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Effect of intensity of short-wavelength light on electroencephalogram and subjective alertness


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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.
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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
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... One study (Herljevic et al., 2005) that did not report the pre-dark adaptation has been indicated in the text. A lightbox or a ganzfeld dome directly lit the participants' eyes in low ambient light except for three cases (Kayaba et al., 2014;Lin et al., 2019;Lin and Westland, 2020) where the test light source was suspended. These studies reported light intensity at eye level, and this value was considered in calculations. ...
... It has been demonstrated that nighttime exposure to shortwavelength light (λmax: 475 nm) improveed alertness (Lin et al., 2019) in comparison to dim light (< 1 lx). At λmax: 479 and 460 nm, this effect reached significance after midnight in comparison to longwavelength (λmax: 627 nm) (Papamichael et al., 2012) and middlewavelength light (λmax: 550-555 nm) (Cajochen et al., 2005;Lockley et al., 2006;Rahman et al., 2014). ...
... The age range of the participants was 19-35 y. Except for one study that did not report using a pupil dilator (Sahin and Figueiro, 2013), the others (Cajochen et al., 2005;Lin et al., 2019;Lin and Westland, 2020) did not administer a pupil dilator. experiments (Phipps-Nelson et al., 2009;Figueiro et al., 2009) did not improve reaction time significantly compared to dim condition (< 1 lx). ...
Light is detected in the eye by three classes of photoreceptors (rods, cones, and intrinsically photosensitive retinal ganglion cells (ipRGCs)) that are each optimized for a specific function and express a particular light-detecting photopigment. The significant role of short-wavelength light and ipRGCs in improving alertness has been well-established; however, few reviews have been undertaken to assess the other wavelengths' effects regarding timing and intensity. This study aims to evaluate the impact of different narrowband light wavelengths on subjective and objective alertness among the 36 studies included in this systematic review, 17 of which were meta-analyzed. Short-wavelength light (∼460–480 nm) significantly improves subjective alertness, cognitive function, and neurological brain activities at night, even for a sustained period (∼6h) (for λmax: 470/475 nm, 0.4 < |Hedges's g| < 0.6, p < 0.05), but except early morning, it almost does not show this effect during the day when melatonin level is lowest. Long-wavelength light (∼600–640 nm) has little effect at night, but significantly increases several measures of alertness at lower irradiance during the daytime (∼1h), particularly when there is homeostatic sleep drive (for λmax: ∼630 nm, 0.5 < |Hedges's g| < 0.8, p < 0.05). The results further suggest that melanopic illuminance may not always be sufficient to measure the alerting effect of light.
... In two studies by Lin and colleagues, the researchers analyzed the neural effects of short-wavelength (blue) lighting [57] and longwavelength (red) lighting [56] in different intensities. The results indicated that EEG power in the beta range was significantly higher after exposure to moderate-intensity blue light (160 lx) compared to lower levels of blue light (minimal light, 40 lx, and 80 lx). ...
... Will brain activity features (i.e., EEG data) be modulated in a predictable fashion during the first seconds of exposure to varied illuminance levels (RQ1a) and CCT (RQ1b)? Based on former EEG studies in real environments [14,57], we decided to investigate an expanded gradation of lighting conditions in VR while considering the acute effect of light during the first 10 s of exposure. ...
... There was a significant linear positive correlation between color temperature and frontal frequency band-power in the theta, alpha, and gamma bands, with smaller yet significant effect in the beta band. This is in line with the findings of Lin and colleagues [57], except that these prior researchers did not investigate the activation of the gamma (30-40 Hz) band associated with blue light. Our findings indicate that there were some common dynamics involved in brain responses to both higher illumination levels and higher "blue" CCT, such as reductions in the α/γ ratio in frontal brain regions. ...
Investigating human responses to light can reveal important information with the potential to improve environmental design, circadian health, cognitive performance, and overall wellbeing. In this study, the researchers used VR immersion, EEG, and a machine-learning approach to better understand the relationship between brain activity and two important lighting properties—the illumination level and the correlated color temperature (CCT). Participants (N = 25) were asked to experience 17 different artificial lighting conditions and rate their perceived arousal and pleasure levels, and then adjust the lighting to their optimal preference. The results from the experiment demonstrated an association of illumination level and CCT with specific EEG band-features in the frontal and parietal brain regions. Our machine-learning classification approach was able to predict participants' behavioral choices of desired vs. non-desired lighting based on the EEG data from their first 10 s of exposure, a finding that has notable implications for the potential development of brain–computer interfaces for automatic lighting adjustment.
... The beta range (160 lux) revealed a remarkable difference compared to the three lighting conditions. According to a KSS score, Subjective sleepiness was considerably reduced in 160 lux conditions than in dim light conditions, affirming a high alerting effect [36]. These findings delineate that short wavelengths, except for a few frequency bins, induce less alertness than longer wavelengths. ...
... In the same year, Lockley et al. established an inverse proportionality between melatonin suppression and arousal of alertness [74]. Contrastingly, Lin et al. expressed a pronounced stimulatory effect of red light for the arousal of alertness while conserving melatonin levels [36]. These studies are consistent with Plitnick et al. and Figueiro et al., where red light elicited subjective alertness, but not at the expense of melatonin [75,76]. ...
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Circadian rhythms confer a biological clock of all living beings, comprising oscillations in a range of physiological variables, including body temperature and melatonin, that regulate the sleep/wake cycle rhythmically. Both variables have been marked to influence the sleep/wake cycle; even so, the interrelationship among the triad (body temperature, melatonin & sleepiness/alertness) is still unknown. The current literature review is envisioned to examine the contemporary details regarding the interaction between melatonin, body temperature, and sleepiness/alertness. All the included information is procured from the latest review articles, systematic & meta-analytical literature reviews, and original research reports. Findings revealed that melatonin and body temperature collectively contribute to the formation of sleep. An increase in melatonin induces fluctuations in body temperature. Both physiologic variables serve as close indicators of sleepiness/alertness. However, modulating factors such as light, environmental temperature, and timing of melatonin administration (with the circadian clock) may impact the overall outcomes. A significant number of studies are required to infer the underlying processes by which these factors influence the circadian clock.
... It indicates that visual work needs appropriate illuminance; too high or too low light stimulation is not conducive to good visual performance. Lin [74,75] also found that higher intensity blue light had a stronger alerting effect, but that the effect of intensity on alertness was not linear. In a recent field study, a small sample of subjects showed a significant relationship between subjective alertness and horizontal illuminance without the presence of any additional confounding variables [76]. ...
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Exposure to light during overtime work at night in confined spaces may disrupt the normal circadian clock, affect hormone secretion, sleep quality and performance, thereby posing great risks to the physical and mental health of night workers. Integrative lighting should be adopted to reduce the disturbance of normal physiological rhythm, while meeting the visual requirements of work. Through adjustable LED (CCT 6000 K/2700 K) and different vertical illuminance, five lighting patterns with different circadian stimuli (CS = 0.60, 0.30. 0.20, 0.10 and 0.05) were conducted, respectively, in a sleep lab using a within-subject design. Each lighting pattern lasted for 5 h every night. Eight healthy adults were recruited to complete the night work and their salivary melatonin, Karolinska sleepiness scale (KSS), Psychomotor Vigilance Task (PVT) and sleep quality were tested. The results showed that subjective sleepiness and melatonin concentration increased rapidly under low intervention (CS = 0.05) with the best sleep quality, while they decreased in high intervention (CS = 0.60) at night and led to significantly higher levels of sleepiness the next morning (p < 0.05). For the PVT, the middle intervention (CS = 0.30) showed the lowest response time and least errors (p < 0.05), suggesting that appropriate illuminance can improve visual performance. To reduce biorhythm disruptions, lower lighting stimulation is preferred during night work. For difficult visual tasks, high illuminances may not improve visual performance; just a slight increase in the existing lighting levels is adequate. Lighting interventions have a clear impact on sleep improvement and work capacity for those working overtime, and they may be translatable to other shift work scenarios.
... Lighting CCT has drawn much attention to the influence of lighting on human psychological processes [36] and leads to a variety of improvements in users' wellbeing, functioning, and task performance [9] CCT of light has been shown to improve cognitive function [37], physiological and brain dynamics [38]- [40], subjective alertness, performance, and evening fatigue [14], [41], as well as wellbeing and productivity in the corporate setting [9], [42]. Researchers also found that NIF effects are expected to be stronger when exposed to monochromatic blue light or polychromatic light with a high CCT [43], [44] However, several empirical studies found no or little effects of CCT on subjective mood and performance, and these effects found in other research studies may actually be due to illumination differences [45]- [48]. ...
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This paper presents a novel approach to assessing human lighting adjustment behavior and preference in diverse lighting conditions through the evaluation of emotional feedback and behavioral data using VR. Participants (n= 27) were exposed to different lighting (n=17) conditions with different levels of illuminance and correlated color temperature (CCT) with a randomized order in a virtual office environment. Results from this study significantly advanced our understanding of preferred lighting conditions in virtual reality environments, influenced by a variety of factors such as illuminance, color temperature, order of presentation, and participant demographics. Through a comprehensive analysis of user adjustment profiles, we obtained insightful data that can guide the optimization of lighting design across various settings.
... Light has been shown to have strong non-visual effects on a range of biological functions, such as the regulation of human emotion and the circadian system [15]. CCT is a key factor of light and has been shown to affect human physiology as well as psychology [16]. In manned spacecraft, most lighting uses fluorescent or LED technology. ...
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The hygiene area is one of the most important facilities in a space station. If its environmental lighting is appropriately designed, it can significantly reduce the psychological pressure on astronauts. This study investigates the effect of correlated colour temperature (CCT) on heart rate, galvanic skin response, emotion and satisfaction in the hygiene area of a space station. Forty subjects participated in experiments in a hygiene area simulator with a controlled lighting environment. The lighting conditions included 2700 K, 3300 K, 3600 K, 5000 K and 6300 K; physiological responses (heart rate, galvanic skin response), as well as emotion and satisfaction, were recorded. The results showed that CCT significantly influenced the participants’ physiological and subjective responses in the space station hygiene area. 6300 K led to the best emotion and satisfaction levels, the highest galvanic skin response and the lowest heart rate. The opposite was true for 2700 K.
... 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.
The non-visual effects of light have become a hot topic in the study of how lighting environments affect humans. For an extended time, living and working in an isolated, confined, and enclosed (ICE) environment can have negative effects on the physiological and psychological issues of humans. In addition to the research on people's traditional visual ergonomics in the lighting environment, a new development trend is to pay attention to the ergonomics issue produced by non-visual (NV) effects, such as circadian rhythm, sleep, mental health, and performance, in the lighting environment. To protect the physical and mental well-being of individuals working in the enclosed cabins and to improve performance, it is vital to further develop new ergonomic research methodologies for the lighting environment. This paper reviewed relevant studies from the previous five years and follows the highly cited papers forward and backward to gain insight into the study and evaluation context of the non-visual effects of light. Based that, it is analyzed that the researches on sleep, alertness, and ergonomics in the enclosed cabins that induced by integrated lighting (IL, integrating the visual and non-visual effects of light). Reviewing research on the non-visual effects of light in the domains of medicine, ergonomics, and application, it is advised that integrated lighting ergonomics (ILE) research be conducted for crew living and working in the enclosed spaces, and that its objectives, methods, and design principles about ILE be described.
In complex human-machine systems such as spacecraft, poor astronaut performance leads to dangerous accidents, and assessing the functional state of astronauts during a mission has positive impacts on risk reduction and efficiency. This paper aimed to assess the functional state of astronauts in performing target tracking tasks of different difficulty at three different short-wavelength light intensities (40 lx, 80 lx, and 160 lx) in a simulated space station module with a head-mounted display (HMD) and electroencephalogram (EEG) equipment, and collect EEG and task performance changes as well, aiming to better understand the cognitive behavior of astronauts during spacecraft operations. Thirty healthy participants were recruited for this experiment and their EEG physiological signals were collected during simulated astronauts in conducting target tracking tasks. Meanwhile, all participants wore a head-mounted display (HMD) to perform target tracking tasks of low, medium, and high difficulty in three intensities (40 lx, 80 lx, and 160 lx) of short-wavelength light (\(\lambda_{max}\) = 475 nm), while remaining in the darkness (<1 lx). All the participants’ EEG power in the beta range after exposure to 160 lx light was significantly higher than that to 40 lx and 80 lx light, or it kept in the darkness. In addition, alpha and theta power were significantly lower in 160 lx light than in darkness. This study provides some evidence that nighttime short-wavelength light exposure can improve the astronaut task performance in performing target tracking.KeywordsShort-wavelength lightTarget trackingEEGTask performance
The efficiency and convenience of gesture shortcuts have an important influence on user experience. However, it is unknown how the number of permitted swiping angles and their allowable range affect users’ performance and experience. In the present study, young and old users executed swiping in multiple directions on smartphones. Results showed that multiple allowable angles resulted in slower swiping speed and poorer user experience than the single allowable angle condition. However, as the number of allowable angles increased, only old users showed a significant decrease in swiping accuracy. Vertical-up and upper-right swiping were faster than swiping in the horizontal directions. Furthermore, narrower operable range of swiping only reduced swiping accuracy in the tilted direction. Though old users performed worse on swiping than younger users, their subjective ratings were more positive than younger users’. Suggestions on how to design swiping gestures on the human-mobile interface were discussed.KeywordsGesture shortcutsSwipe gesturesSwipe angleAge differenceUser experience
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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.
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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.
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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.
Significance The use of light-emitting electronic devices for reading, communication, and entertainment has greatly increased recently. We found that the use of these devices before bedtime prolongs the time it takes to fall asleep, delays the circadian clock, suppresses levels of the sleep-promoting hormone melatonin, reduces the amount and delays the timing of REM sleep, and reduces alertness the following morning. Use of light-emitting devices immediately before bedtime also increases alertness at that time, which may lead users to delay bedtime at home. Overall, we found that the use of portable light-emitting devices immediately before bedtime has biological effects that may perpetuate sleep deficiency and disrupt circadian rhythms, both of which can have adverse impacts on 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.