ArticlePDF Available

Abstract and Figures

Short-wavelength light is known to have an effect on human alertness in the night-time. However, there are very few studies that focus on the effect of intensity of light on alertness. This study evaluates the acute alerting ability of short-wavelength light of three different intensities (40 lux, 80 lux and 160 lux). Eight subjects participated in a 60-minute exposure protocol for four evenings, during which electroencephalogram (EEG) as well as subjective sleepiness data were collected. EEG power in the beta range was significantly higher after subjects were exposed to 160 lux light than after they were exposed to 40 lux, 80 lux light or remained in darkness. Also, the alpha theta power was significantly lower under 160 lux light then in darkness. These results show that the effect of intensity on alertness is not linear and further work should be done to investigate the threshold intensity that is required to produce an alerting effect.
Content may be subject to copyright.
Effect of intensity of short-wavelength
light on electroencephalogram and
subjective alertness
J Lin MSc , S Westland PhD and V Cheung PhD
School of Design, University of Leeds, Leeds, UK
Received 15 May 2019; Revised 22 July 2019; Accepted 1 August 2019
Short-wavelength light is known to have an effect on human alertness in the night-
time. However, there are very few studies that focus on the effect of intensity of
light on alertness. This study evaluates the acute alerting ability of short-
wavelength light of three different intensities (40 lux, 80 lux and 160 lux). Eight
subjects participated in a 60-minute exposure protocol for four evenings, during
which electroencephalogram (EEG) as well as subjective sleepiness data were
collected. EEG power in the beta range was significantly higher after subjects were
exposed to 160 lux light than after they were exposed to 40 lux, 80 lux light or
remained in darkness. Also, the alpha theta power was significantly lower under
160 lux light then in darkness. These results show that the effect of intensity on
alertness is not linear and further work should be done to investigate the threshold
intensity that is required to produce an alerting effect.
1. Introduction
Light has been shown to exert strong non-
visual effects on a range of biological
functions such as the regulation of human
circadian system. Exposure to light in the
evening and night-time, especially of short-
wavelength (but not necessarily limited to
short-wavelengths), has been shown to lead to
an increase in alertness in humans. This effect
is suggested to be related to circadian disrup-
tion. Circadian disruption is associated with
reduced levels of the hormone melatonin and
is primarily (though note that rods and
cones may also participate in this process
mediated by activation of the intrinsically
photosensitive retinal ganglion cells which
respond to short-wavelength light most
strongly. Exposure to light in the evening
can inhibit the production of melatonin which
otherwise would naturally build-up in the
body during the late-evening hours.
Studies to date have linked the alerting
effects of light to its ability to suppress
However, hormonal changes
might not be the only pathway mediating
the non-visual effects of light. More recent
studies have suggested that acute melatonin
suppression is not needed for light to evoke
alertness responses in humans. For example,
it has been shown that both short-wavelength
(blue) and long-wavelength (red) lights
increased alertness at night, as measured by
EEG, but only blue light suppressed mela-
tonin significantly.
Light exposure during
the day has no impact on modulating mela-
though it has been shown to affect
objective and subjective alertness in the
afternoon – as measured by EEG and the
Karolinska Sleepiness Scale (KSS).
studies have clearly demonstrated that light
can increase alertness independent of light-
induced melatonin suppression.
Address for correspondence: J Lin, School of Design,
University of Leeds, Leeds LS2 9JT, UK.
Lighting Res. Technol. 2020; 52: 413–422
ßThe Chartered Institution of Building Services Engineers 2019 10.1177/1477153519872801
Studies on the non-visual effects of light
have suggested that the alerting effect of light
exposure during the daytime is more modest
than its effect during night-time.
Bright light
exposure at night has been shown to reliably
increase alertness.
These findings suggest
that the impact of light on alertness is a
complex physical, physiological and psycho-
logical activity that can result from different
pathways. Although melatonin level is asso-
ciated with circadian rhythm, EEG power
fluctuations reflect the immediate neuroendo-
crine responses.
EEG has been one of the measures often
used to evaluate acute alertness change, since
light can have an impact on EEG measures
without affecting melatonin levels.
One study
investigated how 48-minute exposures to
three lighting conditions (red, blue and
dark) affected subjects and found that EEG
alpha and alpha theta power were both
lower after the exposure to red and blue
lights compared to the darkness condition.
Similarly, another study compared short-
wavelength light, long-wavelength light and
darkness, and found that alpha power was
significantly lower after 30 minutes under
both the short- and long-wavelength light
than remaining in darkness.
Red and blue
lights have been found to increase beta signals
and reduce sleepiness relative to preceding
dim light exposure.
By looking into individ-
ual EEG frequencies, it was also suggested
that short-wavelength light in particular
enhances high alpha activity.
With these
findings, it is generally agreed that a decrease
in low EEG frequencies (theta alpha) power
and an increase in high EEG frequencies
(beta) power are associated with an increase
in alertness.
Short-wavelength light is becoming a crit-
ical safety concern. For example, there have
been concerns about home lighting in the
evening, where tungsten filament lamps of
low correlated colour temperature (CCT)
have been replaced by solid-state lighting of
higher CCT; the use of emissive electronic
displays may also be responsible for the
increasing sleep problem.
Differences in
the properties of lighting were shown to
affect individuals in various ways. Past
studies have tried to define and quantify the
timing, illuminance levels, exposure duration
and wavelength distribution of the light
required to evoke alerting responses.
A study has looked at how three different
illuminances ranging from 3 lux to 9100 lux
affect EEG activity over 6.5 hours of expos-
ure, and a dose-response relationship was
found in subjective alertness and EEG
Other studies have also demon-
strated a non-linear relationship between
light intensity and circadian shifts.
It is
generally agreed that brighter light has a
stronger alerting ability than dimmer light.
However, there is no consensus yet about the
threshold of light intensity needed to produce
these effects.
2. Method
The alerting effect of intensity of light in
humans has so far received little attention.
This work is concerned with exploring the
threshold intensity of light needed to evoke
acute alertness responses in humans at night-
time. Based on the notion that melatonin
suppression is not the only mechanism con-
tributing to light-induced alertness, this study
has measured both subjective and objective
alertness using KSS and EEG, respectively.
The objective, specifically, is to investigate the
effect of three intensities (40 lux, 80 lux and
160 lux) of a short-wavelength light (
475 nm), compared to remain in darkness
(51 lux), on human alertness during the
2.1. Test participants
Nine participants (aged 28 3.4 years; five
females) were recruited for the within-subject,
414 J Lin et al.
Lighting Res. Technol. 2020; 52: 413–422
four-session study. All participants went
through a pre-screening procedure where
individual sleep/rise time was collected and
the daily consumption of nicotine, caffeine
and alcohol was reported. Smokers and those
who were rated as extreme late chronotypes
(e.g. those who went to bed after 1am) were
excluded. The study was approved by the
University of Leeds Ethics Committee and all
participants signed informed consent forms
prior to the study. An information sheet was
given and participants were asked to refrain
from caffeine and alcohol intake three hours
prior to the experiment, and to try to main-
tain a regular, constant sleep schedule during
the entire experimental period. As a result,
there is no report of any major health
problems or currently taking any medica-
tions. One participant did not finish all of the
experimental sessions, and their data was
excluded from further analysis. In total, the
results produced from eight participants (aged
28 3.6 years; five females) are reported here.
2.2. Lighting conditions
Light was delivered through 12 luminaires
(LEDs, provided by Thouslite Lighting
System) mounted in the ceiling of a room
with white walls and grey carpets. The light-
ing system provides spectral tunable lighting
based on multi-channel LED technology.
Participants were asked to sit under the light
whilst reading, with a white table in front of
them (Figure 1). The lighting measures were
taken within the flat reading area on the table.
Four light settings were used: a dim (CCT
2000 K, 51 lux) and three short-wavelength
lighting conditions. The short-wavelength
condition had a peak at about 480 nm and
was approximately Gaussian with a half-
width half-height of 35 nm. Three intensities
were 40 lux, 80 lux and l60 lux (1 lux). The
spectra of the three test lighting conditions
were measured with an X-Rite i1Pro spectro-
photometer (Figure 2). The a-opic irradiance
for each lighting was calculated according to
the new CIE S 026 /E:2018
(Table 1).
2.3. Experiment protocol
Each participant completed four sessions
over four nights, all starting at the same time
(8 p.m.). Participants were fitted with EEG
electrodes prior to the start of the exposure.
The order of the conditions (Dim, Blue 40 lux,
80 lux and 160 lux) was selected randomly for
each participant to avoid potential sequence
effects. Sessions were separated by at least
72 hours for the same participant to avoid
potential carry-over effects.
During each evening study EEG was con-
tinuously recorded over 60 minutes. EEG
data was collected using B-Alert Live
Software with wireless advanced brain moni-
toring (ABM) EEG device (X10 headset with
standard sensor strips). Recordings consisted
of EEG with nine electrode positions (Fz, Cz,
Figure 1 Lighting room showing the position of the
participant and the luminaires
Effect of short-wavelength light on alertness 415
Lighting Res. Technol. 2020; 52: 413–422
Poz, F3, F4, C3, C4, P3 and P4) and
two reference mastoid electrodes. The elec-
trode impedance test was performed each
time before experiment to ensure the
good conductivity between the scalp and
electrodes, thus the good quality of the
signal. The EEG signal was band-passed to
1 to 40 Hz and decontaminated using ABM’s
validated artefact identification and decon-
tamination algorithms which identify and
remove five artefact types: electromyogram,
electrooculogram, excursions, saturations
and spikes. Power spectral density (PSD)
was computed by performing Fast Fourier
Transform with application of a Kaiser
window. PSD of selected 1-Hz bins was
averaged after application of a 50% over-
lapping window across three one-second
Under the Dim condition, participants
were kept in the dim light for 60 minutes.
Under the Blue condition, test lights were
energized for 40 minutes, preceded by a
20-minute dim (51 lux) period.
Subjective sleepiness was evaluated using
the KSS, a self-reporting scale that ranges
from 1 (‘extremely alert’) to 9 (‘very sleepy,
fighting sleep’).
This scale has previously
been shown to be sensitive to changes in
sleepiness and the alerting effects of
The KSS was rated three times
(every 20 minutes – at the 20th, 40th and 60th
minutes) during each session. Participants
were asked to rate themselves from 1 to 9,
according to their sleepiness. For the duration
of the 60 minutes the participants were free to
read a book. They were also asked to keep
their eyes open and reduce head movement
380 400 420 440 460 480 500 520 540 560 580 600 620 640 660 680
Relative spectral power (%)
Wavelength (nm)
Figure 2 Spectral power distributions of three test lighting conditions
Table 1 -Opic irradiance (mW/m
) for three lighting conditions and 1 lux daylight (for reference)
-opic irradiance for S-cone-opic M-cone-opic L-cone-opic Rhodopic Melanopic
40 lux 157.98 131.44 80.48 277.64 324.25
80 lux 340.38 273.25 167.00 580.18 678.81
160 lux 716.54 557.33 340.56 1187.21 1389.97
1 lux D65 0.82 1.46 1.63 1.45 1.33
416 J Lin et al.
Lighting Res. Technol. 2020; 52: 413–422
throughout the experiment. No other activ-
ities (e.g. using electronic devices, eating or
talking) were allowed (Figure 3).
3. Results
3.1. EEG
EEG measures collected from nine elec-
trode sites were averaged to produce overall
EEG PSD, and then grouped into the follow-
ing frequency bins: 5–9 Hz (theta alpha),
8–9 Hz (lower alpha), 11–13 Hz (higher
alpha), and 13–30 Hz (beta). In each fre-
quency range, EEG power averaged over the
40 minutes under test lighting was normalized
to the initial 20 minutes of dim light period.
One-way analysis of variance (ANOVA)
was performed using the normalized power
in each of the frequency ranges studied. Post-
hoc t tests (with Bonferroni corrections)
were used to further compare the signifi-
cance between lighting conditions. Analyses
were performed using IBM SPSS Statistics 25
and the results for beta ranges are listed in
Table 2.
One-way ANOVA revealed a close to
significant main effect of lighting condition
in the normalized theta alpha (F
p¼0.059) and a significant main effect of
lighting condition in beta (F
p¼0.001). No significant difference was
observed in lower alpha (F
p¼0.701) or higher alpha (F
p¼0.765) ranges. Post-hoc pairwise compari-
sons found significant differences between
Dim and 160 lux, 40 lux and 160 lux, 80 lux
and 160 lux in beta range (Table 2). Figure 4
shows the results of normalized power for
four lighting conditions in four frequency
ranges studied (where * indicates statistical
significance). Power in theta alpha was lower
after exposure to 40 lux and 160lux blue lights
than after remaining in the Dim condition.
Power in beta range was significantly higher
after exposure to 160 lux blue lights than after
exposure to the other three lighting
Elapsed Time (min)
0102030 405060
Blue, 40lx
Blue, 80lx
Blue, 160lx
Dim, <1lx
Figure 3 Experimental design
Table 2 Pairwise comparisons for EEG beta
Pairs Significance*
Dim–40 lux 1.000
Dim–80 lux 1.000
Dim–160 lux 0.001*
40–80 lux 1.000
40–160 lux 0.005*
80–160 lux 0.025*
*Statistically significant (p0.05).
Effect of short-wavelength light on alertness 417
Lighting Res. Technol. 2020; 52: 413–422
conditions. Compared to Dim, exposure to
160 lux blue light has also reduced lower
alpha power and increased high alpha power,
although these differences did not reach
statistical significance (p40.05). Figure 5
shows the individual EEG beta power values.
3.2. Subjective sleepiness (KSS)
Mean scores over the experimental condi-
tion were normalized to the initial Dim
session. One-way ANOVA was performed
and post-hoc t tests (with Bonferroni correc-
tions) were used to further compare the
significance between lighting conditions. The
results are listed in Table 3.
ANOVA revealed a significant difference
between Dim and 160 lux conditions. Figure 6
shows the results for the normalized KSS
scores under four lighting conditions (where *
indicates statistical significance). Mean score
in 160 lx condition was significantly lower
than score in Dim condition (a lower KSS
score means more alertness). Mean scores
under 40 lux and 80 lux conditions were lower
than score under the Dim, and higher than
score under the 160 lux condition, although
these differences did not reach statistical
significance (p40.05). Figure 7 shows the
individual KSS scores.
4. Discussion
This study investigated how exposures to
short-wavelength lights of three different
intensities (40 lux, 80 lux and 160 lux) affect
objective and subjective alertness during the
night-time. Results showed the effect of
intensity on EEG theta alpha (5–9 Hz) and
beta (13–30 Hz) powers. Exposure to 40 lux
and 160 lux lights reduced theta alpha power
compared to remaining in the Dim condition.
Exposure to 160 lux light significantly
increased beta power compared to the Dim,
40 lux and 80 lux light conditions. It has been
observed and agreed in many studies that the
decrease in theta alpha power and the
theta_alpha l_alpha h_alpha beta
Normalized power
Dim 40lx 80lx 160lx
Figure 4 Mean standard error of the mean normalized EEG power for four frequency ranges
Table 3 Pairwise comparisons for KSS
Pairs Significance*
Dim–40 lux 0.240
Dim–80 lux 0.252
Dim–160 lux 0.024*
40–80 lux 0.973
40–160 lux 0.209
80–160 lux 0.198
KSS: Karolinska Sleepiness Scale.
*Statistically significant (p0.05).
418 J Lin et al.
Lighting Res. Technol. 2020; 52: 413–422
increase in beta power indicate greater alert-
ness. It has also been suggested that reduction
in EEG alpha power (8–12 Hz) is related
to alertness increase, and the increase in
high-frequency alpha activity especially is
associated with the circadian regulation of
We did not find a significant effect
on lower or higher alpha power, which might
be due to the limited sample size. Considering
the practical difficulties in conducting the
study, we included eight participants, which is
relatively small (but nevertheless sufficient to
show some statistically significant results in
theta alpha and beta ranges). The results of
lower and higher alpha actually showed the
consistent trend with other results, although
these are not statistically significant. To
combine the findings in EEG together, this
study showed that exposure to 160 lux blue
light significantly increases alertness com-
pared to Dim, 40 lux and 80 lux conditions;
exposure to 40 lux and 80 lux also increase
alertness compared to Dim light, although
not as significant as 160 lux light.
Furthermore, 40 lux and 80 lux exposure did
not show a large difference between each
In the result alpha power was split into two
parts. The full alpha range was initially
examined and there were no significant
results. However, in some studies, high
alpha power alone was examined (as high
alpha is also suggested to be a specific marker
for alertness). Therefore in this study, alpha
power was then split into higher alpha and
lower alpha for further analysis. As shown in
Figure 4, the two parts seem to have opposite
patterns. In lower alpha, Dim light condition
has the greatest power, whereas in higher
alpha, 160 lux light condition has the greatest
power. One possible explanation might be
that the lower part of alpha is close to the
theta range (where alertness is negatively
related to the power), and the higher part of
alpha is closer to beta (where alertness is
positively related to the power). However,
these results would need further study to
assess this possibility.
The subjective alertness (KSS) reported is
consistent with the above EEG results.
Participants rated themselves as sleepier in
Normalized power
Dim 40lx 80lx 160lx
Figure 5 Individual EEG power values in beta range (the
same symbol indicates the values obtained from the
same participant)
Dim 40lx 80lx 160lx
Mean KSS score
Figure 6 Mean standard error of the mean normalized
KSS scores (lower scores indicate greater alertness)
Normalized scores
Dim 40lx 160lx
Figure 7 Individual KSS scores (the same symbol indi-
cates the values obtained from the same participant)
Effect of short-wavelength light on alertness 419
Lighting Res. Technol. 2020; 52: 413–422
the Dim condition, and more alert under the
blue lights. With the Dim condition having
the highest score and 160 lux having the
lowest, this again shows a significant alerting
effect of 160 lux compared to Dim light. Both
40 lux and 80 lux exposure were rated in
between the Dim and 160 lux conditions, at
about the same level. In addition, participants
were asked to report changes on their bed
time and any other unusual feelings (including
a sleep problem) after experiments. As a
result, there is no report on unusual bed
time shifts after exposure; however, one
participant reported suffering from headache
at night after being kept in blue light.
Very few studies have so far looked into the
effect of intensity of short-wavelength light on
alertness. In some studies, blue light of 40 lux
has been suggested to have an alerting effect.
Some other studies, for example, have com-
pared light of 40 lux at 2500 K, 3000 K and
6500 K,
and light of 295lux at 2700 K and
209 lux at 5600 K.
These studies, however,
have focussed on spectral composition or
exposure duration, rather than light intensity.
This study extends the research on the
effect of intensity on light-induced alertness.
The findings suggested that, firstly, a certain
level of intensity is needed to induce alertness
(to produce a significant effect a higher level
of intensity might be needed). Secondly, the
relations between intensity and alertness
change is not linear, which certain param-
eters, e.g. the intensity that could maximally
increase alertness might be identified. Lastly,
these threshold intensities could be difficult to
measure. Assuming that the relations between
intensity and alertness are not linear, the closer
to the threshold, the smaller the difference
would be. Study of higher precision is required
in order to detect smaller effect, e.g. a bigger
sample size. The practical difficulties in con-
ducting such experiment limit the sample size
that is normally included, whereas the small
sample size further limits the statistical power
to detect the subtle effect. The other limitation
is that reading a book during the experiment
might have affected participants’ brain activ-
ity, although this is difficult to avoid. In
similar studies, participants will normally be
allowed to conduct light tasks such as cross-
word puzzles
over the relatively long exposure
hours. However, they were asked to read
continuously and try to maintain their mood
and attention throughout the session, so to
control the potential effect as much as possible.
5. Conclusions
This study provides some evidence that short-
wavelength light exposure in the evening can
increase human alertness and that this can occur
relatively quickly (even though some other
studies have suggestion that melatonin inhib-
ition, for example, may have a longer time
course). Both objective and subjective results
also suggest that for the lighting conditions
tested in the present study, light of higher
intensity has a stronger alerting effect than light
of lower intensity. These findings, in themselves,
do not enable a threshold effect to be identified.
However, the methodology described in this
study may provide a basis for future on-going
work to address this question explicitly.
Declaration of conflicting interests
The authors declared no potential conflicts of
interest with respect to the research, author-
ship, and/or publication of this article.
The authors received no financial support for
the research, authorship, and/or publication
of this article.
J Lin
420 J Lin et al.
Lighting Res. Technol. 2020; 52: 413–422
1 Hattar S, Lucas RJ, Mrosovsky N, Thompson
S, Douglas RH, Hankins MW, Lem J, Biel M,
Hofmann F, Foster RG, Yau KW.
Melanopsin and rod–cone photoreceptive sys-
tems account for all major accessory visual
functions in mice. Nature 2003; 424: 75.
2 Figueiro MG, Bullough JD, Bierman A, Fay
CR, Rea MS. On light as an alerting stimulus
at night. Acta Neurobiologiae Experimentalis
2007; 67: 171.
3 Figueiro MG, Bierman A, Plitnick B, Rea MS.
Preliminary evidence that both blue and red
light can induce alertness at night. BMC
Neuroscience 2009; 10: 105.
4 Figueiro MG, Rea MS. The effects of red and
blue lights on circadian variations in cortisol,
alpha amylase, and melatonin. International
Journal of Endocrinology. DOI: 10.1155/2010/
5 Figueiro MG, Rea MS. Sleep opportunities
and periodic light exposures: impact on bio-
markers, performance and sleepiness. Lighting
Research and Technology 2011; 43: 349–369.
6 Sahin L, Figueiro MG. Alerting effects of
short-wavelength (blue) and long-wavelength
(red) lights in the afternoon. Physiology and
Behavior 2013; 116: 1–7.
7 Badia P, Myers B, Boecker M, Culpepper J,
Harsh JR. Bright light effects on body tem-
perature, alertness, EEG and behavior.
Physiology and Behavior 1991; 50: 583–588.
8 Jung TP, Makeig S, Stensmo M, Sejnowski TJ.
Estimating alertness from the EEG power
spectrum. IEEE Transactions on Biomedical
Engineering 1997; 44: 60–69.
9 Figueiro MG, Sahin L, Wood B, Plitnick B.
Light at night and measures of alertness and
performance: implications for shift workers.
Biological Research for Nursing 2016; 18:
10 Okamoto Y, Rea MS, Figueiro MG. Temporal
dynamics of EEG activity during short-and
long-wavelength light exposures in the early
morning. BMC Research Notes 2014; 7: 113.
11 Plitnick B, Figueiro MG, Wood B, Rea MS.
The effects of red and blue light on alertness
and mood at night. Lighting Research and
Technology 2010; 42: 449–458.
12 Lockley SW, Evans EE, Scheer FA, Brainard
GC, Czeisler CA, Aeschbach D. Short-wave-
length sensitivity for the direct effects of light
on alertness, vigilance, and the waking elec-
troencephalogram in humans. Sleep 2006; 29:
13 Chang AM, Aeschbach D, Duffy JF, Czeisler
CA. Evening use of light-emitting eReaders
negatively affects sleep, circadian timing, and
next-morning alertness. Proceedings of the
National Academy of Sciences 2015; 112:
14 Cajochen C. Alerting effects of light. Sleep
Medicine Reviews 2007; 11: 453–464.
15 Cajochen C, Zeitzer JM, Czeisler CA, Dijk DJ.
Dose-response relationship for light intensity
and ocular and electroencephalographic cor-
relates of human alertness. Behavioural Brain
Research 2000; 115: 75–83.
16 Boivin DB, Duffy JF, Kronauer RE, Czeisler
CA. Dose-response relationships for resetting
of human circadian clock by light. Nature
1996; 379: 540.
17 Zeitzer JM, Dijk DJ, Kronauer RE, Brown
EN, Czeisler CA. Sensitivity of the human
circadian pacemaker to nocturnal light:
melatonin phase resetting and suppression.
The Journal of Physiology 2000; 526:
18 Commission Internationale de l’E
´clairage. CIE
System for Metrology of Optical Radiation for
ipRGC-Influenced Responses to Light. CIE S
026/E:2018. Vienna: CIE, 2018.
19 Shahid A, Wilkinson K, Marcu S, Shapiro
CM. Karolinska sleepiness scale (KSS). In:
STOP, THAT and One Hundred Other Sleep
Scales. New York: Springer, 2011.
20 Cajochen C, Brunner DP, Kra
¨uchi K, Graw P,
Wirz-Justice A. EEG and subjective sleepiness
during extended wakefulness in seasonal
affective disorder: circadian and homeostatic
influences. Biological Psychiatry 2000; 47:
21 Aeschbach D, Matthews JR, Postolache TT,
Jackson MA, Giesen HA, Wehr TA. Two
circadian rhythms in the human electro-
encephalogram during wakefulness. American
Journal of Physiology-Regulatory, Integrative
and Comparative Physiology 1999; 277:
Effect of short-wavelength light on alertness 421
Lighting Res. Technol. 2020; 52: 413–422
22 Chellappa SL, Steiner R, Blattner P, Oelhafen
P, Go
¨tz T, Cajochen C. Non-visual effects of
light on melatonin, alertness and cognitive
performance: can blue-enriched light keep us
alert? PloS One 2011; 6: e16429.
23 Nagare R, Plitnick B, Figueiro MG. Effect of
exposure duration and light spectra on night-
time melatonin suppression in adolescents and
adults. Lighting Research and Technology 2019;
51: 530–543.
422 J Lin et al.
Lighting Res. Technol. 2020; 52: 413–422
... 15 In a previous study, we have investigated the alerting effect of short-wavelength light at three light levels (40 lx, 80 lx and 160 lx) in the evening. 16 Results showed that 160 lx light significantly increased alertness, as evaluated by EEG and self-rating questionnaire (Karolinska Sleepiness Scale, KSS). This study aims to expand on the previous work by investigating the impact of long-wavelength on the measures of EEG power and KSS. ...
... Experiment protocol of this study is kept consistent with the previous study. 16 Each participant completed two sessions over two nights, starting at around the same time (8 p.m.). Participants were fitted with EEG electrodes prior to the start of the exposure. ...
... Figure 6 shows the results of normalised power for six lighting conditions in three frequency ranges studied (where * indicates statistical significance). Note that the results of dim, 40 lx, 80 lx and 160 lx Blue light from the previous study 16 are added in Figure 6 to give a better comparison. The results showed that EEG beta power is significantly higher after exposure to 160 lx Blue light than remaining in Dim light (p50.05). ...
Full-text available
This study extends previous findings on the effect of different levels of short-wavelength light on human alertness. This study explores the alerting ability of long-wavelength light at two levels (40 lx and 160 lx). Eight subjects took part in the 60-minute experiment for each of two nights, during which their objective alertness and subjective alertness were evaluated using electroencephalogram and questionnaire. Results show that both levels increased electroencephalogram beta power, which shows a different pattern compared with the previous findings on short-wavelength light. These results strongly suggest that although short-wavelength light may impact alertness through circadian system, long-wavelength light will have to achieve that through other pathways. The further comparison between current and previous results also suggests that long-wavelength light is just as strong on acute alerting ability, as shown by electroencephalogram measures and self-rating questionnaire, as short-wavelength light.
... It is suggested that the effective use of colours in the design of classrooms do have significant impacts on students' perceptual performances. Interestingly, some studies carried out explored the intensity lighting impacts have on people's electroencephalogram (EEG) power [15,16]. Results have demonstrated the stimulus of short and long wavelength light on people's alpha, theta, and beta power, suggesting that coloured light can promote acute alertness and improve performance on tasks requiring sustained attention. ...
... It is suggested that the effective use of colours in the design of classrooms do have significant impacts on students' perceptual performances. Interestingly, some studies carried out explored the intensity lighting impacts have on people's electroencephalogram (EEG) power [15,16]. ...
Full-text available
The purpose of this study was to explore the influence of environmental colour on people's lateral and logical abilities. This was done by evaluating study participants' response time and error rate when completing six types of psychometric tests that were performed in various hue backgrounds on a computer. To maximise the colour stimulation provided by the monitor, the experiment was carried out in a dark laboratory. Analysis of participants' response time and error rate showed that different colours could significantly influence arousal and impulsiveness, which suggests that colour has indirect impacts on cognitive abilities. Further analysis revealed that different colours had various effects depending on the type of psychometric test given. These findings suggest that future research on environmental design should consider how to effectively use colour to impact people's performance and behaviour.
... Event-related potential (ERP) study by Okamoto and Nakagawa (Okamoto & Nakagawa, 2015) point to an alerting effect of shorter-wavelength light by means of an increase in P300 amplitude. A study by Lin et al. (Lin, Westland, & Cheung, 2019) evaluated the acute alerting effects of short-wavelength light of three different intensities (40, 80, and 160 lux). EEG beta was significantly higher after exposure to 160 lux light than after exposure to 40 lux, 80 lux light, or dark condition. ...
Background: Since the discovery of ipRGCs (intrinsic photosensitive retinal ganglion cells) in the retina, new research possibilities for studying the effects of light on the regulation of various behavioral and physiological functions that are independent of image formation arose. As ipRGCs are most sensitive to light of short wavelengths (460-480nm), this dissertation focuses on current topics related to the use of blue light, emphasizing its influence on circadi-an rhythms, sleep and cognitive performance and possible applications in clinical and non-clinical settings. Aims: The first study aimed to explore the effects of 20 minutes of narrow-bandwidth light exposure of different wavelengths on various neuropsychological and neurophysiological parameters of vigilance in healthy volunteers. The objective of the second study was to assess the effect of combining CBT-I (cognitive-behavioral therapy for insomnia) with wearing blue-light blocking glasses 90 minutes before bedtime on subjective and objective sleep pa-rameters and daily symptoms (anxiety, depression, hyperarousal). The third study aimed to examine subjective sleep quality in a population of healthy volunteers and its association with evening and night light exposure to screens of media devices. Methods: In the first study, twelve healthy volunteers went through 3 sessions of 20 minutes of light exposure of different wavelengths (455, 508, and 629 nm, with an irradiance of 14 μW/cm2), while EEG was recorded (including ERP (event-related potential) P300 and spec-tral characteristics) and behavioral data (subjective sleepiness, reaction time) gathered. In the second study, 30 patients completed a CBT-I group therapy program, with groups randomly assigned to either active (blue-light filtering glasses) condition, or placebo (glasses without filtering properties) condition. Patients were continually monitored by wristwatch actigraphy, kept their sleep diaries, and completed a standard questionnaire battery at admission and after the end of the program. Lastly, 693 participants in total completed an online questionnaire battery consisting of several sleep-related questionnaires: PSQI, FSS, MCTQ, MEQ and add-ed questions assessing the timing and character of the evening and night exposure to electron-ic devices (TV, PC, tablets and phones) and the use of various filters blocking short-wavelength light. Results: Our analyses showed that the short-wavelength light condition (455nm) in the first study, was found to be the most effective in terms of its alerting effect for the following vari-ables: subjective sleepiness, the latency of P300 response and absolute EEG power in higher beta (24-34 Hz) and gamma (35-50 Hz) range. The second study showed a greater reduction of anxiety symptoms in the active vs. placebo group of patients and significant prolongation of subjective total sleep time in the active group. When pre- and post-treatment results were compared in both groups separately, significant differences were observed for the scores in the depression and hyperarousal scales in the active group only. In the active group, there was also a significant reduction of subjective sleep latency and an increase of subjective total sleep time without a change in objective sleep duration, which was significantly shortened in the placebo group. In the third study, our analyses showed that longer cumulative exposure to screen light in the evening was associated with greater sleep inertia in the morning and longer sleep latency on workdays. Furthermore, exposure to screen light 1.5h before sleep or during night awakenings was also associated with a decreased chance to wake up before the alarm time, larger social jet-lag, more pronounce daytime dysfunction, decreased subjective sleep quality, and more fatigue. A statistical trend for an increase in the duration of sleep on week-days was also found in participants using blue-light filters in the evening hours. Conclusion: Our results provide valuable insight into the alerting effects of short-wavelength (blue) light. We also show that avoiding blue light in the evening may help reduce the phase-delaying effect of light and facilitate an improvement in sleep parameters and psychiatric symptoms. Altogether, these results may contribute to the development of new lighting or light-filtering systems and may also be applicable for healthy sleep promotion in both the general and clinical populations.
... However, it is not clear whether people's responses to colour stimulations can be better triggered in V R sy stems. Our first hy pothesis is that emotional responses can be affected by different coloured lighting conditions, in line with previous findings [1][2]29,49]. Our second hypothesis is that in a V R replica of the same env ironment, participants' would hav e similar, but not the same, emotional responses to those evoked by colour stimulations produced by real environment. ...
Full-text available
Many studies have shown that colour can affect emotional and physiological responses in real environments but do the same effects occur in virtual environments? This study investigated human subjective and objective responses to different coloured lighting environments, first in a physical laboratory (PE) and then in an approximately identical virtual reality (VR) environment, using three experimental techniques. Data from a smiley-face self-reporting exercise and from electroencephalography (EEG) revealed differential effects of coloured lighting in both the PE and VR environments. However, although data from the Positive and Negative Affect Schedule (PANAS) revealed an effect of coloured lighting in the RE, the same effects were not statistically significant in the VR. We suggest that this might be because of a limited sample size. The results of this study demonstrate the potential of colour for positive emotional effect in an immersive 'real-world' environment for participants in a natural state, i.e. not engaged in any specific cognitive activity. Importantly, the results also indicate that in a VR replica of the same environment, participants also experienced an increase in positive emotions.
... As reported in recent literature, the impact of lighting goes beyond comfort and safety issues. Illumination level and environmental color seem to have different effects on perception and physiological parameters [8,9] . Therefore, this article is based on these studies by monitoring changes in physiological parameters and subjective emotions under different lights, hoping to play a greater role in lighting design applications. ...
An experiment based on physiological parameters and subjective emotional changes is designed to analyze the sound‐light fusion effects. The different effects caused by music in major and minor keys is studied. Three colorful lighting with main wavelength at 623, 537, 445 nm, respectively, as well as two white lighting with 3000 K CCT and 6000 K CCT are evaluated in the same process. Results show that the physiological response to music is stronger than that of the lighting stimulus. Music plays a major role in the sound‐light fusion environment, and the physiological perception under dual‐factor stimulation is stronger than that of single factor. Moreover, music and light interact with each other when they stimulate emotions at the same time. The superposition of two positively related factors can strengthen the effects on emotion. The studies may give suggestions to the designers when they design a lighting show with music or an immersive and interactive lighting project.
Full-text available
It is well known that exposure to light, especially of short wavelength, enhances human alertness during the nighttime. However, more information is needed to elucidate the effects of light wavelength on alertness at other times of day. The present study investigated how two narrowband light spectra affected human alertness during the morning after awakening. We measured electroencephalography (EEG) during 48-minute exposure to narrowband short- and long-wavelength light and darkness in the early morning. Power densities of EEG during each light exposure were calculated. The time course of EEG power indicated that, compared with remaining in darkness, the power in the alpha frequency range (8-13 Hz) was significantly lower after approximately 30 minutes of exposures to both the short- and the long-wavelength light. These results suggest that not only short-wavelength light but also long-wavelength light, which does not suppress melatonin levels at night, can affect alertness in the early morning. These results suggest that the alerting effects of light in the early morning hours may be mediated by mechanisms other than those that are exclusively sensitive to short-wavelength light.
Full-text available
This study was designed to explore the roles that long- and short-wavelength lights have on momentary mood and alertness at night. Twenty-two subjects participated in a mixed-design experiment, where we measured the impact of two levels of long- and short-wavelength lights on brain activity and on self-assessments of alertness, sleepiness and mood. Measurements were obtained 60 minutes prior to, during and after light exposure. Results showed that the red and the blue lights increased electroencephalographic beta power (12—30 Hz), reduced sleepiness, and increased positive affect relative to the previous dim-light period indicating that alertness and mood can be affected by light without necessarily stimulating the melatonin pathway. The impact of light was modest, however, compared to the increase in fatigue over the course of the night.
Full-text available
Light exposure can cascade numerous effects on the human circadian process via the non-imaging forming system, whose spectral relevance is highest in the short-wavelength range. Here we investigated if commercially available compact fluorescent lamps with different colour temperatures can impact on alertness and cognitive performance. Sixteen healthy young men were studied in a balanced cross-over design with light exposure of 3 different light settings (compact fluorescent lamps with light of 40 lux at 6500K and at 2500K and incandescent lamps of 40 lux at 3000K) during 2 h in the evening. Exposure to light at 6500K induced greater melatonin suppression, together with enhanced subjective alertness, well-being and visual comfort. With respect to cognitive performance, light at 6500K led to significantly faster reaction times in tasks associated with sustained attention (Psychomotor Vigilance and GO/NOGO Task), but not in tasks associated with executive function (Paced Visual Serial Addition Task). This cognitive improvement was strongly related with attenuated salivary melatonin levels, particularly for the light condition at 6500K. Our findings suggest that the sensitivity of the human alerting and cognitive response to polychromatic light at levels as low as 40 lux, is blue-shifted relative to the three-cone visual photopic system. Thus, the selection of commercially available compact fluorescent lights with different colour temperatures significantly impacts on circadian physiology and cognitive performance at home and in the workplace.
This study investigated how light exposure duration affects melatonin suppression, a well-established marker of circadian phase, and whether adolescents (13–18 years) are more sensitive to short-wavelength (blue) light than adults (32–51 years). Twenty-four participants (12 adolescents, 12 adults) were exposed to three lighting conditions during successive 4-h study nights that were separated by at least one week. In addition to a dim light (<5 lux) control, participants were exposed to two light spectra (warm (2700 K) and cool (5600 K)) delivering a circadian stimulus of 0.25 at eye level. Repeated measures analysis of variance revealed a significant main effect of exposure duration, indicating that a longer duration exposure suppressed melatonin to a greater degree. The analysis further revealed a significant main effect of spectrum and a significant interaction between spectrum and participant age. For the adolescents, but not the adults, melatonin suppression was significantly greater after exposure to the 5600 K intervention (43%) compared to the 2700 K intervention (29%), suggesting an increased sensitivity to short-wavelength radiation. These results will be used to extend the model of human circadian phototransduction to incorporate factors such as exposure duration and participant age to better predict effective circadian stimulus.
There are at least four reasons why a sleep clinician should be familiar with rating scales that evaluate different facets of sleep. First, the use of scales facilitates a quick and accurate assessment of a complex clinical problem. In three or four minutes (the time to review ten standard scales), a clinician can come to a broad understanding of the patient in question. For example, a selection of scales might indicate that an individual is sleepy but not fatigued; lacking alertness with no insomnia; presenting with no symptoms of narcolepsy or restless legs but showing clear features of apnea; exhibiting depression and a history of significant alcohol problems. This information can be used to direct the consultation to those issues perceived as most relevant, and can even provide a springboard for explaining the benefits of certain treatment approaches or the potential corollaries of allowing the status quo to continue. Second, rating scales can provide a clinician with an enhanced vocabulary or language, improving his or her understanding of each patient. In the case of the sleep specialist, a scale can help him to distinguish fatigue from sleepiness in a patient, or elucidate the differences between sleepiness and alertness (which is not merely the inverse of the former). Sleep scales are developed by researchers and clinicians who have spent years in their field, carefully honing their preferred methods for assessing certain brain states or characteristic features of a condition. Thus, scales provide clinicians with a repertoire of questions, allowing them to draw upon the extensive experience of their colleagues when attempting to tease apart nuanced problems. Third, some scales are helpful for tracking a patient's progress. A particular patient may not remember how alert he felt on a series of different stimulant medications. Scale assessments administered periodically over the course of treatment provide an objective record of the intervention, allowing the clinician to examine and possibly reassess her approach to the patient. Finally, for individuals conducting a double-blind crossover trial or a straightforward clinical practice audit, those who are interested in research will find that their own clinics become a source of great discovery. Scales provide standardized measures that allow colleagues across cities and countries to coordinate their practices. They enable the replication of previous studies and facilitate the organization and dissemination of new research in a way that is accessible and rapid. As the emphasis placed on evidence-based care grows, a clinician's ability to assess his or her own practice and its relation to the wider medical community becomes invaluable. Scales make this kind of standardization possible, just as they enable the research efforts that help to formulate those standards. The majority of Rating Scales in Sleep and Sleep Disorders:100 Scales for Clinical Practice is devoted to briefly discussing individual scales. When possible, an example of the scale is provided so that readers may gain a sense of the instrument's content. Groundbreaking and the first of its kind to conceptualize and organize the essential scales used in sleep medicine, Rating Scales in Sleep and Sleep Disorders:100 Scales for Clinical Practice is an invaluable resource for all clinicians and researchers interested in sleep disorders. © Springer Science+Business Media, LLC 2012. All rights reserved.
This scale [1] measures the subjective level of sleepiness at a particular time during the day. On this scale subjects indicate which level best reflects the psycho-physical sate experienced in the last 10 min. The KSS is a measure of situational sleepiness. It is sensitive to fluctuations.
Rotating-shift workers, particularly those working at night, are likely to experience sleepiness, decreased productivity, and impaired safety while on the job. Light at night has been shown to have acute alerting effects, reduce sleepiness, and improve performance. However, light at night can also suppress melatonin and induce circadian disruption, both of which have been linked to increased health risks. Previous studies have shown that long-wavelength (red) light exposure increases objective and subjective measures of alertness at night, without suppressing nocturnal melatonin. This study investigated whether exposure to red light at night would not only increase measures of alertness but also improve performance. It was hypothesized that exposure to both red (630 nm) and white (2,568 K) lights would improve performance but that only white light would significantly affect melatonin levels. Seventeen individuals participated in a 3-week, within-subjects, nighttime laboratory study. Compared to remaining in dim light, participants had significantly faster reaction times in the GO/NOGO test after exposure to both red light and white light. Compared to dim light exposure, power in the alpha and alpha-theta regions was significantly decreased after exposure to red light. Melatonin levels were significantly suppressed by white light only. Results show that not only can red light improve measures of alertness, but it can also improve certain types of performance at night without affecting melatonin levels. These findings could have significant practical applications for nurses; red light could help nurses working rotating shifts maintain nighttime alertness, without suppressing melatonin or changing their circadian phase. © The Author(s) 2015.
In the past 50 y, there has been a decline in average sleep duration and quality, with adverse consequences on general health. A representative survey of 1,508 American adults recently revealed that 90% of Americans used some type of electronics at least a few nights per week within 1 h before bedtime. Mounting evidence from countries around the world shows the negative impact of such technology use on sleep. This negative impact on sleep may be due to the short-wavelength-enriched light emitted by these electronic devices, given that artificial-light exposure has been shown experimentally to produce alerting effects, suppress melatonin, and phase-shift the biological clock. A few reports have shown that these devices suppress melatonin levels, but little is known about the effects on circadian phase or the following sleep episode, exposing a substantial gap in our knowledge of how this increasingly popular technology affects sleep. Here we compare the biological effects of reading an electronic book on a light-emitting device (LE-eBook) with reading a printed book in the hours before bedtime. Participants reading an LE-eBook took longer to fall asleep and had reduced evening sleepiness, reduced melatonin secretion, later timing of their circadian clock, and reduced next-morning alertness than when reading a printed book. These results demonstrate that evening exposure to an LE-eBook phase-delays the circadian clock, acutely suppresses melatonin, and has important implications for understanding the impact of such technologies on sleep, performance, health, and safety.
A within-subjects study investigated the impact of sleep opportunities and periodic light exposures on biomarkers, performance and sleepiness over 27-hour sessions. Ten subjects experienced three experimental sleep sessions: No sleep; sleep for 3 hours; and sleep for 7 hours. Subjects remained in dim red light for every experimental session, except when they were exposed to 40 lux of 470-nm light at the cornea for 50 minutes. Saliva samples for biomarker assays, performance scores on psychomotor vigilance tests and self-reports of sleepiness were collected just prior to and at the end of the light exposures. All measures follow circadian patterns that mark the transitions between daytime and nighttime, but they have different forms and are differentially affected by light exposure, sleep and circadian time.
Light has an acute effect on neuroendocrine responses, performance, and alertness. Most studies to date have linked the alerting effects of light to its ability to suppress melatonin, which is maximally sensitive to short-wavelength light. Recent studies, however, have shown alerting effects of white or narrowband short-wavelength lights during daytime, when melatonin levels are low. While the use of light at night to promote alertness is well understood, it is important to develop an understanding of how light impacts alertness during the daytime, especially during the post-lunch hours. The aim of the current study was to investigate how 48-minute exposures to short-wavelength blue light (λmax=470 nanometers [nm]) or long-wavelength red light (λmax=630nm) close to the post-lunch dip hours affect electroencephalogram measures in participants with regular sleep schedules. Power in the alpha, alpha theta, and theta ranges was significantly lower (p<0.05) after participants were exposed to red light than after they remained in darkness. Exposure to blue light reduced alpha and alpha theta power compared to darkness, but these differences did not reach statistical significance (p>0.05). The present results extend those performed during the nighttime, and demonstrate that light can be used to increase alertness in the afternoon, close to the post-lunch dip hours. These results also suggest that acute melatonin suppression is not needed to elicit an alerting effect in humans.