Duration Of Light Exposure Research Articles

The duration of artificial light defines sexual signalling in the common glow-worm

Artificial light at night is increasing globally, interfering with both sensory ecology and temporal rhythms of organisms, from zooplankton to mammals. This interference can change the behaviour of the affected organisms, and hence compromise the viability of their populations. Limiting the use of artificial light may mitigate these negative effects. Accordingly, we investigated whether the duration of artificial light affects sexual signalling in female glow-worms, Lampyris noctiluca, which are flightless and attract flying males to mate by emitting glow that is interfered by light pollution. The study included three treatments: no artificial light (control), 15 min of artificial light, and 45 min of artificial light. The results show that females were more likely to cease glowing when the exposure to light was longer. Furthermore, small females were more likely to cease their glow, and responded faster to the light, than larger females. These findings suggest that glow-worms can react rapidly to anthropogenic changes in nocturnal light levels, and that prolonged periods of artificial light trigger females to stop sexual signalling. Thus, limiting the duration of artificial light can mitigate the adverse effects of light pollution on sexual signalling, highlighting the importance of such mitigation measures.Significance statementInterest in the effects of artificial light at night on animal behaviour has increased in recent years. With evidence for its negative impact accumulating, potential remedies, such as limiting the duration of light exposure, have emerged. To date, however, knowledge on the effectiveness of these methods has remained very limited. We show that female European common glow-worms, which are wingless beetles that glow to attract flying males to mate, responded to prolonged artificial light exposure by discontinuing their glow. Such non-glowing females are not expected to find a mate, making it difficult for them to reproduce. Hence, our study indicates that the duration of artificial light should be limited to protect this night-active beetle and its opportunities for effective sexual signalling. Because many other nocturnal species also need darkness, this study provides valuable information for the development and use of less disruptive night-time lights.

Thermal- vs Light-Induced On-Surface Polymerization.

On-surface polymerization is a powerful bottom-up approach that allows for the growth of covalent architectures with defined properties using the two-dimensional confinement of a highly defined single-crystal surface. Thermal heating is the preferred approach to initiate the reaction, often via cleavage of halogen substituents from the molecular building blocks. Light represents an alternative stimulus but has, thus far, only rarely been used. Here, we present a direct comparison of on-surface polymerization of dibromo-anthracene molecules, induced either thermally or by light, and study the differences between the two approaches. Insight is obtained by a combination of scanning tunneling microscopy, locally studying the polymer shape and size, and X-ray photoelectron spectroscopy, which identifies bond formation by averaging over large surface areas. While the polymer length increases slowly with the sample heating temperature, illumination promotes only the formation of short covalent structures, independent of the duration of light exposure. Moreover, irradiation with UV light at different sample temperatures highlights the important role of molecular diffusion across the surface.

Long Term Monomer Elution of Bulk-Fill and Conventional Resin Composites

The process of elution of unreacted monomers from dental resin composites can adversely affect their biocompatibility and longevity. In this regard, it is of interest to monitor relies on unreacted monomers from SonicFill, especially since this new type of bulk-fill composite materials entered dental practice with their simplified and shortened application protocol. This study aimed to assess long term monomer elution from bulk- fill (SonicFill) and conventional low shrinkage resin composites (FiltekP60 and FiltekUltimate), applied in 2mm layer thickness and stored in different extraction media - 6-month period exposure in artificial saliva, followed by 24 hours exposure in 75% ethanol solution. Analysis of monomer elution was performed using HPLC-MS. Monomers detected in artificial saliva were: UDMA and EDB from the conventional composites. No eluted monomers were detected from SonicFill. In just 24 hours of exposure in 75% alcoholic solution, components were extracted from all the materials that were not extracted for 6 months in the artificial saliva: Bis-GMA, TEGDMA, EDB from SonicFill; Bis-GMA from Filtek P60, and Filtek Ultimate. There was a new peak in the release of UDMA from Filtek P60 and Filtek Ultimate. Data reveal, that the extraction medium is extremely important for the separation of monomers. The degree of polymerization cannot completely influence the release of monomers into the surrounding environment. Internal factors, concerning materials composition, are more important, than the ability to control clinically degree of polymerization by intensity and duration of light exposure.

Toxic effect of light on oocyte and pre-implantation embryo: a systematic review.

In the female reproductive tract, oocytes and embryos are in a dark environment, while during the in vitro fertilization (IVF) they are exposed to various visible and invisible lights such as daylight, microscope, and laminar hood fluorescent lights. Studies have shown that light could damage cellular compartments of oocytes and embryos and consequently decrease rates of fertilization, development, and blastocyst formation. However, due to the lack of consensus about the effects of light on the embryos, and subsequently the inability to make definitive decisions regarding the light exposure management to improve IVF results, in the present study, we systematically reviewed the effect of light with different wavelengths and intensities on pre-implantation embryos. The toxic impact of light depends on the wavelength, intensity, and duration of light exposure and also the stage of embryo. Therefore, reducing the observation time of embryos out of the incubator and also using light filters can alleviate the detrimental effect of light in IVF labs.

Photosynthetic response to different light exposures and associated environmental conditions of the subaerial, epilithic green alga Trentepohlia umbrina (Chlorophyta, Ulvophyceae)

ABSTRACT The potentially biodeteriogenic, subaerial green alga Trentepohlia umbrina is widely distributed on shaded substrates with northern aspects. This preference for low light was confirmed by a recent survey in Lazio, Italy. However, the same survey revealed an isolated occurrence of extensive growths of T. umbrina-dominated biofilms on surfaces with diverse aspects that ranged from highly exposed to shaded. Prior studies of Trentepohlia photosynthesis have been restricted to single sites, so this multi-aspect site was particularly interesting to understand the photoacclimation potential of Trentepohlia. Photosynthetic pigment concentrations and chlorophyll fluorescence (in situ and ex situ) were used to assess the photosynthetic response to changes in light exposure and humidity. Pigment contents and photoinhibition decreased, while the maximum photosynthetic rate and the level of light that saturated photosynthesis increased with an increasing light exposure duration (ranging from c. 5 to 300 min d–1 of exposure to sunlight). Laboratory tests of relative humidity (RH) on biofilm photosynthesis showed no recorded activity up to 32% RH, only 26% of the maximum activity at 77% RH, and full activity at 92% RH. When T. umbrina was in the desiccated state a lowering of basal of chlorophyll a fluorescence emission and a loss of variable fluorescence occurred. This suppression of fluorescence when cells are desiccated is known to result in photoprotection of reaction centres from continuing high irradiances, as the enhanced thermal dissipation replaces slower and potentially damaging energy transfer to the functional reaction centres. It was concluded that T. umbrina has a much wider environmental range than previously thought, but its growth is very slow and may be overlooked during cultural heritage surveillance, leading to inconspicuous chronic degradation of outdoor stone substrata.

Investigating photodegradation of antibodies governed by the light dosage

The present study investigated the photodegradation of three different monoclonal antibodies (mAb) by visible light. Several chromatographic techniques, such as size-exclusion and hydrophobic interaction chromatography as well as mass spectrometry were used to measure relative changes of various oxidation related monoclonal antibody species. The results show that visible light is indeed capable of inducing the formation of protein photo-oxidation products, such as acidic, basic, hydrophilic, and several other protein species with altered physicochemical properties. Although, the formation rate of degradants of these three protein species was dependent on the light source’s intensity (I), their yield is clearly correlated to the applied light dosage (ld), which is defined as the product of light intensity I and irradiation time t (light dosage = I·t). Hence, our findings indicate that the degradation of monoclonal antibodies can be described according to the Bunsen-Roscoe reciprocity law. This correlation can be useful to assess the impact of photodegradation of biologics with regards to changes in light intensity and/or duration of light exposure of the protein, e.g. during the manufacturing of biologics.

111 Artificial Light-Triggered Sleep Deprivation May Lead to Allodynia in Rodent Model

IntroductionThe combination of artificial light and lack of exposure to natural light can delay the circadian clock, dysregulate the circadian cycle, and decrease alertness upon waking. This effect has been especially significant during the COVID-19 pandemic, where overexposure to artificial light at improper hours has contributed to increased rates of clinical insomnia. Artificial light may also contribute to concomitant neurological conditions such as primary headache, but the mechanisms by which light triggers sleep deprivation-induced headache are not well-understood.MethodsTo measure pain sensitivity, we habituated 13 wild-type male mice to von Frey filaments applied to the periorbital area until there was no response to 0.6g stimulus. We then applied 5 lux of continuous dim light to mice during their usual 12-hour dark cycle. The 12-hour light cycle remained unchanged with 200 lux continuous light. Three groups of mice experienced the dim light stimulus for one, three, or five consecutive days. Ambulation and rest activity were measured using SOF-812 Activity Monitor machines. After the experiment concluded, we waited 24 hours and measured mechanical threshold using von Frey filaments at 1, 3, 5, 8, and every 3 days subsequently until mice no longer responded to 0.6g stimulus.ResultsArtificial light triggered changes in circadian behavior including increased number of rest periods during 12-hour dark (dim light) cycle and shortened sleep duration during 12-hour light cycle. Following the artificial light stimulus, there was a significant decrease in mechanical threshold (P<0.05), representing allodynia. The one-day group displayed one day of significant allodynia. The three-day group displayed three days of significant allodynia. The five-day group displayed five days of significant allodynia.ConclusionArtificial light may trigger circadian dysregulation, and the duration of artificial light exposure seemed to be directly correlated to the duration of allodynia up to one week after the stimulus was removed. We will repeat these experiments and analyze CNS and PNS tissue samples to understand the underlying physiological and biochemical bases of how artificial light triggers sleep deprivation-induced headache. This knowledge could increase our understanding of the pathophysiology and comorbidity of sleep deprivation and headache.Support (if any)Funding was received from the National Institute of Health (NS104200).

A theoretical approach for therapeutic artificial supplementary lighting in elderly living spaces

Depression is a leading cause of disability and death worldwide. Due to physiological and psychological degeneration, the elderly suffer from an increased risk and incidence of depression. Light therapy (LT), a non-intrusive approach for treating depression, exerts powerful effects on emotional and cognitive disorders, and can thus be installed in elderly living spaces (ELSs) in order to provide daily intervention that prevents the occurrence of the early phase of depression, delays its development, and promotes rehabilitation over its entire course. LT requires specific thresholds of light intensity, exposure duration, exposure time, and spectrum. The high incidence of seasonal affective disorder (SAD) triggered by daylight deprivation (caused by seasonal solar variation) suggests that daylight is insufficient for stable LT. Thus, custom-designed supplementary artificial lighting is needed.In this work, based on literature review and a synthesis of the light patterns related to antidepressant efficacy, visual comfort, and visual characteristics of the elderly, we recommended a set of a priori technical thresholds for light therapy installations in ELSs. Accordingly, using Radiance with Chengdu as a study case, we calculated the quantity and distribution of daylight and compared supplementary artificial lighting from the ceiling (horizontal lighting) and walls (vertical lighting), finding that vertical lighting is more advantageous in terms of both uniformity and energy efficiency for creating a lighting environment for daily light intervention in ELSs. This study introduces a theoretical approach for therapeutic lighting design, and the conclusions can provide technical guidance for applying light therapy in ELSs.

Association of time outdoors and patterns of light exposure with myopia in children

Background/aimsTo evaluate the association of reported time outdoors and light exposure patterns with myopia among children aged 9 years from the Growing Up in Singapore Towards Healthy Outcomes birth cohort.MethodsWe...

Photosensitizers and Exposure Times To Light Showed Tissue Compatibility In Isogenic Mice

Objective: The aim of this study was to evaluate the subcutaneous tissue response after different protocols to photodynamic therapy (PDT). In Phase 1, were tested the diode laser (used for 1min) associated to the photosensitizer phenothiazine chloride solution (PCS) in different concentrations. In Phase 2 – the diode laser and LED were tested associated to two different photosensitizers, PCS and Curcumin, in different exposure times of light application. Material and Methods: After 7, 21 and 63-days the animals were euthanized and the subcutaneous tissue processed to histological analysis. Qualitative and semi-quantitative descriptions of the inflammatory process and immunohistochemical technique were performed. The obtained data were analyzed by Kruskal-Wallis and Dunn’s post-test (alpha = 0.5). Results: On Phase 1, the tissue response was very similar among the groups. For the inflammatory infiltrate, PCS with concentration of 10mg/mL exhibited the most intense reaction (p &gt; 0.05). On Phase 2, at 7-days period, the analyzed parameters presented small magnitude and after 21 and 63-days, all the parameters demonstrated tissue compatibility. Conclusion: Both photosensitizers presented proper tissue compatibility regardless the different concentrations used on Phase 1 and different durations of light exposure on Phase 2. Keywords Photodynamic therapy; Phenothiazine chloride solution; Curcumin; Isogenic mice; Subcutaneous tissue.

A meta-analysis on the relationship between goose age and egg weight

Although many studies have attempted to determine the effect of goose age on egg weight, the relationship remains unclear. We conducted a meta-analysis of the relevant literature in an attempt to provide clarity on this question. We found that goose egg weight changes with age and that he greatest amount of yolk is produced following the second laying season, after which laying performance tends to decline. However, there was considerable heterogeneity among research study results that appears to be caused by ad libitum feed consumption. Interestingly, there have been no studies on the correlation between goose yolk weight and uterine secretions. These parameters change with age and can be easily evaluated through measurements of goose egg component weight in different laying seasons. Following the meta-analysis, we hypothesize that estrogen is a key factor in determining egg weight. Our findings suggest that poultry farms can adjust feed formulations and the duration of light exposure as geese age to optimize egg production. Estrogen concentrations may also be adjusted through diet supplementation as geese age to increase their productive lifespans.

Spectral sensitivity of circadian phase resetting, melatonin suppression and acute alerting effects of intermittent light exposure

Intermittent light (IML) pulses are more efficient per minute of exposure than continuous exposure in resetting the phase of the human circadian pacemaker. We assessed the spectral sensitivity in phase resetting, melatonin suppression and alertness induced by IML pulses. Twelve healthy young adults (6 females; mean age ± SD = 25.4 ± 3.6 years) were exposed to six monochromatic light pulses (2.8 × 1013 photons/cm2/s) over a 6.5 h window during the biological night. Six participants (3F) received 6 × 15-minute 460 nm (blue) pulses and six participants received 6 × 2-minute 555 nm (green) light pulses. Results were compared to historical data in 16 individuals who received continuous 460 nm (n = 8) or 555 nm (n = 8) light exposure using an identical protocol. As expected, long duration continuous 460 nm light exposure induced the largest total phase delay shifts, but intermittent 555 nm light induced the largest phase delay shifts per minute of the photic stimulus. Melatonin suppression was significantly higher under continuous light exposure compared to intermittent exposure patterns, and for 460 nm versus 555 nm exposure (under both light patterns). These data extend prior work showing a non-linear relationship between light exposure duration and phase resetting responses and illustrate the potential role of light wavelength, and therefore photoreceptor recruitment, in mediating these responses.

Cytotoxic effect of photodynamic liposome gel combined with trastuzumab on drugresistant breast cancer cells in vitro

To evaluate the cytotoxic effect of photodynamic therapy (PDT) combined with targeted therapy using cross-linked liposomes and gels (Ce6-PC-Tmab@A-Gel) loaded with photosensitizer Chlorin (Ce6) and the tumor-targeting drug Trastuzumab (Tmab) in drug-resistant HER2+ breast cancer cells. Ce6-PC-Tmab liposomes were prepared using the thin-film hydration method. The general properties, encapsulation efficiency and near-infrared responsivity of the nanoparticles were evaluated. Ce6-PC-Tmab@A-Gel with a shear response was prepared by freeze drying and stirring crosslinking, and its microstructure was observed with scanning electron microscopy (SEM) and the shear response evaluated using a rheometer. The inhibitory effect of Ce6-PC-Tmab@A-Gel in drug-resistant HER2+ breast cancer SK-BR-3 cells was assessed with cytotoxicity assay (MTT assay) combined with near-infrared light. The particle size of Ce6-PC-Tmab was 239.7±9.7 nm and the potential was -2.03±0.09 mV. The entrapment efficiency of Tmab by Ce6-PC-Tmab liposomes was (40.22± 0.73)%. The prepared Ce6-PC-Tmab@A-Gel had a good shear response with excellent drug release characteristics under nearinfrared light, and increased intensity and duration of near-infrared light exposure enhanced Tmab release from the gel. Ce6-PC-Tmab@A-Gel was stable at room temperature and in a simulated tumor microenvironment (pH 6.25). Cytotoxicity assay (MTT) showed that Ce6-PC-Tmab@A-Gel combined with near-infrared light resulted in a survival rate of (31.37±1.73)% in SKBR-3 cells, much lower than that in the control group and other treatment groups (P < 0.01); the combined treatment also had a high efficiency of ROS production, and ROS release reached (22.36 ± 0.11)% after 2 min of near-infrared light exposure. The prepared Ce6-PC-Tmab@A-Gel has good near-infrared light response release characteristics to ensure effective targeted therapy with Tmab. The injectable gel system potentially allows long-term local drug release in the tumor to improve the treatment efficacy against drug-resistant breast cancer.

Modeling Circadian Phototransduction: Quantitative Predictions of Psychophysical Data.

A revised computational model of circadian phototransduction is presented. The first step was to characterize the spectral sensitivity of the retinal circuit using suppression of the synthesis of melatonin by the pineal gland at night as the outcome measure. From the spectral sensitivity, circadian light was defined. Circadian light, thereby rectifies any spectral power distribution into a single, instantaneous photometric quantity. The second step was to characterize the circuit’s response characteristic to different amounts of circadian light from threshold to saturation. By doing so a more complete instantaneous photometric quantity representing the circadian stimulus was defined in terms of both the spectral sensitivity and the response magnitude characteristic of the circadian phototransduction circuit. To validate the model of the circadian phototransduction circuit, it was necessary to augment the model to account for different durations of the circadian stimulus and distribution of the circadian stimulus across the retina. Two simple modifications to the model accounted for the duration and distribution of continuous light exposure during the early biological night. A companion paper (https://www.frontiersin.org/articles/10.3389/fnins.2020.615305/full) provides a neurophysiological foundation for the model parameters.

Environmental light exposure, rest-activity rhythms, and symptoms of inattention and hyperactivity: An observational study of Australian preschoolers

Environmental light increases acute alertness and is the main regulator of the circadian clock in humans. In turn, circadian processes are strongly associated with inattention and hyperactivity symptoms in both children and adults. Evidence from animal studies suggest that light exposure may affect inattention and hyperactivity related behaviors during critical windows in early development. However, very little is known about the associations between light exposure, rest-activity rhythms and symptoms of inattention and hyperactivity in young children. Our aim was to examine whether the stability in rest-activity rhythms and the dosage, intensity and duration of environmental light were associated with symptoms of inattention and hyperactivity in children between 3 and 6 years of age. The present study used a subsample of the E4Kids Study. Objective measures of light exposure and stability of rest-activity rhythms were collected from 48 preschool children continuously over a period of two weeks. Parental reports of inattention and hyperactivity symptoms were collected concurrently and again 12 months later. Longer durations of light exposure were strongly associated with lower levels of hyperactivity symptoms at baseline (b = −0.64, CI = −0.97; −0.25), but not at follow up. The stability of rest-activity rhythms was associated with hyperactivity symptoms at follow up (b = −0.44, −0.81; −0.08), but not at baseline. Neither the stability of rest-activity rhythms or light exposure were associated with inattention symptoms. We provide the first evidence that the duration and intensity of environmental light exposure is inversely and strongly associated with symptoms of hyperactivity in young children in a naturalistic setting. Potential mechanistic pathways are discussed.

Влияние продолжительности светового воздействия на микроциркуляторное русло кожи по данным лазерной допплеровской флоуметрии в эксперименте

We studied the effect of long-term light exposure (model 18:6) on the functioning of regulatory mechanisms of the skin microcirculatory channel in the experiment. The study of microcirculation was performed using the method of laser Doppler flowmetry. It was found that prolonged light exposure causes impaired regulation of blood flow in the microcirculatory bed (reduction of amplitudes of endothelial, neurogenic and myogenic oscillations) and reduced tissue perfusion. The severity of hemodynamic disorders increases with increasing duration of light exposure. Decrease in perfusion and progression of violations of active factors regulating the processes of microcirculation indicate a negative effect of light exposure on tissue perfusion, which may serve as a risk factor for cardiovascular pathology.

Personal lighting conditions of office workers: An exploratory field study

Light enables us to see and perceive our environment but it also initiates effects beyond vision, such as alertness. Literature describes that at least six factors are relevant for initiating effects beyond vision. The exact relationship between these factors and alertness is not yet fully understood. In the current field study, personal lighting conditions of 62 Dutch office workers (aged 49.7 ± 11.4 years) were continuously measured and simultaneously self-reported activities and locations during the day were gathered via diaries. Each office worker participated 10 working days in spring 2017. Personal lighting conditions were interpreted based on four of the six factors (light quantity, spectrum, timing, and duration of light exposure). Large individual differences were found for the daily luminous exposures, illuminances, correlated colour temperatures, and irradiances measured with the blue sensor area of the dosimeter. The average illuminance (over all participants and all days) over the course of the day peaked three times. The analysis of the duration of light exposure demonstrated that the participants were on average only exposed to an illuminance above 1000 lx for 72 minutes per day. The interpretation of personal lighting conditions based on the four factors provides essential information since all of these factors may be relevant for initiating effects beyond vision. The findings in the current paper give first in-depth insight in the possibilities to interpret personal lighting conditions of office workers.

Influence of attenuated reflected solar radiation from the vineyard floor on volatile compounds in Cabernet Sauvignon grapes and wines of the north foot of Mt. Tianshan

In this study, fruit-zone microclimate was modified by three treatments, including inter-row mulch (M), the combination of leaf removal applied at the onset of veraison and inter-row mulch (MLR-BV), and the combination of leaf removal applied at complete veraison and inter-row mulch (MLR-EV), in a semi-arid climate in three consecutive years (2015–2017). M decreased fruit-zone reflected solar radiation from vineyard floor and low temperature (10–20 °C) duration, whereas it increased soil temperature and high temperature (> 30 °C) duration. MLR-BV and MLR-EV increased fruit-zone incident photosynthetically active radiation while decreased the duration of 20–25 °C compared to M. Notably, M significantly decreased grape total norisoprenoid concentrations in 2015–2017, and total terpenoid concentrations in 2015–2016. Applying leaf removal applied at the onset of veraison could compensate the decreases of total norisoprenoids and terpenoids caused by M when two treatments were applied together. Besides, M significantly increased grape total C6/C9 compound concentrations, besides, (Z)-3-hexen-1-ol concentrations were significantly higher in grapes of M than those of MLR-BV in 2015–2017. Light exposure and high temperature duration after veraison had strong positive correlations with total norisoprenoids and terpenoids, besides, low temperature duration was positively correlated with total norisoprenoids. In addition, light exposure after veraison had strong negative correlations with total C6/C9 compounds. With respect to the volatile compounds in wines, M significantly decreased the concentrations of isopentanol and ethyl acetate, and the concentrations of ethyl cinnamate, phenylacetaldehyde, phenylethyl alcohol and 3-methylthio-1-propanol were significantly lower in MLR-BV and MLR-EV than in M. The outcome of this study can assist winegrowers to properly adjust vineyard managements to optimize the concentrations of desired volatile compounds in grapes and wines.

Photo-irradiation induced green synthesis of highly stable silver nanoparticles using durian rind biomass: effects of light intensity, exposure time and pH on silver nanoparticles formation

The purpose of this work is to single-pot biosynthesize silver nanoparticles (AgNPs) using the extract from mesocarp and endocarp of durian rind under photo-irradiation. Without adding chemical substance, flavonoids, phenolic compounds and glucose dissolved in the extract served as the reducing agent; while proteins acted as the particle-stabilizing agent in the formation of AgNPs. The synthesis parameters i.e. light intensity, exposure duration, and pH value directly associated with the nucleation, growth, and aggregation of nanoparticles. The amount of synthesized AgNPs increased with increasing visible light intensity and exposure duration, while the size and stability of nanoparticles were decided by pH value adjustment. The size of synthesized AgNPs decreased when the pH value increased, on the contrary, the size increased when the pH value decreased. Under the optimized synthesis conditions (visible light intensity of 13,430 lx and pH value of 8.5), approximately 99% of silver ions was reduced to the spherical AgNPs with the mean diameter of 11.4 ± 3.2 nm within 5 min. The AgNPs remained uniformly dispersed in de-ionized water at no less than six months. The present environmental-friendly method is facile, rapid, and cost effective for the large scale preparation of AgNPs. The obtained AgNPs synthesized under optimum conditions could be applied for use in various fields such as antimicrobial activity, biosensors, and catalysis in the near future.

Predictions of melatonin suppression during the early biological night and their implications for residential light exposures prior to sleeping

The magnitude of nocturnal melatonin suppression depends upon the spectrum, amount, and duration of light exposure. The functional relationship between melatonin suppression and the light spectrum and amount have been previously described. Only one duration-dependent parameter was needed to extend this functional relationship to predict nocturnal melatonin suppression during the early biological night from a variety of published studies. Those predictions suggest that ambient lighting commonly found in North American homes will not suppress melatonin for durations up to 3 h, whereas extended use of self-luminous displays in the home prior to sleep can.