Seasonal and time-of-day variations in acute non-image forming effects of illuminance level on performance,physiology, and subjective well-being

This study investigated seasonal and time-of-day dependent moderations in the strength and direction of acute diurnal non-image forming (NIF) effects of illuminance level on performance, physiology, and subjective well-being. Even though there are indications for temporal variations in NIF-responsiveness to bright light, scientific insights into potential moderations by season are scarce. We employed a 2 (Light: 165 versus 1700 lx at the eye level, within) × 2 (Season: autumn/winter versus spring, between) × 2 (Time of day: morning versus afternoon, between) mixed-model design. During each of the two 90-min experimental sessions, participants (autumn/winter: N = 34; spring: N = 39) completed four measurement blocks (incl. one baseline block of 120 lx at the eye level) each consisting of a Psychomotor Vigilance Task (PVT) and a Backwards Digit-Span Task (BDST) including easy trials (4–6 digits) and difficult trials (7–8 digits). Heart rate (HR) and skin conductance level (SCL) were measured continuously. At the end of each lighting condition, subjective sleepiness, vitality, and mood were measured. The results revealed a clear indication for significant Light * Season interaction effects on both subjective sleepiness and vitality, which appeared only during the morning sessions. Participants felt significantly more vital and less sleepy in winter, but not in spring during bright light exposure in the morning. In line with these subjective parameters, participants also showed significantly better PVT performance in the morning in autumn/winter, but not in spring upon bright light exposure. Surprisingly, for difficult working memory performance, the opposite was found, namely worse performance during bright light exposure in winter, but better performance when exposed to bright light in spring. The effects of bright versus regular light exposure on physiology were quite subtle and largely nonsignificant. Overall, it can be concluded that acute illuminance-induced NIF effects on subjective alertness and vitality as well as objectively measured vigilance in the morning are significantly moderated by season. Possibly, these greater illuminance-induced benefits during the morning sessions in autumn/winter compared to spring occurred due to increased responsiveness to bright light exposure as a function of a relatively low prior light dose in autumn/winter.     

Diurnal Variation in Mood and Performance in a Time-Isolated Environment

In order to document circadian rhythmicity in various psychological functions under the chronobiologically 'pure' condition of temporal isolation, a battery of mood and performance tests were administered about 6 times per day to a heterogeneous group of 18 subjects (ages 19-81, 5 female). Each subject spent about 5 days in temporal isolation, entrained to a routine equivalent to his/her own habitual sleep/wake cycle. Average time of day functions were obtained for the mood and performance variables, and compared to rectal temperature data subjected to exactly the same statistical analysis. Significant time of day effects were found in the mood variables of alertness, sleepiness, weariness, effort required, happiness and well-being. Times of 'best' mood were different from the time of peak temperature. Moreover, the minima of sleepiness, weariness and effort occurred earlier in the day than the maximum of alertness. Significant time of day effects were also found in the speed with which search and dexterity tasks were completed. Only the dexterity tasks showed a complete parallelism with the temperature rhythm.     

Psychosocial group intervention to enhance self-management skills of people with dementia and their caregivers: study protocol for a randomized controlled trial

ABSTRACT: BACKGROUND: After diagnosis of a dementing illness patients and their spouses have many concerns related to the disease and their future. This often leads to poor psychological well-being and reduced health related quality of life (HRQoL) of the family. Support for self-management skills has been proven to be an effective method to improve prognosis of asthma, heart failure and osteoarthritis. However, self-management interventions have not been studied in dementia. Therefore, our aim was to examine in an objective-oriented group intervention the efficacy of self-management support program (SMP) on the HRQoL of dementia patients and their spousal caregivers as well as on the sense of competence and psychological well-being of care-givers. METHODS: During the years 2011-12, 160 dementia patients and their spouses will be recruited from memory clinics and randomized into two arms: 80 patients for group-based SMP sessions including topics selected by the participants, 80 patients will serve as controls in for usual community care. Sessions may include topics on dementia, community services, active lifestyle and prevention for cognitive decline, spousal relationship, future planning and emotional well-being. The patients and spouses will have their separate group sessions (10 participants/group) once a week for 8 weeks. Main outcome measures will be patients' HRQoL (15D) and spousal caregivers' HRQoL (RAND-36), and sense of competence (SCQ). Secondary measures will be caregivers' psychological well-being (GHQ-12) and coping resources, patients' depression, cognition and signs of frailty. Data concerning admissions to institutional care and the use and costs of health and social services will be collected during a two year follow-up. DISCUSSION: This is a "proof -of-concept" study to explore the efficacy of group support for self-management skills among dementia families. It will also provide data on cost-effectiveness of the intervention.     

The inner clock—Blue light sets the human rhythm

Visible light synchronizes the human biological clock in the suprachiasmatic nuclei of the hypothalamus to the solar 24‐hour cycle. Short wavelengths, perceived as blue color, are the strongest synchronizing agent for the circadian system that keeps most biological and psychological rhythms internally synchronized. Circadian rhythm is important for optimum function of organisms and circadian sleep–wake disruptions or chronic misalignment often may lead to psychiatric and neurodegenerative illness. The beneficial effect on circadian synchronization, sleep quality, mood, and cognitive performance depends not only on the light spectral composition but also on the timing of exposure and its intensity. Exposure to blue light during the day is important to suppress melatonin secretion, the hormone that is produced by the pineal gland and plays crucial role in circadian rhythm entrainment. While the exposure to blue is important for keeping organism's wellbeing, alertness, and cognitive performance during the day, chronic exposure to low‐intensity blue light directly before bedtime, may have serious implications on sleep quality, circadian phase and cycle durations. This rises inevitably the need for solutions to improve wellbeing, alertness, and cognitive performance in today's modern society where exposure to blue light emitting devices is ever increasing.      

Effects of Artificial Dawn and Morning Blue Light on Daytime Cognitive Performance,Well-being,Cortisol and Melatonin Levels

Light exposure elicits numerous effects on human physiology and behavior, such as better cognitive performance and mood. Here we investigated the role of morning light exposure as a countermeasure for impaired cognitive performance and mood under sleep restriction (SR). Seventeen participants took part of a 48h laboratory protocol, during which three different light settings (separated by 2?wks) were administered each morning after two 6-h sleep restriction nights: a blue monochromatic LED (light-emitting diode) light condition (BL; 100?lux at 470?nm for 20?min) starting 2?h after scheduled wake-up time, a dawn-simulating light (DsL) starting 30?min before and ending 20?min after scheduled wake-up time (polychromatic light gradually increasing from 0 to 250?lux), and a dim light (DL) condition for 2?h beginning upon scheduled wake time (<8?lux). Cognitive tasks were performed every 2?h during scheduled wakefulness, and questionnaires were administered hourly to assess subjective sleepiness, mood, and well-being. Salivary melatonin and cortisol were collected throughout scheduled wakefulness in regular intervals, and the effects on melatonin were measured after only one light pulse. Following the first SR, analysis of the time course of cognitive performance during scheduled wakefulness indicated a decrease following DL, whereas it remained stable following BL and significantly improved after DsL. Cognitive performance levels during the second day after SR were not significantly affected by the different light conditions. However, after both SR nights, mood and well-being were significantly enhanced after exposure to morning DsL compared with DL and BL. Melatonin onset occurred earlier after morning BL exposure, than after morning DsL and DL, whereas salivary cortisol levels were higher at wake-up time after DsL compared with BL and DL. Our data indicate that exposure to an artificial morning dawn simulation light improves subjective well-being, mood, and cognitive performance, as compared with DL and BL, with minimal impact on circadian phase. Thus, DsL may provide an effective strategy for enhancing cognitive performance, well-being, and mood under mild sleep restriction.     

Predicting human nocturnal nonvisual responses to monochromatic and polychromatic light with a melanopsin photosensitivity function

The short-wavelength (blue) light sensitivity of human circadian, neurobehavioral, neuroendocrine, and neurophysiological responses is attributed to melanopsin. Whether melanopsin is the sole factor in determining the efficacy of a polychromatic light source in driving nonvisual responses, however, remains to be established. Monochromatic (λ(max) 437, 479, and 532 nm administered singly and in combination with 479 nm light) and polychromatic (color temperature: 4000 K and 17000 K) light stimuli were photon matched for their predicted ability to stimulate melanopsin, and their capacity to affect nocturnal melatonin levels, auditory reaction time, and subjective alertness and mood was assessed. Young, healthy male participants aged 18-35 yrs (23.6?±?3.6 yrs [mean?±?SD]; n=12) participated in 12 overnight sessions that included an individually timed 30-min nocturnal light stimulus on the rising limb of the melatonin profile. At regular intervals before, during, and after the light stimulus, subjective mood and alertness were verbally assessed, blood samples were taken for analysis of plasma melatonin levels, and an auditory reaction time task (psychomotor vigilance task; PVT) was performed. Proc GLM (general linear model) repeated-measures ANOVA (analysis of variance) revealed significantly lower melatonin suppression with the polychromatic light conditions (4000 and 17000 K) compared to the "melanopsin photon-matched" monochromatic light conditions (p相似文献   

Scenario analysis of the future of medicines.

Planning future policy for medicines poses difficult problems. The main players in the drug business have their own views as to how the world around them functions and how the future of medicines should be shaped. In this paper we show how a scenario analysis can provide a powerful teaching device to readjust peoples'' preconceptions. Scenarios are plausible, not probable or preferable, portraits of alternative futures. A series of four of alternative scenarios were constructed: "sobriety in sufficiency," "risk avoidance," "technology on demand," and "free market unfettered." Each scenario was drawn as a narrative, documented quantitatively wherever possible, that described the world as it might be if particular trends were to dominate development. The medical community and health policy markers may use scenarios to take a long term view in order to be prepared adequately for the future.     

Influence of constant light and darkness, light intensity, and light spectrum on plasma melatonin rhythms in senegal sole

Light is the most important synchronizer of melatonin rhythms in fish. This paper studies the influence of the characteristics of light on plasma melatonin rhythms in sole. The results revealed that under long-term exposure to constant light conditions (LL or DD), the total 24 h melatonin production was significantly higher than under LD, but LL and DD conditions influenced the rhythms differently. Under LL, melatonin remained at around 224 pg/ml throughout the 24 h, while under DD a significant elevation (363.6 pg/ml) was observed around the subjective evening. Exposure to 1 h light pulses at MD (mid-dark) inhibited melatonin production depending on light intensity (3.3, 5.3, 10.3, and 51.9 microW/cm(2)). The light threshold required to reduce nocturnal plasma melatonin to ML (mid-light) values was 5.3 microW/cm(2). Melatonin inhibition by light also depended on the wavelength of the light pulses: while a deep red light (lambda>600 nm) failed to reduce plasma melatonin significantly, far violet light (lambda(max)=368 nm) decreased indoleamine's concentration to ML values. These results suggest that dim light at night (e.g., moonlight) may be perceived and hence affect melatonin rhythms, encouraging synchronization to the lunar cycle. On the other hand, deep red light does not seem to inhibit nocturnal melatonin production, and so it may be used safely during sampling at night.     

Effect of microwaves of nonthermal intensity on the number of aberrant hepatocytes in rats

It was shown on rats that the effect of permanently generated electromagnetic field (a whole-body exposure) during 45 days (7h a day, the energy flux density of 10 microW/cm2) caused a decrease in number of hepatocytes with the affected chromosomes. Some part of animals exposed to higher energy loading (PD - 50 microW/cm2, 20 days, 7 h/day) showed the increase of aberrant cells level. A single exposure at 500 microW/cm2 and a ten-fold exposure at 50 microW/cm2 (10 days, 7h a day) were shown to be ineffective.     

Prospective time estimation over a night without sleep

The aim of the present study was to investigate the time of night effect on prospective time estimation efficiency. Fifty-four participants took part in six consecutive experimental sessions from 10:00 p.m. to 8:00 a.m. at intervals of 2 h, during which they had to carry out two kinds of tasks (simple reaction time and prospective time estimation), give an evaluation of their subjective alertness, and record body temperature. In agreement with previous data on body temperature, subjective alertness and performance in simple reaction time showed a significant decrease during the night, while performance in prospective time estimation did not change over the night. Taking into account circadian typology we found that morning-types tended to produce significantly shorter time intervals and less time estimation accuracy than evening-types. With reference to recent cognitive timing models and data derived from free-running conditions, it is hypothesised that internal pace-makers pulse at different rates between the extreme chronotypes.     

Absence of daytime 50 Hz, 100 microT(rms) magnetic field or bright light exposure effect on human performance and psychophysiological parameters

The purpose of this study was to reproduce and extend two earlier studies of the effects of human exposure to 50 Hz magnetic fields (MF). In a recent paper, we described results of two double-blind investigations performed to examine effects of 100 microT(rms) 50 Hz MF exposure on psychological parameters in the same group of healthy human volunteers. In each exposure session, at 1 week intervals, with sham, continuous, and intermittent (15 s ON/OFF cycles) MF conditions, mood ratings, performance measures, and electrophysiological measures were taken. In the first study, significant amplitude changes were observed in the event-related brain potentials (ERP) recorded during a dichotic listening task. In the second study, latency and reaction time (RT) slowing were seen on a visual discrimination task (P(300) paradigm). Although these results were little related to the number of parameters analysed, they indicate that low level 50 Hz MF might have a slight influence on ERP and RT under specific circumstances of sustained attention. Before concluding that moderately strong MF exposure can influence cognitive function, previous results should be replicated, using the same paradigms with another group of healthy volunteers. In the present study, 18 healthy subjects were exposed to three experimental sessions of 30 min each, given at 1 week intervals. The sessions consisted of continuous 100 microT(rms) 50 Hz MF exposure, sham condition, and bright light (5000 lux) exposure. The study was performed double-blind, with the exposure order counter-balanced. The data on mood, ERP, RT, and other performance measures did not show any differences among the sham exposure, light exposure, and MF exposure conditions. The results of this study do not support the hypothesis that extremely low frequency (ELF) MF exposure affects the brain's electrical activity or cognitive function at field strength (100 microT(rms)) similar to that found in very close proximity of some household and industrial electrical appliances and well in excess of the average MF strength (c. 0.1 microT) found in homes. The sensitivity of the experiment was possibly not sufficient to detect an effect at this relatively low MF, and larger sample sizes would be required in further studies.     

Prenatal exposure to 900 MHz, cell-phone electromagnetic fields had no effect on operant-behavior performances of adult rats

To clarify potential health risks of radio-frequency electromagnetic fields (EMFs) used in cellular telephone technology to the developing brain, Wistar rats were continuously exposed during pregnancy to a low-level (0.1 mW/cm(2)) 900 MHz, 217 Hz pulse modulated EMF that approximated the highest legal exposure of normal populations to the radiation of base antennas of the GSM digital cell-phone technology. Whole body average specific absorption rate (SAR) values for the freely roaming, pregnant animals were measured in models; they ranged between 17.5 and 75 mW/kg. The offspring of exposed and of sham-exposed dams were coded and tested later as adults in a battery of ten simultaneously operated test chambers (Skinner boxes) during night time. Eight groups of ten coded animals in each group were tested for learning deficits in a sequence of nine, computer-controlled, 15 h sessions of the food-reinforced contingency Differential Reinforcement of Rate with increasing performance requirements. Two different sets of events were recorded: The food-reinforced lever-pressing activity of the animals and the inter-response intervals (IRIs) between consecutive lever presses. IRI-occurence patterns discriminated consistently between "learners" and "non-learners". Analyses of performance scores and of IRI-patterns both showed that exposure in-utero to the GSM field did not induce any measurable cognitive deficits.     

Circadian Adaptation to Night Shift Work Influences Sleep,Performance, Mood and the Autonomic Modulation of the Heart

Our aim was to investigate how circadian adaptation to night shift work affects psychomotor performance, sleep, subjective alertness and mood, melatonin levels, and heart rate variability (HRV). Fifteen healthy police officers on patrol working rotating shifts participated to a bright light intervention study with 2 participants studied under two conditions. The participants entered the laboratory for 48 h before and after a series of 7 consecutive night shifts in the field. The nighttime and daytime sleep periods were scheduled during the first and second laboratory visit, respectively. The subjects were considered “adapted” to night shifts if their peak salivary melatonin occurred during their daytime sleep period during the second visit. The sleep duration and quality were comparable between laboratory visits in the adapted group, whereas they were reduced during visit 2 in the non-adapted group. Reaction speed was higher at the end of the waking period during the second laboratory visit in the adapted compared to the non-adapted group. Sleep onset latency (SOL) and subjective mood levels were significantly reduced and the LF∶HF ratio during daytime sleep was significantly increased in the non-adapted group compared to the adapted group. Circadian adaptation to night shift work led to better performance, alertness and mood levels, longer daytime sleep, and lower sympathetic dominance during daytime sleep. These results suggest that the degree of circadian adaptation to night shift work is associated to different health indices. Longitudinal studies are required to investigate long-term clinical implications of circadian misalignment to atypical work schedules.     

PREDICTING HUMAN NOCTURNAL NONVISUAL RESPONSES TO MONOCHROMATIC AND POLYCHROMATIC LIGHT WITH A MELANOPSIN PHOTOSENSITIVITY FUNCTION

The short-wavelength (blue) light sensitivity of human circadian, neurobehavioral, neuroendocrine, and neurophysiological responses is attributed to melanopsin. Whether melanopsin is the sole factor in determining the efficacy of a polychromatic light source in driving nonvisual responses, however, remains to be established. Monochromatic (λ_max 437, 479, and 532?nm administered singly and in combination with 479?nm light) and polychromatic (color temperature: 4000 K and 17000 K) light stimuli were photon matched for their predicted ability to stimulate melanopsin, and their capacity to affect nocturnal melatonin levels, auditory reaction time, and subjective alertness and mood was assessed. Young, healthy male participants aged 18–35 yrs (23.6?±?3.6 yrs [mean?±?SD]; n?=?12) participated in 12 overnight sessions that included an individually timed 30-min nocturnal light stimulus on the rising limb of the melatonin profile. At regular intervals before, during, and after the light stimulus, subjective mood and alertness were verbally assessed, blood samples were taken for analysis of plasma melatonin levels, and an auditory reaction time task (psychomotor vigilance task; PVT) was performed. Proc GLM (general linear model) repeated-measures ANOVA (analysis of variance) revealed significantly lower melatonin suppression with the polychromatic light conditions (4000 and 17000 K) compared to the “melanopsin photon-matched” monochromatic light conditions (p?<?.05). In contrast, subjective alertness was significantly lower under the 479?nm monochromatic light condition compared to the 437 and 532?nm monochromatic and both polychromatic light conditions. The alerting responses more reflected the total photon content of the light stimulus. The demonstration that the melatonin suppression response to polychromatic light was significantly lower than predicted by the melanopsin photosensitivity function suggests this function is not the sole consideration when trying to predict the efficacy of broadband lighting. The different spectral sensitivity of subjective alertness and melatonin suppression responses may imply a differential involvement of the cone photopigments. An analysis of the photon densities in specific wavelength bands for the polychromatic lights used in this and the authors' previous study suggests the spectral composition of a polychromatic light source, and particularly the very short-wavelength content, may be critical in determining response magnitude for the neuroendocrine and neurobehavioral effects of nocturnal light. (Author correspondence: v.revell@surrey.ac.uk)     

Unintended pregnancy and women's psychological well-being in Indonesia

Few studies have examined the impact of unintended pregnancy on women in developing countries. This paper examines the impact of unintended pregnancy on Indonesian women's psychological well-being. It is hypothesized that experiencing unintended pregnancy is associated with lower psychological well-being and that use of family planning and small family size are associated with higher levels of psychological well-being. Data are drawn from a 1996 survey of 796 women aged 15-49 from two Indonesian provinces, Lampung and South Sumatra. This article focuses on the 71% of women (n=562) who answered all 41 survey items related to psychological well-being. In cluster analysis, women grouped into three clusters, differentiated by their scores on four scales of well-being established through factor analysis (general negative feelings, satisfaction with relationships, satisfaction with economic/family/personal conditions, and negative feelings regarding domestic issues). Women in cluster 3 were characterized mainly by their high level of psychological well-being. Women in cluster 1 had the lowest level of well-being, and women in cluster 2 were in the middle. Multinomial logistic regression was used to assess jointly the effect of unintended pregnancy, contraceptive use, number of children and other factors on a woman's level of psychological well-being. Unintended pregnancy was associated with lower levels of psychological well-being and contraceptive use was associated with higher levels of psychological well-being, while number of children was not associated with level of well-being. Women who had experienced an unintended pregnancy were less likely to be in the high psychosocial well-being cluster versus both the medium and low clusters. In addition, women using contraception were more likely to be classified in the high than in the low or medium well-being clusters.     

Bright light during nighttime: effects on the circadian regulation of alertness and performance

The present studies evaluated to what extent duration (all-night or 4-hour exposures) and timing of nocturnal bright light (BL) (beginning or end of the night) modulate effects on vigilance. The results showed that all-night BL exposure is able to alleviate the nocturnal decrements in alertness and performance. However, under certain circumstances, this continuous BL exposure may induce adverse effects on mood and finally reveal to be counterproductive. Shorter BL exposure (4 h) during nighttime helps improve mood and performance, although the effects of short BL pulses were less efficacious than all-night BL exposure. The latter part of the night appears the best time for using the alerting effect of BL. The immediate alerting effect of BL seems to be mediated by a global activation of the central nervous system.     

The effect of GSM and TETRA mobile handset signals on blood pressure, catechol levels and heart rate variability

An acute rise in blood pressure has been reported in normal volunteers during exposure to signals from a mobile phone handset. To investigate this finding further we carried out a double blind study in 120 healthy volunteers (43 men, 77 women) in whom we measured mean arterial pressure (MAP) during each of six exposure sessions. At each session subjects were exposed to one of six different radio frequency signals simulating both GSM and TETRA handsets in different transmission modes. Blood catechols before and after exposure, heart rate variability during exposure, and post exposure 24 h ambulatory blood pressure were also studied. Despite having the power to detect changes in MAP of less than 1 mmHg none of our measurements showed any effect which we could attribute to radio frequency exposure. We found a single statistically significant decrease of 0.7 mmHg (95% CI 0.3-1.2 mmHg, P = .04) with exposure to GSM handsets in sham mode. This may be due to a slight increase in operating temperature of the handsets when in this mode. Hence our results have not confirmed the original findings of an acute rise in blood pressure due to exposure to mobile phone handset signals. In light of this negative finding from a large study, coupled with two smaller GSM studies which have also proved negative, we are of the view that further studies of acute changes in blood pressure due to GSM and TETRA handsets are not required.     

Short‐term exposure to mobile phone base station signals does not affect cognitive functioning or physiological measures in individuals who report sensitivity to electromagnetic fields and controls

Individuals who report sensitivity to electromagnetic fields often report cognitive impairments that they believe are due to exposure to mobile phone technology. Previous research in this area has revealed mixed results, however, with the majority of research only testing control individuals. Two studies using control and self‐reported sensitive participants found inconsistent effects of mobile phone base stations on cognitive functioning. The aim of the present study was to clarify whether short‐term (50 min) exposure at 10 mW/m² to typical Global System for Mobile Communication (GSM) and Universal Mobile Telecommunications System (UMTS) base station signals affects attention, memory, and physiological endpoints in sensitive and control participants. Data from 44 sensitive and 44 matched‐control participants who performed the digit symbol substitution task (DSST), digit span task (DS), and a mental arithmetic task (MA), while being exposed to GSM, UMTS, and sham signals under double‐blind conditions were analyzed. Overall, cognitive functioning was not affected by short‐term exposure to either GSM or UMTS signals in the current study. Nor did exposure affect the physiological measurements of blood volume pulse (BVP), heart rate (HR), and skin conductance (SC) that were taken while participants performed the cognitive tasks. Bioelectromagnetics 30:556–563, 2009. © 2009 Wiley‐Liss, Inc.     

Human nonvisual responses to simultaneous presentation of blue and red monochromatic light

Blue light sensitivity of melatonin suppression and subjective mood and alertness responses in humans is recognized as being melanopsin based. Observations that long-wavelength (red) light can potentiate responses to subsequent short-wavelength (blue) light have been attributed to the bistable nature of melanopsin whereby it forms stable associations with both 11-cis and all-trans isoforms of retinaldehyde and uses light to transition between these states. The current study examined the effect of concurrent administration of blue and red monochromatic light, as would occur in real-world white light, on acute melatonin suppression and subjective mood and alertness responses in humans. Young healthy men (18-35 years; n = 21) were studied in highly controlled laboratory sessions that included an individually timed 30-min light stimulus of blue (λ(max) 479 nm) or red (λ(max) 627 nm) monochromatic light at varying intensities (10(13)-10(14) photons/cm(2)/sec) presented, either alone or in combination, in a within-subject randomized design. Plasma melatonin levels and subjective mood and alertness were assessed at regular intervals relative to the light stimulus. Subjective alertness levels were elevated after light onset irrespective of light wavelength or irradiance. For melatonin suppression, a significant irradiance response was observed with blue light. Co-administration of red light, at any of the irradiances tested, did not significantly alter the response to blue light alone. Under the current experimental conditions, the primary determinant of the melatonin suppression response was the irradiance of blue 479 nm light, and this was unaffected by simultaneous red light administration.