis of the sensitivity of human circadian, neuroendocrine, and alerting responses to ocular light and provide a straightforward framework to inform lighting design and practice.
... Evidence-based recommendations for modifying our light environment and light exposure to enhance its beneficial effects whilst minimizing negative ones are being sought in architectural lighting design, lighting regulations, and building standards [2,54,55]. An international group of experts led by Brown and Wright recently proposed a minimum of 250 lux (melanopic EDI) daytime level, 10 lux evening level and a 1 lux maximum as the night level [56]. ...
Full-text available
Exposure to light affects our physiology and behaviour through a pathway connecting the retina to the circadian pacemaker in the hypothalamus – the suprachiasmatic nucleus (SCN). Recent research has identified significant individual differences in the non-visual effects of light,mediated by this pathway. Here, we discuss the fundamentals and individual differences in the non-visual effects of light. We propose a set of actions to improve our evidence database to be more diverse: understanding systematic bias in the evidence base, dedicated efforts to recruit more diverse participants, routine deposition and sharing of data, and development of data standards and reporting guidelines.
... This kind of technology is an essential tool in smart lighting systems, allowing occupants to manually adjust the correlated colour temperature (CCT) or other (visual) characteristics depending on the observers' preferences or task 19 . However, at particular times of day (for instance, during the 2-3 h before bedtime or during sleep), chromaticity choices at higher CCTs, which might also increase the light exposure in the short-wavelength range, are not recommended because of their enhanced effectivity to suppress melatonin and increase alertness [20][21][22] . Thus, there could be a conflict between the users' visual preferences of chromaticity and the degree of triggering circadian responses if other crucial metrics such as the time of light exposure and light intensity remain steady. ...
Full-text available
Smart integrative lighting systems aim to support human health and wellbeing by capitalising on the light-induced effects on circadian rhythms, sleep, and cognitive functions, while optimising the light’s visual aspects like colour fidelity, visual comfort, visual preference, and visibility. Metameric spectral tuning could be an instrument to solve potential conflicts between the visual preferences of users with respect to illuminance and chromaticity and the circadian consequences of the light exposure, as metamers can selectively modulate melanopsin-based photoreception without affecting visual properties such as chromaticity or illuminance. This work uses a 6-, 8- and 11-channel LED luminaire with fixed illuminance of 250 lx to systematically investigate the metameric tuning range in melanopic equivalent daylight illuminance (EDI) and melanopic daylight efficacy ratio (melanopic DER) for 561 chromaticity coordinates as optimisation targets (2700 K to 7443 K ± Duv 0 to 0.048), while applying colour fidelity index Rf criteria from the TM-30-20 Annex E recommendations (i.e. Rf≥ 85, Rf,h1≥ 85). Our results reveal that the melanopic tuning range increases with rising CCT to a maximum tuning range in melanopic DER of 0.24 (CCT: 6702 K, Duv: 0.003), 0.29 (CCT: 7443 K, Duv: 0) and 0.30 (CCT: 6702, Duv: 0.006), depending on the luminaire’s channel number of 6, 8 or 11, respectively. This allows to vary the melanopic EDI from 212.5–227.5 lx up to 275–300 lx without changes in the photopic illuminance (250 lx) or chromaticity (Δu′v′≤ 0.0014). The highest metameric melanopic Michelson contrast for the 6-, 8- and 11-channel luminaire is 0.16, 0.18 and 0.18, which is accomplished at a CCT of 3017 K (Duv: − 0.018), 3456 K (Duv: 0.009) and 3456 K (Duv: 0.009), respectively. By optimising ~ 490,000 multi-channel LED spectra, we identified chromaticity regions in the CIExy colour space that are of particular interest to control the melanopic efficacy with metameric spectral tuning.
This paper introduces a novel approach to integrate orientation-dependent spectral properties of daylight in urban planning. These spectral characteristics of light at façades are represented in spectral daylight potential diagrams (SDPDs). The applicability of SDPDs is subsequently discussed in the context of non-image forming (NIF) effects, comparing the NIF effectiveness of skylight at façades—represented in the melanopic daylight (D65) efficacy ratio —based on SDPDs to the generally assumed CIE standard illuminant D65 and the horizontal correlated colour temperature (CCT) widely used in existing software. This analysis comprises the impact of (i) prevailing sky conditions and (ii) obstruction levels on the spectral characteristics of skylight on different façade orientations. Our core findings suggest that not considering the directionality of the colour information of skylight from clear sky conditions might lead to underestimation (D65) or overestimation (horizontal CCT) of the NIF effectiveness of skylight offered at façades. When designing for NIF responses, the first potentially leading to increased energy consumption, the latter to a lower NIF response as designed for. These findings not only advance our scientific knowledge of the spectral properties of daylight but also provide a simplified methodological framework for assessing the NIF effectiveness of daylight in urban settings.
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Improving indoor lighting conditions at the workplace has the potential to support proper circadian entrainment of hormonal rhythms, sleep, and well-being. We tested the effects of optimized dynamic daylight and electric lighting on circadian phase of melatonin, cortisol and skin temperatures in office workers. We equipped one office room with an automated controller for blinds and electric lighting, optimized for dynamic lighting (= Test room), and a second room without any automated control (= Reference room). Young healthy participants (n = 34) spent five consecutive workdays in each room, where individual light exposure data, skin temperatures and saliva samples for melatonin and cortisol assessments were collected. Vertical illuminance in the Test room was 1177 ± 562 photopic lux (mean ± SD) , which was 320 lux higher than in the Reference room (p < 0.01). Melanopic equivalent daylight (D65) illuminance was 931 ± 484 melanopic lux in the Test room and 730 ± 390 melanopic lux in the Reference room (p < 0.01). Individual light exposures resulted in a 50 min earlier time of half-maximum accumulated illuminance in the Test than the Reference room (p < 0.05). The melatonin secretion onset and peripheral heat loss in the evening occurred significantly earlier with respect to habitual sleeptime in the Test compared to the Reference room (p < 0.05). Our findings suggest that optimized dynamic workplace lighting has the potential to promote earlier melatonin onset and peripheral heat loss prior bedtime, which may be beneficial for persons with a delayed circadian timing system.
In this field study, we tested the effects of dynamic light scenarios and personal illuminance on visual experience, sleepiness, cognitive performance and sleep in an operational office. Two dynamic light scenarios, different in timing but with equal luminous exposure, were tested against a reference scenario in a counterbalanced crossover design. Frequent assessments of visual experience, alertness, performance and sleep showed that in both dynamic light scenarios visual comfort was slightly lower compared to the constant scenario. Additionally, sleepiness was lowest in the scenario with the brighter light timed around noon, whereas task performance and actual sleep were not significantly affected. The measured personal illuminances did not predict sleepiness and performance, yet variation and timing of these illuminances did positively relate to sleep onset and duration. When studying or implementing light scenarios aiming to deliver integrative lighting, the spatial and behavioral context should be considered as well.
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The experiment was targeted to develop design strategies and methods by testing the complex interplay between the dynamics of daylight and electrical lighting in an office. The double dynamic lighting design concept is based on the idea of adding task lighting, with a directionality referring to the daylight inflow and a variation on direct/diffuse lighting and respective changes in colour temperature respond to sky conditions and daylight levels. The experiment was conducted in an office space at Aalborg University in Copenhagen from September to December 2019. Four participants moved in and worked in the office with four-week periods of respective standard static lighting as a baseline, and dynamic lighting. In a parallel mixed method approach with interviews and questionnaires, the dynamic lighting was compared to the baseline and to a control group. The results indicate that the dynamic lighting periods had a positive effect on visual comfort, perceived atmosphere and work engagement. The studies helped to develop the definition of five dynamic light settings. Seasonal changes, time of day, dynamic sunscreens and individual needs for task lighting can be implemented in future field experiments as additional dynamic parameters to meet individual needs and circadian potentials for double dynamic light.
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Background: The effect of circadian disruption on the bio-psychological clock system has been widely studied. However, the mechanism and the association of circadian rhythm disruption with mental health and physiological responses are still unclear. Therefore, this study was conducted to investigate the effects of circadian rhythm disruption on mental health and physiological responses among shift workers and the general population. Methods: A total of 42 subjects participated in this quasi-experimental study. Participants were divided into a group of shift workers (n = 20) and a general population group (n = 22). Polysomnography tests, blood tests (cortisol, triglycerides and glucose), and psychological tests (Abbreviated Profile of Mood States, General Health Questionnaire-28, Working Memory and Processing Speed Indexes of the Wechsler Adult Intelligent Scale (WAIS-IV) were used to examine the effects of circadian rhythm disruption. Results: The results showed a significant relationship between circadian rhythm disruption and mood (r = 0.305, p < 0.05). The findings of this study also indicated that there was a significant effect of circadian rhythm disruption on mood (F(2,40) = 8.89, p < 0.001, η2 =0.182), processing speed (F(2,40) = 9.17, p < 0.001, η2 = 0.186) and working memory (F(2,40) = 4.963, p < 0.01, η2 = 0.11) in shift workers and the general population. Conclusions: Our findings showed that circadian rhythm disruption affects mood and cognitive performance, but it does not significantly affect psychological wellbeing and physiological responses. Future studies are warranted to examine moderator and mediator variables that could influence the circadian rhythm disruption.
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Ocular light exposure has important influences on human health and well-being through modulation of circadian rhythms and sleep, as well as neuroendocrine and cognitive functions. Current patterns of light exposure do not optimally engage these actions for many individuals, but advances in our understanding of the underpinning mechanisms and emerging lighting technologies now present opportunities to adjust lighting to promote optimal physical and mental health and performance. A newly developed, SI-compliant standard provides a way of quantifying the influence of light on the intrinsically photosensitive, melanopsin-expressing, retinal neurons that mediate these effects. The present report provides recommendations for lighting, based on an expert-scientific consensus and expressed according to this new measurement standard. These recommendations are supported by a comprehensive analysis of the sensitivity of human ‘non-visual’ responses to ocular light, are centred on an easily measured quantity (melanopic equivalent daylight (D65) illuminance), and provide a straightforward framework to inform lighting design and practice.
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Human perception and vision have evolved in response to dynamic daylight, a combination of radiation from direct sunlight and diffuse skylight, which has created a flow of variations in light, in terms of direct:diffuse distribution, intensities and spectrum. This study investigates the qualities of the flow of light in an office after adding ceiling-mounted spotlights (32° tilt angle) to traditional diffuse ceiling panels. The intention is to create a flow of task light – a light-zone at each work-plane – complementing the directionality of the natural daylight inflow from the windows. An experiment was carried out in an office, in two parts. Four ratios of direct:diffuse light were tested by 30 people. Then one ratio was tested in five combinations of high, neutral and low color temperatures by 15 people in two daylight situations: overcast and clear sky. The visual light quality and perceived atmosphere of the office environment was tested through questionnaires, reaction cards and semi-structured interviews. The direct flow of light is recommended to be more than 15% of the total illuminance at the work-plane to provide the distinct visual appearance of modeling and a cozier atmosphere, which is preferable for socializing, and less than 45% to avoid glare and high contrast for visual tasks. Direct warm and diffuse cool lighting were perceived as the most natural but were not always preferred. There is an indication of slight preference for cooler ambient lighting in clear sky situations and warmer ambient lighting in overcast situations. Especially the preference in relation to sky conditions needs to be further investigated. A field study will implement these findings in a double dynamic lighting concept responding to daylight level and sky character. Strong individual preferences for combinations of color temperatures was identified, this open up new research areas for personalized flows of light in future dynamic lighting designs.
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As a critical factor in the built environment, lighting presents considerable influence on occupants. Previous research across static lighting conditions has found that both illuminance and correlated color temperature (CCT) affect occupants' physiological and psychological functioning. However, little research has been conducted on the non-visual impacts of dynamic lighting with daily variation in illuminance and CCT levels. The purpose of this study is to better understand the impact of dynamic lighting on office occupants' health, well-being and experience at a living lab. Fifteen participants were recruited to work in three office modules for four months. Four lighting conditions were designed and implemented in this study, including two static lighting conditions and two dynamic lighting conditions with a specific predefined control scheme. A prototype lighting system with enhanced control capabilities was configured and implemented to ensure the desired lighting environment protocol. Both objective methods and subjective surveys were used to assess the behavioral and physiological outcomes of interest, including mental stress, sleep, productivity, satisfaction, mood, visual comfort and perceived naturalness. The results showed that the daytime behavioral impacts were either positive or mixed. Specifically, a significant alertness increase was observed in the afternoon, indicating a potential solution to reduce the natural feelings of sleepiness during the workday. There was also a marginal benefit for mood. The nighttime impacts include a significant decrease in perceived sleep quality and sleep time after subjects were exposed to dynamic lighting. No significant differences were observed for mental stress, productivity, visual comfort, or perceived naturalness. The findings present additional insights into the non-visual impacts of dynamic lighting and give recommendations for further investigations.
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Electric light has enabled humans to conquer the night, but light exposure at night can disrupt the circadian timing system and is associated with a diverse range of health disorders. To provide adequate lighting for visual tasks without disrupting the human circadian timing system, a precise definition of circadian spectral sensitivity is required. Prior attempts to define the circadian spectral sensitivity curve have used short (≤90-min) monochromatic light exposures in dark-adapted human subjects or in vitro dark-adapted isolated retina or melanopsin. Several lines of evidence suggest that these dark-adapted circadian spectral sensitivity curves, in addition to 430- to 499-nm (blue) wavelength sensitivity, may include transient 400- to 429-nm (violet) and 500- to 560-nm (green) components mediated by cone- and rod-originated extrinsic inputs to intrinsically photosensitive retinal ganglion cells (ipRGCs), which decay over the first 2 h of extended light exposure. To test the hypothesis that the human circadian spectral sensitivity in light-adapted conditions may have a narrower, predominantly blue, sensitivity, we used 12-h continuous exposures of light-adapted healthy human subjects to 6 polychromatic white light-emitting diode (LED) light sources with diverse spectral power distributions at recommended workplace levels of illumination (540 lux) to determine their effect on the area under curve of the overnight (2000–0800 h) salivary melatonin. We derived a narrow steady-state human Circadian Potency spectral sensitivity curve with a peak at 477 nm and a full-width half-maximum of 438 to 493 nm. This light-adapted Circadian Potency spectral sensitivity permits the development of spectrally engineered LED light sources to minimize circadian disruption and address the health risks of light exposure at night in our 24/7 society, by alternating between daytime circadian stimulatory white light spectra and nocturnal circadian protective white light spectra.
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Ocular light drives a range of non‐visual responses in humans including suppression of melatonin secretion and circadian phase‐resetting. These responses are driven by intrinsically photosensitive retinal ganglion cells (ipRGCs) which combine intrinsic, melanopsin‐based, phototransduction with extrinsic rod/cone mediated signals. As a result of this arrangement it has remained unclear how best to quantify light to predict its non‐visual effects. To address this, we analysed data from nineteen different laboratory studies that measured melatonin suppression, circadian phase resetting and/or alerting responses in humans to a wide array of stimulus types, intensities and durations with or without pupil dilation. Using newly established SI‐compliant metrics to quantify ipRGC‐influenced responses to light we show that melanopic illuminance consistently provides the best available predictor for responses of the human circadian system. In almost all cases melanopic illuminance is able to fully account for differences in sensitivity to stimuli of varying spectral composition, acting to drive responses that track variations in illumination characteristic of those encountered over civil twilight (~1‐1000 lux melanopic equivalent daylight illuminance). Collectively our data demonstrate widespread utility of melanopic illuminance as a metric for predicting the circadian impact of environmental illumination. These data therefore provide strong support for the use of melanopic illuminance as the basis for guidelines that seek to regulate light exposure to benefit human health and to inform future lighting design.
We examined whether dynamically changing light across a scheduled 16‐h waking day influences sleepiness, cognitive performance, visual comfort, melatonin secretion, and sleep under controlled laboratory conditions in healthy men. Fourteen participants underwent a 49‐h laboratory protocol in a repeated‐measures study design. They spent the first 5‐h in the evening under standard lighting, followed by an 8‐h nocturnal sleep episode at habitual bedtimes. Thereafter, volunteers either woke up to static light or to a dynamic light that changed spectrum and intensity across the scheduled 16‐h waking day. Following an 8‐h nocturnal sleep episode, the volunteers spent another 11‐h either under static or dynamic light. Static light attenuated the evening rise in melatonin levels more compared to dynamic light as indexed by a significant reduction in the melatonin AUC prior to bedtime during static light only. Participants felt less vigilant in the evening during dynamic light. After dynamic light, sleep latency was significantly shorter in both the baseline and treatment night while sleep structure, sleep quality, cognitive performance and visual comfort did not significantly differ. The study shows that dynamic changes in spectrum and intensity of light promote melatonin secretion and sleep initiation in healthy men.
This paper discusses the rise of human-centric lighting and its current status in lighting. We summarise the human benefits associated with light and lighting and show that human-centric lighting has sound motivations, despite being tainted by misleading marketing claims. The phrase integrative lighting avoids the hype and encapsulates what lighting aspires to be. Embodied in these concepts are some things old and some things new. The old is twofold. First, without diminishing the value of lighting products, the core ingredient for good human outcomes is good design, driven by a design team. Second, light is still for vision, and lighting for visibility, visual comfort and visual amenity is as important as ever. Complementing the old is new awareness and responsibility for how light and lighting influence non-visual responses in humans. Circadian, neuroendocrine and neurobehavioural responses are important for human health and should be considered on-par with visual responses. This awareness leads toward lighting design solutions with increased contrast between day and night. The parties responsible for addressing non-visual responses to light and lighting are evolving. Architects, lighting professionals, lighting equipment manufacturers, medical professionals, building owners and individuals all have a stake, but who should drive decisions and in what proportion?
LED *Shared senior authors. light sources have a discontinuous light spectrum with a prominent ‘blue’ peak between 450 and 470 nm that influences non-image forming responses in humans. We tested an LED lighting solution mimicking a daylight spectrum on visual comfort, circadian physiology, daytime alertness, mood, cognitive performance and sleep. Fifteen young males twice spent 49 hours in the laboratory under a conventional-LED and under a daylight-LED condition in a balanced cross over design flanked by a baseline and a post-light exposure night. Despite different light spectra, the photopic lux and the correlated colour temperature of the lighting were the same for both LEDs. The colour rendering index and the melanopic strength were 25.3% and 21%, respectively, higher for the daylight LED than the conventional LED. The volunteers had better visual comfort, felt more alert and happier in the morning and evening under daylight LED than conventional LED, while the diurnal melatonin profile, psychomotor vigilance and working memory performance were not significantly different. Delta EEG activity (0.75–4.5 Hz) was significantly higher after daylight-LED than conventional-LED exposure during the post-light exposure night. We have evidence that a daylight-LED solution has beneficial effects on visual comfort, daytime alertness, mood and sleep intensity in healthy volunteers.