Circadian phase delay induced by phototherapeutic devices

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Abstract
The Canadian Forces has initiated a multiple study project to optimize circadian phase changes using appropriately timed phototherapy and/or ingestion of melatonin for those personnel on long-range deployments and shift workers. The work reported here compared four phototherapeutic devices for efficacy in effecting circadian phase delays. In a partially counterbalanced treatment order, 14 subjects (7 men and 7 women), ages 18-51 yr, participated in 5 weekly experimental sessions of phototherapy with 4 different phototherapy devices (light tower, light visor, Litebook, LED spectacles) and a no-phototherapy control. Phototherapy was applied from 24:00 to 02:00 on night. (1) Dim light melatonin onset (DLMO) was assessed on night 1 and night. (2) Subjects were tested for psychomotor performance (serial reaction time, logical reasoning, and serial subtraction tasks) and completed the Stanford Sleepiness Scale on night 1 at 19:00, 23:00, 01:00, 02:00, and 03:00. After phototherapy, subjects completed a phototherapy side-effects questionnaire. All phototherapy devices produced melatonin suppression and significant phase delays. Sleepiness was significantly decreased with the light tower, the light visor, and the Litebook. Task performance was only slightly improved with phototherapy. The LED spectacles and light visor caused greater subjective performance impairment, more difficulty viewing the computer monitor and reading printed text than the light tower or the Litebook. The light visor, the Litebook, and the LED spectacles caused more eye discomfort than the light tower. The light tower was the best device, producing melatonin suppression and circadian phase change while relatively free of side effects.
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RESEARCH ARTICLE
Circadian Phase Delay Induced by Phototherapeutic
Devices
Michel A. Paul, James C. Miller, Gary Gray, Fred Buick,
Sofi Blazeski, and Josephine Arendt
PAUL MA, MILLER JC, GRAY G, BUICK F, BLAZESKI S, ARENDT J.
Circadian phase delay induced by phototherapeutic devices. Aviat
Space Environ Med 2007; 78:645–52.
Introduction: The Canadian Forces has initiated a multiple study
project to optimize circadian phase changes using appropriately timed
phototherapy and/or ingestion of melatonin for those personnel on
long-range deployments and shift workers. The work reported here
compared four phototherapeutic devices for efficacy in effecting circa-
dian phase delays. Methods: In a partially counterbalanced treatment
order, 14 subjects (7 men and 7 women), ages 18–51 yr, participated in
5 weekly experimental sessions of phototherapy with 4 different photo-
therapy devices (light tower, light visor, Litebook, LED spectacles) and a
no-phototherapy control. Phototherapy was applied from 24:00 to 02:00
on night 1. Dim light melatonin onset (DLMO) was assessed on night 1
and night 2. Subjects were tested for psychomotor performance (serial
reaction time, logical reasoning, and serial subtraction tasks) and com-
pleted the Stanford Sleepiness Scale on night 1 at 19:00, 23:00, 01:00,
02:00, and 03:00. After phototherapy, subjects completed a photother-
apy side-effects questionnaire. Results: All phototherapy devices pro-
duced melatonin suppression and significant phase delays. Sleepiness
was significantly decreased with the light tower, the light visor, and the
Litebook. Task performance was only slightly improved with photother-
apy. The LED spectacles and light visor caused greater subjective per-
formance impairment, more difficulty viewing the computer monitor
and reading printed text than the light tower or the Litebook. The light
visor, the Litebook, and the LED spectacles caused more eye discomfort
than the light tower. Conclusions: The light tower was the best device,
producing melatonin suppression and circadian phase change while
relatively free of side effects.
Keywords: phototherapy, melatonin suppression, dim light melatonin
onset, circadian phase delay.
B
OTH MILITARY AND civilian personnel experi-
ence circadian desynchrony resulting from overseas
travel or shift work. Because of these observations and
operational concerns, the Canadian Forces has initiated
a multiple-study project to identify effective counter-
measures using light therapy and melatonin for circa-
dian dysynchrony. This paper reports the first study,
which compared four commercially available photo-
therapy devices to induce a circadian phase delay.
The pineal hormone melatonin is synthesized with a
circadian rhythm which derives from the suprachias-
matic nucleus of the hypothalamus (1). Melatonin is
normally secreted during the dark phase of the 24-h day
and both the timing and the duration of secretion are
primarily governed by light exposure. Exposure to
bright light at night (17) suppresses melatonin secretion
and it is considered to be the best marker of circadian
phase and circadian photoreception (1). Others have
demonstrated that both natural sunlight and bright ar-
tificial light are effective in controlling circadian
rhythms (2,6,9,16) with morning light resulting in ad-
vances and evening light resulting in delays in the
melatonin rhythm (10). The onset of melatonin secre-
tion is known as dim light melatonin onset (DLMO) and
can be used as a circadian phase marker for advances
and delays (1,17). The time of DLMO can range from
18:00 to beyond midnight (16).
Brainard et al. (7) explored narrow energy band light
(509 nm) for efficacy in suppression of melatonin. Rea
et al. (21) evaluated the two sets of retinal photorecep-
tors involved in vision (rods and cones), demonstrating
that a rod-dominated mechanism (peak 507 nm), as
opposed to cones (peak 555 nm), is implicated in light-
induced suppression of melatonin in humans. Wright
et al. compared wavelengths of monochromatic light in
the blue/green area of the spectrum and found that
melatonin is better suppressed by shorter wavelengths
(470, 497, and 525 nm) with best suppression of mela-
tonin occurring at 497 nm (26). However, of these three
wavelengths, they found the best circadian advance
was caused by 470 nm (27). In independent laboratories,
Thapan et al. (22) and Brainard et al. (5) developed an
action spectrum for melatonin suppression with almost
identical characteristics, with peak suppression being at
about 460 470 nm. Most recently, Warman et al. (24)
and Lockley et al. (18) have shown the efficacy of short
wavelength light for phase shifting human rhythms.
Phototherapeutic treatments (artificial bright light
therapy) were achieved first by high ambient room
lighting, and later by light boxes that directed light into
the face (eyes) of subjects under treatment. These treat-
ments initially used broad light energy spectra. How-
ever, in the last few years, there has been considerable
From the DRDC Toronto, Toronto, Ontario, Canada (M. A. Paul, G.
Gray, F. Buick, S. Blazeski); USAF AFRL, Brooks City-Base, San
Antonio, TX (J. C. Miller); and the Centre for Chronobiology, Univer-
sity of Surrey, Surrey, UK (J. Arendt).
This manuscript was received for review in October 2006. It was
accepted for publication in April 2007.
Address reprint requests to: Michel A. Paul, M.Sc., Defence
Research and Development Canada-Toronto, 1133 Sheppard Ave.
W., P.O. Box 2000, North York, Ontario M3M 3B9, Canada; mpaul@
drdc-rddc.gc.ca.
Reprint & Copyright © by Aerospace Medical Association, Alexan-
dria, VA.
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refinement of phototherapeutic treatment devices such
that they now often incorporate very specific, narrow
(monochromatic) light energy bands. These new de-
vices include the Litebook, light tower, light visor, and,
most recently, LED spectacles. The goal of this study
was to compare these four phototherapeutic devices for
efficacy in melatonin suppression and to determine
which device provoked the biggest circadian phase
change.
METHODS
We used a counterbalanced treatment order, repeated-
measures protocol to compare the efficacy of melatonin
suppression and phase delay across the four photo-
therapeutic devices and a “no phototherapy control”
condition. Salivary melatonin levels were assessed
every 30 min between 19:00 and 03:30 (18 samples per
night). Emitted light intensity and light frequency out-
put, expressed as standardized radiance over wave-
length, was measured for each device and is illustrated
in Fig. 1. None of these devices produces any significant
heat. The conditions and related devices were as fol-
lows:
1. Control: no phototherapy and laboratory lighting
kept below 10 lx.
2. Litebook (The Litebook Company, Medicine Hat,
Alberta, Canada; www.litebook.com): about half
the size of a laptop and powered by standard
electricity (AC); has an array of small LEDs, which
emit bright light at a light intensity of 1500 lx at 60
cm from the light array. Subjects sat in front of the
Litebook (lightbook) positioned so their eyes were
60 cm from the light array. The lightbook emitted
mainly monochromatic light to the subjects at 465
nm (blue light) with a broad tail in the longer
visible wavelengths.
3. LED spectacles (prototypes were used; not yet
commercially available): has non-optical lenses
with two small light-emitting diodes (LEDs) sus-
pended from the spectacle frame in front of each
eye. The LEDs are mounted on stiff wire that
allows the LEDs to be set to 12 mm from each eye
so that the eye-level light intensity of the LED
spectacles was similar to that from the Litebook,
i.e., 1500 lx. The LED spectacles presented mono-
chromatic light of 510 nm (green light). They are
powered by a 9-V battery.
4. Light tower (light tower) (Sunnex Biotechnologies,
Winnipeg, Manitoba, Canada; www.sunnexbiotech
.com): two towers of two fluorescent light tubes per
tower, each tower about 45 cm high with one tower
mounted on each end of the base plate. The eye-level
light intensity at 60 cm from the eye was about 350
lx. The light tower emits monochromatic light of 500
nm (green light) and is powered by standard elec-
tricity (AC).
5. The Feel Bright Light (light visor) (Physician En-
gineered Products, Fryeburg, ME; www.feelbright
light.com): this visor-mounted (with Velcro) device
has an array of three LED lights in front of each eye.
The LED light arrays are about 10 cm from the eyes
and the light energy output can be set to either 8000
or 12,000 lx at eye level. The 8000-lx output level was
used in this study. The light visor emits monochro-
matic light of 505 nm (green light) and is powered by
a rechargeable lithium battery.
Subjects/Subject Exclusion Criteria
The 14 normal healthy subjects (7 men and 7 women)
ranged from 18 –51 yr in age (mean 30.5 SD 9.98 yr).
All subjects passed a screening medical designed to
preclude anyone for whom phototherapy might be con-
tra-indicated (e.g., taking photosensitizing medication)
or who might be taking medications (e.g.,
-adrenergic
antagonists or antidepressants) that affect psychomotor
performance and/or melatonin (1) and, therefore,
would confound experimental results. The protocol was
approved by the DRDC-Toronto Human Research
Ethics Committee, and all subjects provided written
informed consent according to the declaration of Hel-
sinki. The subjects were compensated for their partici-
pation according to the DRDC-Toronto guidelines for
subject stress allowance.
Procedures
The phototherapeutic and salivary melatonin collec-
tion procedures of Wright et al. (28) were used. Each
experimental condition was conducted over two consec-
utive nights, each starting at 18:30 (night 1 and night 2).
Experimental conditions were separated by 1 wk to
allow subjects to return to their circadian baselines.
Participants were instructed to have their evening meal
before arriving at the laboratory and to avoid alcohol
and caffeine-containing substances during all experi-
mental days. After 18:30, the subjects were restricted to
drinking water only. Subjects were provided with a
light sandwich immediately after the 23:30 saliva sam-
ple on both nights, consumed no less than 15 min prior
to the next saliva sample at 24:00.
From 18:30, room illumination was kept to less than
10 lx. During the entire salivary sampling window ex-
cept when undergoing psychomotor testing on night 1,
all subjects were required to remain semi-recumbent on
Wavelength (nanometers)
300 350 400 450 500 550 600 650 700 750 800
0.0
0.2
0.4
0.6
0.8
1.0
1.2
tower
visor
litebook
spectacles
Normalized radiation
Fig. 1. Normalized radiance plotted over wavelength (nm) for each
of the four phototherapeutic devices (light tower, light visor, litebook,
and LED spectacles).
PHOTOTHERAPEUTICS & CIRCADIAN PHASE—PAUL ET AL.
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lounge chairs in dim light watching television or vid-
eos. The television monitor was kept at least 2.0 m
distant from the subjects to limit extraneous light from
the television to less than 10 lx. Subject wakefulness was
monitored by the data collectors. During the rare occur-
rence of a subject falling asleep, a data collector would
awaken the subject by gently shaking his or her shoul-
der. On night 1, all subjects provided salivary samples
from 19:00 to 03:30 every 30 min. Light therapy (light-
book, LED spectacles, light tower, or light visor) and ‘no
phototherapy control’ took place from 24:00 to 02:00.
Participants slept in their assigned laboratory bedrooms
from 03:30 to 10:30 on night 1. On night 2, the same
procedure was followed, but without light exposure
and without psychomotor performance and with com-
pletion of saliva collection at 01:00. The subjects were
released at 01:00 on night 2.
During the study, in order to avoid possible effects of
postural changes on salivary melatonin levels sug-
gested in previous studies (8,11,19), all subjects re-
mained semi-recumbent in lounge chairs throughout
each evening, except when undergoing the 2-h photo-
therapy session for each of the four phototherapy
devices. Salivary samples were assayed for melatonin
content via RIA (Radio-Immuno-Assay) (23) by a con-
tract laboratory (Gamma Dynacare, London, Ontario,
Canada).
Prior to the study, all subjects were trained to asymp-
totic performance (over 12 iterations) on the 3 psy-
chomotor tasks: SRT—serial reaction time (25); LRT—
logical reasoning (3); and SST—serial subtraction task
(13). All the psychomotor tasks and sleep/fatigue ques-
tionnaires (14) were administered from laptop comput-
ers and took 10 min to complete.
Subjects were run in syndicates of five subjects (two
syndicates) and four subjects (one syndicate). While the
order of experimental conditions (control, Litebook,
LED spectacles, light tower, light visor) was counter-
balanced between syndicates, they were constant
within a syndicate to avoid experimental error due to
light levels from one subject’s device confounding an
adjacent subject using another device. On night 1, each
subject performed a baseline psychomotor test session
at 19:00. Thereafter, the subjects were tested for psy-
chomotor performance at 23:00, 01:00 (halfway through
the 2-h phototherapy session), again at 02:00 immedi-
ately after phototherapy, and at 03:00 or 1 h after pho-
totherapy was completed.
At the end of the 02:00 psychomotor test session, all
subjects completed a phototherapy side-effects ques-
tionnaire. This questionnaire consisted of 10 questions
presented as 7-point Likert-type scales where 1 no
effect and 7 maximum effect. Questions assessed
whether during or after phototherapy there were any
subjective changes in performance, blurriness of vision,
eye discomfort, headaches, difficulty viewing the mon-
itor, or difficulty reading a book or magazine.
To compare the amount of melatonin suppression
between experimental conditions, a percentage melato-
nin suppression value was calculated for each subject.
Melatonin suppression on night 1 was defined as
[(melatonin at 23:55 (immediately prior to photother-
apy) melatonin at 01:55 (immediately prior to the end
of phototherapy)/melatonin at 23:55] 100 (28). Lewy
and Sack (15), in formulating DLMO, proposed sam-
pling the melatonin concentration in blood at approxi-
mately uniform intervals and then designating the first
sample that exceeded a prescribed threshold as the
melatonin onset. According to Lewy, the variability
introduced by such a procedure is less than might be
expected. The difference in DLMO times calculated by
the method of Lewy and Sack (15) between night 1 and
night 2 was the measure of phase delay. Circadian
phase assessment by measurement of melatonin in
blood is comparable to circadian phase assessment by
measurement of melatonin in saliva (23).
Melatonin suppression data and the circadian
phase delay data were submitted to a single-factor,
5-level, repeated-measures ANOVA (5 conditions).
The dependent variable for each of the three psy-
chomotor tasks (# of correct responses) and the Stan-
ford Sleepiness Scale ratings were plotted over time
for each of the five conditions (control, Litebook,
tower, LED spectacles, and light visor) and sleepiness
ratings. Each performance variable was subjected to a
2-factor, repeated-measures ANOVA that compared
it to the control condition (2 conditions x 5 trials). The
Least Significant Difference test was used for post hoc
assessment of significant main effects and interac-
tions. Statistical significance was accepted at the 95%
level of confidence.
RESULTS
Melatonin Suppression and Phase Delay Data
During control, one subject had a pre-phototherapy
salivary melatonin content of 0.9 pg ml
1
, which in
-
creased to 4.95 pg ml
1
at 02:00, suggesting that this
subject was phase delayed before participation. The
melatonin suppression calculation showed an unex-
pected increase in melatonin (as distinct from a sup-
pression of melatonin) with the standard deviation of
the absolute value of this data point being 15 SDs from
the standard deviation of the data set. This subject is a
volunteer firefighter and responded to a nocturnal
alarm and was consequently up most of the night on the
night prior to reporting to the laboratory. Therefore, the
melatonin suppression and phase change data from this
subject are not included in these results. The night 1
melatonin profiles of the remaining 13 subjects for each
of the 5 conditions (light tower, light visor, no-photo-
therapy control, lightbook, and LED spectacles) are
shown in Fig. 2. There were no significant differences
pre-light treatment by condition [ANOVA, F(40, 480)
0.78, p 0.83].
In order to assess changes in salivary melatonin lev-
els across conditions during phototherapy, a 2-factor
repeated-measures ANOVA (5 levels of condition 5
trials) was employed. The four trials represent the sa-
liva samples collected from just before phototherapy
(23:45) to just before the end of phototherapy (01:55).
There was a significant main effect of condition
[F(4,48) 6.03, p 0.0005], a significant main effect
of trials [F(4,48) 14.42, p 0.000001], and a
PHOTOTHERAPEUTICS & CIRCADIAN PHASE—PAUL ET AL.
647
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significant condition trial interaction [F(16,192)
4.97, p 0.000001]. Post hoc assessment of the main
effect of condition indicates that melatonin suppression
associated with each of the four phototherapy devices
was significantly greater than during the no-photother-
apy control. Post hoc assessment of the main effect of
trials indicates that greatest melatonin suppression
(over all conditions) occurred at the 00:25 sample. Post
hoc assessment of the condition trial interaction
confirms that there was no significant melatonin sup-
pression throughout the no-phototherapy control con-
dition, and that at each of the sample times during
phototherapy (00:25, 00:55, 01:25, and 01:55), all four
phototherapy devices gave significant melatonin sup-
pression relative to the no-phototherapy control, except
the 00:55 sample for the LED spectacles (Fig. 2).
The repeated-measures ANOVA for the percent mel-
atonin suppression data shown in Fig. 3A yielded a
significant main effect of condition [F(4,48) 20.94,
p 0.00001]. Post hoc testing of this main effect re-
vealed that melatonin suppression attributable to each
of the four phototherapy devices was greater than con-
trol (light tower, p 0.000001; feel bright light visor,
p 0.00001; Litebook, p 0.00002; and LED spectacles,
p 0.012). There was no difference in suppression
between the light tower and the light visor, nor be-
tween the Litebook and the LED spectacles, but the
suppression attributable to the tower and visor was
greater than the Litebook and the spectacles (Fig. 3A).
The ANOVA for the phase delay data yielded a sig-
nificant main effect of condition [F(4,48) 11.48,
p 0.000001]. Post hoc testing of this main effect re-
vealed the circadian phase delay attributable to each of
the four phototherapy devices was greater than control
(light tower, p 0.000001; feel bright light visor,
p 0.00002; lightbook, p 0.016; and LED spectacles,
p 0.004). There was no difference in phase delay
between the light tower and the light visor, or between
the lightbook and the LED spectacles, but the phase
delay attributable to the tower and the visor was greater
than the lightbook and the spectacles (Fig. 3B). The
outcomes of the main effects (Conditions and Trials)
and the Conditions Trials interactions for each of the
sleepiness and psychomotor performance data are illus-
trated in Table I.
Sleepiness Data
Sleepiness increased over time during both control
and phototherapy conditions (Fig. 4A). The light tower
reduced sleepiness scores significantly at the end of the
phototherapy session (02:00, p 0.003) and 1 h later
(03:00, p 0.00001). The light visor reduced sleepiness
during and after phototherapy (01:00, p 0.0006; 02:00,
p 0.0003; 03:00, p 0.001). With the lightbook, sub-
jects were less sleepy after (03:00, p 0.014), but not
during phototherapy.
Psychomotor Testing/SRT Data
SRT performance declined after 23:00, including
through the phototherapy period for controls and with
all four devices (Fig. 4B). Compared with no photother-
apy, both the light tower and light visor improved
performance during and after phototherapy. The LED
spectacles improved SRT performance only at the end
of phototherapy relative to controls. The lightbook did
not improve SRT performance relative to control.
Time (hrs)
18:00:00 20:00:00 22:00:00 00:00:00 02:00:00 04:00:00
Average Salivary Melatonin (p-gm/mL)
0
2
4
6
8
10
12
14
16
Tower
Visor
Control
Lightbook
Spectacles
phototherapy
period
Fig. 2. Average salivary melatonin (pg ml
1
) over time for each of
five conditions (tower, visor, no phototherapy control, lightbook, and
spectacles). All values are mean SEM.
% melatonin suppression
-100
-
80
-60
-40
-20
0
A
**
ns
ns
p<.003,.000003
p<.032,.0001
Treatment Condition
phase delay (minutes)
0
10
20
30
40
50
60
light tower
500 n.m.
350 lux
Light Visor
505 n.m.
8,000 lux
no-photo
therapy
Control
LED Spectacles
510 n.m.
1,500lux
Litebook
465 n.m.
1,500 lux
ns p<.0004,.002
p<.02
ns
* *
B
Fig. 3. Percent A) melatonin suppression and B) circadian phase
delay. All values are mean SEM and are plotted over phototherapeutic
treatment conditions. Each phototherapeutic device is labeled with its
light energy frequency and emitted light output in eye-level lx on the
abscissa of Fig. 2B.
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Psychomotor Testing/LRT Data
LRT performance was worse after 23:00 on the last
three trials at 01:00, 02:00, and 03:00 for the control
condition and with all four phototherapy devices
(Fig. 4C). The light tower and LED spectacles did not
improve LRT performance relative to controls. The light
visor improved LRT performance only after photother-
apy (03:00, p 0.026), and with the lightbook, LRT
scores were better only during phototherapy at 01:00
(p 0.047).
Psychomotor Testing/SST Data
There were no significant fatigue related changes in
performance on the SST over time (Fig. 4D). Relative to
the no-phototherapy control, none of the devices im-
proved SST performance. With the LED spectacles, per-
formance on the SST task was slightly worse during
phototherapy.
Phototherapy Side-Effect Data
Of the 10 questions in the side-effect questionnaire, 4
questions yielded significant differences across the 4
phototherapeutic devices (Fig. 5). The significant side
effect findings were related to the impact of photother-
apy on perceived performance (Fig. 5A), eye discomfort
(Fig. 5B), difficulty viewing the computer monitor
(Fig. 5C), and difficulty reading a book or magazine
during phototherapy (Fig. 5D). The question asked
about blurred vision during phototherapy was similar
to, and generated the same results as, the question
about difficulty viewing the computer monitor.
The 1-way repeated measures ANOVA assessing
each of the four devices for subjective performance
impairment [F(3,36) 2.79, p 0.05] was significant.
Post hoc assessment of this ANOVA indicated that the
light visor (p 0.02) and LED spectacles (p 0.027)
caused more perceived performance impairment than
the light tower (Fig. 5A). The 1-way repeated measures
ANOVA assessing the four phototherapy devices for
eye discomfort [F(3,36) 6.47, p 0.001] was also
significant. Post hoc assessment of this ANOVA indi-
cated that the light visor (p 0.0001), the lightbook
(p 0.044), and the LED spectacles (p 0.008) each
caused more eye discomfort than the light tower, with
the light visor causing the most eye discomfort and the
lightbook and LED spectacles causing less but similar
eye discomfort than the light visor (Fig. 5B).
The 1-way repeated measures ANOVA assessing the
four phototherapy devices for difficulty viewing the
computer monitor [F(3,36) 7.71, p 0.0004] was
significant. Post hoc assessment of this ANOVA indi-
cated that the light visor (p 0.006) and the LED
spectacles (p 0.0005) caused more difficulty viewing
the computer monitor than the tower and the lightbook
(Fig. 5C). The 1-way repeated measures ANOVA assess-
ing the four phototherapy devices for difficulty viewing
the computer monitor [F(3,36) 17.74, p 0.000001] was
significant as well. Post hoc assessment of this ANOVA
indicated that the light visor (p 0.00001) and the LED
spectacles (p 0.000001) caused much more difficulty
reading a book or magazine than the light tower or the
lightbook. There was no difference between the light
visor and the LED spectacles or between the light tower
and the lightbook in terms of difficulty viewing the
computer monitor or difficulty reading (Figure 5D).
DISCUSSION
The amount of light required to suppress melatonin
is individually variable and depends on intensity and
wavelength; however, previous light exposure (both
short- and long-term) can influence response (4,12,20).
In recent controlled experiments, approximately 50-lx
broad-spectrum white light appears to be the minimum
average intensity needed for detectable suppression
(29). The current data indicate that while all four devices
resulted in melatonin suppression and induced a phase
delay, the light tower and light visor were more effective
than the lightbook or LED spectacles (Fig. 3A, 3B).
The devices varied considerably in light intensity,
and in emitted energy wavelength. While the lightbook
and the LED spectacles were similar in emitted light
intensity (1500 lx at eye level), Fig. 1 indicates that the
lightbook had a light output peak at 465 nm with a
TABLE I. STATISTICAL DATA (CONDITIONS, TRIALS, AND CONDITIONS TRIALS INTERACTIONS) COMPARING FOUR
PHOTOTHERAPY DEVICES AGAINST A NO-PHOTOTHERAPY CONTROL FOR CHANGES IN SLEEPINESS AND THREE
PSYCHOMOTOR PERFORMANCE TASKS.
Tower Visor Litebook LED Specs
SSS Condition F(1,12) 6.23, p 0.028 n.s. n.s. F(1,12) 5.66, MSe 6.92,
p 0.035
Trials F(4,48) 24.57, p 0.000001 F(4,48) 18.23, p 0.000001 F(4,48) 33.1, p 0.000001 F(4,48) 19.1, p 0.000001
C T F(4,48) 4.85, p 0.0003 F(4,48) 4.26, p 0.005 F(4,48) 3.49, p 0.014 n.s.
SRT Condition F(1,12) 5.43, p 0.038 n.s. n.s. n.s.
Trials F(4,48) 3.45, p 0.017 F(4,48) 4.52, p 0.004 F(4,48) 5.18, p 0.001 F(4,48) 3.84, p 0.009
C T n.s. n.s. n.s. F(4,48) 2.95, p 0.029
LRT Condition n.s. n.s. n.s. n.s.
Trials F(4,48) 5.35, p 0.001 F(4,48) 6.47, p 0.0003 F(4,48) 7.57, p 0.00008 F(4,48) 6.47, p 0.0003
C T n.s. F(4,48) 2.65, p 0.045 F(4,48) 2.91, p 0.031 n.s.
SST Condition n.s. n.s. n.s. n.s.
Trials n.s. n.s. n.s. F(4,48) 2.88, p 0.032
C T n.s. n.s. n.s. n.s.
SSS Stanford Sleepiness Scale; SRT Serial Reaction Time; LRT Logical Reasoning task; SST Serial Subtraction task; C T condition
trial; n.s. not significant.
PHOTOTHERAPEUTICS & CIRCADIAN PHASE—PAUL ET AL.
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broad tail of output in the longer wavelengths, whereas
the LED spectacles emitted only monochromatic light at
510 nm. The light tower (500 nm) and the light visor
(505 nm) were very similar in terms of emitted light
energy wavelength, but they were very dissimilar in
terms of emitted light intensity (light tower 350 lx, and
light visor 8000 lx). What was most surprising was that
the light tower achieved a numerically superior circa-
dian phase delay in spite of the fact that it emits less
than 5% of the light intensity emitted by the light visor.
Clearly, neither melatonin suppression nor circadian
phase changes are linear functions of light intensity
even with similar light energy wavelengths (500 nm vs.
Stanford sleepiness
scale scores
1
2
3
4
5
6
Control
Litebook
LightVisor
LightTower
LEDspectacles
A
# of correct responses
to SRT task
180
190
200
210
220
230
240
B
# of correct responses
to LR task
35
40
45
50
55
60
C
Time (hrs)
# of correct responses
to SS task
25
30
35
40
45
50
55
D
1900 0100
0200
03002300
1900 0100
0200
03002300
1900 0100
0200
03002300
1900 0100
0200
03002300
Fig. 4. A) Stanford Sleepiness Scales scores, B) number of correct
responses to Serial Reaction Time (SRT) task, C) number of correct
responses to Logical Reasoning (LR) task, and D) number of correct re-
sponse to Serial Subtraction (SS) task. All values are mean SEM and are
plotted over phototherapeutic treatment condition and trials [Time (h)].
Performance Impairment
1
2
3
4
5
6
7
A
p<.019
nsns
ns
p<.027
Eye Discomfort
1
2
3
4
5
6
7
B
p<.008
p<.0001
p<.044
p<.032
ns
ns
Difficulty Viewing
Computer Monitor
1
2
3
4
5
6
7
p<.001
p<.0005
ns
ns
p<.006
p<.001
C
Difficulty Reading
Book / Magazine
1
2
3
4
5
6
7
D
p<.00001
ns
p<.0001
ns
p<.000001
Light
Tower
Light
Visor
Litebook
LED
Spectacles
p<.00002
Fig. 5. Subjective impact of phototherapy across devices on A)
psychomotor performance, B) eye discomfort, C) difficulty viewing the
computer monitor, and D) difficulty reading a book or magazine. All
values are mean SEM and are plotted over phototherapeutic device.
PHOTOTHERAPEUTICS & CIRCADIAN PHASE—PAUL ET AL.
650 Aviation, Space, and Environmental Medicine Vol. 78, No. 7 July 2007
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505 nm). It is interesting to speculate why this is so. One
possibility is that a lower emitted light intensity would
allow the pupils of the individuals receiving light ther-
apy to remain more dilated, whereas bright light would
tend to constrict pupil diameter. One way to assess the
difference in pupil size would be to measure pupil
diameters of a group of subjects as they undergo pho-
totherapy with each of the four devices used in this
study. However, we speculate that even if we could
quantify differences in pupil size while undergoing
phototherapy with each of these devices, those different
pupil sizes would probably not explain how less than
5% of similar wavelength monochromatic light (light
tower) would be as effective, or better, than the much
more intense light of the light visor. Given the subjec-
tive reports of eye problems with the visor, perhaps the
subjects tended to close their eyes during phototherapy
with this device. Another possibility relates to subjec-
tive eye discomfort experienced with the visor whereby
subjects might well have avoided glare by exhibiting a
higher blink frequency or by blinking for longer dura-
tion or by looking downwards, away from the glare
(discussed later).
Compared with the no-phototherapy control condi-
tion, when the subjects underwent phototherapy, they
were less sleepy (or more alert) at the end of photother-
apy and an hour after phototherapy with the light
tower. They were also less sleepy during, at the end of,
and an hour after phototherapy with the light visor, and
an hour after phototherapy with the lightbook. The
LED spectacles, unlike the other three phototherapy
devices, produced no significant condition by trial in-
teraction. Thus, there were no specific times at which
the subjects were more alert on the LED spectacles than
during control. However, since there were main effects
of condition and trials, the subjects were generally less
sleepy during phototherapy with all four devices than
during control and sleepiness increased (alertness de-
creased) over time (trials) during all conditions includ-
ing control.
The improvements in psychomotor performance in-
duced by phototherapy with all four devices were min-
imal in this study. SRT only improved by phototherapy
with the LED spectacles and then only transiently by
10% (about 20 responses over the 3 min of the SRT task)
at the end of light therapy (relative to no-phototherapy
control). All four devices resulted in an approximately
10% increase in LRT performance (about five to six
responses over the 3 min of the LRT task) either during
or after phototherapy. There were no improvements on
the SST task. Our study may have been underpowered
to detect changes, since our a priori design calculations
indicated that 28 subjects were required to have a
power of 80% to detect a difference of 4 responses per
minute (about a 6% change in performance in our
tasks). However, the primary purpose of this study was
to compare the four phototherapeutic devices for effi-
cacy in suppression of nocturnal melatonin and in cir-
cadian phase delay. Evaluating whether or not
nocturnal phototherapy would improve psychomotor
performance was a secondary goal. Further, having our
subjects conduct visual-based psychomotor testing in
different light levels (control at less than 10 lx, light
tower at 350 lx, visor at 8000 lx, and lightbook and LED
spectacles at 1500 eye-level lx) created an experimental
confound. Therefore, in our next phototherapy study
we will forgo visual-based psychomotor testing and use
an auditory-based reaction time task to eliminate the
confound due to varying light levels.
The phototherapy side-effect data suggested that the
two devices that provided the highest light energy out-
put (light visor and LED spectacles) produced more
perceived negative impact on psychomotor perfor-
mance than the lightbook and the light tower (Fig. 5A).
The light tower produced significantly less eye discom-
fort than the other three devices (Fig. 5B). The light
visor and the LED spectacles caused significant diffi-
culty viewing the computer monitors, whereas the light
tower and the lightbook did not (Fig. 5C). The light
visors and the LED spectacles made reading a book or
magazine very difficult, if not impossible (as reported
by some subjects), whereas the light tower and the
lightbook did not impair reading ability (Fig. 5D).
It is apparent by the phototherapy side-effect data
that the eye discomfort associated with three of the
phototherapy devices (light visor, lightbook, and LED
spectacles) might well cause some glare avoidance be-
havior such as the wearer having a higher blink fre-
quency or blinking for longer duration. We noted that
some subjects, when wearing the spectacles, would
tend to tilt their head back (in order to have the light
energy fall on their eyelids as opposed to their pupils)
if they were not engaged with the computer in order to
perform psychomotor testing or attempting to read
from the computer. When this occurred, the data col-
lectors would direct the subjects to look at the computer
screen. The subjects were also encouraged to read by
placing a book or magazine front of the computer
screen (as opposed to laying flat on the desk). We note
also that the lightbook had to be placed on one side of
the psychomotor test computer at each work station
and this could easily facilitate glare avoidance behavior
even if the subjects appeared to be looking at the com-
puter as instructed.
From our perspective, the ideal phototherapeutic de-
vice would be small, easily portable, wearable, and
battery powered. However, such a device should have
lower light intensity in order to avoid eye discomfort
and glare avoidance behavior caused by very bright
light. Perhaps our findings that the light tower is quite
effective (in spite of relatively low emitted light levels)
will result in some manufacturers configuring portable,
wearable, and battery-powered devices with lower
emitted light energy output.
Conclusions
The light tower and the light visor suppressed noc-
turnal melatonin and produced greater circadian phase
changes than the other two devices. However, the light
visor was not attractive from a user-acceptability point
of view since it caused significant levels of perceived
performance impairment, eye discomfort, and difficulty
reading the computer monitor or printed text. Clearly,
the light tower was the best choice of these four devices
PHOTOTHERAPEUTICS & CIRCADIAN PHASE—PAUL ET AL.
651
Aviation, Space, and Environmental Medicine Vol. 78, No. 7 July 2007
Delivered by Ingenta to: Aerospace Medical Association Member
IP: 69.144.153.181 On: Sat, 07 May 2016 17:23:51
Copyright: Aerospace Medical Association
in that it produced good circadian phase change and
did not have any significant negative side effects. Hav-
ing battery-operated portability (similar to the light
visor and the LED spectacles) in a low intensity but
very effective device like the light tower (which was
dependent on 110 V/220 V electrical supply) would be
helpful for effecting circadian phase changes in a mili-
tary field setting and would also be helpful to civilian
travelers interested in using portable phototherapy de-
vices to mitigate the effects of jet lag.
ACKNOWLEDGMENTS
We are indebted to Sharon McFadden for the spectral analysis of
the light output for each of our phototherapy devices. We are also
indebted to our data collectors (Andrea Hawton, Quan Lam, Wendy
Sullivan-Kwantes, Elaine Maceda, Sgt. Michelle Senkiw, 2
nd
Lt.
Amitabh Chauhan, 2
nd
Lt. Rohan D’Souza, O/Cdt. Do Kim, and
O/Cdt. Chris Paronuzzi), without whose commitment and skill this
study could not have been completed.
REFERENCES
1. Arendt J. Melatonin: characteristics, concerns and prospects. J Biol
Rhythms 2005; 20:291–303.
2. Arendt J, Broadway J. Light and melatonin as zeitgebers in man.
Chronobiol Int 1987; 4:347–50.
3. Baddley AD. A 3 min reasoning test based on grammatical trans-
formation. Psychonomic Science 1968; 10:341–2.
4. Brainard GC, Hanifin JP. Photons, clocks, and consciousness.
J Biol Rhythms 2005; 20:314–25.
5. Brainard GC, Hanifin JP, Greeson JM, Byrne B, Glickman G,
Gerner E, et al. Action spectrum for melatonin regulation in
humans: evidence for a novel circadian photoreceptor. J Neu-
rosci 2001; 21:6405–12.
6. Brainard GC, Lewy AJ, Menaker M, Frederickson RH, Miller LS,
Welever RG. Dose-response relationship between light irradi-
ance and the suppression of plasma melatonin in human vol-
unteers. Brain Res 1988; 454:212–8.
7. Brainard GC, Lewy AJ, Menaker M, Fredrickson RH, Miller LS,
Weleber RG, et al. Effect of light wavelength on suppression of
nocturnal plasma melatonin in normal volunteers. Ann NY
Acad Sci 1985; 453:3768.
8. Cagnacci A, Krauchi K, Wirz-Justice A, Volpe A. Homeostatic
versus circadian effects of melatonin on core body temperature
in humans. J Biol Rhythms 1997; 12:509–17.
9. Czeisler CA, Allan JS, Strogatz SH, Ronda JM, Sanchez R, Rios
CD. Bright light resets the human circadian pacemaker inde-
pendent of the timing of the sleep-wake cycle. Science 1986;
233:667–71.
10. Czeisler CA, Klerman EB. Circadian and sleep-dependent regu-
lation of hormone release in humans. Recent Prog Horm Res
1999; 54:97–132.
11. Deacon S, Arendt J. Posture influences melatonin concentrations
in plasma and saliva in humans. Neurosci Lett 1994; 167:191– 4.
12. Hebert MSK, Lee MC, Eastman CI. The effects of prior light
history on the suppression of melatonin by light in humans. J
Pineal Res 2002; 33:198–203.
13. Heslegrave RJ, Angus RG. The effects of task duration and work-
session location on performance degradation induced by sleep
loss and sustained cognitive work. Behav Res Methods Inst
Comp 1985; 17:592–603.
14. Hoddes E, Zarcone V, Smythe H, Phillips R, Dement WC. Quan-
tification of sleepiness: a new approach. Psychophysiology
1973; 10:431–6.
15. Lewy AJ, Sack RL. The dim light melatonin onset as a marker for
circadian phase position. Chronobiol Int 1989; 6:93–102.
16. Lewy AJ, Sack RL. The role of melatonin and light in the human
circadian system. In: Buijs RM, Kalsbeek A, Rominj HJ, Pen-
narta CMA, Mirmiran M, eds. Progress in brain research,
Vol III. Amsterdam: Elsevier Science BV; 1996.
17. Lewy AJ, Wehr TA, Goodwin FK, Newsome DA, Markey SP.
Light suppresses melatonin secretion in humans. Science 1980;
210:1267–9.
18. Lockley SW, Brainard GC, Czeisler CA. High sensitivity of the
human circadian melatonin rhythm to resetting by short wave-
length light. J Clin Endocrinol Metab 2003; 88:1267–9.
19. Nathan PJ, Jeyaseelan AS, Burrows GD, Norman TR. Modulation
of plasma melatonin concentration by changes in posture. J
Pineal Res 1998; 24:219–23.
20. Owen J, Arendt J. Melatonin suppression in human subjects by
bright and dim light in Antarctica: time and season-dependent
effects. Neurosci Lett 1992; 137:181–4.
21. Rea MS, Bullough JD, Figueiro MG. Human melatonin suppres-
sion by light: a case for scotopic efficiency. Neurosci Lett 2001;
299:45–8.
22. Thapan KJ, Arendt J, Skene DJ. An action spectrum for melatonin
suppression: evidence for a novel non-rod, non-cone photo
receptor system in humans. J Physiol (Lond) 2001; 535:261–7.
23. Voultsios A, Kennaway DJ, Dawson D. Salivary melatonin as a
circadian phase marker: validation and comparison to plasma
melatonin. J Biol Rhythms 1997; 12:457–66.
24. Warman VL, Dijk DJ, Warman GR, Arendt J, Skene DJ. Phase
advancing human circadian rhythmns with sort wavelength
light. Neurosci Lett 2003; 342:37–40.
25. Wilkinson RT, Houghton D. Portable four-choice reaction time
test with magnetic tape memory. Behav Res Methods Inst
Comp 1975; 7:441–6.
26. Wright HR, Lack LC. Effect of light wavelength on suppression
and phase delay of the melatonin rhythm. Chronobiol Int 2001;
18:801–8.
27. Wright HR, Lack LC, Kennaway DJ. Differential effects of light
wavelength in phase advancing the melatonin rhythm. J Pineal
Res 2004; 36:1–5.
28. Wright HR, Lack LC, Partridge KJ. Light emitting diodes can be
used to phase delay the melatonin rhythm. J Pineal Res 2001;
31:350–5.
29. Zeitzer JM, Dijk DJ, Kronauer R, Brown E, Czeisler C. Sensitivity
of the human circadian pacemaker to nocturnal light: melato-
nin phase resetting and suppression. J Physiol (Lond) 2000;
526(Pt 3):695–702.
PHOTOTHERAPEUTICS & CIRCADIAN PHASE—PAUL ET AL.
652 Aviation, Space, and Environmental Medicine Vol. 78, No. 7 July 2007
    • "As Paul et al. showed, light tower use between 00.00 and 02.00 a.m. causes melatonin suppression and thus diminishes sleepiness in the work place (reported p < 0.003) [63] . Even a delayed sleep phase syndrome can be counteracted by exposure to bright light in the early morning and avoidance of light in the evening . "
    [Show abstract] [Hide abstract] ABSTRACT: Background Excessive fatigue and insomnia are common among shift workers and can lead to negative effects such as reduced work performance, processing errors, accidents at work, absenteeism, reduced quality of life, and symptoms of depression. Moreover, work in rotating shifts can be a risk factor for different somatic and psychiatric diseases and may contribute to poor health, especially in elder adults and women. This review aims to show non-pharmacological preventive measures against fatigue and insomnia in shift workers. Method Computerized literature searches in MedLine and in the Cochrane Library were performed with the following key words: shift work disorder, fatigue, insomnia, shift work, measures, treatment, therapy, strategies and coping. The search was limited to non-pharmacological studies that were conducted on human subjects and published as English-language articles in peer-reviewed journals since 1970. Additional studies were identified through the reference sections of relevant articles. Eighteen articles on fatigue in shift workers, including six original research articles with a total sample size of 3504 probands consisting of industrial workers, office employees, aircraft maintenance engineers, and non-shift workers working in simulated shifts, were analyzed, as well as seven articles on insomnia, including an original research article with a sample size of 26 media workers. Also, 4 reviews on shift work disorder were analyzed. Main The occurrence of fatigue and insomnia in shift workers associated with a working period is described as shift work disorder. Estimations on the prevalence of shift work disorder in shift workers vary between 5 % and about 20 %; about one in three shift workers is affected by insomnia and up to 90 % of shift workers report regular fatigue and sleepiness at the workplace. We concluded that there is a necessity for treatments to improve the sleep quality of the shift working population. The most common non-pharmacological recommendations to improve sleep quality and to reduce insomnia and fatigue were scheduling, bright light exposure, napping, psychoeducation for sleep hygiene, and cognitive-behavioral measures. Conclusion Some important preventive coping strategies for fatigue associated with shift work such as napping and exposure to bright light have already been investigated and are generally approved. A few studies also provide good evidence for the efficacy of cognitive-behavioral techniques in the treatment of chronic primary and comorbid insomnia. These coping strategies summarized in this paper should be considered in the workplace health promotion programs of each work environment to improve working conditions for shift workers and to save money.
    Full-text · Article · Dec 2016
    • "Anecdotally (author's experience), blue-enriched light was disliked by some Antarctic subjects, but appreciated by others. Monochromatic green light as a 2-h pulse from  J. Arendt a light tower, for melatonin suppression and phase shifting, was best tolerated in laboratory experiments (Paul et al., 2007), but in another study its effects were short-lived compared to monochromatic blue light (Gooley et al., 2010). The authors of the latter report suggest that light treatment should be directed to both cone photoreceptors and melanopsin cells for maximum effect. "
    [Show abstract] [Hide abstract] ABSTRACT: At Arctic and Antarctic latitudes, personnel are deprived of natural sunlight in winter and have continuous daylight in summer: light of sufficient intensity and suitable spectral composition is the main factor that maintains the 24-h period of human circadian rhythms. Thus, the status of the circadian system is of interest. Moreover, the relatively controlled artificial light conditions in winter are conducive to experimentation with different types of light treatment. The hormone melatonin and/or its metabolite 6-sulfatoxymelatonin (aMT6s) provide probably the best index of circadian (and seasonal) timing. A frequent observation has been a delay of the circadian system in winter. A skeleton photoperiod (2×1-h, bright white light, morning and evening) can restore summer timing. A single 1-h pulse of light in the morning may be sufficient. A few people desynchronize from the 24-h day (free-run) and show their intrinsic circadian period, usually >24h. With regard to general health in polar regions, intermittent reports describe abnormalities in various physiological processes from the point of view of daily and seasonal rhythms, but positive health outcomes are also published. True winter depression (SAD) appears to be rare, although subsyndromal SAD is reported. Probably of most concern are the numerous reports of sleep problems. These have prompted investigations of the underlying mechanisms and treatment interventions. A delay of the circadian system with "normal" working hours implies sleep is attempted at a suboptimal phase. Decrements in sleep efficiency, latency, duration, and quality are also seen in winter. Increasing the intensity of ambient light exposure throughout the day advanced circadian phase and was associated with benefits for sleep: blue-enriched light was slightly more effective than standard white light. Effects on performance remain to be fully investigated. At 75°S, base personnel adapt the circadian system to night work within a week, in contrast to temperate zones where complete adaptation rarely occurs. A similar situation occurs on high-latitude North Sea oil installations, especially when working 18:0006:00h. Lack of conflicting light exposure (and "social obligations") is the probable explanation. Many have problems returning to day work, showing circadian desynchrony. Timed light treatment again has helped to restore normal phase/sleep in a small number of people. Postprandial response to meals is compromised during periods of desynchrony with evidence of insulin resistance and elevated triglycerides, risk factors for heart disease. Only small numbers of subjects have been studied intensively in polar regions; however, these observations suggest that suboptimal light conditions are deleterious to health. They apply equally to people living in temperate zones with insufficient light exposure. (Author correspondence: [email protected] /* */)
    Full-text · Article · Apr 2012
    • "In all the above mentioned studies, volunteers were tested under stringently controlled conditions, which are crucial for determining spectral sensitivity, but leave open the question of whether this sensitivity could be utilized in more practical scenarios to shift circadian rhythms, to alleviate jet lag and shift work symptoms, and to improve alertness and cognitive performance at the workplace and at house settings [17]. Lamps and light-producing devices emitting exclusively or relatively more short-wavelength energy are now commercially available [18]. Compact fluorescent (CF) lamps that provide correlated lamp colour temperature (CCT) [in kelvin (K)], that indicate the relative proportion of warm versus cool colours in a light source, are very often sold, because of the low energy consumption and governmental regulations to replace traditional incandescent bulbs. "
    [Show abstract] [Hide abstract] ABSTRACT: 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.
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