Investigating the contribution of short wavelengths in the alerting effect of bright light

Circadian light therapy and light dose for depressed young people: a systematic review and meta-analysis

Background

Empirical evidence has shown that light therapy (LT) can reduce depression symptoms by stimulating circadian rhythms. However, there is skepticism and inconclusive results, along with confusion regarding dosing. The purpose of this study is to quantify light as a stimulus for the circadian system and create a dose-response relationship that can help reduce maladies among adolescents and young adults (AYAs). This will provide a reference for light exposure and neural response, which are crucial in the neuropsychological mechanism of light intervention. The study also aims to provide guidance for clinical application.

Methods

The latest quantitative model of CLA (circadian light) and CSt,f (circadian stimulus) was adopted to quantify light dose for circadian phototransduction in youth depression-related light therapy. Articles published up to 2023 through Web of Science, Cochrane Library, Medline (OVID), CINAHL, APA PsycINFO, Embase, and Scholars were retrieved. A meta-analysis of 31 articles (1,031 subjects) was performed using Stata17.0, CMA3.0 (comprehensive meta-analysis version 3.0) software, and Python 3.9 platform for light therapy efficacy comparison and dose-response quantification.

Results

Under various circadian stimulus conditions (0.1 < CSt,f < 0.7) of light therapy (LT), malady reductions among AYAs were observed (pooled SMD = -1.59, 95%CI = -1.86 to -1.32; z = -11.654, p = 0.000; I2 = 92.8%), with temporal pattern (p = 0.044) and co-medication (p = 0.000) suggested as main heterogeneity sources. For the efficacy advantage of LT with a higher circadian stimulus that is assumed to be influenced by visualization, co-medication, disease severity, and time pattern, sets of meta-analysis among random-controlled trials (RCTs) found evidence for significant efficacy of circadian-active bright light therapy (BLT) over circadian-inactive dim red light (SMD = -0.65, 95% CI = -0.96 to -0.34; z = -4.101, p = 0.000; I2 = 84.9%) or circadian-active dimmer white light (SMD = -0.37, 95% CI = -0.68 to -0.06; z = -2.318, p = 0.02; I2 = 33.8%), whereas green-blue, circadian-active BLT showed no significant superiority over circadian-inactive red/amber light controls (SMD = -0.21, 95% CI = -0.45 to 0.04; z = -2.318, p = 0.099; I2 = 0%). Overall, circadian-active BLT showed a greater likelihood of clinical response than dim light controls, with increased superiority observed with co-medication. For pre-to-post-treatment amelioration and corresponding dose-response relationship, cumulative duration was found more influential than other categorical (co-medication, severity, study design) or continuous (CSt,f) variables. Dose-response fitting indicated that the therapeutic effect would reach saturation among co-medicated patients at 32-42 days (900-1,000 min) and 58-59 days (1,100-1,500 min) among non-medicated AYAs. When exerting high circadian stimulus of light therapy (0.6 < CSt,f < 0.7), there was a significantly greater effect size in 1,000-1,500 min of accumulative duration than <1,000 or >1,500 min of duration, indicating a threshold for practical guidance.

Limitations

The results have been based on limited samples and influenced by a small sample effect. The placebo effect could not be ignored.

Conclusions

Although the superiority of LT with higher circadian stimulus over dimmer light controls remains unproven, greater response potentials of circadian-active BLT have been noticed among AYAs, taking co-medication, disease severity, time pattern, and visual characteristics into consideration. The dose-response relationship with quantified circadian stimulus and temporal pattern had been elaborated under various conditions to support clinical depression treatment and LT device application in the post-pandemic era.

The impact of wavelength on acute non-visual responses to light: A systematic review and meta-analysis

Light is detected in the eye by three classes of photoreceptors (rods, cones, and intrinsically photosensitive retinal ganglion cells (ipRGCs)) that are each optimized for a specific function and express a particular light-detecting photopigment. The significant role of short-wavelength light and ipRGCs in improving alertness has been well-established; however, few reviews have been undertaken to assess the other wavelengths' effects regarding timing and intensity. This study aims to evaluate the impact of different narrowband light wavelengths on subjective and objective alertness among the 36 studies included in this systematic review, 17 of which were meta-analyzed. Short-wavelength light (∼460-480 nm) significantly improves subjective alertness, cognitive function, and neurological brain activities at night, even for a sustained period (∼6h) (for λmax: 470/475 nm, 0.4 < |Hedges's g| < 0.6, p < 0.05), but except early morning, it almost does not show this effect during the day when melatonin level is lowest. Long-wavelength light (∼600-640 nm) has little effect at night, but significantly increases several measures of alertness at lower irradiance during the daytime (∼1h), particularly when there is homeostatic sleep drive (for λmax: ∼630 nm, 0.5 < |Hedges's g| < 0.8, p < 0.05). The results further suggest that melanopic illuminance may not always be sufficient to measure the alerting effect of light.

Blue-light filtering spectacle lenses for visual performance, sleep, and macular health in adults

BACKGROUND

'Blue-light filtering', or 'blue-light blocking', spectacle lenses filter ultraviolet radiation and varying portions of short-wavelength visible light from reaching the eye. Various blue-light filtering lenses are commercially available. Some claims exist that they can improve visual performance with digital device use, provide retinal protection, and promote sleep quality. We investigated clinical trial evidence for these suggested effects, and considered any potential adverse effects.

OBJECTIVES

To assess the effects of blue-light filtering lenses compared with non-blue-light filtering lenses, for improving visual performance, providing macular protection, and improving sleep quality in adults.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL; containing the Cochrane Eyes and Vision Trials Register; 2022, Issue 3); Ovid MEDLINE; Ovid Embase; LILACS; the ISRCTN registry; ClinicalTrials.gov and WHO ICTRP, with no date or language restrictions. We last searched the electronic databases on 22 March 2022.

SELECTION CRITERIA

We included randomised controlled trials (RCTs), involving adult participants, where blue-light filtering spectacle lenses were compared with non-blue-light filtering spectacle lenses.

DATA COLLECTION AND ANALYSIS

Primary outcomes were the change in visual fatigue score and critical flicker-fusion frequency (CFF), as continuous outcomes, between baseline and one month of follow-up. Secondary outcomes included best-corrected visual acuity (BCVA), contrast sensitivity, discomfort glare, proportion of eyes with a pathological macular finding, colour discrimination, proportion of participants with reduced daytime alertness, serum melatonin levels, subjective sleep quality, and patient satisfaction with their visual performance. We evaluated findings related to ocular and systemic adverse effects. We followed standard Cochrane methods for data extraction and assessed risk of bias using the Cochrane Risk of Bias 1 (RoB 1) tool. We used GRADE to assess the certainty of the evidence for each outcome.

MAIN RESULTS

We included 17 RCTs, with sample sizes ranging from five to 156 participants, and intervention follow-up periods from less than one day to five weeks. About half of included trials used a parallel-arm design; the rest adopted a cross-over design. A variety of participant characteristics was represented across the studies, ranging from healthy adults to individuals with mental health and sleep disorders. None of the studies had a low risk of bias in all seven Cochrane RoB 1 domains. We judged 65% of studies to have a high risk of bias due to outcome assessors not being masked (detection bias) and 59% to be at high risk of bias of performance bias as participants and personnel were not masked. Thirty-five per cent of studies were pre-registered on a trial registry. We did not perform meta-analyses for any of the outcome measures, due to lack of available quantitative data, heterogenous study populations, and differences in intervention follow-up periods. There may be no difference in subjective visual fatigue scores with blue-light filtering lenses compared to non-blue-light filtering lenses, at less than one week of follow-up (low-certainty evidence). One RCT reported no difference between intervention arms (mean difference (MD) 9.76 units (indicating worse symptoms), 95% confidence interval (CI) -33.95 to 53.47; 120 participants). Further, two studies (46 participants, combined) that measured visual fatigue scores reported no significant difference between intervention arms. There may be little to no difference in CFF with blue-light filtering lenses compared to non-blue-light filtering lenses, measured at less than one day of follow-up (low-certainty evidence). One study reported no significant difference between intervention arms (MD - 1.13 Hz lower (indicating poorer performance), 95% CI - 3.00 to 0.74; 120 participants). Another study reported a less negative change in CFF (indicating less visual fatigue) with high- compared to low-blue-light filtering and no blue-light filtering lenses. Compared to non-blue-light filtering lenses, there is probably little or no effect with blue-light filtering lenses on visual performance (BCVA) (MD 0.00 logMAR units, 95% CI -0.02 to 0.02; 1 study, 156 participants; moderate-certainty evidence), and unknown effects on daytime alertness (2 RCTs, 42 participants; very low-certainty evidence); uncertainty in these effects was due to lack of available data and the small number of studies reporting these outcomes. We do not know if blue-light filtering spectacle lenses are equivalent or superior to non-blue-light filtering spectacle lenses with respect to sleep quality (very low-certainty evidence). Inconsistent findings were evident across six RCTs (148 participants); three studies reported a significant improvement in sleep scores with blue-light filtering lenses compared to non-blue-light filtering lenses, and the other three studies reported no significant difference between intervention arms. We noted differences in the populations across studies and a lack of quantitative data. Device-related adverse effects were not consistently reported (9 RCTs, 333 participants; low-certainty evidence). Nine studies reported on adverse events related to study interventions; three studies described the occurrence of such events. Reported adverse events related to blue-light filtering lenses were infrequent, but included increased depressive symptoms, headache, discomfort wearing the glasses, and lower mood. Adverse events associated with non-blue-light filtering lenses were occasional hyperthymia, and discomfort wearing the spectacles. We were unable to determine whether blue-light filtering lenses affect contrast sensitivity, colour discrimination, discomfort glare, macular health, serum melatonin levels or overall patient visual satisfaction, compared to non-blue-light filtering lenses, as none of the studies evaluated these outcomes.

AUTHORS' CONCLUSIONS

This systematic review found that blue-light filtering spectacle lenses may not attenuate symptoms of eye strain with computer use, over a short-term follow-up period, compared to non-blue-light filtering lenses. Further, this review found no clinically meaningful difference in changes to CFF with blue-light filtering lenses compared to non-blue-light filtering lenses. Based on the current best available evidence, there is probably little or no effect of blue-light filtering lenses on BCVA compared with non-blue-light filtering lenses. Potential effects on sleep quality were also indeterminate, with included trials reporting mixed outcomes among heterogeneous study populations. There was no evidence from RCT publications relating to the outcomes of contrast sensitivity, colour discrimination, discomfort glare, macular health, serum melatonin levels, or overall patient visual satisfaction. Future high-quality randomised trials are required to define more clearly the effects of blue-light filtering lenses on visual performance, macular health and sleep, in adult populations.

A randomized controlled trial on the effects of blue-blocking glasses compared to partial blue-blockers on sleep outcomes in the third trimester of pregnancy

OBJECTIVE

Sleep disturbances are common in pregnancy. Blocking blue light has been shown to improve sleep and may be a suitable intervention for sleep problems during pregnancy. The present study investigated the effects of blue light blocking in the evening and during nocturnal awakenings among pregnant women on primary sleep outcomes in terms of total sleep time, sleep efficiency and mid-point of sleep.

METHODS

In a double-blind randomized controlled trial, 60 healthy nulliparous pregnant women in the beginning of the third trimester were included. They were randomized, using a random number generator, either to a blue-blocking glass intervention (n = 30) or to a control glass condition constituting partial blue-blocking effect (n = 30). Baseline data were recorded for one week and outcomes were recorded in the last of two intervention/control weeks. Sleep was measured by actigraphy, sleep diaries, the Bergen Insomnia Scale, the Karolinska Sleepiness Scale and the Pre-Sleep Arousal Scale.

RESULTS

The results on the primary outcomes showed no significant mean difference between the groups at posttreatment, neither when assessed with sleep diary; total sleep time (difference = .78[min], 95%CI = -19.7, 21.3), midpoint of sleep (difference = -8.9[min], 95%CI = -23.7, 5.9), sleep efficiency (difference = -.06[%], 95%CI = -1.9, 1.8) and daytime functioning (difference = -.05[score points], 95%CI = -.33, .22), nor by actigraphy; total sleep time (difference = 13.0[min], 95%CI = -9.5, 35.5), midpoint of sleep (difference = 2.1[min], 95%CI = -11.6, 15.8) and sleep efficiency (difference = 1.7[%], 95%CI = -.4, 3.7). On the secondary outcomes, the Bergen Insomnia Scale, the Karolinska Sleepiness Scale and the Pre-Sleep Arousal Scale the blue-blocking glasses no statistically significant difference between the groups were found. Transient side-effects were reported in both groups (n = 3).

CONCLUSIONS

The use of blue-blocking glasses compared to partially blue-blocking glasses in a group of healthy pregnant participants did not show statistically significant effects on sleep outcomes. Research on the effects of blue-blocking glasses for pregnant women with sleep-problems or circadian disturbances is warranted.

TRIAL REGISTRATION

The trial is registered at ClinicalTrials.gov (NCT03114072).

Evening wear of blue-blocking glasses for sleep and mood disorders: a systematic review

Blue-blocking glasses, also known as amber glasses, are plastic glasses that primarily block blue light. Blue-blocking glasses have been studied as a sleep intervention for insomnia, delayed sleep-phase disorder, shift work, jet lag, and nonpathologic sleep improvement. Blue-blocking glasses have also been studied as a treatment for bipolar disorder, major depression, and postpartum depression. Blue-blocking glasses improve sleep by inducing dim-light melatonin onset by reducing activation of intrinsically photosensitive retinal ganglion cells (ipRGCs) which are most sensitive to blue light and are a major input for circadian regulation; their mechanism for mood regulation is unclear but may be similar to that of dark therapy for bipolar disorder where patients are kept in darkness for an extended period every night. A systematic search of the scientific literature identified a total of 29 experimental publications involving evening wear of blue-blocking glasses for sleep or mood disorders. These consisted of 16 randomized controlled trials (RCTs) published in journals with a total of 453 patients, 5 uncontrolled trials, 1 case series, 1 case study, and 6 abstracts from conference proceedings. Only 1 case study and 1 RCT were for acutely manic patients but both found substantial decreases in manic symptoms with the use of blue-blocking glasses; these give preliminary clinical evidence of efficacy that makes blue-blocking glasses a high-yield intervention to study for bipolar disorder. Findings in the 3 publications for major depression and postpartum depression were heterogeneous and conflicting as to their efficacy. Out of the 24 publications focusing on sleep, there was substantial evidence for blue-blocking glasses being a successful intervention for reducing sleep onset latency in patients with sleep disorders, jet lag, or variable shift work schedules. Given the well-established biological mechanism and clinical research showing that blue-blocking glasses are effective for inducing sleep, they are a viable intervention to recommend to patients with insomnia or a delayed sleep phase.

Objective and Subjective Characteristics of Vigilance under Different Narrow-Bandwidth Light Conditions: Do Shorter Wavelengths Have an Alertness-Enhancing Effect?

The aim of this study was to explore the effects of 20 min of narrow-bandwidth light exposure of different wavelengths (455, 508, and 629 nm, with irradiance of 14 µW/cm2) on various neuropsychological and neurophysiological parameters of vigilance in healthy volunteers and to provide further evidence of the behavioral (subjective sleepiness, reaction time) and electrophysiological (P300 and spectral characteristics) responses to light. The results show that the short-wavelength light condition (455 nm) was found to be most effective in terms of its alerting effect for the following variables: subjective sleepiness, latency of P300 response, and absolute EEG power in higher beta (24-34 Hz) and gamma (35-50 Hz) range at each of the 19 recording electrodes. However, no differences in current power density were observed at the level of cortical EEG sources estimated by exact low-resolution electromagnetic tomography. Our results are in line with other research that shows significant alerting effects of blue (short-wavelength) light in comparison to lights of longer wavelengths. Our results confirm earlier findings that exposure to short-wavelength light during the day may enhance cognitive performance in task-specific scenarios.

Visual and non-visual properties of filters manipulating short-wavelength light

Purpose

Optical filters and tints manipulating short‐wavelength light (sometimes called ‘blue‐blocking’ or ‘blue‐attenuating’ filters) are used in the management of a range of ocular, retinal, neurological and psychiatric disorders. In many cases, the only available quantification of the optical effects of a given optical filter is the spectral transmittance, which specifies the amount of light transmitted as a function of wavelength.

Methods

We propose a novel physiologically relevant and retinally referenced framework for quantifying the visual and non‐visual effects of these filters, incorporating the attenuation of luminance (luminous transmittance), the attenuation of melanopsin activation (melanopsin transmittance), the colour shift, and the reduction of the colour gamut (gamut reduction). Using these criteria, we examined a novel database of spectral transmittance functions of optical filters (n = 121) which were digitally extracted from a variety of sources.

Results

We find a large diversity in the alteration of visual and non‐visual properties. The spectral transmittance properties of the examined filters vary widely, in terms of shapes and cut‐off wavelengths. All filters show relatively more melanopsin attenuation than luminance attenuation (lower melanopsin transmittance than luminous transmittance). Across the data set, we find that melanopsin transmittance and luminous transmittance are correlated.

Conclusions

We suggest that future studies and examinations of the physiological effects of optical filters quantify the visual and non‐visual effects of the filters beyond the spectral transmittance, which will eventually aid in developing a mechanistic understanding of how different filters affect physiology. We strongly discourage comparing the downstream effects of different filters on, e.g. sleep or circadian responses, without considering their effects on the retinal stimulus.

Light therapy with boxes or glasses to counteract effects of acute sleep deprivation

Sleep deprivation, in the context of shift work, is an increasing major public health issue. We aimed to determine whether early light administration can counteract sleep deprivation effects, and to compare LED-glasses with a traditional light therapy box. This cross-over design study included 18 individuals exposed to light therapy for 30 minutes at 5 am after one night of complete sleep deprivation, to mimic the night shift condition. Individuals were randomly exposed to 10,000 Lux light box, 2,000 Lux LED blue-enriched glasses, and control (ambient dim-light at 8 lux). Alertness, cognition and mood were assessed throughout the night and following morning. Five women and 13 men (mean 24.78 year old) presented with a progressive and increasing alteration of alertness, cognition, and mood during each sleep deprivation. A rebound was observed at 8 am resulting from the circadian drive overriding cumulative sleep homeostatic effects. Morning light significantly improved sleepiness and sustained attention from 5 to 7 am. These effects were comparable between devices and significantly different from control. Both devices were overall well and similarly tolerated. Early morning light therapy in the condition of sleep loss may have broad practical applications to improve sleepiness, sustained attention and subsequent risk of accidents.

A 6-day combined wake and light therapy trial for unipolar depression

BACKGROUND

There are a dozen studies on double or triple chronotherapy in depression (sleep deprivation [wake therapy] + light therapy + sleep advance/stabilization). We investigated efficacy and feasibility of a modified triple chronotherapy protocol.

METHODS

Thirty-five hospitalized patients with moderately severe non-seasonal depressive disorder, mostly free from antidepressants, underwent a 6-day protocol consisting of partial sleep deprivation late in the second half of the night (from 4:00 to 8:00) in a light therapy room (blue-enhanced white light increased hourly from 600→1300→2200→2800 lx) alternating with recovery nights with morning light treatment from 7:00 to 8:00. Patients were randomized to wear glasses with no filter (clear, N = 19) or filtering blue wavelength (orange-appearance, light intensity diminution by ∼70%, N = 16) during the treatments. Sleep was targeted to be shifted at least 1 h earlier. Depression was scored using HDRS-17 (Hamilton Depression Rating Scale) and BDI-II (Beck Depression Inventory-II) - before and after the 6-days treatment, HDRS-6-SR - daily, and visual analogue scales (VAS) for mood and energy - several times every day.

RESULTS

Depression levels significantly declined following the first night and after 6-days treatment, with no difference between white and orange lights. Nevertheless, some superiority of white light emerged with respect to response rate (mood VAS), immediate effect during the 4-h treatment sessions (energy VAS), and expected treatment outcomes. All patients successfully advanced bedtime/wake-up (by 30-40 minutes) and resisted naps during daytime.

LIMITATIONS

Relatively small sample size.

CONCLUSIONS

The modified triple chronotherapy was well tolerated and improved depression. Light spectrum/intensity plays some role in the response.

Bright environmental light improves the sleepiness of nightshift ICU nurses

Background

Shift work can disturb circadian homeostasis and result in fatigue, excessive sleepiness, and reduced quality of life. Light therapy has been shown to impart positive effects in night shift workers. We sought to determine whether or not prolonged exposure to bright light during a night shift reduces sleepiness and enhances psychomotor performance among ICU nurses.

Methods

This is a single-center randomized, crossover clinical trial at a surgical trauma ICU. ICU nurses working a night shift were exposed to a 10-h period of high illuminance (1500–2000 lx) white light compared to standard ambient fluorescent lighting of the hospital. They then completed the Stanford Sleepiness Scale and the Psychomotor Vigilance Test. The primary and secondary endpoints were analyzed using the paired t test. A p value <0.05 was considered significant.

Results

A total of 43 matched pairs completed both lighting exposures and were analyzed. When exposed to high illuminance lighting subjects experienced reduced sleepiness scores on the Stanford Sleepiness Scale than when exposed to standard hospital lighting: mean (sem) 2.6 (0.2) vs. 3.0 (0.2), p = 0.03. However, they committed more psychomotor errors: 2.3 (0.2) vs. 1.7 (0.2), p = 0.03.

Conclusions

A bright lighting environment for ICU nurses working the night shift reduces sleepiness but increases the number of psychomotor errors.

Trial registration

ClinicalTrials.gov, NCT03331822. Retrospectively registered on 6 November 2017.

Effects of blue- and red-enriched light on attention and sleep in typically developing adolescents

Differential effects of blue- and red-enriched light on attention and sleep have been primarily described in adults. In our cross-over study in typically developing adolescents (11-17 years old), we found attention enhancing effects of blue- compared to red-enriched light in the morning (high intensity of ca. 1000 lx, short duration: <1 h) in two of three attention tasks: e.g. better performance in math tests and reduced reaction time variability in a computerized attention test. In our pilot study, actigraphy measures of sleep indicated slight benefits for red- compared to blue-enriched light in the evening: tendencies toward a lower number of phases with movement activity after sleep onset in the complete sample and shorter sleep onset latency in a subgroup with later evening exposure times. These findings point to the relevance of light concepts regarding attention and sleep in typically developing adolescents. Such concepts should be developed and tested further in attention demanding contexts (at school) and for therapeutic purposes in adolescents with impaired attention or impaired circadian rhythms.

Revisiting the alerting effect of light: A systematic review

Light plays an essential role in maintaining alertness levels. Like other non-image-forming responses, the alerting effect of light is influenced by its spectral wavelength, duration and intensity. Alertness levels are also dependent on circadian rhythm (process C) and homeostatic sleep pressure (process S), consistent with the classic two-process model of sleep regulation. Over the last decade, there has been increasing recognition of an additional process (referred to as the third process) in sleep regulation. This third process seems to receive sensory inputs from body systems such as digestion, and is usually synchronised with process C and process S. Previous studies on the alerting effect of light have been mostly conducted in laboratories. Although these studies are helpful in delineating the impact of process C and process S, their ability to assist in understanding the third process is limited. This systematic review investigated the factors that influence the alerting effect of light by examining randomised controlled trials and randomised or counterbalanced crossover studies. Factors that influence light's alerting effect were examined with reference to the three-process model. The post-illuminance alerting effect was examined separately due to its potential to offer flexible workplace-based light interventions to increase or maintain employees' alertness.

Investigation of an Immediate Effect of Bright Light on Oxygen Consumption, Heart Rate, Cortisol, and α-Amylase in Seasonal Affective Disorder Subjects and Healthy Controls

BACKGROUND

Body (fat) mass has been shown to decrease following bright light treatment for overweight women, irrespective of their seasonal (light) dependence. It is not known if this is due to an (immediate) increase of metabolism.

METHODS

Ten women with seasonal affective disorder (SAD) and 10 non-SAD women matched by age, body mass index, and menopausal status participated in a laboratory study in the morning, twice within 1-5 days. During one session, bright light (4,300 lx) was presented for 30 min, and during the other session, red light (250 lx "placebo") was used. After an initial 15 min of sitting quietly in an experimental chamber, 10-min measurements were done before, at the end, and 15 min after light exposure; the subjects remained seated for 80 min in total. The measurements included 5-min oxyspirography (oxygen consumption, carbon dioxide emission, and heart rate), saliva sampling for the estimation of cortisol and α-amylase concentrations, and self-rating of mood, energy, and sleepiness.

RESULTS

There was no light-specific effect on the measured variables, except that sleepiness was reduced more with bright light than with red light in the combined group. α-Amylase values were lower in the SAD patients than in the non-SAD controls.

CONCLUSIONS

Morning artificial bright light, in comparison with dim red light, had no immediate effect on metabolism and resting sympathetic tone, though subjective sleepiness decreased more with bright light. SAD patients have low salivary α-amylase levels, indicating lower sympathetic tone.

Acute effects of different light spectra on simulated night-shift work without circadian alignment

Short-wavelength and short-wavelength-enhanced light have a strong impact on night-time working performance, subjective feelings of alertness and circadian physiology. In the present study, we investigated acute effects of white light sources with varied reduced portions of short wavelengths on cognitive and visual performance, mood and cardiac output.Thirty-one healthy subjects were investigated in a balanced cross-over design under three light spectra in a simulated night-shift paradigm without circadian adaptation.Exposure to the light spectrum with the largest attenuation of short wavelengths reduced heart rate and increased vagal cardiac parameters during the night compared to the other two light spectra without deleterious effects on sustained attention, working memory and subjective alertness. In addition, colour discrimination capability was significantly decreased under this light source.To our knowledge, the present study for the first time demonstrates that polychromatic white light with reduced short wavelengths, fulfilling current lighting standards for indoor illumination, may have a positive impact on cardiac physiology of night-shift workers without detrimental consequences for cognitive performance and alertness.