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R E S E A R C H A R T I C L E Open Access
The effects of low-intensity narrow-band
blue-light treatment compared to bright
white-light treatment in sub-syndromal
seasonal affective disorder
Ybe Meesters
1*
, Wim H. Winthorst
1
, Wianne B. Duijzer
1
and Vanja Hommes
2
Abstract
Background: The discovery of a novel photoreceptor in the retinal ganglion cells with a highest sensitivity of
470-490 nm blue light has led to research on the effects of short-wavelength light in humans. Several studies
have explored the efficacy of monochromatic blue or blue-enriched light in the treatment of SAD. In this study,
a comparison has been made between the effects of broad-wavelength light without ultraviolet (UV) wavelengths
compared to narrow-band blue light in the treatment of sub-syndromal seasonal affective disorder (Sub-SAD).
Method: In a 15-day design, 48 participants suffering from Sub-SAD completed 20-minute sessions of light
treatment on five consecutive days.
22 participants were given bright white-light treatment (BLT, broad-wavelength light without UV 10 000 lux,
irradiance 31.7 Watt/m
2
) and 26 participants received narrow-band blue light (BLUE, 100 lux, irradiance
1.0 Watt/m
2
). All participants completed daily and weekly questionnaires concerning mood, activation, sleep
quality, sleepiness and energy. Also, mood and energy levels were assessed by means of the SIGH-SAD, the primary
outcome measure.
Results: On day 15, SIGH-SAD ratings were significantly lower than on day 1 (BLT 54.8 %, effect size 1.7 and BLUE
50.7 %, effect size 1.9). No statistically significant differences were found on the main outcome measures.
Conclusion: Light treatment is an effective treatment for Sub-SAD. The use of narrow-band blue-light treatment is
equally effective as bright white-light treatment.
Trial registration: This study was registered in the Dutch Trial Register (Nederlands Trial Register TC = 4342) (20-12-2013).
Keywords: sub-SAD, Light treatment, Narrow-band blue light
Background
Seasonal Affective Disorder (SAD), winter type, is a
well-studied syndrome, characterized by almost yearly
recurring depressive episodes in autumn/winter alternat-
ing with symptom free episodes in spring/summer.
The syndrome was recognized in the early eighties of
the previous century and has been included in consecu-
tive editions of the Diagnostic and Statistical Manual
of Mental Disorders [1]. This classification system
describes the syndrome as a seasonal pattern of major
depressive disorder or alternatively as a bipolar I or
bipolar II disorder. SAD is a serious affective disorder,
and those suffering from it often need professional help.
Exposure to bright light is the treatment of choice for
patients suffering from SAD winter type [2–4]. An
increasing number of studies have shown the positive
effects of light treatment on this type of seasonal
depression.
Apart from people suffering from SAD, there are those
suffering from less severe complaints in wintertime. The
main difference is that, according to the diagnostic cri-
teria of DSM, the latter fail to meet the number of
* Correspondence: y.meesters@umcg.nl
1
University of Groningen, University Medical Center Groningen, University
Center for Psychiatry, PO Box 30001, Groningen 9700 RB, The Netherlands
Full list of author information is available at the end of the article
© 2016 Meesters et al. Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0
International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and
reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to
the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver
(http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
Meesters et al. BMC Psychiatry (2016) 16:27
DOI 10.1186/s12888-016-0729-5
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
complaints required for a DSM diagnosis. Because the
diagnostic criteria of SAD are not fulfilled, these com-
plaints are known as sub-syndromal SAD (sub-SAD).
Sub-SAD can be considered to be part of a continuum
of seasonality between no complaints at all and severely
depressed.
Sub-syndromal SAD
People suffering from sub-SAD in wintertime gener-
ally experience hypersomnia, a lack of energy, a
craving for carbohydrates and weight gain, or a
decreased interest in socializing. These symptoms
sometimes are accompanied by a lowered mood, but
not by an actual depression.
Kasper et al. [5, 6] have described the criteria of
sub-SAD. These include a regular pattern of seasonal
(winter) problems (in at least two consecutive winters
for a minimum period of 4 weeks), such as decreased
energy levels, less efficiency at work, decreased interest
in socializing, changed eating habits (eating more carbo-
hydrates and weight gain) and changed sleep patterns
(more sleep). Subjects regard these difficulties as normal
and do not see them as the symptoms of an illness. They
do not seek professional help, nor do others suggest they
do so. These difficulties are not recognized by people
outside the subjects’inner social circle and are easily
attributed to “being overworked”or “having the flu”.
The symptoms are not disturbing subjects’lives in any
major degree. Subjects have no history of major depres-
sion, nor do they suffer from any physical illness.
Although sub-SAD complaints are less severe than
those of SAD, this does not imply that sub-SAD is
completely harmless. Lack of energy or hypersomnia
can, among other things, lead to social dysfunctioning,
frustrate educational opportunities, or lead to problems
in relationships or work-related problems in wintertime.
Several studies have described positive effects of light in
treating sub-SAD [7–10].
Kasper et al. also formulated sub-SAD criteria based
on the Seasonal Pattern Assessment Questionnaire
(SPAQ, [11]). These are often used in epidemiological
studies [12] to discriminate between SAD and sub-SAD.
Among these criteria, the score on a subscale of the
SPAQ, the Global Seasonality Score (GSS), is used as a
cut-off point. The results of these studies show that the
prevalence of sub-SAD is about 2-4 times higher than
the prevalence of SAD [13–15].
However, the use of the SPAQ as a discriminator
between SAD and sub-SAD has been criticized [16, 17]:
a high score on the GSS does not make a person
depressed by definition. In view of this, in the present
study, we used the Mini-International Neuropsychiatric
Interview (MINI, [18]) for diagnosing/excluding depres-
sion. Potential participants who fulfilled the criteria of a
mood disorder according to the MINI were excluded
from the design. The Structural Interview Guide for the
Hamilton Depression Rating Scale-Seasonal Affective
Disorder (SIGH-SAD, [19]) was used for measuring the
severity of the depressive symptoms.
Blue light
The discovery of a novel photoreceptor in the retinal
ganglion cells [20–23] with a maximum sensitivity of
470–490 nm to blue light has led to research on the ef-
fects of short-wavelength light on humans. These non-
image forming (NIF) photoreceptors play a role in regu-
lating the biological clock [24–26], but also project dir-
ectly to several other areas of the brain [22, 27].
Several studies have explored the efficacy of mono-
chromatic blue or blue-enriched light in the treatment
of SAD. When more blue light was added to the
spectrum of a bright-light treatment lamp (10 000 lux,
Tcc = 17 000 K) the response was similar to that after
exposure to bright white-light therapy (BLT, 10 000 lux,
Tcc = 5 000 K) [28]. A possible explanation of this result
was thought to be the saturation of the ocular receptors
due to very high illuminance levels. In order to examine
this, another study using the same design has compared
moderate-intensity blue-enriched light (750 lux, Tcc = 17
000 K) with BLT (10 000 lux, Tcc = 5 000 K) in the
treatment of SAD. This study did not show any differ-
ences in the therapeutic responses between the two light
conditions [29] either.
With the invention of blue light-emitting diodes,
narrow-band light sources fitting the maximum sensitiv-
ity of the NIF photoreceptors became readily available.
Studies were undertaken to explore the use of LED
technology in the treatment of seasonal complaints
comparing the effects of light of different wavelengths.
The therapeutic responses to blue light were found to be
superior to those of red light [30, 31]. The effects of
blue-enriched white LED light were found to be superior
to placebo (deactivated ion-generator) [32] but similar to
the effects of blue light [33]. In a study comparing the
effects of low-intensity narrow-band blue light (BLUE)
to the effects of high-intensity BLT, no differences in
therapeutic outcome were found [34].
Although the effects of both light treatment and blue
or blue-enriched light specifically have been studied
repeatedly in SAD populations, only a small number of
studies investigating the effects of light treatment in
sub-SAD is available.
This is the first study exploring the effects of blue light
on people with sub-SAD. As a control we used bright
white-light therapy. We assessed effects on mood, en-
ergy, different aspects of activation, sleepiness, and sleep
quality in the two conditions and looked for possible
differences related to age and gender. In a previous study
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of an SAD population [28] no difference in efficacy was
found between daily 20- and 30-minute sessions of ex-
posure to bright light. In this study the effects of white
and blue light in a 20-minute treatment have been com-
pared for the first time. We hypothesize that both treat-
ments are effective and that the therapeutic effects of
BLUE are larger than those of BLT.
The human lens yellows with age, and yellow lenses
can filter out short-wavelength light. Therefore older
participants may profit less from the blue-light condi-
tion. In this study, the results of older participants have
also been compared to those of younger participants.
Methods
In the winters of 2010-2011 and 2011-2012 (October 1st
to February 10th) subjects were recruited mainly by
means of advertisements in regional papers, websites
and small news items in magazines. Potential partici-
pants were roughly screened by means of a short phone
survey. After that written information was sent to them
and they were invited for an interview at the SAD out-
patient clinic of the University Center for Psychiatry in
Groningen. Participants in the screening interview were
assessed by means of a standardized structured inter-
view, the Mini-International Neuropsychiatric Interview
(MINI, [18]). Subjects meeting the criteria of depression
or any other psychiatric diagnosis from the DSM-IV-TR
[1] were excluded from further screening.
The remaining subjects were assessed by means of the
SIGH-SAD [19]. A SIGH-SAD score of ≥12 and < 18 was
needed for inclusion in the design. Subjects with a score
below 12 hardly differ from healthy people and were,
therefore, excluded. In addition to the SIGH-SAD ques-
tionnaire subjects filled out the Seasonal Pattern Assess-
ment Questionnaire (SPAQ, 7). The Global Seasonality
Score (GSS) had to be ≥8 for a subject to be included in
the study, but the seasonal complaints also had to be mild
enough so as not to interfere with the subjects’daily lives.
The 15-day protocol started at the latest 7 days after the
screening interview. Participants underwent a 20-minute
light treatment at home on five consecutive working days
(days 4–8), which had to be completed by 8.20 a.m. This
period of 5 days was based on SAD studies that have
shown such a period to be effective [35, 36]. Subjects were
asked to complete daily questionnaires concerning mood,
sleepiness and sleep quality throughout the protocol, and
mood and fatigue questionnaires on a weekly basis. The
subjects visited the clinic on days 1, 8, and 15. The first
3 days before light treatment served as a baseline. A num-
ber of studies have shown that the response after light
treatment still increases after termination of the light
exposure [28, 29, 34, 35, 37]. Therefore, the assessment
procedures were continued for 7 more days after the light
exposure had ended.
Light treatment
Subjects were randomised (controlling for age and gen-
der) to one of the two treatment modalities: either to
the low-illuminance blue-light therapy (BLUE) group or
to the bright white-light therapy (BLT) group. The inter-
viewers were unaware of the treatment subjects were
assigned to. Before starting the interview, participants
were asked not to give any information about the light
condition to the interviewers.
BLUE light (goLITE HF3320, Philips Drachten, The
Netherlands) characteristics were: peak LED wavelength
470 nm (full width half-maximum 25 nm), usage
distance 50 cm positioned on a table top at 45 degrees
sideways, vertical photopic illuminance 100 lux at eye
position, irradiance 1.0 Watt/m
2
, equivalent melanopic
illuminance 770 m-lux [38].
The BLT was a white fluorescent lighting device
(EnergyLight HF3319, Philips Drachten, The Netherlands),
correlated color temperature 5 000 K, vertical photopic
illuminance at 20 cm usage distance 10 000 lux, irradi-
ance 31.7 Watt/m
2
; equivalent melanopic illuminance of
8620 m-lux [38]. Spectral distributions of the two treat-
ment modalities are shown in Fig. 1.
The subjects were instructed to use the lamps as an
addition to their normal room illumination. In that
sense, the BLUE condition was actually blue-enriched
white light. Assuming a 3 000 K TL spectrum, and an
average background illumination of 250 lux, the effective
equivalent melanopic illuminance in both cases in-
creased by 115 m-lux, making the BLT condition one
order of magnitude higher on melanopic illuminance.
Assessment and procedure
We compared the two conditions on a weekly and daily
basis to assess the same issues, using self-rating scales,
and on a weekly basis using standardized structured
interviews. Since all assessment procedures have their
Fig. 1 Spectral-power distributions of the lamps
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own shortcomings (weekly = retrospective; daily = assess-
ment at the moment of the day; self-report: subjective
assessment biased by the opinion of the participant;
standardized structured interview: biased by the opinion
of the interviewers) we used different assessment proce-
dures to strengthen the assessment procedure.
Each of the two conditions started at day 1 (Friday)
with a baseline measurement consisting of a SIGH-SAD
interview (with interviewers blind to the light condition),
the Beck Depression Inventory, second version (BDI-II-
NL, [39]), a fatigue self-rating questionnaire (Short Fa-
tigue Questionnaire, SFQ; [40]), and a questionnaire
aiming to evaluate subjects’expectations of the effects of
light therapy. 5-point scale ratings were collected with
the help of this latter questionnaire to check whether
subjects expected to benefit from each treatment modal-
ity (white and blue light), whether they thought each
was a logical treatment and whether they would recom-
mend one or the other to a friend. They filled out this
questionnaire before they had seen the light fixtures.
The SIGH-SAD can be subdivided in a section contain-
ing the Hamilton Rating Scale of Depression (HRSD)
assessing depressive symptoms, and a section assessing
the atypical symptoms (ATYP) that are common in
SAD, such as hypersomnia, a decreased need for social-
izing and carbohydrate craving. Subjects who met all
inclusion criteria were randomly assigned to one of the
two conditions, with gender and age distributed evenly
over the groups.
The SIGH-SAD, the BDI-II-NL and SFQ were repeated
at day 8 (after the 5th light session), and at day 15.
From day 1 onwards, participants filled out question-
naires on a daily basis before 8.00 a.m., 30 minutes after
waking up at the latest, but before light had been
applied. The mean scores on the questionnaires of the
first four days were considered baseline.
These questionnaires dealt with mood, the Adjective
Mood Scale (AMS, [41–43]); sleepiness, Karolinska
Sleepiness Scale (KSS, [44]); and sleep quality, the
Groninger Sleep Quality Scale (GSQS, [45, 46]). Also,
four components of activation were measured, using the
Activation Deactivation-Adjective Check List (AD-ACL,
[47]): General Activation (GA; i.e. energetic, vigorous,
full of pep, active and lively), Deactivation-Sleep (DS; i.e.
sleepy, tired, drowsy, wide awake, and wakeful), High
Activation (HA; i.e. jittery, intense, fearful, clutched-up,
and tense), and General Deactivation (GD; i.e. placid,
calm, at rest, still and quiet). Subjects were asked to
describe their current feelings and to rate the 20 adjec-
tives from the questionnaire on a 4-point scale.
Statistics
Baseline differences between the scores of the two con-
ditions on the SIGH-SAD, the BDI-II and the SFQ were
tested by means of t-tests (continuous outcomes) and
chi-square tests (dichotomous outcomes).
Effect sizes [48] were calculated for each condition.
These effect sizes reflect the differences between base-
line (day 1) and day 15. Results were based on the
weekly assessments of the two conditions and were
compared by means of repeated measures ANOVA. A
responder was defined as a subject who improved by at
least 50 %.
Linear Mixed Models were used to compare the two
conditions on the basis of the daily self-rating question-
naires. An advantage of linear mixed models is that they
allow the inclusion of random effects; i.e. parameters are
allowed to vary across individuals. This may reveal het-
erogeneity in individual growth curves. We used models
with time, condition, and the interaction between time
and condition, with the baseline score as a covariate
(baseline score = mean of the 4 pre-intervention scores).
We fitted models with the baseline score and the 11 days
after the start of the intervention as the repeated mea-
sures and allowed the slope to vary across individuals.
Maximum likelihood estimation was used. We compared
models with different variance-covariance matrices.
Selection of the final model was based on the Bayesian
Information Criterion (BIC; with lower values indicating
better models). If the random effect for slope was found
to be non-significant, this term was removed from the
model (unless this resulted in a higher value of the BIC
criterion). Performing residual diagnostics on the final
models verified regression assumptions.
In a secondary analysis, the potential impact of gender
and age on outcome were examined. To this end, the
interaction time*condition*gender and time*conditio-
n*age were added to the models.
We also evaluated the correlations between the GSS
scores and severity of complaints, both at baseline and
throughout the study.
Analyses were carried out using SPSS 20. A two-tailed
alpha level of 0.05 was used to determine statistical
significance.
The research protocol was approved by the Medical
Ethical Committee of the University Medical Center
Groningen. All participants signed the informed consent
form.
Results
Subjects
Sixty-four potential participants were invited for a selec-
tion interview. Eleven were excluded on the basis of an
unclear diagnosis, symptoms that were not severe
enough or factors having an effect on mood. 53 partici-
pants started the study. Five other participants were ex-
cluded during the design. Two due to incorrect use of
the lamp, one due to failure to complete the assessment
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procedures after Day 1, and two because the inclusion
criteria did not match the scores at the moment of in-
take, which implies that inclusion would have been a
mistake (Fig. 2).
Seven participants (3 in the BLT and 4 in the BLUE
condition) scored >18 on the SIGH-SAD on day 1. In
the screening interview their scores had been below 18.
This difference was caused by their a-typical complaints,
not by depressive symptoms. These subjects were, there-
fore, included in the analysis.
Ultimately, 22 participants (18 women, mean age 38.2
+ 10.2, range 24–51 yr.; 4 men mean age 39.6 + 10.5,
range 24–51 yr.) received white light and 26 participants
(22 women, mean age 38.1 + 11.6, range 18–58 yr. and 4
men mean age 48.3 +12.9, range 31–62 yr.) received
blue light. If the subjects had been divided into two
groups using Kasper’s SPAQ diagnostic criteria of the
global seasonality scores (GSS), GSS < 11 and GSS > 10,
baseline scores on SIGH-SAD were found to be the
same in these groups.
Weekly ratings
Both therapies were found to be highly effective in redu-
cing the SIGH-SAD score and improving energy levels
measured by the atypical symptom part (ATYP) of the
SIGH-SAD (Fig. 3).
No statistically significant differences were found be-
tween light conditions on any of the weekly outcome
measures. This also holds when the results are con-
trolled for gender, age, severity of complaints (measured
with the SIGH-SAD, HRSD, ATYP, or with the BDI-II,
or SFQ), and expectations (measured with a self-rating
questionnaire on day 1).
In both conditions the complaints assessed with the
different instruments decreased during the 15-day
period (Fig. 3 and Table 1): SIGH-SAD, 24 items, main
effect ‘time’F (2,45) = 53.9, p< 0.001), with no significant
differences between conditions (main effect “condition”
F (1,46) = 1.13, ns), nor over time between conditions
(interaction effect “time*condition”F (2,45) = 0.06, ns).
When dividing the SIGH-SAD in “typical”(HRSD) and
“atypical”(ATYP) symptoms, the following is found: for
HRSD (17-items Table 1) a main effect “time”F (2,45) =
22.04, ns; main effect “condition”F (1,46) = 0.35, ns;
main effect “time*condition”F (2,45) = 0.28, ns and for
ATYP (7 items, Table 1) a main effect “time”F (2,45) =
45.9, p= < 0.001; main effect “condition”F (1,46) = 1.09,
ns; main effect “time*condition”F (2,45) = 0.05, ns.
Based on the scores of the weekly assessed self-rating
instruments the results for the BDI-II that were found
had a main effect “time”F(2,45) = 35.13, p< 0.001; main
effect “condition”F (1,46) = 0.11, ns; main effect
“time*condition”F (2,45) = 1.77, ns. For the SFQ were
found a main effect “time”F (2,45) = 16.77, p< 0.001;
main effect “condition”F (1,46) = 0.20,ns; main effect
“time*condition”F (2,45) = 0.1, ns.
In the absence of a clinical mood disorder, the atypical
symptoms play a more prominent role in the seasonal
difficulties as measured with the SIGH-SAD. At baseline,
the subjects scored highest on fatigability and hypersomnia.
Fig. 2 Flowchart inclusion of participants
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Daily questionnaires
The results based on the scores of the daily self-rating
questionnaires are shown in Table 2. One participant of
the BLT condition was excluded from the analysis due to
failure to fill out daily questionnaires during the baseline
period and the majority of the following days. Conse-
quently, in these analyses data of 47 subjects were used.
The time effect was significant in all models. Both
groups ended with equal scores on the daily question-
naires. For the KSS and General Deactivation subscale
of the AD-ACL a significant effect of the interaction
time*condition was found. Subjects receiving white light
showed a larger decline in scores on the KSS and GD
subscale of the AD-ACL compared to the blue light
condition.
For the questionnaires concerning Mood, Sleep and
the subscales Deactivation-Sleep, General Activation and
High Activation of the AD-ACL the interaction
time*condition was not significant.
We also examined the influence of gender and age on
the outcomes. No interaction effects were found be-
tween gender or age on the one hand, and time or
time*condition on the other. Adjustments for gender
and age did not cause any substantial changes in the
results either. Therefore, gender and age have not been
included in the final models.
SPAQ
The severity of the GSS score of the SPAQ is not related
to the severity of baseline SIGH-SAD, HRSD or ATYP
scores when two groups are created on the basis of a
GSS cut-off score of 11 (Table 3). In the BLT group 8
out of 22 had a GSS score of 11 or higher (36.4 %), 1
subject had a GSS score of 17. In the BLUE group 7 out
Fig. 3 Scores on the SIGH-SAD (range 0-75). BLT =Bright Light Treatment, n= 22., BLUE = narrowband blue light treatment n= 26. SIGH-SAD =
total score on the SIGH-SAD (24 item version, range 0-75); HRSD: sum score of the Hamilton Rating Scale for Depression items (17 item version,
range 0-52) of the SIGH-SAD; A-TYP: sum score of the Atypical question items of the SIGH-SAD (range 0-23). Error Bars = standard deviation. For
further explanation and abbreviations: see text
Table 1 Weekly average scores (+SD)
Instrument (range) Condition N Day1 (SD) Day 8 (SD) Day 15 (SD) Effect Size d % Decrease Responder N (in %)
SIGH-SAD (0-75) BLT 22 15.5 (2.4) 7.7 (5.1) 7.0 (6.5) 1.7 54.8 13 (59)
BLUE 26 16.3 (2.6) 9.1 (5.6) 8.1 (5.6) 1.9 50.7 16 (61.5)
HRSD (0-52) BLT 22 6.5 (2.2) 3.0 (2.3) 3.0 (4.0) 1.1 53.8 13 (59)
BLUE 26 6.5 (2.5) 3.8 (2.8) 3.2 (2.8) 1.2 50.7 17 (65)
ATYP (0-23) BLT 22 9.0 (2.7) 4.7 (3.5) 4.0 (3.9) 1.5 55.6 15 (68)
BLUE 26 9.8 (2.5) 5.3 (3.5) 4.9 (3.7) 1.6 50.0 14 (54)
BDI-II (0-63) BLT 22 15.0 (4.3) 9.1 (5.1) 7.5 (5.8) 1.5 50.0 11 (50)
BLUE 26 13.9 (4.8) 9.4 (5.7) 9.7 (7.5) 0.7 30.2 9 (35)
SFQ (4-28) BLT 22 18.7 (3.3) 15.7 (3.9) 15.5 (3.5) 0.9 24.1 4 (18.1)
BLUE 26 18.2 (3.4) 15.1 (3.5) 15.5 (4.1) 0.7 21.5 5 (19.2)
Cohen’s d effect size and response percentage from day 1 to day 15, as rated by the scale adapted for seasonal symptoms SIGH-SAD (24 items), the Hamilton Rat-
ing Scale for depression (HRSD, 17 items), and the atypical symptoms ATYP (7 items), the score on the Beck Depression Inventory-II (BDI-II) and the Short Fatigue
Questionnaire (SFQ) for each condition. BLT = bright white light treatmen t; BLUE = narrow-band blue-light treatment. Responder = subject with an improvement of
at least 50 %
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of 26 had a GSS score of 11 or higher (27.9 %). When
comparing the two conditions (high vs. low GSS scores)
based on the SIGH-SAD scores, we find the main effect
‘time’F (2,45) = 50.55, p< 0.001, with no significant
differences between conditions (main effect “condition”
F (1,46) = 0.081, ns) or over time between conditions
(interaction effect “time*condition”F (2,45) = 3.14, ns).
Side effects and evaluation
Participants spontaneously reported some side effects.
9 % of the participants in the BLT condition reported
headaches, 9 % experienced headaches and nausea, and
9 % had headaches and felt hyper during the treatment.
In the BLUE condition 8 % of the participants reported
headaches, 4 % experienced headaches and nausea and
another 4 % reported headaches and palpitations during
the treatment. Also, in the BLUE condition, 4 % reported
dry eyes and yet another 4 % reported diarrhoea during
treatment. No statistically significant difference in the
number of side effects between the conditions was
found, though.
Participants seem to equally like the colours white or
blue. Participants in the conditions would also like to
get the same treatment the following year, as well as the
remaining part of the season. The participants who re-
ceived blue light were a little happier with the treatment
than those receiving white light. However, there are no
significant differences between the two conditions.
Discussion
To the best of our knowledge, this is the first study look-
ing at the effects of blue light on a population suffering
from sub-SAD. We compared low-intensity blue-light
treatment to the bright-white light treatment used in the
treatment of sub-SAD.
Since this is a field study, there is no controlled for all
factors that can contribute to the therapeutic outcome.
We assume that those factors are equally distributed
about the two conditions.
Both treatment conditions were highly effective in
reducing symptoms of sub-SAD, as measured by weekly
interviews and self-reported ratings. The effects of BLUE
light treatment were comparable to those of the bright
white-light treatment.
This is also the first time the effectiveness of only
20 minutes of daily light exposure has been studied. The
SIGH-SAD analysis showed that both mood and atypical
symptoms improved after one week of light intervention
(see Fig. 3).
At baseline, the severity was mainly driven by atypical
symptoms: lack of energy, fatigability, hypersomnia, and
less so by mood disturbances. The most pronounced
effect of light treatment was observed on the atypical
Table 2 Daily self-rating questionnaires
Outcome Model Estimate P-value
Sleepiness (KSS) Time -0.139 .000
condition -0.561 .123
time*condition 0.089 .015
baseline 0.476 .000
Mood (AMS) Time -0.767 .007
condition -0.597 .738
time*condition 0.335 .372
baseline 0.788 .000
Sleep (GSQS) Time -0.116 .021
condition -0.263 .608
time*condition 0.037 .583
baseline 0.422 .002
Deactivation Sleep (AD-ACL) Time -0.188 .002
condition -0.390 .352
time*condition 0.078 .330
baseline 0.758 .000
General Activation (AD-ACL) Time -0.213 .003
condition -0.161 .744
time*condition 0.100 .304
baseline 0.746 .000
High Activation (AD-ACL) Time -0.032 .563
condition -0.473 .165
time*condition 0.094 .216
baseline 0.887 .000
General Deactivation (AD-ACL) Time -0.098 .029
condition -0.361 .225
time*condition 0.121 .047
baseline 0.901 .000
Results of regression analyses. Bold data reflects significant
time*condition results
Table 3 Effects of high vs. low GSS score on primary outcome
N SIGH-SAD SIGH-SAD SIGH-SAD HRSD HRSD HRSD ATYP ATYP ATYP
Day 1 Day 8 Day 15 Day 1 Day 8 Day 15 Day 1 Day 8 Day 15
GSS total < 11 33 15.64 9.1 7 6.6 3.6 2.6 9.1 5.5 4.4
GSS total > 10 11 16.67 7.1 8.9 6.3 3.1 4.1 10.4 4 4.8
SIGH-SAD scores, HRSD scores and Atypical scores(ATYP) on days 1, 8 and 15 in relation to SPAQ GSS scores. The subdivision of the scores on GSS items is based
on median scores in the direction of the mean scores
Meesters et al. BMC Psychiatry (2016) 16:27 Page 7 of 10
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
symptoms of hypersomnia and fatigability. This is in line
with observations of Rastad et al. [49]. Both HRSD and
BDI-II ratings were relatively low at baseline: scores of 8
or lower on HRSD and 10 or lower on BDI-II are typical
of healthy populations. This overall relatively low sever-
ity at baseline limits the range of improvement (and the
percentage of responders defined by 50 % improvement
of a score) compared to the effects of light treatment on
SAD populations we observed in earlier studies [28, 34].
So far, no methodologically justified placebo condition
is available for light treatment. In light research, various
placebo-like conditions have been used, such as imagin-
ary light [50]; invisible light [37], extra-ocular light [51],
low-intensity light [29], or a placebo condition totally
unrelated to light, such as a deactivated ion generator
[32]. Responses to these ‘placebo’conditions have varied
from 36 to 46 %. Although the response rates in this
study, in both conditions are higher (54.8 and 50.7 %) it
cannot be ruled out with certainty that these effects are
due to placebo effects.
In a number of epidemiological studies a subdivision
between SAD and sub-SAD is made on the basis of the
GSS scores of the SPAQ [8, 52]. In this study, there is
no relation between the severity of the GSS scores and
the severity of the seasonal difficulties as measured by
the SIGH-SAD (Table 3). This is in line with the findings
of Hardin et al. [17], Magnusson [16] and Terman [53].
Because of the overlap between subjects with sub-SAD
and SAD who reached scores of GSS 11 or higher and
report at least a moderate problem on the SPAQ it is
argued that a GSS cut-off score of 17 is more realistic
when making a distinction between these two groups
[53, 54]. In our population, only 1 subject (2.1 %)
reached a GSS score of 17, with a SIGH-SAD score of
21 and a HRSD score of 5 before treatment. These find-
ings support our decision not to use SPAQ GSS scores
as a criterion to subdivide groups of persons suffering
from SAD and sub-SAD in this study.
Like previous studies comparing blue-enriched treat-
ment modalities to BLT in the treatment of SAD [28, 29,
34], this study also shows no significant differences in
the clinically relevant responses to light for the sub-SAD
group. The difference in photopic illuminance of the
two conditions is two orders of magnitude (10 000 lux
vs 100 lux), whereas the difference in the equivalent
melanopic illuminance [38] is about one order of magni-
tude. The equivalent melanopic illuminance of BLUE
light treatment is of the same order of magnitude as
melanopic illuminance of 1000 photopic lux, 5000 K
white fluorescent light. No difference in effects on
people with seasonal problems has been shown over a
wide range of high light intensities. Similar saturation
was reported for alerting effects of light [55], and for
melatonin suppression [56], where responses were
already at a maximum, and the same between 1000 and
10000 lux of white 4000 K fluorescent light. The finding
that we observe the same magnitude of effects across a
larger range of photopic illuminance, but similar ranges
of melanopic illuminance as in the studies above sup-
ports the hypothesis that ipRGCs play a role in mediat-
ing the effects of light when treating SAD and sub-SAD.
The results of most daily questionnaires are in line
with the results of the weekly ratings. Both groups ended
with equal scores on these questionnaires. The only dif-
ference between the two conditions found was a quicker
decrease of the scores of the KSS and GD subscale of
the AD-ACL for subjects receiving white light compared
to subjects receiving blue light. We have no explanation
for these two exceptions. The questionnaires were filled
out after waking up and before light treatment in the
morning, except at day 1, when questionnaires were
filled out at the clinic at the start of the programme later
in the morning. When leaving out the data from day 1
from the calculations, this did not show a difference in
the results, so possible circadian effects on the scores of
day 1 did not influence the results.
Stuhlmiller [57] stated that the effects of the seasons
on psychological changes are inconsistent and contro-
versial and are influenced by the appreciation of cultural
perception and adaptation. This study shows that expos-
ure to artificial light is beneficial for sub-SAD sufferers.
Mood, energy levels, fatigability and sleep improve.
Therefore, we think it is helpful to recognise that sea-
sonal difficulties are related to more than cultural per-
ception and adaptation.
The results of this study are in line with the dual vul-
nerability hypothesis, [58], which suggests that there is a
vulnerability for the influences of the seasons as well as
a vulnerability for the development of a depression. The
difference between SAD and sub-SAD may be that sub-
SAD sufferers are less vulnerable to developing a depres-
sion but are vulnerable to the effects of the seasons.
The human lens yellows with age, and yellow lenses
can filter out short-wavelength light. For this reason, we
examined the effect of age in both conditions, but were
especially interested in the effects of age in the BLUE
condition. We did not find any age-related differences.
There are several possible explanations for this: it may
be that the light-intensity is still sufficiently high, causing
the transmitted light to be sufficient for a therapeutic ef-
fect, or it may be that a different adaptation mechanism
exists which compensates for lower transmission in the
blue range. This latter explanation is supported by two
studies looking at biological consequences of reduced
blue-light exposure by changed lens transmittance [59,
60]. Giménez et al. [59] looked at the melatonin secre-
tion of young subjects wearing orange lenses and found
that after 2 weeks the response to light was the same as
Meesters et al. BMC Psychiatry (2016) 16:27 Page 8 of 10
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
before they wore lenses. Najjar et al. [60] found de-
creased lens transmission in the blue range in older
people, but without consequences for overall melatonin
suppression. Based on our results with BLT or BLUE
light conditions we cannot claim one or the other to be
more effective for a certain age group, at least within the
age range explored.
Although subjects were randomized to one of the
intervention modalities, rather than being allowed to se-
lect the light colour of preference, the final evaluation
does not reveal any significant differences in treatment
appreciation. The side effects reported are in line with
the earlier observed reactions to bright-light treatment.
Conclusions
In this study, people with sub-SAD completed 5 days
of light treatment at home by either bright white-
light therapy or low intensity blue LED-light therapy.
Their condition was assessed by blinded interviewers
and by self-assessments on a weekly basis, as well as
via daily questionnaires over 2 weeks. 20 minutes of
exposure to morning light on 5 days resulted in im-
proved mood and improved energy levels, reduced
fatigability and hypersomnia symptoms, which are the
most striking symptoms in this population. No significant
difference in treatment efficacy was found, neither in any
of the weekly measures, nor in the majority of daily
assessments.
Symptoms of Sub-SAD can be reduced effectively with
light treatment, with the use of narrow-band blue-light
treatment being equally effective as bright white-light
treatment.
Abbreviations
AD-ACL: activation deactivation adjective checklist; GA: General Activation;
DS: deactivation –sleep; HA: High Activation; GD: General Deactivation;
AMS: Adjective Mood Scale; ATYP: atypical symptoms; BDI-II-NL: beck
depression inventory, second version, Dutch version; BLT: bright white-light
therapy; BLUE: blue light therapy; DSM: Diagnostic and Statistical Manual of
Mental Disorders; GSQS: Groninger Sleep Quality Scale; HRSD: Hamilton
Rating Scale for Depression; KSS: Karolinska Sleepiness Scale; MINI:
Mini-International Neuropsychiatric Interview; NIF: non- image forming;
SAD: Seasonal Affective Disorder; SFQ: Short Fatigue Questionnaire;
SIGH-SAD: Structural Interview Guide for the Hamilton Depression Rating,
Scale- Seasonal Affective Disorder version; SPAQ: Seasonal Pattern
Assessment Questionnaire; GSS: Global Seasonality Score of the SPAQ;
Sub-SAD: sub-syndromal seasonal affective disorder.
Competing interests
YM has received research funding and served as a consultant for Royal;
Philips Electronics NV and The Litebook Company Ltd.; VH is an employee of
Philips Consumer Lifestyle, Amsterdam, The Netherlands; WHW and WBD
reported no potential conflicts of interest.
Authors’contributions
The original version of the experimental protocol was written by YM and VH.
YM served as principal investigator. WBD participated in the clinical conduct
of the trial and was the research coordinator. WHW contributed to the
statistical data analysis. The final manuscript was written by YM, with comments
of all co-authors, all of whom read and approved the final manuscript.
Acknowledgements
The authors are grateful to all subjects participating in this study, and to
Elske Bos, Joep Vries, Douwe van Tuinen, Annelies Nieman, Rachel Oziël
and Harry Blijleven for their contribution to this project, to Josie Borger for
the improvement of the English and Philips Consumer Lifestyle, Amsterdam,
The Netherlands for funding.
Author details
1
University of Groningen, University Medical Center Groningen, University
Center for Psychiatry, PO Box 30001, Groningen 9700 RB, The Netherlands.
2
Philips Consumer Lifestyle Drachten, Drachten, The Netherlands.
Received: 10 June 2015 Accepted: 1 February 2016
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