Differences In Light Exposure Research Articles

Associations between light exposure and sleep timing and sleepiness while awake in a sample of UK adults in everyday life

Experimental and interventional studies show that light can regulate sleep timing and sleepiness while awake by setting the phase of circadian rhythms and supporting alertness. The extent to which differences in light exposure explain variations in sleep and sleepiness within and between individuals in everyday life remains less clear. Here, we establish a method to address this deficit, incorporating an open-source wearable wrist-worn light logger (SpectraWear) and smartphone-based online data collection. We use it to simultaneously record longitudinal light exposure (in melanopic equivalent daylight illuminance), sleep timing, and subjective alertness over seven days in a convenience sample of 59 UK adults without externally imposed circadian challenge (e.g., shift work or jetlag). Participants reliably had strong daily rhythms in light exposure but frequently were exposed to less light during the daytime and more light in pre-bedtime and sleep episodes than recommended [T. M. Brown et al., PLoS Biol. 20, e3001571 (2022)]. Prior light exposure over several hours was associated with lower subjective sleepiness with, in particular, brighter light in the late sleep episode and after wake linked to reduced early morning sleepiness (sleep inertia). Higher pre-bedtime light exposure was associated with longer sleep onset latency. Early sleep timing was correlated with more reproducible and robust daily patterns of light exposure and higher daytime/lower night-time light exposure. Our study establishes a method for collecting longitudinal sleep and health/performance data in everyday life and provides evidence of associations between light exposure and important determinants of sleep health and performance.

Characterizing light-dark cycles in the Neonatal Intensive Care Unit: a retrospective observational study.

Objectives: To characterize bedside 24-h patterns in light exposure in the Neonatal Intensive Care Unit (NICU) and to explore the environmental and individual patient characteristics that influence these patterns in this clinical setting. Methods: We conducted a retrospective cohort study that included 79 very preterm infants who stayed in an incubator with a built-in light sensor. Bedside light exposure was measured continuously (one value per minute). Based on these data, various metrics (including relative amplitude, intradaily variability, and interdaily stability) were calculated to characterize the 24-h patterns of light exposure. Next, we determined the association between these metrics and various environmental and individual patient characteristics. Results: A 24-h light-dark cycle was apparent in the NICU with significant differences in light exposure between the three nurse shifts (p < 0.001), with the highest values in the morning and the lowest values at night. Light exposure was generally low, with illuminances rarely surpassing 75 lux, and highly variable between patients and across days within a single patient. Furthermore, the season of birth and phototherapy had a significant effect on 24-h light-dark cycles, whereas no effect of bed location and illness severity were observed. Conclusion: Even without an official lighting regime set, a 24-h light-dark cycle was observed in the NICU. Various rhythmicity metrics can be used to characterize 24-h light-dark cycles in a clinical setting and to study the relationship between light patterns and health outcomes.

Characterizing the modern light environment and its influence on circadian rhythms.

Humans have largely supplanted natural light cycles with a variety of electric light sources and schedules misaligned with day-night cycles. Circadian disruption has been linked to a number of disease processes, but the extent of circadian disruption among the population is unknown. In this study, we measured light exposure and wrist temperature among residents of an urban area during each of the four seasons, as well as light illuminance in nearby outdoor locations. Daily light exposure was significantly lower for individuals, compared to outdoor light sensors, across all four seasons. There was also little seasonal variation in the realized photoperiod experienced by individuals, with the only significant difference occurring between winter and summer. We tested the hypothesis that differential light exposure impacts circadian phase timing, detected via the wrist temperature rhythm. To determine the influence of light exposure on circadian rhythms, we modelled the impact of morning and night-time light exposure on the timing of the maximum wrist temperature. We found that morning and night-time light exposure had significant but opposing impacts on maximum wrist temperature timing. Our results demonstrate that, within the range of exposure seen in everyday life, night-time light can delay the onset of the maximum wrist temperature, while morning light can lead to earlier onset. Our results demonstrate that humans are minimizing natural seasonal differences in light exposure, and that circadian shifts and disruptions may be a more regular occurrence in the general population than is currently recognized.

An Objective Comparison of Light Intensity and Near-Visual Tasks Between Rural and Urban School Children in China by a Wearable Device Clouclip.

PurposeTo compare light intensity and near-visual tasks objectively between rural and urban children.MethodsClouclip, a wearable device, was applied to assess metrics of these two factors in 78 fifth-grade students from an urban and from a rural school.ResultsThe light intensity experienced by urban students was found significantly lower both in the school period (614.05 ± 178.77 vs. 918.41 ± 257.81 lux, P < 0.001) and on the weekend (444.53 ± 216.65 vs. 882.21 ± 536.67 lux, P < 0.001). The duration of exposure to bright light (>1000 lux) was also substantially shorter for urban students. Although no significant difference was found in near work–related behaviors during the school period and the weekend, for the after-school period the urban students had a shorter average viewing distance (30.94 ± 4.14 vs. 34.81 ± 3.93 cm, P < 0.001), a longer accumulated duration of near work (2.25 ± 0.53 vs. 1.95 ± 0.46 hours, P = 0.010), a greater time ratio of near work (56% ± 14% vs. 49% ± 14%, P = 0.045), and a greater time ratio of excessively close near work (49% ± 13% vs. 40% ± 12%, P = 0.001).ConclusionsOur data indicate there were substantial differences in light exposure and near-work metrics between the two regions. The correlation between these differences and the discrepancy in regional myopia prevalence needs further investigation.Translational RelevanceThe objective quantification of these metrics might help explain the varied myopia prevalence among regions.

Influence of seasons upon personal light exposure and longitudinal axial length changes in young adults.

To investigate the association between objectively measured ambient light exposure and longitudinal axial length changes (and their seasonal variations) over a period of 12months in young adults. This prospective longitudinal observational study included 43 healthy young adult university students (21 emmetropes and 22 myopes) aged between 18 and 30years. Three axial length measurements were collected at 6-month intervals (i.e. at baseline, 6 and 12months), in summer and winter to determine the axial eye growth. Personal ambient light exposure data were measured in winter and summer months with wearable sensors, from which the mean daily time exposed to bright (outdoor) light levels (>1000lux) was derived. Greater daily bright light exposure was associated with less axial eye growth (β=-0.002, p=0.006) over 12months. In summer, myopes exhibited significantly greater changes in axial length (mean change 0.04±0.05mm) compared to emmetropes (-0.01±0.05mm) (p=0.001), but there was no significant difference between refractive groups in winter. Emmetropes also spent significantly greater time in outdoor light levels in summer compared to winter (p<0.0001), while myopes spent similar time outdoors during both seasons (p=0.12). Differences in light exposure between summer and winter were also associated with seasonal differences in axial eye growth (p=0.026). In young adults, greater time spent in bright light was associated with slower longitudinal axial eye growth. Seasonal light exposure and axial length changes were dependent on refractive error in this population and also exhibited an inverse relationship.

Objectively Measured Light Exposure During School and Summer in Children.

Significant differences in light exposure were observed between school and summer in children, whereas activity and sleep were similar. Associations between parent and child behaviors suggest a potential mechanism for how myopia is transmitted from parents to children through patterns of environmental exposure, in addition to genetic factors. Objectively measured time outdoors, light exposure, activity, and sleep were examined in children during school and summer and assessed with eye growth. Associations between parent and child behaviors were evaluated. Children (aged 7.6 ± 1.8 years, n = 60) in Houston, TX, wore an actigraph device for three 2-week sessions (fall school, spring school, summer) to quantify time outdoors, light exposure, activity, and sleep. Cycloplegic autorefraction (WAM-5500; Grand-Seiko, Tokyo, Japan) and axial length (LenStar; Haag-Streit AG, Koeniz, Switzerland) were measured at baseline and 1 year. A subset of parents wore the device during their child's first 2-week session to compare behaviors (n = 33). Children spent 94.4 ± 30.6 minutes per day outdoors in spring, 110.6 ± 45.7 minutes in summer, and 72.2 ± 31.0 minutes in fall, with significant differences between sessions (P < .0001). Daily activity and sleep duration were similar across sessions (P = .73 and .06, respectively). Axial growth rate decreased with light exposure, but did not reach significance after adjusting for baseline axial length, age, sex, activity, and parental myopia (P = .073). Parent and child time outdoors and sleep duration were significantly correlated (P = .0002 and 0.026, respectively). Significant differences in light exposure were observed between school and summer, whereas activity and sleep were constant throughout the year. Children's behaviors were associated with their parent's behaviors, which may represent a modifiable component to potential environmental influences on eye growth. However, light exposure was not a significant environmental influence on axial growth in this study.

Seasonal Differences in Light Exposure and the Associations With Health and Well-Being in Older Adults: An Exploratory Study.

Objective:This article reports summer verses winter seasonal variations across a suite of blue light, illuminance levels and health and well-being indicators.Background:The quality of lighting in care homes has been assessed previously, yet seasonal comparisons and the associations with sleep quality are limited. This exploratory study investigates light exposure in two seasons to determine the changes over time and the associations with health and well-being.Methods:In a repeated measures design, 16 older people (aged 72–99 years) living in a care home had their personal light exposure and sleep/wake patterns monitored for 4 days. Cognitive ability, mental well-being, daytime physical activity, and visual function were assessed. Mean light levels at preset times across the day, duration in light exposure over 1,000 lux, and sleep parameters were computed. Statistical investigations included correlations exploring associations and paired means tests to detect the changes between seasons.Results:The mean morning illuminance level in summer was 466 lux and 65 lux in winter. Duration in bright light over 1,000 lux was 46 min in summer and 3 min in winter. Light measures were significantly higher in summer. There was no statistical difference in sleep quality parameters between seasons, but there were significant difference in daytime physical activity level (i.e., this was higher in summer).Conclusion:The findings indicate low level of light exposures experienced in both seasons, with exposure levels being particularly low in winter. This provides new insights into the limited amount of light older people receive independent of season and the possible impacts on sleep and daytime physical activity level.

Photosynthetic Acclimation of Symbiodinium in hospite Depends on Vertical Position in the Tissue of the Scleractinian Coral Montastrea curta.

Coral photophysiology has been studied intensively from the colony scale down to the scale of single fluorescent pigment granules as light is one of the key determinants for coral health. We studied the photophysiology of the oral and aboral symbiont band of scleractinian coral Montastrea curta to investigate if different acclimation to light exist in hospite on a polyp scale. By combined use of electrochemical and fiber-optic microsensors for O2, scalar irradiance and variable chlorophyll fluorescence, we could characterize the physical and chemical microenvironment experienced by the symbionts and, for the first time, estimate effective quantum yields of PSII photochemistry and rates of electron transport at the position of the zooxanthellae corrected for the in-tissue gradient of scalar irradiance. The oral- and aboral Symbiodinium layers received ∼71% and ∼33% of surface scalar irradiance, respectively, and the two symbiont layers experience considerable differences in light exposure. Rates of gross photosynthesis did not differ markedly between the oral- and aboral layer and curves of PSII electron transport rates corrected for scalar irradiance in hospite, showed that the light use efficiency under sub-saturating light conditions were similar between the two layers. However, the aboral Symbiodinium band did not experience photosynthetic saturation, even at the highest investigated irradiance where the oral layer was clearly saturated. We thus found a different light acclimation response for the oral and aboral symbiont bands in hospite, and discuss whether such response could be shaped by spectral shifts caused by tissue gradients of scalar irradiance. Based on our experimental finding, combined with previous knowledge, we present a conceptual model on the photophysiology of Symbiodinium residing inside living coral tissue under natural gradients of light and chemical parameters.

Distribution of GNAQ and GNA11 Mutation Signatures in Uveal Melanoma Points to a Light Dependent Mutation Mechanism.

Uveal melanomas (UM) originate from melanocytes in the interior wall of the eye, namely from the iris, ciliary body and the choroid with marked differences in light exposure (from dark anterior to illuminated posterior). In contrast to UV radiation, focused or converging visible light readily reaches the retina and can damage DNA which possibly contributes to UM development. In this report choroidal, ciliochoroidal and iridociliary melanomas were analyzed for GNAQ and GNA11 mutations which were subsequently correlated to the location of tumor origin. Hotspot mutations in GNAQ and GNA11 can be divided in A>T and in A>C mutation signatures. The GNAQ A626C mutation (Q209P) was almost exclusively observed in choroidal melanomas from the illuminated posterior side. On the other hand, ciliochoroidal UM from the dark anterior side with mostly A>T mutations were clearly associated with light-colored eyes. Combined these data suggest a light and a pigment dependent etiology in UM development.

School Schedules Affect Sleep Timing in Children and Contribute to Partial Sleep Deprivation

ABSTRACTAlthough the environmental light/dark cycle is the main zeitgeber for the human species, the social cues seem to be important in the synchronization of circadian rhythms. In Brazil, the existence of two school schedules—one with only morning classes (MG) and other with only afternoon classes (AG)—allows the investigation of the effect of school activities on light exposure and sleep/wake patterns in children. Forty‐seven children wore wrist actimeters for a week for registration of light and sleep data. MG children presented shorter sleep duration on school days than the children from the AG. The results showed that during school days MG children were exposed to bright light earlier in the morning when compared to AG children. Nevertheless, there were no differences in light exposure after sunset. The results reflect the role of school schedules and artificial light in shaping light exposure, and its association with sleep timing in children.

Light exposure and depression in hospitalized adult patients with cystic fibrosis

BackgroundDepression is common in CF. Light therapy is used to treat depression, but exposure in hospitalized CF patients has not been studied. To determine the potential for improvement in depressive symptoms in CF patients, we measured light exposure in hospitalized CF patients. MethodsLight exposure was measured during hospitalization for 30 adult CF patients over 1 week. Depressive symptoms and quality of life were assessed simultaneously using the Center for Epidemiologic Studies Depression Scale (CES-D>16 positive for depression) and the CFQ-R. Results50% of patients were depressed, with a significant increase in length of stay between depressed and non-depressed patients (15.4 vs. 11.7 days, p=0.032). Only 23% of patients had >60min of light exposure >1000lx during 1 week, with average light exposure of 62lx. There was no difference in light exposure between a new hospital room customized for natural light exposure and traditional rooms. Vitamin D was non-significantly decreased in depressed CF patients (25.1 vs. 32.6ng/ml, p=0.052). LimitationsThe study was not blinded, which may affect patient light preferences. The cohort size was limited to a single center. Inclusion bias may be present as patients could refuse enrollment based on the nature of the study. ConclusionsHospitalized CF adults have a high incidence of depressive symptoms associated with longer hospitalizations. Hospital settings are associated with low light exposure and phototherapy may be an option for rapid treatment of depression in hospitalized CF patients.

Kinematic analysis of overground locomotion in chicks incubated under different light conditions.

Domestic chicks walk within 3-4 hr after hatching following 21 days of incubation. However, differences in light exposure can vary incubation duration. Based on pilot studies, we predicted that there would be a positive relationship between incubation duration and locomotor competence at hatching. Embryos were incubated in one of three conditions that varied light duration and intensity, and overground locomotor performance was tested on the day of hatching. Chicks incubated in continuous bright light hatched 1-2 days earlier than chicks incubated in less or no light. Kinematic findings indicated that locomotor skill was similar across incubation conditions and led us to reject our hypothesis. We propose that light may accelerate locomotor development without adversely affecting skill. Our findings raise two important implications for future studies: whether light exposure accelerates locomotor circuit development; and/or it unmasks adaptive motor skill by accelerating development of other physiological systems.

Effect of Nest Box Availability on the Circadian Activity Rhythm of Common Marmosets (Callithrix jacchus)

The effect of nest box availability on the circadian activity rhythm (CAR) was compared in a diurnal primate kept in two conditions: with and without nest box, in a light-dark (LD) cycle (12:12) and constant light (LL). Marmosets kept in LD without nest box showed a longer duration of the activity phase (α), smaller day-to-day variability in activity onset and offset and higher levels of activity, particularly towards the end of the activity time. In LL, all animals maintained with nest box expressed free-running CAR, but without nest box, 3 of the 4 individuals showed relative coordination with the outdoor LD cycle, possibly due to social synchronization with captive marmosets maintained outdoors. All animals showed longer α and higher levels of activity without nest box. Thus, the availability of a nest box is an important aspect in maintaining marmosets, influencing CAR expression in this diurnal primate in LD and LL conditions, possibly due to differences in light exposure that induces masking. Further studies are needed to evaluate the effects of the unavailability of a nest box on CAR in LL conditions.

Effect of Light Perception on Menarche in Blind Women

ABSTRACTPurpose: The role of light on human reproductive development is unclear. Women with varying degrees of visual impairment appear to have altered reproductive function compared to sighted women. These differences have been attributed in part to differences in light exposure between the sighted and the blind. The present study was conducted to determine whether differences exist in reproductive measures among blind women with at least light perception (LP) compared to women with no perception of light (NPL). Methods: We studied 1,392 (LP, n = 968; NPL, n = 417; unreported, n = 7) blind women across North America between 2005 and 2007. Statistical analysis was conducted using Student's two-sample t tests and multivariate logistic or linear regression. Models were adjusted for current age, body mass index (BMI) and BMI at age 18. Results: NPL women reported an earlier menarche (mean age, 12.16, standard deviation ± 1.53) than LP women (mean age, 12.46, ± 1.57 yrs). The adjusted odds ratio (OR) for each increasing year of menarche among NPL women compared to LP women, was 0.88 (95% confidence intervals [CI]: 0.81–0.96). When those women NPL from birth were compared to all others, the adjusted odds ratio was strengthened (OR: 0.80, 95% CI: 0.68–0.94). When we examined the association between age at onset of NPL and age at menarche, we found a significant positive association with earlier menarche being associated with an earlier age category of loss of light perception (test for trend p < 0.01). Conclusions: Our findings suggest that lack of light perception affects reproductive development in women.

Does shift work cause cancer?

Does shift work cause cancer?

Daily Light Exposure in Morning-Type and Evening-Type Individuals

Morning-type individuals (M-types) have earlier sleep schedules than do evening types (E-types) and therefore differ in their exposure to the external light-dark cycle. M-types and E-types usually differ in their endogenous circadian phase as well, but whether this is the cause or the consequence of the difference in light exposure remains controversial. In this study, ambulatory monitoring was used to measure 24-h light exposure in M-type and E-type subjects for 7 consecutive days. The circadian phase of each subject was then estimated in the laboratory using the dim-light melatonin onset in saliva (DLMO) and the core body temperature minimum (Tmin). On average, M-types had earlier sleep schedules and earlier circadian phases than E-types. They also showed more minutes of daily bright light exposure (> 1000 lux) than E-types. As expected, the 24-h patterns of light exposure analyzed in relation to clock time indicated that M-types were exposed to more light in the morning than E-types and that the reverse was true in the late evening. However, there was no significant difference when the light profiles were analyzed in relation to circadian phase, suggesting that, on average, the circadian pacemaker of both M-types and E-types was similarly entrained to the light-dark cycle they usually experience. Some M-types and E-types had different sleep schedules but similar circadian phases. These subjects also had identical light profiles in relation to their circadian phase. By contrast, M-types and E-types with very early or very late circadian phases showed large differences in their profiles of light exposure in relation to their circadian phase. This observation suggests that in these individuals, early or late circadian phases are related to relatively short and long circadian periods and that a phase-delaying profile of light exposure in M-types and a phase-advancing profile in E-types are necessary to ensure a stable entrainment to the 24-h day.

Inter-subject differences in constitutive expression levels of the clock gene in man

Circadian rhythms are generated, both at the level of the whole organism and at the cellular level, by biological clocks involving a set of clock genes. We previously performed a randomised, placebo-controlled, double-blind trial examining the effect of six months of pioglitazone (30 mg per day) therapy on neointima volume after coronary stenting in patients with coronary artery disease but without diabetes. In a subgroup of 15 patients from each group, a whole blood sample was taken at the beginning of the trial and at an eight-week clinical follow-up for isolation of total RNA using a PAXgene system. Using real time RT-PCR with relative quantitation, we investigated whether pioglitazone treatment altered clock gene expression in RNA extracted from peripheral white blood cells (PBCs). No significant changes in clock gene expression were noted in either placebo (99+/-45%) or pioglitazone-treated subjects (101+/-35%) after eight weeks. These data potentially extend previous findings that the clock gene is constitutively expressed over 24 hours to eight weeks. We observed a large range of inter-subject differences in expression levels of the clock gene. The difference between the mean value for the lowest expression individual (DeltaCT 8.8) and the highest expression individual (DeltaCT 3.7) revealed an approximately 34-fold difference in relative clock gene expression levels. These differences may arise through differences in light exposure, polymorphic variants of the clock gene affecting gene expression and/or post-transcriptional regulation. They could influence susceptibility to disruption of normal circadian rhythms, which occur in pathophysiological conditions pertaining to diabetes and cardiovascular disease.

Characterization of a type II chlorophyll a/b-binding protein gene (Lhcb2*Pp1) in peach. II. mRNA abundance in developing leaves exposed to sun or shade.

Leaf development of shoots exposed to full sunlight and shoots shaded by the canopy was followed in field-grown, mature peach trees (Prunus persica (L.) Batsch, cv. Loring) during the first half of the 1995 growing season. The architecture and size of shaded shoots and sun-exposed shoots differed significantly. Total number of leaves produced on shaded shoots was significantly less than on sun-exposed shoots throughout the season, and differences in leaf number between light conditions increased as the season progressed. The overall patterns of leaf development along sun-exposed and shaded shoots were qualitatively similar. The expression pattern of the type II chlorophyll a/b-binding protein gene, Lhcb2*Pp1, determined by RNA abundance in leaves at different positions along the shoot, was also similar between the two light conditions. The major difference between sun-exposed and shaded leaves was a lower abundance of Lhcb2*Pp1 RNA in mature, shaded leaves compared with sun-exposed leaves. Although the number of fruit per shoot was significantly lower on shaded shoots than on sun-exposed shoots, the rate of fruit drop was not substantially different during the growing season, indicating that quantitative differences in leaf initiation and growth caused by differences in light exposure did not adversely affect fruit retention. However, based on comparison with a previous study of leaf development in non-fruiting trees, reproductive development slowed the rate of vegetative growth without affecting the overall pattern of leaf development along the shoots.

Photic entrainment in hamsters: effects of simulated twilights and nest box availability.

Entrainment of wheel-running activity rhythms was compared in hamsters exposed to daily light-dark (LD) cycles with abrupt transitions between 0 and 10 lux or with artificial twilights simulating summer solstice conditions at 41 degrees N latitude but truncated at 10 lux. The photoperiod in LD-rectangular was set at 16.24 h, equating the total light (in lux.min) emitted under the two schedules. The LD cycles were maintained for 35 days and were followed by 14 days of constant darkness (DD). Half the animals in each condition had access to a dark nest box connected to the outer compartment by a tunnel, the remaining animals being confined to a single compartment. Body temperature and locomotor activity inside the nest boxes were recorded by telemetry. Movements between the nest box and the outer compartment were monitored and the data were used to calculate light exposure at different times of the day. In all groups, the phase angle difference between wheel-running onset and dusk was more positive than that between activity offset and dawn. Hamsters with access to nest boxes, however, had later onsets, earlier offsets, and shorter activity durations (alpha s) than those without. These effects could be accounted for by the difference in light exposure between the nest and no-nest animals, particularly light exposure in the morning. The inclusion of twilights also resulted in later onsets and shorter alpha s, but the differences were relatively small and were only observed in the nest animals. The day-to-day variability in activity onset was negatively correlated with onset time and was smaller in the twilight/nest animals than in the other three groups. Most animals showed an expansion of alpha during the first few days of DD, resulting from a rapid advance of activity onsets relative to offsets. The period of the rhythms, determined from the first five activity onsets in DD, was negatively correlated with the balance of evening and morning light exposure. These results are discussed in the context of nonparametric entrainment of compound pacemakers.

Letter to the Editor

Dr. Aase's question about the possibility that differences in exposure to light might have accounted for our observed differences in bilirubin levels is, of course, germane. During the course of our study, we became aware of the reports which described the effect of light on degradation of bilirubin. However, we could determine no differences in light exposure between the two populations under study nor, because of the physical arrangements of the nurseries, did there appear to be any possibility that there would be seasonal variations in the amount of light exposure.