ArticlePDF Available

High Sensitivity of Human Melatonin, Alertness, Thermoregulation, and Heart Rate to Short Wavelength Light


Abstract and Figures

Light can elicit acute physiological and alerting responses in humans, the magnitude of which depends on the timing, intensity, and duration of light exposure. Here, we report that the alerting response of light as well as its effects on thermoregulation and heart rate are also wavelength dependent. Exposure to 2 h of monochromatic light at 460 nm in the late evening induced a significantly greater melatonin suppression than occurred with 550-nm monochromatic light, concomitant with a significantly greater alerting response and increased core body temperature and heart rate ( approximately 2.8 x 10(13) photons/cm(2)/sec for each light treatment). Light diminished the distal-proximal skin temperature gradient, a measure of the degree of vasoconstriction, independent of wavelength. Nonclassical ocular photoreceptors with peak sensitivity around 460 nm have been found to regulate circadian rhythm function as measured by melatonin suppression and phase shifting. Our findings-that the sensitivity of the human alerting response to light and its thermoregulatory sequelae are blue-shifted relative to the three-cone visual photopic system-indicate an additional role for these novel photoreceptors in modifying human alertness, thermophysiology, and heart rate.
Content may be subject to copyright.
High Sensitivity of Human Melatonin, Alertness,
Thermoregulation, and Heart Rate to Short
Wavelength Light
Christian Cajochen, Mirjam Mu¨ nch, Szymon Kobialka, Kurt Kra¨uchi, Roland Steiner, Peter Oelhafen,
Selim Orgu¨ l, and Anna Wirz-Justice
Centre for Chronobiology (C.C., M.M., S.K., K.K., A.W.-J.), Psychiatric University Clinic, CH-4025 Basel, Switzerland;
Institute of Physics (R.S., P.O.), University of Basel, CH-4056 Basel, Switzerland; and Eye Clinic, University Hospital
(S.O.), CH-4012 Basel, Switzerland
Light can elicit acute physiological and alerting responses in
humans, the magnitude of which depends on the timing, in-
tensity, and duration of light exposure. Here, we report that
the alerting response of light as well as its effects on thermo-
regulation and heart rate are also wavelength dependent. Ex-
posure to2hofmonochromatic light at 460 nm in the late
evening induced a significantly greater melatonin suppres-
sion than occurred with 550-nm monochromatic light, con-
comitant with a significantly greater alerting response and
increased core body temperature and heart rate (2.8 10
/sec for each light treatment). Light diminished
the distal-proximal skin temperature gradient, a measure of
the degree of vasoconstriction, independent of wavelength.
Nonclassical ocular photoreceptors with peak sensitivity
around 460 nm have been found to regulate circadian rhythm
function as measured by melatonin suppression and phase
shifting. Our findings—that the sensitivity of the human alert-
ing response to light and its thermoregulatory sequelae
are blue-shifted relative to the three-cone visual photopic
system—indicate an additional role for these novel photore-
ceptors in modifying human alertness, thermophysiology, and
heart rate. (J Clin Endocrinol Metab 90: 1311–1316, 2005)
HE HUMAN CIRCADIAN timing system is sensitive to
ocular light exposure. The effects of light depend on the
circadian phase at which light is administered: light given
after the core body temperature (CBT) nadir advances the
phase of circadian rhythms, whereas light given before the
CBT nadir induces delays. This can be quantified by a
so-called “human phase-response curve to light” (1, 2).
Besides the timing of exposure, the intensity of light (i.e.
irradiance) also plays a crucial role in human circadian-
phase resetting (3, 4). The irradiance dose-response func-
tion to a single episode of light in the phase-delay region
can be characterized by a logistic function with high sen-
sitivity, such that half of the maximal resetting response
achieved in response to bright light (9100 lux) is obtained
with just 1% of this light (dim room light of 100 lux; see
Ref. 4). Recent results indicate that very low intensity
monochromatic light in the short-wave range (460 nm)
also affects the human circadian timing system and is
capable of inducing a significantly greater phase shift than
monochromatic light at 555 nm (the peak of the three-cone
photopic visual system) (5). Furthermore, short wave-
length light between 436 and 456 nm induced a phase
advance similar to that for polychromatic light (i.e. white
light) containing 185-fold more photons (6). These studies
clearly demonstrate that the human circadian timing sys-
tem is highly sensitive to ocular light exposure, particu-
larly in the short wavelength range.
Besides circadian phase shifts, light also elicits acute phys-
iological effects in humans such as a rapid suppression of
melatonin at night (for review, see Ref. 7), an increase in CBT
(8–11) and heart rate (12), and an immediate dose-dependent
alerting response, measured subjectively and objectively via
the electroencephalogram (10). Brainard et al. (13, 14) have
consistently shown that short wavelength light at around 460
nm is most effective in acutely suppressing human melatonin
levels. Furthermore, Hankins and Lucas (15) have recently
shown that acute light responses in the human electroreti-
nogram (ERG) are highly dependent on wavelength, such
that light at 483 nm elicited the strongest reduction in cone
ERG b wave–implicit time.
The acute effects of light, as well as the circadian effects,
seem to be mediated by the eyes. Thus, acute elevation of
body temperature and suppression of melatonin are not
observed when the eyes are covered (11, 16) or when light
is administered to the skin in the popliteal region (17–19).
There is mounting evidence that nonrod and noncone
photoreceptors might form the basis of this nonimage-
forming photoreceptive pathway mediating both the
circadian and direct effects of light in rodents (20, 21)
(for review, see Ref. 22). Therefore, we hypothesized that
the acute effect of light on melatonin, alertness, thermo-
regulation, and heart rate is blue-shifted, such that short
wavelength light at 460 nm induces a greater melatonin-
suppressing, alerting, hyperthermic, and tachycardic effect
than light at 550 nm.
First Published Online December 7, 2004
Abbreviations: CBT, Core body temperature; CP, constant posture;
DPG, distal-proximal skin temperature gradient; ERG, electroretino-
gram; SCN, suprachiasmatic nuclei.
JCEM is published monthly by The Endocrine Society (http://www., the foremost professional society serving the en-
docrine community.
0021-972X/05/$15.00/0 The Journal of Clinical Endocrinology & Metabolism 90(3):1311–1316
Printed in U.S.A. Copyright © 2005 by The Endocrine Society
doi: 10.1210/jc.2004-0957
on April 11, 2005 jcem.endojournals.orgDownloaded from
Subjects and Methods
Study participants
Ten male volunteers (age range, 21–29 yr; mean, 25.9 3.8 sd) were
studied. All study participants were nonsmokers, free from medical,
psychiatric, and sleep disorders as assessed by history, a physical ex-
amination, and questionnaires. An ophthalmological examination was
carried out before the study began and after completion of the study by
one of our coauthors (S.O.) to exclude volunteers with visual impair-
ments as well as to be certain that our light application was not harmful.
The volunteers were instructed to abstain from caffeine and alcohol for
1 wk before the study; their compliance was verified with urinary
toxicological analysis on the day of admission to the laboratory. They
were asked to keep a regular sleep-wake schedule (bedtimes and wa-
ketimes within 30 min of self-selected target time) during the week
before their admission to the laboratory. Adherence to this regular
schedule was verified with a wrist actigraph (Cambridge Neurotech-
nologies, Cambridge, UK) and daily sleep diaries. All volunteers gave
written informed consent. The protocol, screening questionnaires, and
consent form were approved by the Ethical Committee of Basel (Basel,
Switzerland) and were in agreement with the Declaration of Helsinki.
Study protocol
The study consisted of three arms, performed in a balanced order,
separated by a 1-wk intervening period (Fig. 1). There were no changes
in sleep quality or sleep-wake cycles during the intervening week. On
the basis of the habitual bedtimes of the volunteers, a constant posture
(CP) protocol started 10 h after usual waketime in the early evening (e.g.
1800 h) and ended the next day, 2 h after usual waketime (e.g. 1000 h).
Under CP conditions, the volunteers experienced a controlled, lying-
down episode of 1.5 h under 2 lux, followed by a 2-h dark adaptation
episode under complete darkness (zero lux). After that, light exposure
was initiated for the next 2 h. During this 2-h episode, the volunteers
received either monochromatic light at 460 nm, monochromatic light at
550 nm, or no light (zero lux). After this, the volunteers remained awake
for another 1.5-h episode under 2 lux (polychromatic white light), before
they were allowed to sleep for 7.75 h. One study participant developed
a mild cold during one of the study legs and was therefore excluded from
additional analysis.
Light exposure
Monochromatic light exposure (2 h) was scheduled at a circadian
phase at which polychromatic, white light exposure induces robust
phase delays (1, 2, 23) and alerting effects (24). The monochromatic light
was generated by a 300-W arc-ozone-free Xenon lamp (Thermo Oriel,
Spectra Physics, Stratford, CT), filtered by either 460 or 550 nm (Inter-
ference filter, 10 nm half-peak bandwidth, Spectra Physics, Stratford,
CT). Monochromatic light was transmitted via two glass-fiber bundles
(L.O.T. Oriel-Suisse, Romanel-sur Morges, Switzerland) through the
wall, into the soundproofed and temperature-controlled chronobiology
suite, onto the goggles that covered the volunteers’ eyes. The custom-
built goggles (K. Haug AG, Basel, Switzerland) consisted of two spheres
(27.5-mm inner radius) coated with white reflectance paint (two com-
ponents polyurethane-acryl antifading paint; Lachenmeier & Co. AG,
Basel, Switzerland). Each sphere was illuminated via three branches of
the main fiber-optic cable to provide constant uniform illumination.
Equal photon densities (2.8 10
/sec) for the 460- and
550-nm wavelength light were administered. This irradiance level (12.1
for 460 nm and 10.05
for 550 nm) was chosen ac
cording to recently reported results on monochromatic light on the
human circadian timing system (5). Irradiances were measured with a
laser power meter (Laser Check, Coherent, Auburn, CA) before the
beginning and at the end of each light exposure. During light exposure
as well as during the no-light condition, volunteers were asked to keep
their eyes open and to fix their gaze on the middle of the spheres. A
technician checked the latter by online monitoring the polysomno-
graphic recordings and also verifying that the subjects remained awake.
The volunteers’ pupils were not dilated to avoid possible repercussions
of the dilation agent per se on thermoregulation, heart rate, and alertness.
However, we tested the effects of the light stimulus on pupil constriction
by applying monocular light exposure (light via the goggle of the right
eye) and concomitantly measuring the pupil size on the left eye via an
infrared camera. The entire control protocol was conducted at the same
time of day (evening), with the same light intensity on six subjects.
Results from the control experiment revealed a significantly smaller
pupil size after the short wavelength light at 460 nm than after light at
550 nm in comparison to the dark condition [P 0.01; Duncan’s multiple
range test performed after a one-way ANOVA for repeated measures
with the factor light condition (P 0.02; dark, 460 and 550 nm)].
Assessment of subjective sleepiness
Subjective sleepiness was assessed every 30 min on the Karolinska
Sleepiness Scale (25), with a visual analog scale throughout scheduled
wakefulness. Because the participants wore goggles during the light
exposure and during the no-light condition, the Karolinska Sleepiness
Scale and the visual analog scale were read out loud by a technician and
transmitted via the interphone to the volunteers’ room.
CBT and eight surface skin temperatures from different body regions
were recorded continuously throughout the study, using a rectal probe
and skin thermocouples, with data stored in 20-sec epochs. Distal and
proximal skin temperatures as well as the distal-proximal skin temper-
ature gradient (DPG) were calculated according to the procedures de-
scribed in Ref. 26.
Heart rate
Standard electrocardiogram leads were placed on the lateral thorax
and on the sternum. The signal was recorded on the Vitaport-3 digital
system at 256 Hz. An off-line algorithm (System Hofstetter, SHS,
Allschwil, Switzerland) detected heart rate by the length of R-R intervals.
Salivary melatonin
Saliva was collected at 30-min intervals during scheduled wakeful-
ness. A direct double-antibody RIA was used for the melatonin assay,
validated by gas-chromatography-mass spectroscopy (Bu¨ hlmann Lab-
FIG. 1. Overview of the protocol design.
After 1.5 h under 2 lux, subjects were
dark adapted for 2 h, followed by an-
other2hindarkness or light exposure
at 460 nm or 550 nm (for details about
the light exposures, see Subjects and
Methods). Subsequently, subjects spent
1.5 h under 2 lux before they were al-
lowed to sleep for 8 h. The entire pro-
tocol was carried out under constant re-
cumbent posture conditions in bed.
Saliva samples were collected, and
sleepiness ratings were taken, both in
half-hourly intervals.
1312 J Clin Endocrinol Metab, March 2005, 90(3):1311–1316 Cajochen et al. Effects of Monochromatic Light on Humans
on April 11, 2005 jcem.endojournals.orgDownloaded from
oratories, Scho¨nenbuch, Switzerland) (27). The minimum detectable
dose of melatonin (analytical sensitivity) was determined to be 0.2 pg/
ml. The functional least-detectable dose using the less than 20% coef-
ficient of interassay variation criterion was less than 0.65 pg/ml, and
individual serum and saliva melatonin profiles showed excellent par-
allelism (r 0.977– 0.999; slopes 0.21–0.63) (27).
Statistical analysis of the time course was carried out for each variable
using two-way ANOVAs for repeated measures on factor light condition
and time interval with Huynh-Feldt’s statistics. P values were based on
corrected degrees of freedom, but the original degrees of freedom are
reported. The statistical package SAS (version 6.12, SAS Institute Inc.,
Cary, NC) was used. For post hoc comparisons, one-sided Duncan’s
multiple range tests were used. To correct for multiple comparisons, the
resulting P values were alpha-corrected according to the procedures
described in Ref. 28.
Melatonin suppression and subjective sleepiness
Monochromatic light exposure caused a wavelength-
dependent suppression of salivary melatonin (Fig. 1, top
panel), as indicated by a significant two-way interaction of the
factors light condition and time interval (F
3.6; P
0.001). Post hoc comparisons yielded a significant melatonin
suppression after light at 460 nm compared with no light and
to light at 550 nm 30 min after the start of light exposure,
which continued for the remainder of the light-exposure
episode (for post hoc comparisons, see Fig. 2). Salivary mel-
atonin levels during monochromatic light at 550 nm were
only slightly but significantly suppressed during the first
hour of light exposure (Fig. 2). Subjective sleepiness ratings
changed in parallel [interaction light condition time in-
terval (F
1.7; P 0.05)]. Post hoc comparisons yielded
a significant decrease in subjective sleepiness during the
460-nm light exposure compared with 550-nm light exposure
and no light, starting 30 min after lights on (Fig. 2, second
panel). There was no significant difference in sleepiness be-
tween the 550-nm light exposure and the no-light condition.
Thermoregulation and heart rate
Light exposure changed the time course of CBT [interac-
tion light condition time interval (F
2.9; P 0.02)
(Fig. 2, third panel)]. The evening decline of CBT was signif-
icantly attenuated by light at 460 nm starting about 1 h after
lights on (Fig. 2), remaining significantly higher throughout
the remainder of the 1.5-h interval before sleep. No differ-
ences were found between the condition with light at 550 nm
and the no-light condition. A similar pattern was found for
heart rate, as indexed by beats per min [interaction light
condition time interval (F
3.1; P 0.01) (Fig. 2,
bottom panel)]. Although the effect was short lasting, post hoc
comparisons revealed a significantly higher heart rate during
the 460- nm light condition starting 1.5 h after lights on
compared with 550 nm and the no-light condition and lasting
for the first 20 min of the after-light exposure episode.
Although repercussions of light at 460 and 550 nm were
clearly visible in the time course of both proximal and distal
skin temperatures, no significant interaction terms were
found (Fig. 3, top two panels). However, the derived measure
of the DPG that is used as an estimate of the degree of
vasodilation (29) yielded a significant interaction term (F
1.8; P 0.03) (Fig. 3, bottom panel). Post hoc comparisons
revealed a significant decrease in the DPG during both 460-
and 550-nm light exposures compared with the no-light
These results demonstrate that the alerting response to
light is wavelength dependent, such that short wavelength
light (460 nm) is more effective than longer wavelength light
(550 nm) in reducing sleepiness in the evening. Furthermore,
our controlled study provides evidence that the effects of
light on thermoregulation and heart rate are similarly wave-
length dependent.
Our data are in good agreement with recent findings that
the human circadian pacemaker is highly sensitive to short
wavelength light (13, 30), as indexed by action spectra for
human melatonin suppression and assessment of human
circadian phase resetting (5, 6). On the basis of these previous
studies, we expected a significantly more pronounced atten-
uation of the nocturnal melatonin increase after light at the
shorter wavelength (460 nm), a hypothesis that was clearly
verified. We have obtained very similar results as Brainard
et al. (13) who reported approximately 60% suppression of
melatonin after2hoflight at 460 nm and at 12.1
Therefore, melatonin levels in 460 nm did not increase during
the light exposure, whereas in the 550-nm condition, they
additionally increased very similarly as shown by Lockley et
al. (5). To our knowledge, this is the first report showing that
human alertness levels as well as thermophysiology are
highly sensitive to this short wavelength light. With the
exception of the proximal and distal skin temperatures, all
other variables (i.e. salivary melatonin, subjective sleepiness,
CBT, and heart rate) responded more strongly to 460- than
550-nm light. However, light at 550 nm was not inactive
because it induced a subtle, short-lasting but significant mel-
atonin suppression. What is interesting is that both wave-
lengths decreased the DPG to a similar extent. Why the
effects of light on the skin temperatures were not wavelength
dependent remains to be elucidated. Although our study was
conducted under very controlled laboratory conditions (i.e.
CP, room temperature, and food intake), skin temperatures
exhibit large inter- and intraindividual variance (31). There-
fore, it may be that this measure did not provide enough
power to differentiate between the two wavelengths. How-
ever, there are two possibilities: 1) the DPG may indeed be
a very sensitive measure for subtle illuminance changes;
and/or 2) that it immediately reflects a minute-to-minute
level of cognitive arousal independent of the sensory mo-
dality of the signal. The DPG increase during the dark-ad-
aptation episode, which was unusual at this circadian phase
as previously measured under 8 lux of ambient-light levels
in a constant routine protocol (26, 31), can be interpreted in
both ways—a diminution to zero lux and a diminution of
sensory input, leading to relaxation. Interestingly, this in-
creased DPG was also paralleled by an unusually early in-
crease in subjective sleepiness and an unusually early
evening melatonin onset. Furthermore, evidence for the re-
sponsiveness of DPG comes from the decrease in this mea-
Cajochen et al. Effects of Monochromatic Light on Humans J Clin Endocrinol Metab, March 2005, 90(3):1311–1316 1313
on April 11, 2005 jcem.endojournals.orgDownloaded from
sure seen after the 4-h dark episode in the no-light condition,
when the volunteers were under 2 lux (Fig. 2, bottom panel).
The DPG reflected very sensitively whether the lights were
on or off. Besides the DPG, the increase in heart rate during
the 460-nm light exposure may well be another indication
that the autonomous nervous system acutely responds to
light with an increase in sympathetic tone—a response that
seems particularly susceptible to short wavelength light.
Many studies have shown that exposure to white poly-
chromatic light during the evening or nighttime increases
alertness (8, 10, 24, 32–35) and CBT (8 –10, 19, 34, 35). There
is also evidence that light may acutely affect heart rate (12).
Previously, we have found a dose-response relationship be-
tween the magnitude of the alerting response to light and its
irradiance, such that half of the maximum alerting response
to bright light at 9100 lux was obtained with room light of
approximately 100 lux (10). However, the duration of light
exposure in this study was rather long (6.5 h), and the dose
relationship was only present in the latter part of the light
exposure (10). In contrast, the present study revealed that
light at 460 nm of very low intensity (5 photopic lux or 116.6
scotopic lux) was already effective after about 40 min of
exposure, which corroborates high specificity for light in the
short wavelength range, and shows that the nonimage-form-
ing visual system does not simply count or average photons,
but rather depends on exposure to particular wavelengths of
energy. In fact, during the 460-nm light condition, volunteers
in our experiment probably received fewer photons, because
their pupil size was smaller than in the 550-nm light condi-
tion (based on our data from the control experiment; see
Subjects and Methods). Therefore, the melatonin suppression
and the alerting response was underestimated from what
they would have been had the subjects’ pupils been artifi-
cially dilated. Despite fewer photons, 460-nm light was more
efficient on the above-described variables than 550 nm,
which corroborates its effectiveness also in the absence of
pupil dilators.
Our results demonstrate that besides regulating human
circadian rhythms, the nonclassical photoreceptors are also
involved in the regulation of the acute effects of light, which
has until now only been shown for ERG responses (15).
Although it is possible that the central circadian pacemaker
located in the suprachiasmatic nuclei (SCN) is involved in
both phase shifting and acute responses to light, it is not clear
that these share a common mechanism. It has been proposed
that acute changes in CBT may be primary events mediating
circadian phase-shift responses (36). There is, however, con-
trary evidence; previous administration of melatonin can
completely reverse the acute CBT elevation induced by
nighttime bright light without greatly altering light-induced
phase shifts (23, 37, 38). Whether the delayed decline in CBT
represents only an acute effect of light or whether it is the
initiation of a circadian phase delay would have required a
longer study. We may interpret the sustained evening max-
imum in CBT only after 460-nm light exposure as evidence
FIG. 2. Effects of a 2-h light exposure at 460 nm (F), 550 nm (Œ), and
no light (f) in the evening under CP conditions (i.e. supine in bed) on
salivary melatonin levels, subjective sleepiness as rated on the Karo-
linska Sleepiness Scale, CBT, and heart rate [mean values (n 9) and
SEM]. For clarity, the SEM values for the 550-nm light condition were
not plotted. Significant post hoc comparisons (P 0.05; Duncan’s
multiple range test corrected for multiple comparisons) are indicated
by the following symbols: *, 460-nm light vs. no light; E, 550-nm light
vs. no light; and ƒ, 460-nm light vs. 550-nm light. The prelight ex-
posure episode represents a 2-h dark adaptation episode under zero
lux, whereas the light level in the 1.5-h post-light exposure was 2 lux.
1314 J Clin Endocrinol Metab, March 2005, 90(3):1311–1316 Cajochen et al. Effects of Monochromatic Light on Humans
on April 11, 2005 jcem.endojournals.orgDownloaded from
for the latter explanation of a selective circadian phase delay
The mechanisms by which light induces acute physiolog-
ical responses and shifts circadian phase seem to diverge at
some level. Besides the SCN, candidate retinal projections for
the acute effects of light are the pretectal area (39), the in-
tergeniculate leaflet (40), and the ventromedial preoptic area
(41). It is clear that for light to rapidly suppress melatonin
secretion, retinal projections to the SCN are necessary. There-
fore, it has been suggested that the mechanism by which light
exposure may reduce sleepiness is by its suppression of
melatonin synthesis (8, 10, 24). However, there is recent
evidence that these effects appear to be mediated by mech-
anisms that are separate from melatonin suppression (42). It
is more likely to be the ventromedial preoptic area that in-
nervates all of the major nuclei of the ascending monoam-
inergic and, in particular, the histaminergic system and plays
a key role in wakefulness and electroencephalogram arousal
(43, 44).
All of the above-mentioned brain regions receive projec-
tions from intrinsically photosensitive retinal ganglion cells
for which the photopigment melanopsin has recently been
identified (45). Melanopsin is present in the human retina
(46), and melanopsin-containing retinal ganglion cells are
directly photosensitive at a
of 484 nm in the rat (47).
Melanopsin expression defines a subset of retinal ganglion
cells that play a broad role in the regulation of nonvisual
photoreception, providing projections that contribute to cir-
cadian entrainment, negative masking, the regulation of
sleep-wake states, and the pupillary reflex (for citations, see
Ref. 45). Our results add to these functions, suggesting that
changes in human alertness and aspects of autonomic control
(thermoregulation and heart rate) are influenced, if not reg-
ulated, by the nonvisual system via the photopigment mela-
nopsin. A definite answer to this would be to investigate
people lacking the classical receptors, or having a melanop-
sin deficiency, to the see repercussions this may have on
light-induced changes in alertness, thermoregulation, and
heart rate. At least in blind mice, melanopsin is required for
nonimage-forming photic responses. However, there is still a
debate (see Ref. 48) as to whether the photopigment melanopsin
is the only candidate for nonvisual ocular photoreception.
It will be interesting to test whether short wavelength light
is more efficient in the workplace environment, where high
alertness levels are required, and in the treatment of seasonal
affective disorder; although in all putative applications, the
blue-light damage potential needs to be evaluated (49). An
important physiological question is whether the decline in
alertness and thermoregulation with age is a consequence of
age-related changes in lens transmittance at the short-wave
range (50).
We thank Dr. Corinna Schnitzler for medical screenings; Claudia
Renz, Giovanni Balestrieri, and Marie-France Dattler for their help in
data acquisition; and the volunteers for participating.
Received May 27, 2004. Accepted November 23, 2004.
Address all correspondence and requests for reprints to: Christian
Cajochen, Ph.D., Centre for Chronobiology, Psychiatric University
Clinic, Wilhelm Kleinstr. 27, CH-4025 Basel, Switzerland. E-mail:
This research was supported by the Velux Foundation (Glarus, Swit-
zerland) and in part by The Swiss National Foundation Grants START
3130-054991.98 and 3100-055385.98 (to C.C.).
1. Khalsa SB, Jewett ME, Cajochen C, Czeisler CA 2003 A phase response curve
to single bright light pulses in human subjects. J Physiol 549:945–952
FIG. 3. Effects of a 2-h light exposure at 460 nm (F), 550 nm (Œ), and
no light (f) in the evening under CP conditions (i.e. supine in bed) on
proximal and distal skin temperatures as well as the DPG [mean
values (n 9) and SEM]. For clarity, the SEM values for the 550-nm
light condition were not plotted. Significant post hoc comparisons (P
0.05; Duncan’s multiple range test corrected for multiple compari-
sons) are indicated by the following symbols: *, 460-nm light vs. no
light; E, 550-nm light vs. no light; and ƒ, 460-nm light vs. 550-nm
light. The prelight exposure episode represents a 2-h dark adaptation
episode under zero lux, whereas the light level in the 1.5-h post-light
exposure was 2 lux.
Cajochen et al. Effects of Monochromatic Light on Humans J Clin Endocrinol Metab, March 2005, 90(3):1311–1316 1315
on April 11, 2005 jcem.endojournals.orgDownloaded from
2. Minors DS, Waterhouse JM, Wirz-Justice A 1991 A human phase-response
curve to light. Neurosci Lett 133:36 40
3. Boivin DB, Duffy JF, Kronauer RE, Czeisler CA 1996 Dose-response rela-
tionships for resetting of human circadian clock by light. Nature 379:540 –542
4. Zeitzer JM, Dijk DJ, Kronauer RE, Brown EN, Czeisler CA 2000 Sensitivity
of the human circadian pacemaker to nocturnal light: melatonin phase reset-
ting and suppression. J Physiol 526:695–702
5. Lockley SW, Brainard GC, Czeisler CA 2003 High sensitivity of the human
circadian melatonin rhythm to resetting by short wavelength light. J Clin
Endocrinol Metab 88:4502– 4505
6. Warman VL, Dijk DJ, Warman GR, Arendt J, Skene DJ 2003 Phase advancing
human circadian rhythms with short wavelength light. Neurosci Lett 342:
7. Brainard G, Rollag MD, Hanifin JP 1997 Photic regulation of melatonin in
humans: ocular and neural signal transduction. J Biol Rhythms 12:575–578
8. Badia P, Myers B, Boecker M, Culpepper J 1991 Bright light effects on body
temperature, alertness, EEG and behavior. Physiol Behav 50:583–588
9. Cajochen C, Dijk DJ, Borbe´ly AA 1992 Dynamics of EEG slow-wave activity
and core body temperature in human sleep after exposure to bright light. Sleep
10. Cajochen C, Zeitzer JM, Czeisler CA, Dijk DJ 2000 Dose-response relation-
ship for light intensity and ocular and electroencephalographic correlates of
human-alertness. Behav Brain Res 115:75–83
11. Dijk DJ, Cajochen C, Borbe´ly AA 1991 Effect of a single 3-hour exposure to
bright light on core body temperature and sleep in humans. Neurosci Lett
121:59 62
12. Scheer FA, Van Doornen LJ, Buijs RM 2004 Light and diurnal cycle affect
autonomic cardiac balance in human; possible role for the biological clock.
Auton Neurosci 110:44 48
13. Brainard GC, Hanifin JP, Greeson JM, Byrne B, Glickman G, Gerner E,
Rollag MD 2001 Action spectrum for melatonin regulation in humans: evi-
dence for a novel circadian photoreceptor. J Neurosci 21:6405–6412
14. Brainard G, Hanifin JP, Rollag MD, Greeson J, Byrne B, Glickman G, Gerner
E, Sanford B 2001 Human melatonin regulation is not mediated by the three
cone photopic visual system. J Clin Endocrinol Metab 86:433–436
15. Hankins MW, Lucas RJ 2002 The primary visual pathway in humans is
regulated according to long-term light exposure through the action of a non-
classical photopigment. Curr Biol 12:191–198
16. Czeisler CA, Shanahan TL, Klerman EB, Martens H, Brotman DJ, Emens JS,
Klein T, Rizzo JF 1995 Suppression of melatonin secretion in some blind
patients by exposure to bright light. N Engl J Med 332:6 –11
17. Lockley SW, Skene DJ, Thapan K, English J, Ribeiro D, Haimov I, Hampton
S, Middleton B, Von Schantz M, Arendt J 1998 Extraocular light exposure
does not suppress plasma melatonin in humans. J Clin Endocrinol Metab
18. He´bert M, Martin SK, Eastman CI 1999 Nocturnal melatonin secretion is not
suppressed by light exposure behind the knee in humans. Neurosci Lett
19. Ru¨ ger M, Gordijn MC, Beersma DG, de Vries B, Daan S 2003 Acute and
phase-shifting effects of ocular and extraocular light in human circadian phys-
iology. J Biol Rhythms 18:409 419
20. Freedman MS, Lucas RJ, Soni B, von Schantz M, Munoz M, David-Gray Z,
Foster R 1999 Regulation of mammalian circadian behavior by non-rod, non-
cone, ocular photoreceptors. Science 284:502–504
21. Lucas RJ, Freedman MS, Munoz M, Garcia-Fernandez JM, Foster RG 1999
Regulation of the mammalian pineal by non-rod, non-cone, ocular photore-
ceptors. Science 284:505–507
22. Foster RG 2004 Seeing the light. . . in a new way. J Neuroendocrinol 16:179 –180
23. Kra¨uchi K, Cajochen C, Danilenko KV, Wirz-Justice A 1997 The hypothermic
effect of late evening melatonin does not block the phase delay induced by
concurrent light in human subjects. Neurosci Lett 232:57– 61
24. Cajochen C, Kra¨uchi K, Danilenko KV, Wirz-Justice A 1998 Evening ad-
ministration of melatonin and bright light: interactions on the EEG during
sleep and wakefulness. J Sleep Res 7:145–157
25. Gillberg M, Kecklund G, Åkerstedt T 1994 Relations between performance
and subjective ratings of sleepiness during a night awake. Sleep 17:236 –241
26. Kra¨uchi K, Cajochen C, Mo¨ri D, Graw P, Wirz-Justice A 1997 Early evening
melatonin and S-20098 advance circadian phase and nocturnal regulation of
core body temperature. Am J Physiol 272(4 Pt 2):R1178–R1188
27. Weber JM, Schwander JC, Unger I, Meier D 1997 A direct ultrasensitive RIA
for the determination of melatonin in human saliva: comparison with serum
levels. J Sleep Res 26:757
28. Curran-Everett D 2000 Multiple comparisons: philosophies and illustrations.
Am J Physiol Regul Integr Comp Physiol 279:R1–R8
29. Kra¨uchi K, Cajochen C, Werth E, Wirz-Justice A 2000 Functional link between
distal vasodilation and sleep-onset latency? Am J Physiol Regul Integr Comp
Physiol 278:R741–R748
30. Thapan K, Arendt J, Skene DJ 2001 An action spectrum for melatonin sup-
pression: evidence for a novel non-rod, non-cone photoreceptor system in
humans. J Physiol 535:261–267
31. Kra¨uchi K, Wirz-Justice A 1994 Circadian rhythm of heat production, heart
rate, and skin and core temperature under unmasking conditions in men. Am J
Physiol Regul Integr Comp Physiol 267:R819 –R829
32. Lavoie S, Paquet J, Selmaoui B, Rufiange M, Dumont M 2003 Vigilance levels
during and after bright light exposure in the first half of the night. Chronobiol
Int 20:1019 –1038
33. French J 1990 Effects of bright light illuminance of body temperature in human
performance. Ann Rev Chronopharmacol 7:37–40
34. Myers BL, Badia P 1993 Immediate effects of different light intensities on body
temperature and alertness. Physiol Behav 54:199 –202
35. Wright Jr KP, Myers BL, Plenzler SC, Drake CL, Badia P 2000 Acute effects
of bright light and caffeine on nighttime melatonin and temperature levels in
women taking and not taking oral contraceptives. Brain Res 873:310 –317
36. Deacon S, Arendt J 1995 Melatonin-induced temperature suppression and its
acute phase-shifting effects correlate in a dose-dependent manner in humans.
Brain Res 688:77– 85
37. Cagnacci A, Soldani R, Yen SS 1997 Contemporaneous melatonin adminis-
tration modifies the circadian response to nocturnal bright light stimuli. Am J
Physiol Regul Integr Comp Physiol 41:R482–R486
38. Ha¨to¨nen T, Alila A, Laakso ML 1996 Exogenous melatonin fails to counteract
the light-induced phase delay of human melatonin rhythm. Brain Res 710:
39. Miller AM, Obermeyer WH, Behan M, Benca RM 1998 The superior col-
liculus-pretectum mediates the direct effects of light on sleep. Proc Natl Acad
Sci USA 95:8957– 8962
40. Harrington ME 1997 The ventral lateral geniculate nucleus and the inter-
geniculate leaflet: interrelated structure in the visual and circadian systems.
Neurosci Biobehav Rev 21:705–727
41. Lu J, Shiromani P, Saper CB 1999 Retinal input to the sleep-active ventrolateral
preoptic nucleus in the rat. Neurosci 93:209 –214
42. Phipps-Nelson J, Redman JR, Dijk DJ, Rajaratnam SM 2003 Daytime expo-
sure to bright light, as compared to dim light, decreases sleepiness and im-
proves psychomotor vigilance performance. Sleep 26:695–700
43. Aston-Jones G, Rajkowski J, Cohen J 1999 Role of locus coeruleus in attention
and behavioral flexibility. Biol Psychiatry 46:1309 –1320
44. Lin JS, Hou Y, Sakai K, Jouvet M 1996 Histaminergic descending inputs to
the mesopontine tegmentum and their role in the control of cortical activation
and wakefulness in the cat. J Neurosci 16:1523–1537
45. Gooley JJ, Lu J, Fischer D, Saper CB 2003 A broad role for melanopsin in
nonvisual photoreception. J Neurosci 23:7093–7106
46. Provencio I, Rodriguez IR, Jiang G, Hayes WP, Moreira EF, Rollag MD 2000
A novel human opsin in the inner retina. J Neurosci 20:600 605
47. Berson DM, Dunn FA, Takao M 2002 Phototransduction by retinal ganglion
cells that set the circadian clock. Science 295:1070 –1073
48. Foster RG, Hankins M, Lucas RJ, Jenkins A, Mun˜ oz M, Thompson S, Apple-
ford JM, Bellingham J 2003 Non-rod, non-cone photoreception in rodents and
teleost fish. In: Novartis Foundation Symposium, ed. Molecular clocks and
light signalling. Chichester, UK: Wiley; 3–30
49. Reme´ CE, Wenzel A, Grimm C, Iseli HP 2003 Mechanisms of blue light-
induced retinal degeneration and the potential relevance for age-related mac-
ular degeneration. Chronobiol Int 20:1186–1187
50. Charman WN 2003 Age, lens transmittance, and the possible effects of light
on melatonin suppression. Ophthalmic Physiol Opt 23:181–187
JCEM is published monthly by The Endocrine Society (, the foremost professional society serving the
endocrine community.
1316 J Clin Endocrinol Metab, March 2005, 90(3):1311–1316 Cajochen et al. Effects of Monochromatic Light on Humans
on April 11, 2005 jcem.endojournals.orgDownloaded from
... Moreover, a smaller decrease in CBT (0.2°C) was observed with shorter wavelengths than with longer wavelengths [59]. Among 15, two studies documented a decreased melatonin concentration with increased CBT [60,61]. Two studies reported that longer wavelengths could not reduce CBT in the evening [60,62]. ...
... Among 15, two studies documented a decreased melatonin concentration with increased CBT [60,61]. Two studies reported that longer wavelengths could not reduce CBT in the evening [60,62]. It advocates the intercedence of pRGCs (photosensitive retinal ganglion cells) that impedes the light induced-natural CBT decline during the night, similar to the CR-phase shifting, where the impact is especially vulnerable to the shorter wavelengths [63]. ...
... Regarding DPG (distal to proximal SKT gradient), it was discovered that monochromatic light at both 460 and 550 nm prevents the nighttime temperature decline by 0.7°C. Similar effects on DPG were observed following the bright light exposure in the evening and throughout the night [60,66]. Melatonin concentration appeared to be reduced at night post-bright light exposure. ...
Full-text available
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.
... Non-visual effects of light vary with the time of day, light duration, spectral property, and intensity (DIS, 026/E:2018). Many studies have observed the effectiveness of short-wavelength light in enhancing alertness (Cajochen et al., 2005;Vandewalle et al., 2007;Gabel et al., 2013), while different review studies did not find a definite pattern for its effect concerning the timing, duration, and intensity of its exposure. A large body of evidence indicated that acute short-wavelength light with low irradiance improves alertness at night (Cajochen et al., 2005;Xu and Lang, 2018;Lockley et al., 2006;Sunde et al.,), whereas neither alertness (Xu and Lang, 2018) nor performance (Segal et al., 2016) improved significantly during the daytime under short-wavelength (Xu and Lang, 2018;Segal et al., 2016), or middle-wavelength light (Segal et al., 2016). ...
... Many studies have observed the effectiveness of short-wavelength light in enhancing alertness (Cajochen et al., 2005;Vandewalle et al., 2007;Gabel et al., 2013), while different review studies did not find a definite pattern for its effect concerning the timing, duration, and intensity of its exposure. A large body of evidence indicated that acute short-wavelength light with low irradiance improves alertness at night (Cajochen et al., 2005;Xu and Lang, 2018;Lockley et al., 2006;Sunde et al.,), whereas neither alertness (Xu and Lang, 2018) nor performance (Segal et al., 2016) improved significantly during the daytime under short-wavelength (Xu and Lang, 2018;Segal et al., 2016), or middle-wavelength light (Segal et al., 2016). On the other hand, several studies suggest that filtering out shortwavelength from polychromatic white light did not have a declining effect on subjective alertness, and even increased alertness in some instances (Souman et al., 2018;Sasseville et al., 2015). ...
... 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). Three of these studies (Lockley et al., 2006;Papamichael et al., 2012;Rahman et al., 2014) employed pupil dilators. ...
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.
... With the discovery of intrinsically photosensitive retinal ganglion cells (ipRGCs) containing melanopsin pigments [16][17][18] , two main lines of research on non-visual ipRGC -based effects have emerged. On the one hand, in lighting and sleep research, experiments have been conducted in laboratories or real-world settings (e.g., nursing homes, hospitals, schools, offices) to investigate the relationship between light intensity, spectrum, time, duration of light treatment, and non-visual outcomes (e.g., attention, sleep quality, alertness) using conventional photometric and colorimetric parameters such as vertical illuminance in lx, luminance in cd/m 2 , color temperature, and spectral irradiance distributions [16][17][18][19][20][21][22][23][24] . ...
Full-text available
From the beginning of the [Formula: see text] century until today, the demand for lighting systems includes not only visual parameters (brightness, contrast perception, color quality), but also non-visual parameters. It is necessary to define the new non-visual parameters for the realization of the new concept of Human Centric Lighting (HCL) or Integrative Lighting. As a contribution to this approach, many international research groups have tried to quantify the non-visual parameters such as Circadian Stimulus by Rea et. al. in USA ([Formula: see text], [Formula: see text]), Melanopic Equivalent Daylight ([Formula: see text]) illuminance, mEDI of the CIE S 026/E:2018 or the latest formula by Giménez et al., for the nocturnal melatonin suppression. Therefore, it is necessary to analyze the correlation between these non-visual metrics and brightness metrics such as the equivalent luminance of Fotios et al., or the latest brightness model of TU Darmstadt so that scientists, lighting engineers and lighting system users can correctly apply them in their work. In this context, this paper attempts to investigate and analyze these correlations between the three metric groups based on the database of 884 light sources of different light source technologies and daylight spectra. The obtained results show that the latest Circadian Stimulus model of Rea et. al. [Formula: see text] with the improvement of Circadian Light [Formula: see text] ([Formula: see text]) has solved the disadvantage of [Formula: see text], especially for the interrupted point between warm and cold white (about [Formula: see text]) or the junction between negative and positive signal of the opponent channel ([Formula: see text]). Moreover, these three metrics of the three research groups contain a high correlation coefficient, so that one metric can be transformed by linear functions to the other two parameters.
... It starts to rise before two hours of bedtime (21), while the peak of melatonin secretion happens at midnight (69). Researchers found that the monochromatic blue light with a wavelength around 460 nm could better suppress melatonin production than any other wavelength (3,19,57,58,70,72,73,(78)(79)(80) ...
The effects of light on the human body can be generally classified into visual effects (IF) and non-visual effects (NIF). The IF is responsible for vision, while the NIF is responsible for many physiological, psychological, and behavioral rhythms. Daylight has been usually preferred over artificial light to meet the IF and NIF needs. The variable amount, spectral composition, timing, and duration of daylight throughout the day make it more potent in regulating circadian rhythms. Researchers reported that children and adolescents are more sensitive to lighting (both daylight and artificial light) than adults. This calls for special consideration for classrooms design as children spend around 30% of their life in school. Decisions made at the early stages of classroom design significantly impact the visual and non-visual benefits obtained from light, as the built environment can alter the light characteristics inside spaces. These decisions also influence the energy performance of classrooms and schools. This study uses multi-objective optimization to find the optimal classroom design in different climate zones in the U.S. based on visual, non-visual, and energy performance criteria. The visual benefits of daylight are expressed as the daylighting conditions at the horizontal desk-plane, while the non-visual benefits are expressed as the daylighting conditions at the vertical eye-level. Two classrooms-corridors typologies are explored in this dissertation: classrooms connected to single-loaded corridors and classrooms connected to double-loaded corridors. The optimal classrooms design and the design parameters’ level of importance have been identified for both typologies. The Department of Energy (DOE) primary school reference building has been used as a reference model as it represents 70% of U.S. schools. Results have shown that there are similar optimal solutions in terms of each objective across closely located climate zones for the single-loaded corridor typology. The daylighting and energy performance of these classrooms is mainly influenced by the window orientation and window to wall ratio (WWR). The classroom design with the best overall performance in all objectives has rectangular plan and a northeast oriented window. All optimal solutions have 3-5% higher window-to-wall ratio (WWR), higher window head height, and 25-35% less energy use than the reference classroom. Finding the optimal design of classrooms connected to double-loaded corridors is more complex. The oppositely oriented classrooms have competing objectives to improve their daylighting performance. The results indicate that the 3:2 width-to-depth plan shape in most optimal solutions performs better than the 5:4 width-to-depth plan of the reference model. Accordingly, wider windows and higher head height in the optimal design were able to allow more daylighting to the depth of the oppositely oriented classrooms while reducing the energy use. The results show that optimal classrooms’ design connected to double-loaded corridors, including window dimensions, orientation, and WWR vary by the climate zone. Although WWR is the most important design parameter on horizontal desk-plane and vertical eye-level for most cases, other parameters can be at least equally important especially for the vertical eye-level daylighting across different climate zones. The results of this dissertation can give guidance to architects, designers, and decision makers on classrooms design across studied climate zones.
... Previous studies have shown that the effect of a lighting source on the circadian system depends on several factors, particularly the amount of light and SPD (11,12). Depending on these variables, several prediction models have been developed to detect the non-visual effects of light on humans and to simplify the measurements of these effects. ...
Conference Paper
Dynamic LED lighting systems aim to bring the dynamic character of daylight to people's living spaces and to improve the mood, alertness and work performance. The amount and the colour temperature of light correspond to generate such an impact. Thus, the objective of this study is to explore office users’ preferences on dynamic LED lighting systems and daylight together and to analyse changes observed in their arousal, mood and task performance. Objective and subjective measurements were evaluated using statistical analysis. Although no significant difference was found in the mood, attention and executive functions of the participants under different lighting conditions, it was revealed that they preferred to work in brighter and warmer light. Higher illuminance increased arousal, while lower illuminance supported short-term memory.
... The lack of blue light as a result of wearing glasses that block wavelengths less than 530 nm does not suppress melatonin at night as with white light at the same illuminance (800 lx) [44]. The direct activating effects of nighttime light exposure were sensitive to short-wavelength light [45]. Exposure to light at 6500K resulted in greater melatonin suppression, along with improved subjective alertness, visual comfort and well-being in a study. ...
Conference Paper
Human centric lighting is an umbrella concept which covers human health and well-being in general. As the conventional lighting techniques are based on horizontal workplane illuminance, it drives from the vertical eye level illuminance and its spectral distribution triggering the nonvisual effects on humans. That is named as melanopic illuminance consequently. Its metrics have taken their place in lighting design literature and applications, with emergence of related standards subsequently. This literature overview contributes about the understanding the meaning human centric lighting due to transition from visual to non-visual effects of light, and how they direct recent research through light’s impacts on human performance, emotions health and well-being, and relations to energy saving even. The shift from the concept of human centric lighting to circadian lighting design is obvious in very current studies.
... However, no consensus has been reached on the characteristics and rules of lighting's non-visual effects on individuals. Some representative research conclusions include: blue light rich in short-wavelength characteristics (Cajochen et al., 2005;Chellappa et al., 2011;Mills et al., 2007) or high illumination (Cajochen et al., 2000;Figueiro et al., 2016;Smolders et al., 2012) lighting environment has an inhibitory effect on melatonin, which is conducive to reducing sleepiness and improving human alertness (Viola et al., 2008). Human mood tends to be more positive in the presence of high color temperature or rich blue light (Figueiro et al., 2016;Iskra-Golec et al., 2012). ...
Full-text available
Good nighttime road lighting is critical for driving safety. To improve the quality of nighttime road lighting, this study used the triangulation method by fusing "EEG evaluation + subjective evaluation + behavioral evaluation" to qualitatively and quantitatively investigate the response characteristics of different correlated color temperature (CCT) (3500K, 4500K, 5500K, 6500K) on drivers' non-visual indicators (mood, alertness, fatigue and reaction time) under specific driving conditions (monotonous driving; waiting for red light and traffic jam; car-following task). The results showed that the CCT and Task interaction effect is mainly related to individual alertness and reaction time. Individual subjective emotional experience, subjective visual comfort and psychological security are more responsive to changes in CCT than individual mental fatigue and visual fatigue. The subjective and objective evaluation results demonstrated that the EEG evaluation indices used in this study could objectively reflect the response characteristics of various non-visual indicators. The findings also revealed that moderate CCT (4500K) appears to be the most beneficial to drivers in maintaining an ideal state of mind and body during nighttime driving, which is manifested as: good mood experience; it helps drivers maintain a relatively stable level of alterness and to respond quickly to external stimuli; both mental and visual fatigue were relatively low. This study extends nighttime road lighting design research from the perspective of non-visual effects by using comprehensive neuroergonomic evaluation methods, and it provides a theoretical and empirical basis for the future development of a humanized urban road lighting design evaluation system.
Full-text available
Cardiovascular diseases (CVD) are among the leading causes of death worldwide. Many lines of evidence suggest that the disturbances in circadian rhythm are responsible for the development of CVDs; however, circadian misalignment is not yet a treatable trait in clinical practice. The circadian rhythm is controlled by the central clock located in the suprachiasmatic nucleus and clock genes (molecular clock) located in all cells. Dyslipidaemia and vascular inflammation are two hallmarks of atherosclerosis and numerous experimental studies conclude that they are under direct influence by both central and molecular clocks. This review will summarise the results of experimental studies on lipid metabolism, vascular inflammation and circadian rhythm, and translate them into the pathophysiology of atherosclerosis and cardiovascular disease. We discuss the effect of time-respected administration of medications in cardiovascular medicine. We review the evidence on the effect of bright light and melatonin on cardiovascular health, lipid metabolism and vascular inflammation. Finally, we suggest an agenda for future research and recommend on clinical practice.
The discovery of violet-excitable blue-emitting phosphor is a significant breakthrough for the development of phosphor-converted full-spectrum white light-emitting diodes (WLEDs). However, the application of most known violet-excitable blue-emitting phosphors is limited by their low external quantum efficiency (EQE). In this work, we reported on how the EQE values of Eu2+-doped Ba(K)-β-Al2O3 blue-emitting phosphor can be significantly improved through lattice site engineering. By partially substituting K+ for Ba2+, the Eu2+-occupied crystallographic site changes and the coordination polyhedron of Eu2+ shrinks, leading to the increase of crystal field splitting. Consequently, the excitation spectrum exhibits a continuous red shift to match the violet excitation, which enhances the PL intensity of solid solution phosphor (Ba0.4K1.6)0.84Al22O35-α:0.32Eu2+ ((B0.4K1.6)0.84AO:Eu) by 1.42 times compared to that of the end-member Ba1.68Al22O35-α:0.32Eu2+ (B1.68AO:Eu) phosphor. Correspondingly, under the 400 nm violet light excitation, the EQE of optimal blue-emitting (B0.4K1.6)0.84AO:Eu phosphor is up to 53%. Additionally, the phosphor also shows excellent resistance to luminescence thermal quenching (95% at 150 °C). Finally, the WLED fabricated based on (B0.4K1.6)0.84AO:Eu and commercial green and red phosphors exhibited an ultra-high color rending index with Ra = 95.5 and R1-R15 >90. This work offers guidance for tuning the spectral properties of phosphors through lattice site engineering.
Since the use of light and electronic devices is inevitable, the use of blue light filters (in various light sources, electronic devices or optical devices including intraocular lenses) has been shown to improve sleep quality, especially in later hours of the day and during night time. In this study, we examine the effect of the blue light on sleep and wakefulness rhythms and positive and negative emotions. This randomized clinical trial was conducted with 80 AJA University of Medical Sciences employees who use computers at least 2 h a day. All subjects were employees of the discharge unit of Imam Reza Hospital, which is located next to AJA University. The subjects were divided into two groups of 40 people, blue light filter software intervention and sham treatment. Pittsburgh Sleep Quality Index (PSQI), Positive and Negative Affect Schedule (PANAS), Visual Function Questionnaire (VFQ), Epworth Sleepiness Scale (ESS) and salivary melatonin and cortisol levels were assessed for both groups before and 3 months after the intervention. Data analysis was performed using IBM SPSS statistics for windows, version 21.0 (Armonk, NY: IBM Corporation). P value ≤ 0.05 was considered as statistically significant. The results showed that the Pittsburgh sleep scale after the intervention was significantly lower in the intervention group than in the control group. After the intervention, the VFQ was significantly lower in the intervention group than in the control group (P = 0.018). There was no significant difference in the Epworth Sleepiness Scale (ESS) between the two study groups after the intervention (P = 0.370). There was no significant difference in Positive and Negative Affect Schedule (PANAS) in the two study groups after the intervention (P = 0.140). After the intervention, cortisol levels were significantly higher in the intervention group than in the control group (P = 0.006). Also, the amount of cortisol increased significantly in the intervention group (P = 0.028). The amount of melatonin decreased significantly in the intervention group (P = 0.034). The sleep quality score after the intervention was significantly lower in the intervention group than in the control group. This indicates better sleep quality in the intervention group. The results also show that the level of visual fatigue in the intervention group decreased significantly. However, no significant change was detected regarding positive and negative emotions. After the intervention, cortisol levels were significantly higher in the intervention group than the control group. In addition, cortisol levels increased significantly and melatonin levels decreased significantly in the intervention group during the course of study.
Full-text available
In seven subjects sleep was recorded after a single 3-hour (2100-0000 hours) exposure to either bright light (BL, approx. 2,500 lux) or dim light (DL, approx. 6 lux) in a crossover design. The latency to sleep onset was increased after BL. Whereas rectal temperature before onset and during the first 4 hours of sleep was higher after BL than after DL, the time course of electroencephalographic (EEG) slow-wave activity (SWA, EEG power density in the range of 0.75-4.5 Hz) in nonrapid eye movement sleep (NREMS) differed only slightly between the conditions. After BL, SWA tended to be lower than after DL in the first NREMS-REMS cycle and was higher in the fourth cycle at the time when the rectal temperature did not differ. The differences in SWA may have been due to a minor sleep-disturbing aftereffect of BL, which was followed by a rebound. The data are not in support of a close relationship between SWA and core body temperature.
Full-text available
Using 'classical' experimental protocols, a human phase-response curve (PRC) to a single 3-h bright light pulse has been established. When the light pulse was centred slightly before the time of body temperature minimum, the circadian system delayed, whilst a pulse slightly after the minimum advanced it. Maximum phase shifts were about 2 h. When light pulses over 3 successive cycles were used, larger shifts (4-7 h) were produced. It is concluded that the human PRC does not differ in principle from that found in other species, except with respect to the light intensity required.
The present study validated the nine-point Karolinska Sleepiness Scale (KSS) and the new Accumulated Time with Sleepiness (ATS) scale against performance of laboratory tasks. The ATS scale was designed as a method for integrating subjective sleepiness over longer time periods. The subjects were asked if certain symptoms of sleepiness had occurred and, if so, for how long. Six subjects participated twice. Each time they were kept awake during the night (except for a short nap occurring during one of the nights in a counterbalanced order) and were tested at 2200, 0200, 0400 and 0600 hours. The tests included a 10-minute rest period, a 28-minute visual vigilance task and an 11 -minute single reaction time task. KSS and visual analogue scale (VAS) ratings were given before each test, and ATS ratings were given after. Performance deteriorated clearly, and all three rating scales reflected increased sleepiness with time of night. Scores on the KSS and VAS showed high correlations with performance tasks (mean intraindividual correlations were between 0.49 and 0.71). Performance correlated even higher with the ATS ratings (r = 0.73–0.79). Intercorrelations between rating scales were also high (r = 0.65–0.86). It was concluded that there were strong relations between ratings of sleepiness and performance, that the ATS rating scale was at least as good as the other scales and that the ratings were affected by type of task.
Bright (3000 lux) vs dim (100 lux) illuminance levels were compared for associated effects on oral temperature and sustained human performance. A counter balanced repeated measures design was used to assess the 9 male subjects during each of the two illuminance conditions. After practice sessions (0700-1800 hrs), cognitive performance tests were administered by a computer workstation every 2 hrs throughout the test period (1800-1000 hrs). Oral temperature taken immediately after each performance test was elevated during the bright over the dim condition at 2130, 0130, 0330 hrs. Performance on tests for cognitive abilities was improved for the bright over the dim light condition particularly at 2400, 0200 and 0400 hrs. This effect did not endure after the bright light exposure ended. These data suggest that bright illumination may improve performance otherwise susceptible to fatigue, particularly during early morning shifts.
This study examined the effects of bright light exposure, as compared to dim light, on daytime subjective sleepiness, incidences of slow eye movements (SEMs), and psychomotor vigilance task (PVT) performance following 2 nights of sleep restriction. The study had a mixed factorial design with 2 independent variables: light condition (bright light, 1,000 lux; dim light, < 5 lux) and time of day. The dependent variables were subjective sleepiness, PVT performance, incidences of SEMs, and salivary melatonin levels. Sleep research laboratory at Monash University. Sixteen healthy adults (10 women and 6 men) aged 18 to 35 years (mean age 25 years, 3 months). Following 2 nights of sleep restriction (5 hours each night), participants were exposed to modified constant routine conditions. Eight participants were exposed to bright light from noon until 5:00 pm. Outside the bright light exposure period (9:00 am to noon, 5:00 pm to 9:00 pm) light levels were maintained at less than 5 lux. A second group of 8 participants served as controls for the bright light exposure and were exposed to dim light throughout the entire protocol. Bright light exposure reduced subjective sleepiness, decreased SEMs, and improved PVT performance compared to dim light. Bright lights had no effect on salivary melatonin. A significant positive correlation between PVT reaction times and subjective sleepiness was observed for both groups. Changes in SEMs did not correlate significantly with either subjective sleepiness or PVT performance. Daytime bright light exposure can reduce the impact of sleep loss on sleepiness levels and performance, as compared to dim light. These effects appear to be mediated by mechanisms that are separate from melatonin suppression. The results may assist in the development of treatments for daytime sleepiness.
This constant routine study (n=9 men) compared the phase delay of the circadian system induced by a single pulse of evening light (5000 lx at 2100–2400 h) in the presence or absence of exogenous melatonin (5 mg p.o. at 2040 h). On the treatment day, light and melatonin protracted and accelerated, respectively, the evening decline in core body temperature (CBT). Subjective sleepiness ratings showed parallel shifts, the earlier the decline in CBT, the sleepier. On the post-treatment day, light induced a phase delay in the mid-range crossing time of CBT decline independent of whether melatonin was co-administered or not. Subjective sleepiness was delayed in parallel. The phase delay of the circadian system by evening light appears to be independent of an immediate hyperthermic effect and is not mediated by melatonin.
The immediate psychophysiological and behavioral effects of photic stimulation on humans [bright light (BL) of 5K lux or dim light (DL) of 50 lux] were assessed in male subjects (N = 43) under four different conditions. For one condition the same subjects (N = 16) received alternating 90-min blocks of BL and DL during the nighttime h (2300-0800 h) under sustained wakefulness conditions. A second condition was similar to the first except that subjects (N = 8) received photic stimulation during the daytime hours. For the third and fourth conditions different subjects received either continuous BL (N = 10) or continuous DL (N = 9) during the nighttime hours. For the nighttime alternating condition body temperature decreased under DL but either increased or maintained under BL. For the continuous light condition, body temperature dropped sharply across the night under DL but dropped only slightly under BL. Sleepiness was considerably greater under DL than under BL, and the difference became larger as the night progressed. Similarly, alertness, measured by EEG beta activity, was greater under BL, and nighttime performance on behavioral tasks was also generally better. There were no differential effects between BL and DL on any measure during the daytime. These data indicate that light exerts a powerful, immediate effect on physiology and behavior in addition to its powerful influence on circadian organization.
Seven human subjects were exposed to bright light (BL, approx. 2500 lux) and dim light (DL, approx. 6 lux) during 3 h prior to nocturnal sleep, in a cross-over design. At the end of the BL exposure period core body temperature was significantly higher than at the end of the DL exposure period. The difference in core body temperature persisted during the first 4 h of sleep. The latency to sleep onset was increased after BL exposure. Rapid-eye movement sleep (REMS) and slow-wave sleep (SWS; stage 3 + 4 of non-REMS) were not significantly changed. Eight subjects were exposed to BL from 20.30 to 23.30 h while their eyes were covered or uncovered. During BL exposure with uncovered eyes, core body temperature decreased significantly less than during exposure with covered eyes. We conclude that bright light immediately affects core body temperature and that this effect is mediated via the eyes.