Morning light exposure and light therapy for mood, energy, and circadian health.
Light is the strongest zeitgeber — the primary signal that sets your circadian clock. The research on morning light, SAD, and vitamin D is more nuanced than most summaries suggest.
Sunlight is not just about vitamin D or mood in a general sense — it's the primary signal the brain uses to synchronize circadian rhythms. This gives light exposure an unusually broad set of downstream effects, from sleep quality to hormone timing to mood regulation.
Morning bright light is the most reliable circadian intervention available. The suprachiasmatic nucleus (SCN) — the brain's master clock — is exquisitely sensitive to the spectral quality of light in the first hours after waking. RCTs consistently show that 30–60 minutes of bright light exposure (ideally 1000+ lux, outdoors) in the morning advances circadian phase, makes falling asleep at the desired time easier, and improves next-day alertness. Indoor lighting (200–500 lux) is substantially weaker.
Light therapy is an evidence-based treatment for seasonal affective disorder. Meta-analyses of RCTs show that 10,000 lux light boxes used for 20–30 minutes each morning produce antidepressant effects in SAD comparable to medication. The effect sizes are large. The evidence for non-seasonal depression is smaller but positive.
Vitamin D insufficiency is common and linked to multiple outcomes. Deficiency (below 20 ng/mL) is associated with impaired mood, immune function, and bone health in observational data. RCTs for vitamin D supplementation show consistent benefits for bone outcomes, more mixed results for mood. Outdoor light exposure contributes to vitamin D synthesis but is not sufficient year-round at higher latitudes.
Evening light exposure delays sleep timing. Blue-spectrum light in the evening suppresses melatonin and delays sleep onset. Screen light at night is a weaker version of this effect than often portrayed — the absolute lux from screens is low — but the cumulative effect of hours of evening screen exposure before bed is measurable in polysomnography studies.
Chronotype is substantially heritable and determines when the circadian system is most responsive to light. Evening types benefit more from deliberate morning light exposure than morning types. Latitude, season, and skin tone all affect vitamin D synthesis rates. What counts as "morning" light in terms of circadian effect also depends on your natural wake time — the relevant variable is time after waking, not clock time.
Evidence base
50 papers
Raymond W. Lam, Anthony Levitt, Robert D. Levitan +4 more · American Journal of Psychiatry · 2006 · 231 citations
This study found that 8 weeks of daily morning bright light therapy was just as effective as 20 mg/day of fluoxetine for treating winter seasonal affective disorder (SAD), with light therapy showing earlier symptom improvement and fewer side effects, suggesting both are viable options for self-experimentation.
Read the breakdown →Vitamin D vs broad spectrum phototherapy in the treatment of seasonal affective disorder.
F. Michael Gloth, Waqas Alam, Bruce W. Hollis · PubMed · 1999 · 235 citations
A small randomized controlled trial found that a single high dose of vitamin D significantly improved depression symptoms in individuals with Seasonal Affective Disorder (SAD) over one month, while broad-spectrum phototherapy did not, suggesting vitamin D may be a promising self-experimentation target for SAD.
Read the breakdown →Randomized Clinical Trial of Bright Light Therapy for Antepartum Depression
C. Neill Epperson, Michael Terman, Jiuan Su Terman +4 more · The Journal of Clinical Psychiatry · 2004 · 166 citations
This pilot study suggests that daily exposure to 7000 lux bright light for 10 weeks may reduce symptoms of major depression during pregnancy, with an effect size comparable to antidepressant medications, making it a promising area for personal experimentation.
Read the breakdown →Patient room lighting influences on sleep, appraisal and mood in hospitalized people
Marina C. Giménez, Leonie M. Geerdinck, Mathijs O. Versteylen +7 more · Journal of Sleep Research · 2016 · 99 citations
A dynamic lighting system with bright daytime light and dim nighttime light improved objective sleep duration by nearly 30 minutes over five days in hospitalized patients, suggesting that carefully managed light exposure can positively impact sleep.
Read the breakdown →Mohamed Boubekri, Ivy N. Cheung, Kathryn J. Reid +2 more · Journal of Clinical Sleep Medicine · 2014 · 391 citations
Light Therapy in Seasonal Affective Disorder Is Independent of Time of Day or Circadian Phase
Anna Wirz‐Justice · Archives of General Psychiatry · 1993 · 198 citations
This study found that light therapy for Seasonal Affective Disorder (SAD) is equally effective whether administered in the morning (7 AM) or evening (10 PM), suggesting that the exact timing of light exposure relative to your body clock might not be crucial for its antidepressant effects.
Read the breakdown →Kelly J. Rohan, Kathryn A. Roecklein, Kathryn Tierney Lindsey +4 more · Journal of Consulting and Clinical Psychology · 2007 · 88 citations
This study found that both cognitive-behavioral therapy (CBT) and light therapy (LT) alone, and especially their combination, significantly reduced seasonal affective disorder (SAD) symptoms over 6 weeks, with the combined approach leading to a 73% remission rate compared to 20% in a control group, suggesting these are effective strategies to test for managing seasonal depression.
Read the breakdown →Timothy M. Brown, George C. Brainard, Christian Cajochen +15 more · PLoS Biology · 2022 · 538 citations
This expert consensus report provides specific, measurable light exposure targets (in melanopic equivalent daylight illuminance, or melanopic EDI) for daytime, evening, and nighttime to optimise circadian rhythms, sleep quality, and daytime alertness, based on a systematic review of the underlying photobiology.
Read the breakdown →Christian Cajochen, Sylvia R. Frey, Doreen Anders +6 more · Journal of Applied Physiology · 2011 · 701 citations
Many people spend an increasing amount of time in front of computer screens equipped with light-emitting diodes (LED) with a short wavelength (blue range). Thus we investigated the repercussions on melatonin (a marker of the circadian clock), alertness, and cognitive performance levels in 13 young male volunteers under controlled laboratory conditions in a balanced crossover design. A 5-h evening exposure to a white LED-backlit screen with more than twice as much 464 nm light emission {irradiance of 0,241 Watt/(steradian × m(2)) [W/(sr × m(2))], 2.1 × 10(13) photons/(cm(2) × s), in the wavelength range of 454 and 474 nm} than a white non-LED-backlit screen [irradiance of 0,099 W/(sr × m(2)), 0.7 × 10(13) photons/(cm(2) × s), in the wavelength range of 454 and 474 nm] elicited a significant suppression of the evening rise in endogenous melatonin and subjective as well as objective sleepiness, as indexed by a reduced incidence of slow eye movements and EEG low-frequency activity (1-7 Hz) in frontal brain regions. Concomitantly, sustained attention, as determined by the GO/NOGO task; working memory/attention, as assessed by "explicit timing"; and declarative memory performance in a word-learning paradigm were significantly enhanced in the LED-backlit screen compared with the non-LED condition. Screen quality and visual comfort were rated the same in both screen conditions, whereas the non-LED screen tended to be considered brighter. Our data indicate that the spectral profile of light emitted by computer screens impacts on circadian physiology, alertness, and cognitive performance levels. The challenge will be to design a computer screen with a spectral profile that can be individually programmed to add timed, essential light information to the circadian system in humans.
Effects of light on human circadian rhythms, sleep and mood
Christine Blume, Corrado Garbazza, Manuel Spitschan · Somnologie - Schlafforschung und Schlafmedizin · 2019 · 626 citations
Humans live in a 24-hour environment, in which light and darkness follow a diurnal pattern. Our circadian pacemaker, the suprachiasmatic nuclei (SCN) in the hypothalamus, is entrained to the 24-hour solar day via a pathway from the retina and synchronises our internal biological rhythms. Rhythmic variations in ambient illumination impact behaviours such as rest during sleep and activity during wakefulness as well as their underlying biological processes. Rather recently, the availability of artificial light has substantially changed the light environment, especially during evening and night hours. This may increase the risk of developing circadian rhythm sleep-wake disorders (CRSWD), which are often caused by a misalignment of endogenous circadian rhythms and external light-dark cycles. While the exact relationship between the availability of artificial light and CRSWD remains to be established, nocturnal light has been shown to alter circadian rhythms and sleep in humans. On the other hand, light can also be used as an effective and noninvasive therapeutic option with little to no side effects, to improve sleep,mood and general well-being. This article reviews our current state of knowledge regarding the effects of light on circadian rhythms, sleep, and mood.
Andrew J. K. Phillips, William M. Clerx, Conor S. O’Brien +6 more · Scientific Reports · 2017 · 602 citations
The association of irregular sleep schedules with circadian timing and academic performance has not been systematically examined. We studied 61 undergraduates for 30 days using sleep diaries, and quantified sleep regularity using a novel metric, the sleep regularity index (SRI). In the most and least regular quintiles, circadian phase and light exposure were assessed using salivary dim-light melatonin onset (DLMO) and wrist-worn photometry, respectively. DLMO occurred later (00:08 ± 1:54 vs. 21:32 ± 1:48; p < 0.003); the daily sleep propensity rhythm peaked later (06:33 ± 0:19 vs. 04:45 ± 0:11; p < 0.005); and light rhythms had lower amplitude (102 ± 19 lux vs. 179 ± 29 lux; p < 0.005) in Irregular compared to Regular sleepers. A mathematical model of the circadian pacemaker and its response to light was used to demonstrate that Irregular vs. Regular group differences in circadian timing were likely primarily due to their different patterns of light exposure. A positive correlation (r = 0.37; p < 0.004) between academic performance and SRI was observed. These findings show that irregular sleep and light exposure patterns in college students are associated with delayed circadian rhythms and lower academic performance. Moreover, the modeling results reveal that light-based interventions may be therapeutically effective in improving sleep regularity in this population.
Sarah L. Chellappa, Roland Steiner, Peter Blattner +3 more · PLoS ONE · 2011 · 541 citations
BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.
Exposure to Bright Light and Darkness to Treat Physiologic Maladaptation to Night Work
Charles A. Czeisler, Michael P. Johnson, Jeanne F. Duffy +3 more · New England Journal of Medicine · 1990 · 587 citations
Working at night results in a misalignment between the sleep-wake cycle and the output of the hypothalamic pacemaker that regulates the circadian rhythms of certain physiologic and behavioral variables. We evaluated whether such physiologic maladaptation to nighttime work could be prevented effectively by a treatment regimen of exposure to bright light during the night and darkness during the day. We assessed the functioning of the circadian pacemaker in five control and five treatment studies in order to assess the extent of adaptation in eight normal young men to a week of night work. In the control studies, on the sixth consecutive night of sedentary work in ordinary light (approximately 150 lux), the mean (+/- SEM) nadir of the endogenous temperature cycle continued to occur during the night (at 3:31 +/- 0:56 hours), indicating a lack of circadian adaptation to the nighttime work schedule. In contrast, the subjects in the treatment studies were exposed to bright light (7000 to 12,000 lux) at night and to nearly complete darkness during the day, and the temperature nadir shifted after four days of treatment to a significantly later, midafternoon hour (14:53 +/- 0:32; P less than 0.0001), indicating a successful circadian adaptation to daytime sleep and nighttime work. There were concomitant shifts in the 24-hour patterns of plasma cortisol concentration, urinary excretion rate, subjective assessment of alertness, and cognitive performance in the treatment studies. These shifts resulted in a significant improvement in both alertness and cognitive performance in the treatment group during the night-shift hours. We conclude that maladaptation of the human circadian system to night work, with its associated decline in alertness, performance, and quality of daytime sleep, can be treated effectively with scheduled exposure to bright light at night and darkness during the day.
Seasonality in human cognitive brain responses
Christelle Meyer, Vincenzo Muto, Mathieu Jaspar +13 more · Proceedings of the National Academy of Sciences · 2016 · 143 citations
Brain activity during sustained attention peaks in summer and bottoms out in winter, while working memory brain activity peaks in autumn and reaches its lowest in spring — and these seasonal shifts occur even when people are kept in a windowless, climate-controlled lab for 4.5 days, suggesting the human brain carries an internal seasonal clock that affects cognition independently of immediate weather or daylight.
Read the breakdown →Effects of blue light on the circadian system and eye physiology
Gianluca Tosini, Ian T. Ferguson, Kazuo Tsubota · Molecular vision · 2016 · 490 citations
Light-emitting diodes (LEDs) have been used to provide illumination in industrial and commercial environments. LEDs are also used in TVs, computers, smart phones, and tablets. Although the light emitted by most LEDs appears white, LEDs have peak emission in the blue light range (400-490 nm). The accumulating experimental evidence has indicated that exposure to blue light can affect many physiologic functions, and it can be used to treat circadian and sleep dysfunctions. However, blue light can also induce photoreceptor damage. Thus, it is important to consider the spectral output of LED-based light sources to minimize the danger that may be associated with blue light exposure. In this review, we summarize the current knowledge of the effects of blue light on the regulation of physiologic functions and the possible effects of blue light exposure on ocular health.
Daylight: What makes the difference?
Martine Knoop, Oliver Stefani, Bruno Bueno +9 more · Lighting Research & Technology · 2019 · 226 citations
Light is necessary for vision; it enables us to sense and perceive our surroundings and in many direct and indirect ways, via eye and skin, affects our physiological and psychological health. The use of light in built environments has comfort, behavioural, economic and environmental consequences. Daylight has many particular benefits including excellent visual performance, permitting good eyesight, effective entrainment of the circadian system as well as a number of acute non-image forming effects and the important role of vitamin D production. Some human responses to daylight seem to be well defined whilst others require more research to be adequately understood. This paper presents an overview of current knowledge on how the characteristics of daylight play a role in fulfilling these and other functions often better than electric lighting as conventionally delivered.
The influence of the environment and lifestyle on myopia
Sayantan Biswas, Antonio El Kareh, Mariyem Qureshi +5 more · Journal of PHYSIOLOGICAL ANTHROPOLOGY · 2024 · 159 citations
Spending at least 2 hours per day outdoors in natural light appears to reduce the risk of developing myopia in children by roughly 50%, while excessive near work (reading, screens) increases risk independently — but the evidence for adults is weaker, and the mechanisms remain incompletely understood.
Read the breakdown →Antoine Viola, Lynette M. James, Luc J. M. Schlangen +1 more · Scandinavian Journal of Work Environment & Health · 2008 · 562 citations
OBJECTIVES: Specifications and standards for lighting installations in occupational settings are based on the spectral sensitivity of the classical visual system and do not take into account the recently discovered melanopsin-based, blue-light-sensitive photoreceptive system. The authors investigated the effects of exposure to blue-enriched white light during daytime workhours in an office setting. METHODS: The experiment was conducted on 104 white-collar workers on two office floors. After baseline assessments under existing lighting conditions, every participant was exposed to two new lighting conditions, each lasting 4 weeks. One consisted of blue-enriched white light (17 000 K) and the other of white light (4000 K). The order was balanced between the floors. Questionnaire and rating scales were used to assess alertness, mood, sleep quality, performance, mental effort, headache and eye strain, and mood throughout the 8-week intervention. RESULTS: Altogether 94 participants [mean age 36.4 (SD 10.2) years] were included in the analysis. Compared with white light (4000 K), blue-enriched white light (17 000 K) improved the subjective measures of alertness (P<0.0001), positive mood (P=0.0001), performance (P<0.0001), evening fatigue (P=0.0001), irritability (P=0.004), concentration (P<0.0001), and eye discomfort (P=0.002). Daytime sleepiness was reduced (P=0.0001), and the quality of subjective nocturnal sleep (P=0.016) was improved under blue-enriched white light. When the participants' expectation about the effect of the light treatments was entered into the analysis as a covariate, significant effects persisted for performance, alertness, evening fatigue, irritability, difficulty focusing, concentrating, and blurred vision. CONCLUSIONS: Exposure to blue-enriched white light during daytime workhours improves subjective alertness, performance, and evening fatigue.
Cyr M, Artenie DZ, Al Bikaii A +3 more · Sleep Health · 2023 · 15 citations
Raymond W. Lam · American Journal of Psychiatry · 2006 · 52 citations
Light therapy (10,000 lux for 30 minutes each morning) and the antidepressant fluoxetine (20 mg/day) were equally effective at treating winter seasonal affective disorder after 8 weeks, with a 67% response rate in both groups, but light therapy worked faster (showing improvement within 1 week) and caused fewer side effects like agitation and sleep disturbance.
Read the breakdown →Erin E. Michalak, Greg Murray, Anthony Levitt +6 more · Psychological Medicine · 2006 · 28 citations
This study found that both 10,000 lux light therapy and 20 mg fluoxetine significantly improved quality of life in patients with seasonal affective disorder over 8 weeks, with no significant difference between the two treatments, suggesting either can be an effective strategy for improving well-being during winter months.
Read the breakdown →Bright Light Treatment of Winter Depression
Charmane I. Eastman, Michael A. Young, Louis Fogg +2 more · Archives of General Psychiatry · 1998 · 345 citations
BACKGROUND: Bright light therapy is the recommended treatment for winter seasonal affective disorder (SAD). However, the studies with the best placebo controls have not been able to demonstrate that light treatment has a benefit beyond its placebo effect. METHODS: Ninety-six patients with SAD completed the study. Patients were randomly assigned to 1 of 3 treatments for 4 weeks, each 1.5 hours per day: morning light (average start time about 6 AM), evening light (average start about 9 PM), or morning placebo (average start about 6 AM). The bright light (approximately 6000 lux) was produced by light boxes, and the placebos were sham negative-ion generators. Depression ratings using the Structured Interview Guide for the Hamilton Depression Rating Scale, SAD version (SIGH-SAD) were performed weekly. RESULTS: There were no differences among the 3 groups in expectation ratings or mean depression scores after 4 weeks of treatment. However, strict response criteria revealed statistically significant differences; after 3 weeks of treatment morning light produced more of the complete or almost complete remissions than placebo. By 1 criterion (24-item SIGH-SAD score <50% of baseline and < or =8), 61% of the patients responded to morning light, 50% to evening light, and 32% to placebo after 4 weeks of treatment. CONCLUSIONS: Bright light therapy had a specific antidepressant effect beyond its placebo effect, but it took at least 3 weeks for a significant effect to develop. The benefit of light over placebo was in producing more of the full remissions.
The Role of Daylight for Humans: Gaps in Current Knowledge
Mirjam Münch, Anna Wirz‐Justice, Steven A. Brown +7 more · Clocks & Sleep · 2020 · 153 citations
Daylight stems solely from direct, scattered and reflected sunlight, and undergoes dynamic changes in irradiance and spectral power composition due to latitude, time of day, time of year and the nature of the physical environment (reflections, buildings and vegetation). Humans and their ancestors evolved under these natural day/night cycles over millions of years. Electric light, a relatively recent invention, interacts and competes with the natural light-dark cycle to impact human biology. What are the consequences of living in industrialised urban areas with much less daylight and more use of electric light, throughout the day (and at night), on general health and quality of life? In this workshop report, we have classified key gaps of knowledge in daylight research into three main groups: (I) uncertainty as to daylight quantity and quality needed for "optimal" physiological and psychological functioning, (II) lack of consensus on practical measurement and assessment methods and tools for monitoring real (day) light exposure across multiple time scales, and (III) insufficient integration and exchange of daylight knowledge bases from different disciplines. Crucial short and long-term objectives to fill these gaps are proposed.
Daytime Light Exposure Dynamically Enhances Brain Responses
Gilles Vandewalle, Evelyne Balteau, Christophe Phillips +11 more · Current Biology · 2006 · 307 citations
Light Therapy for Seasonal Affective Disorder with Blue Narrow-Band Light-Emitting Diodes (LEDs)
Gena Glickman, Brenda Byrne, Carissa Pineda +2 more · Biological Psychiatry · 2005 · 260 citations
Solar radiation and human health
Asta Juzeniene, P. Brekke, Arne Dahlback +6 more · Reports on Progress in Physics · 2011 · 164 citations
The Sun has played a major role in the development of life on Earth. In Western culture, people are warned against Sun exposure because of its adverse effects: erythema, photoimmunosuppression, photoageing, photocarcinogenesis, cataracts and photokeratitis. However, Sun exposure is also beneficial, since moderate doses give beneficial physiological effects: vitamin D synthesis, reduction of blood pressure and mental health. Shortage of Sun exposure may be even more dangerous to human health than excessive exposure. Avoiding Sun exposure leads to vitamin D deficiency which is associated not only with rickets and osteomalacia, but also with increased risk of cardiovascular disease, multiple sclerosis, rheumatoid arthritis, diabetes, influenza, many types of cancer and adverse pregnancy outcomes. Solar radiation induces nitric oxide release in tissue and immediate pigment darkening which certainly play important roles, although these are still unknown. Action spectra relevant for health are described. We will also review what is known about spectral and intensity variations of terrestrial solar radiation as well as its penetration through the atmosphere and into human skin and tissue.
Seasonal changes, sleep length and circadian preference among twins with bipolar disorder
Reeta Hakkarainen, Carolina Johansson, Tuula Kieseppä +4 more · BMC Psychiatry · 2003 · 84 citations
BACKGROUND: We aimed at studying the seasonal changes in mood and behaviour, the distribution of hospital admissions by season, and the persistence of the circadian type in twins with bipolar disorder and their healthy co-twins. METHODS: All Finnish like-sex twins born from 1940 to 1969 were screened for a diagnosis of bipolar type I disorder. The diagnosis was assessed with a structured research interview, and the study subjects (n = 67) filled in the Seasonal Pattern Assessment Questionnaire (SPAQ) and the Morningness-Eveningness Questionnaire (MEQ). For studying the persistence of the habitual sleep length and circadian type, we used data derived from the Finnish Twin Cohort Questionnaire (FTCQ). Bipolar twins were compared with their healthy co-twins. RESULTS: Bipolar twins had greater seasonal changes in sleep length (p = 0.01) and mood (p = 0.01), and higher global seasonality scores (p = 0.03) as compared with their co-twins with no mental disorder. Sunny days (p = 0.03) had a greater positive effect on wellbeing in the bipolar than healthy co-twins. CONCLUSIONS: Our results support the view that bipolar disorder is sensitive to the environmental influence in general and to the seasonal effect in specific. Exposure to natural light appears to have a substantial effect on wellbeing in twins with bipolar disorder.
Light Exposure and Physical Activity in Myopic and Emmetropic Children
Scott A. Read, Michael J. Collins, Stephen J. Vincent · Optometry and Vision Science · 2014 · 194 citations
PURPOSE: To objectively assess daily light exposure and physical activity levels in myopic and emmetropic children. METHODS: One hundred two children (41 myopes and 61 emmetropes) aged 10 to 15 years old had simultaneous objective measures of ambient light exposure and physical activity collected over a 2-week period during school term, using a wrist-worn actigraphy device (Actiwatch 2). Measures of visible light illuminance and physical activity were captured every 30 seconds, 24 hours a day over this period. Mean hourly light exposure and physical activity for weekdays and weekends were examined. To ensure that seasonal variations did not confound comparisons, the light and activity data of the 41 myopes was compared with 41 age- and gender-matched emmetropes who wore the Actiwatch over the same 2-week period. RESULTS: Mean light exposure and physical activity for all 101 children with valid data exhibited significant changes with time of day and day of the week (p < 0.0001). On average, greater daily light exposure occurred on weekends compared to weekdays (p < 0.05), and greater physical activity occurred on weekdays compared to weekends (p < 0.01). Myopic children (n = 41, mean daily light exposure 915 ± 519 lx) exhibited significantly lower average light exposure compared to 41 age- and gender-matched emmetropic children (1272 ± 625 lx, p < 0.01). The amount of daily time spent in bright light conditions (>1000 lx) was also significantly greater in emmetropes (127 ± 51 minutes) compared to myopes (91 ± 44 minutes, p < 0.001). No significant differences were found between the average daily physical activity levels of myopes and emmetropes (p > 0.05). CONCLUSIONS: Myopic children exhibit significantly lower daily light exposure, but no significant difference in physical activity compared to emmetropic children. This suggests the important factor involved in documented associations between myopia and outdoor activity is likely exposure to bright outdoor light rather than greater physical activity.
Yingying Zhu, Minqi Yang, Ying Yao +4 more · Environment and Behavior · 2017 · 133 citations
This study investigated the impact of indoor illuminance and correlated color temperature (CCT) on healthy adults’ cognitive performance, subjective mood, and alertness during daytime office hours and differences in time-of-day effects. A 2(illuminance) × 2(CCT) × 2(morning vs. afternoon) mixed design ( N = 60) was employed. Participants felt less sleepy in the bright light exposure. The low “cool” lighting induced the least positive mood. The effects of illuminance and CCT on subjective feelings were not time-of-day dependent. The results demonstrated the slowest responses in inhibition, working memory, and recognition of facial expression tasks in the low “warm” lighting. The effect on long-term memory was most pronounced under the high “cool” light exposure, but only in the afternoon for recognition of neutral words. The findings suggest that future research on good indoor lighting should consider illuminance levels and CCT as well as other variables to optimize lighting effects during regular daytime hours.
The Effects of Lighting on Mental and Cognitive Performance: A Structured Systematic Review
Rostam Golmohammadi, Mohsen Mehdinia, Reza Shahida +1 more · Iranian Journal of Ergonomics · 2017 · 5 citations
This systematic review found that lighting, particularly bright daylight-like light (short wavelength, high intensity) in the morning, influences various aspects of cognitive function, mood, and sleep quality, suggesting that optimizing lighting can enhance mental performance and well-being.
Read the breakdown →Rohan Nagare, May Woo, Piers MacNaughton +3 more · International Journal of Environmental Research and Public Health · 2021 · 64 citations
As the primary environmental cue for the body's master biological clock, light-dark patterns are key for circadian alignment and are ultimately fundamental to multiple dimensions of health including sleep and mental health. Although daylight provides the proper qualities of light for promoting circadian alignment, our modern indoor lifestyles offer fewer opportunities for adequate daylight exposure. This field study explores how increasing circadian-effective light in residences affects circadian phase, sleep, vitality, and mental health. In this crossover study, 20 residents spent one week in their apartments with electrochromic glass windows and another week with functionally standard windows with blinds. Calibrated light sensors revealed higher daytime circadian-effective light levels with the electrochromic glass windows, and participants exhibited consistent melatonin onset, a 22-min earlier sleep onset, and higher sleep regularity. In the blinds condition, participants exhibited a 15-min delay in dim light melatonin onset, a delay in subjective vitality throughout the day, and an overall lower positive affect. This study demonstrates the impact of daytime lighting on the physiological, behavioral, and subjective measures of circadian health in a real-world environment and stresses the importance of designing buildings that optimize daylight for human health and wellbeing.
Effects of illuminance and correlated color temperature of indoor light on emotion perception
Yun Li, Taotao Ru, Qingwei Chen +3 more · Scientific Reports · 2021 · 61 citations
The acute non-image forming (NIF) effects of daytime light on momentary mood had been-although not always-established in the current literature. It still remains largely unknown whether short-time light exposure would modulate emotion perception in healthy adults. The current study (N = 48) was conducted to explore the effects of illuminance (100 lx vs. 1000 lx at eye level) and correlated color temperature (CCT, 2700 K vs. 6500 K) on explicit and implicit emotion perception that was assessed with emotional face judgment task and emotional oddball task respectively. Results showed that lower CCT significantly decreased negative response bias in the face judgment task, with labeling ambiguous faces less fearful under 2700 K vs. 6500 K condition. Moreover, participants responded slightly faster for emotional pictures under 6500 K vs. 2700 K condition, but no significant effect of illuminance or CCT on negativity bias was revealed in the emotional oddball task. These findings highlighted the differential role of illuminance and CCT in regulating instant emotion perception and suggested a task-dependent moderation of light spectrum on negativity bias.
Dawn simulation and bright light in the treatment of SAD: a controlled study
David Avery, Derek N. Eder, Mary Ann Bolte +4 more · Biological Psychiatry · 2001 · 123 citations
Light exposure behaviors predict mood, memory and sleep quality
Mushfiqul Anwar Siraji, Manuel Spitschan, Vineetha Kalavally +1 more · Scientific Reports · 2023 · 57 citations
= 28 ± 9) completed the Light Exposure Behavior Assessment tool that measured five light exposure behaviors. They also completed the Morningness-Eveningness Questionnaire, Positive and Negative Affect Schedule, Pittsburgh Sleep Quality Index, and single items assessing trouble in memory and concentration. A partial least square structural equation model, showing 72.72% predictive power, revealed that less use of wearable blue filters outdoors during the day and more within one hour before sleep predicted early peak time (direct effect = -0.25). Increased time spent outdoors predicted a positive affect (direct effect = 0.33) and a circadian phase advancement (direct effect: rising time = 0.14, peak time = 0.20, retiring time = 0.17). Increased use of mobile phone before sleep predicted a circadian phase delay (direct effect: retiring time = -0.25; rising time = -0.23; peak time = -0.22; morning affect = -0.12), reduced sleep quality (direct effect = 0.13), and increased trouble in memory and concentration (total effect = 0.20 and 0.23, respectively). Increased use of tunable, LED, or dawn-simulating electric light in the morning and daytime predicted a circadian phase advancement (direct effect: peak time = 0.15, morning affect = 0.14, retiring time = 0.15) and good sleep quality (direct effect = -0.16). The results provide valuable insights into developing a healthy light diet to promote health and wellness.
Enhancement of nighttime alertness and performance with bright ambient light
Scott S. Campbell, Drew Dawson∥ · Physiology & Behavior · 1990 · 204 citations
F Shishegar, L Bellia, F Bisegna +97 more · International Journal of Advances in Chemical Engineering and Biological Sciences · 2016 · 73 citations
Studies show that the quality of the school environment significantly influences students' academic performance. Among the many attributes of the school environment, light is one of the most visible and talked about ones. Lighting in the classrooms has been the subject of many studies for over a century. In recent years, special attention has been given to the impact of natural light on learning as light has physiological, psychological and behavioral influences on school children as well as workers. A multitude of surveys has indicated also that daylight impacts the health. We believe that workers' and students' health, satisfaction, attention, and consequently performance are improved with the help of natural light. This paper discusses the current literature and design-based evidence to evaluate the impacts of natural light on office workers and students' scholastic performance. Issues of timing and exposure to daylight are also discussed.
Raymond P. Najjar, Luzian Wolf, Jacques Taillard +4 more · PLoS ONE · 2014 · 73 citations
Studies in Polar Base stations, where personnel have no access to sunlight during winter, have reported circadian misalignment, free-running of the sleep-wake rhythm, and sleep problems. Here we tested light as a countermeasure to circadian misalignment in personnel of the Concordia Polar Base station during the polar winter. We hypothesized that entrainment of the circadian pacemaker to a 24-h light-dark schedule would not occur in all crew members (n = 10) exposed to 100-300 lux of standard fluorescent white (SW) light during the daytime, and that chronic non-time restricted daytime exposure to melanopsin-optimized blue-enriched white (BE) light would establish an a stable circadian phase, in participants, together with increased cognitive performance and mood levels. The lighting schedule consisted of an alternation between SW lighting (2 weeks), followed by a BE lighting (2 weeks) for a total of 9 weeks. Rest-activity cycles assessed by actigraphy showed a stable rest-activity pattern under both SW and BE light. No difference was found between light conditions on the intra-daily stability, variability and amplitude of activity, as assessed by non-parametric circadian analysis. As hypothesized, a significant delay of about 30 minutes in the onset of melatonin secretion occurred with SW, but not with BE light. BE light significantly enhanced well being and alertness compared to SW light. We propose that the superior efficacy of blue-enriched white light versus standard white light involves melanopsin-based mechanisms in the activation of the non-visual functions studied, and that their responses do not dampen with time (over 9-weeks). This work could lead to practical applications of light exposure in working environment where background light intensity is chronically low to moderate (polar base stations, power plants, space missions, etc.), and may help design lighting strategies to maintain health, productivity, and personnel safety.
Maaike E. Kompier, K.C.H.J. Smolders, Rick Kramer +2 more · Building and Environment · 2022 · 47 citations
In this field study, we tested the effects of dynamic light scenarios and personal illuminance on visual experience, sleepiness, cognitive performance and sleep in an operational office. Two dynamic light scenarios, different in timing but with equal luminous exposure, were tested against a reference scenario in a counterbalanced crossover design. Frequent assessments of visual experience, alertness, performance and sleep showed that in both dynamic light scenarios visual comfort was slightly lower compared to the constant scenario. Additionally, sleepiness was lowest in the scenario with the brighter light timed around noon, whereas task performance and actual sleep were not significantly affected. The measured personal illuminance did not predict sleepiness and performance, yet variation and timing of these illuminances did positively relate to sleep onset and duration. When studying or implementing light scenarios aiming to deliver integrative lighting, the spatial and behavioral context should be considered as well.
The Influence of Environmental Factors on Sleep Quality in Hospitalized Medical Patients
M. Bano, Federica Chiaromanni, Michela Corrias +8 more · Frontiers in Neurology · 2014 · 62 citations
INTRODUCTION: Sleep-wake disturbances are common in hospitalized patients but few studies have assessed them systematically. The aim of the present study was to assess sleep quality in a group of medical inpatients, in relation to environmental factors, and the switch to daylight-saving time. METHODS: Between March and April 2013, 118 consecutive inpatients were screened and 99 (76 ± 11 years; hospitalization: 8 ± 7 days) enrolled. They slept in double or quadruple rooms, facing South/South-East, and were qualified as sleeping near/far from the window. They underwent daily sleep assessment by standard questionnaires/diaries. Illuminance was measured by a luxmeter at each patient's eye-level, four times per day. Noise was measured at the same times by a phonometer. Information was recorded on room lighting, position of the rolling shutters and number/type of extra people in the room. RESULTS: Compliance with sleep-wake assessment was poor, with a range of completion of 2-59%, depending on the questionnaires. Reported sleep quality was sufficient and sleep timing dictated by hospital routine; 33% of the patients reported one/more sleepless nights. Illuminance was generally low, and rolling shutters half-way down for most of the 24 h. Patients who slept near the window were exposed to more light in the morning (i.e., 222 ± 72 vs. 174 ± 85 lux, p < 0.05 before the switch; 198 ± 72 vs. 141 ± 137 lux, p < 0.01 after the switch) and tended to sleep better (7.3 ± 1.8 vs. 5.8 ± 2.4 on a 1-10 scale, before the switch, p < 0.05; 7.7 ± 2.3 vs. 6.6 ± 1.8, n.s. after the switch). Noise levels were higher than recommended for care units but substantially comparable across times/room types. No significant differences were observed in sleep parameters before/after the switch. CONCLUSION: Medical wards appear to be noisy environments, in which limited attention is paid to light/dark hygiene. An association was observed between sleep quality and bed position/light exposure, which is worthy of further study.
Abnormal Hypothalamic Response to Light in Seasonal Affective Disorder
Gilles Vandewalle, Marc Hébert, Catherine Beaulieu +10 more · Biological Psychiatry · 2011 · 59 citations
Greg Leach, Widya Adidharma, Lili Yan · PLoS ONE · 2013 · 79 citations
Seasonal Affective Disorder (SAD) is one of the most common mood disorders with depressive symptoms recurring in winter when there is less sunlight. The fact that light is the most salient factor entraining circadian rhythms leads to the phase-shifting hypothesis, which suggests that the depressive episodes of SAD are caused by misalignments between the circadian rhythms and the habitual sleep times. However, how changes in environmental lighting conditions lead to the fluctuations in mood is largely unknown. The objective of this study is to develop an animal model for some of the features/symptoms of SAD using the diurnal grass rats Arvichantis niloticus and to explore the neural mechanisms underlying the light associated mood changes. Animals were housed in either a 12∶12 hr bright light∶dark (1000lux, BLD) or dim light∶dark (50lux, DLD) condition. The depression-like behaviors were assessed by sweet-taste Saccharin solution preference (SSP) and forced swimming test (FST). Animals in the DLD group showed higher levels of depression-like behaviors compared to those in BLD. The anxiety-like behaviors were assessed in open field and light/dark box test, however no significant differences were observed between the two groups. The involvement of the circadian system on depression-like behaviors was investigated as well. Analysis of locomotor activity revealed no major differences in daily rhythms that could possibly contribute to the depression-like behaviors. To explore the neural substrates associated with the depression-like behaviors, the brain tissues from these animals were analyzed using immunocytochemistry. Attenuated indices of 5-HT signaling were observed in DLD compared to the BLD group. The results lay the groundwork for establishing a novel animal model and a novel experimental paradigm for SAD. The results also provide insights into the neural mechanisms underlying light-dependent mood changes.
A controlled study of light therapy in women with late luteal phase dysphoric disorder
Raymond W. Lam, Diana Carter, Shaila Misri +3 more · Psychiatry Research · 1999 · 86 citations
A Controlled Trial of Light Therapy for the Treatment of Pediatric Seasonal Affective Disorder
Susan E. Swedo, Albert J. Allen, Carol A. Glod +8 more · Journal of the American Academy of Child & Adolescent Psychiatry · 1997 · 85 citations
Ei Ei Khaing Nang, Gulifeiya Abuduxike, Paul Posadzki +9 more · Tunnelling and Underground Space Technology · 2018 · 56 citations
Aki Kawasaki, Sebastian Wisniewski, Beth Healey +4 more · Scientific Reports · 2018 · 56 citations
Long-term daylight deprivation such as during the Antarctic winter has been shown to lead to delayed sleep timing and sleep fragmentation. We aimed at testing whether retinal sensitivity, sleep and circadian rest-activity will change during long-term daylight deprivation on two Antarctic bases (Concordia and Halley VI) in a total of 25 healthy crew members (mean age: 34 ± 11y; 7f). The pupil responses to different light stimuli were used to assess retinal sensitivity changes. Rest-activity cycles were continuously monitored by activity watches. Overall, our data showed increased pupil responses under scotopic (mainly rod-dependent), photopic (mainly L-/M-cone dependent) as well as bright-blue light (mainly melanopsin-dependent) conditions during the time without direct sunlight. Circadian rhythm analysis revealed a significant decay of intra-daily stability, indicating more fragmented rest-activity rhythms during the dark period. Sleep and wake times (as assessed from rest-activity recordings) were significantly delayed after the first month without sunlight (p < 0.05). Our results suggest that during long-term daylight deprivation, retinal sensitivity to blue light increases, whereas circadian rhythm stability decreases and sleep-wake timing is delayed.
Effects of fluoxetine <i>versus</i> bright light in the treatment of seasonal affective disorder
Stephan Ruhrmann, Siegfried Kasper, Barbara Hawellek +4 more · Psychological Medicine · 1998 · 82 citations
BACKGROUND: Disturbances of serotonergic neurotransmission appear to be particularly important for the pathophysiology of winter depression. This study investigated whether fluoxetine has antidepressant effects comparable to bright light in the treatment of seasonal affective disorder (winter type). METHOD: A randomized, parallel design was used with rater and patients blind to treatment conditions. One week of placebo (phase I) was followed by 5 weeks of treatment (phase II) with fluoxetine (20 mg per day) and a placebo light condition versus bright light (3000 lux, 2 h per day) and a placebo drug. There were 40 patients (20 in each treatment condition) suffering from seasonal affective disorder (SAD) according to DSM-III-R who had a total score on the Hamilton Depression Scale of at least 16. RESULTS: Forty patients entered phase II and 35 completed it (one drop-out in the fluoxetine group and four in the bright light group). Fourteen (70%) of the patients treated with bright light and 13 (65%) of those treated with fluoxetine were responders (NS). The remission rate in the bright light group tended to be superior (bright light 50%, fluoxetine 25%; P = 0.10). Light therapy improved HDRS scores significantly faster, while fluoxetine had a faster effect on atypical symptoms. Light treatment in the morning produced a significantly faster onset of improvement, but at the end of treatment the time of light application seemed not to be crucial. CONCLUSION: Both treatments produced a good antidepressant effect and were well tolerated. An apparently better response to bright light requires confirmation in a larger sample.
Daylighting Metrics for Residential Buildings
John Mardaljevic, Marilyne Andersen, Nicolas Roy +1 more · Infoscience (Ecole Polytechnique Fédérale de Lausanne) · 2011 · 72 citations
It is now widely accepted that the standard method for daylighting evaluation - the daylight factor – is due for replacement with metrics founded on absolute values for luminous quantities predicted over the course of a full year using sun and sky conditions derived from standardised climate files. The move to more realistic measures of daylighting introduces significant levels of additional complexity in both the simulation of the luminous quantities and the reduction of the simulation data to readily intelligible metrics. The simulation component, at least for buildings with standard glazing materials, is reasonably well understood. There is no consensus however on the composition of the metrics, and their formulation is an ongoing area of active research. Additionally, non-domestic and residential buildings present very different evaluation scenarios and it is not yet clear if a single metric would be applicable to both. This study uses a domestic dwelling as the setting to investigate and explore the applicability of daylighting metrics for residential buildings. In addition to daylighting provision for task and disclosing the potential for reducing electric lighting usage, we also investigate the formulation of metrics for non-visual effects such as entrainment of the circadian system.
Haruna Fukushige, Yumi Fukuda, Mizuho Tanaka +7 more · Journal of PHYSIOLOGICAL ANTHROPOLOGY · 2014 · 52 citations
BACKGROUND: The purpose of the present study is to investigate effects of tryptophan intake and light exposure on melatonin secretion and sleep by modifying tryptophan ingestion at breakfast and light exposure during the daytime, and measuring sleep quality (by using actigraphy and the OSA sleep inventory) and melatonin secretion at night. METHODS: Thirty three male University students (mean ± SD age: 22 ± 3.1 years) completed the experiments lasting 5 days and 4 nights. The subjects were randomly divided into four groups: Poor*Dim (n = 10), meaning a tryptophan-poor breakfast (55 mg/meal) in the morning and dim light environment (<50 lx) during the daytime; Rich*Dim (n = 7), tryptophan-rich breakfast (476 mg/meal) and dim light environment; Poor*Bright (n = 9), tryptophan-poor breakfast and bright light environment (>5,000 lx); and Rich*Bright (n = 7), tryptophan-rich breakfast and bright light. RESULTS: Saliva melatonin concentrations on the fourth day were significantly lower than on the first day in the Poor*Dim group, whereas they were higher on the fourth day in the Rich*Bright group. Creatinine-adjusted melatonin in urine showed the same direction as saliva melatonin concentrations. These results indicate that the combination of a tryptophan-rich breakfast and bright light exposure during the daytime could promote melatonin secretion at night; further, the observations that the Rich*Bright group had higher melatonin concentrations than the Rich*Dim group, despite no significant differences being observed between the Poor*Dim and Rich*Dim groups nor the Poor*Bright and Rich*Bright groups, suggest that bright light exposure in the daytime is an important contributor to raised melatonin levels in the evening. CONCLUSIONS: This study is the first to report the quantitative effects of changed tryptophan intake at breakfast combined with daytime light exposure on melatonin secretion and sleep quality. Evening saliva melatonin secretion changed significantly and indicated that a tryptophan-rich breakfast and bright light exposure during the daytime promoted melatonin secretion at this time.
Tutorial: Theoretical Considerations When Planning Research on Human Factors in Lighting
Yvonne de Kort · LEUKOS The Journal of the Illuminating Engineering Society of North America · 2019 · 69 citations
Research on human functioning is notoriously difficult. This particularly holds for the study of light effects, at least if one wants to go beyond establishing that changes in light “have an effect” and understand why this effect occurs—in other words, if one wants to make causal inferences about the mechanism behind it. The latter is, of course, crucial for generalizing insights and being able to use them effectively in other contexts. The culmination of many decades of research has taught us that light affects psychological functioning in numerous ways and through various pathways. This implies that, regardless of the investigator’s particular interests in either of those mechanisms, generally all will be at play, simultaneously, for participants in any lighting study. The present tutorial aims to address this complexity and how to deal with it by concisely describing the most important pathways that we currently are aware of. Such awareness is important both in contemplating the design and methodology of a study and in interpreting results from other studies and generalizing them to a particular application or light design.
Paul H. Desan, Andrea J. Weinstein, Erin E. Michalak +8 more · BMC Psychiatry · 2007 · 72 citations
BACKGROUND: Recent research has emphasized that the human circadian rhythm system is differentially sensitive to short wavelength light. Light treatment devices using efficient light-emitting diodes (LEDs) whose output is relatively concentrated in short wavelengths may enable a more convenient effective therapy for Seasonal Affective Disorder (SAD). METHODS: The efficacy of a LED light therapy device in the treatment of SAD was tested in a randomized, double-blind, placebo-controlled, multi-center trial. Participants aged 18 to 65 with SAD (DSM-IV major depression with seasonal pattern) were seen at Baseline and Randomization visits separated by 1 week, and after 1, 2, 3 and 4 weeks of treatment. Hamilton Depression Rating Scale scores (SIGH-SAD) were obtained at each visit. Participants with SIGH-SAD of 20 or greater at Baseline and Randomization visits were randomized to active or control treatment: exposure to the Litebook LED treatment device (The Litebook Company Ltd., Alberta, Canada) which delivers 1,350 lux white light (with spectral emission peaks at 464 nm and 564 nm) at a distance of 20 inches or to an inactivated negative ion generator at a distance of 20 inches, for 30 minutes a day upon awakening and prior to 8 A.M. RESULTS: Of the 26 participants randomized, 23 completed the trial. Mean group SIGH-SAD scores did not differ significantly at randomization. At trial end, the proportions of participants in remission (SIGH-SAD less than 9) were significantly greater (Fisher's exact test), and SIGH-SAD scores, as percent individual score at randomization, were significantly lower (t-test), with active treatment than with control, both in an intent-to-treat analysis and an observed cases analysis. A longitudinal repeated measures ANOVA analysis of SIGH-SAD scores also indicated a significant interaction of time and treatment, showing superiority of the Litebook over the placebo condition. CONCLUSION: The results of this pilot study support the hypothesis that light therapy with the Litebook is an effective treatment for SAD. TRIAL REGISTRATION: Clinicaltrials.gov: NCT00139997.
Books on this topic
