Daylight Duration Research Articles

Photoperiodic and circadian bifurcation theories of depression and mania.

Seasonal effects on mood have been observed throughout much of human history. Seasonal changes in animals and plants are largely mediated through the changing photoperiod (i.e., the photophase or duration of daylight). We review that in mammals, daylight specifically regulates SCN (suprachiasmatic nucleus) circadian organization and its control of melatonin secretion. The timing of melatonin secretion interacts with gene transcription in the pituitary pars tuberalis to modulate production of TSH (thyrotropin), hypothalamic T3 (triiodothyronine), and tuberalin peptides which modulate pituitary production of regulatory gonadotropins and other hormones. Pituitary hormones largely mediate seasonal physiologic and behavioral variations. As a result of long winter nights or inadequate illumination, we propose that delayed morning offset of nocturnal melatonin secretion, suppressing pars tuberalis function, could be the main cause for winter depression and even cause depressions at other times of year. Irregularities of circadian sleep timing and thyroid homeostasis contribute to depression. Bright light and sleep restriction are antidepressant and conversely, sometimes trigger mania. We propose that internal desynchronization or bifurcation of SCN circadian rhythms may underlie rapid-cycling manic-depressive disorders and perhaps most mania. Much further research will be needed to add substance to these theories.

Circadian synchronization determines critical day length for seasonal responses

A photoperiodic species initiates fat deposition (in migrants) and gonadal recrudescence in response to a specific duration of natural daylight, called critical day length (CD), when light extends in the inductive phase of the endogenous circadian rhythm of photoinducibility (CRP). The molecular basis of species-specificCD, determined by the entrainment of the CRP, has been poorly understood. To investigate this, we measured expression levels of genes implicated in the photoperiod-induced changes in reproduction (EYA3, TSH beta, DIO2, DIO3, GNRH and GNIH) and metabolism (SIRT1, HMGCR, FASN and PPAR alpha) in photosensitive redheaded buntings subjected to light–dark cycles of varying period lengths (T-photocycles). Buntings were exposed to six T22, T24 or T26 photocycles, with 1h additional light at night falling at different phases of the entrained CRP (T2211L=6L:4D:1L:11D; T2411L=6L:4D:1L:13D,T2412L=6L:5D:1L:12D, T2413L=6L:6D:1L:11D; T2612L=6L:5D:1L:14D). Photoinduction at genetic and phenotypic levels in T2412L and T2413L, not T2411L, groups confirmed CD being close to 12h in buntings under T24. Compared to T24, exposure to T22 advanced CD by 1h, as evidenced by photoinduction in the T2211L, not T226L, group. Similarly, CD appeared to be delayed under T26, with no photoinduction in the T2612L group. Further, to show that induction of response under a T-photocycle was because of the interaction of inductive phase of the CRP with 1h during the dark period in each cycle, not with the 6h main light periods falling 2h earlier each successive 24hday in a T22 paradigm, a group of buntings was exposed to 6L:16D (T226L), to which they did not respond. The mRNA expression of genes, particularly TSH beta, DIO2, DIO3 and PPAR alpha, was significantly correlated with changes in reproductive and metabolic phenotypes. These results suggest CRP-entrainment based genetic regulation of the CD, and extend the idea that synchronization with environment is a critical measure in a seasonal species for its temporal adaptation in the wild.

Association between bone stiffness and nutritional biomarkers combined with weight-bearing exercise, physical activity, and sedentary time in preadolescent children. A case–control study

Physical activity (PA) and micronutrients such as calcium (Ca), vitamin D (25OHD), and phosphate (PO) are important determinants of skeletal development. This case–control study examined the association of these nutritional biomarkers and different PA behaviours, such as habitual PA, weight-bearing exercise (WBE) and sedentary time (SED) with bone stiffness (SI) in 1819 2–9-year-old children from the IDEFICS study (2007–2008). SI was measured on the calcaneus using quantitative ultrasound. Serum and urine Ca and PO and serum 25OHD were determined. Children's sports activities were reported by parents using a standardised questionnaire. A subsample of 1089 children had accelerometer-based PA data (counts per minute, cpm). Moderate-to-vigorous PA (MVPA) and SED were estimated. Children with poor SI (below the 15th age-/sex-/height-specific percentile) were defined as cases (N=603). Randomly selected controls (N=1216) were matched by age, sex, and country. Odds ratios (OR) for poor SI were calculated by conditional logistic regression for all biomarkers and PA behaviour variables separately and combined (expressed as tertiles and dichotomised variables, respectively). ORs were adjusted for fat-free mass, dairy product consumption, and daylight duration. We observed increased ORs for no sports (OR=1.39, p<0.05), PA levels below 524cpm (OR=1.85, p<0.05) and MVPA below 4.2% a day (OR=1.69, p<0.05) compared to WBE, high PA levels (<688cpm) and high MVPA (6.7%), respectively. SED was not associated with SI. ORs were moderately elevated for low serum Ca and 25OHD. However, biomarkers were not statistically significantly associated with SI and did not modify the association between PA behaviours and SI. Although nutritional biomarkers appear to play a minor role compared to the osteogenic effect of PA and WBE, it is noteworthy that the highest risk for poor SI was observed for no sports or low MVPA combined with lower serum Ca (<2.5mmol/l) or lower 25OHD (<43.0nmol/l).

Assessment of carbon gains from biocrusts inhabiting a dunefield in the Negev Desert

Biocrusts play an important role in carbon (C) assimilation in arid and semiarid regions. In order to assess C gain in the crusted Hallamish dune field, net photosynthesis (Pn) and respiration (R) were measured at five crust types (A–E) which show a gradual increase in their chlorophyll content (with A<B<C<D<E). Pn and R were calculated per chlorophyll a and b (hereafter a/b) content. Total C input was calculated based on a large database that includes data on the temporal change in the chlorophyll content during the winter growing season, annual daylight and nighttime wetness duration and the cover of each crust type. The data show high similarity of Pn and R per chlorophyll content for all crusts (0.9–1.1 and 0.5–0.6gC(Chla/b)−1h−1, respectively). Both Pn and R showed a gradual increase with chlorophyll content with A≈B<C<D<E, with Pn ranging between 0.0311 (for crust A) and 0.1784 (for crust E) gCm−1h−1. Total calculated C gain for crusts A–E assuming total crust cover ranged between 2.1–8.6gCm−2a−1 for crusts A–D and 50.90gCm−2a−1 for crust E, with total annual input into the crusted areas of the ecosystem and the entire ecosystem being 3.7 and 2.3gCm−2a−1, respectively. In comparison to net ecosystem C exchange (NEE) from arid regions, our findings highlight the important role played by biocrusts in CO2 sequestration and as C provider for an extreme arid ecosystem. Yet, although a conservative approach was adopted, the data should be regarded as rough estimation only. In-situ field measurements are still required in order to substantiate the crust role in the annual C gain.

Implications of longitude and latitude on the size of solar-powered UAV

The implication of solar irradiance and daylight duration on the design of a small solar-powered unmanned aerial vehicle (UAV) that is capable of operating perpetually in various cities around the world was investigated. Solar data in 2013 on 12 cities distributed around the world was collected. The effects of the available solar irradiance and daylight of the city on the maximum take-off weight and wing span of a small solar-powered UAV were studied. The analysis indicates that daylight duration is as important as the available solar irradiance to the performance of the solar-powered UAV. Longitudinal coordinates and elevation have a minor effect on the estimation of daylight duration. Areas considerably high in solar irradiance and daylight duration are more conducive to the effective performance of solar-powered UAVs than other areas. Therefore, cities closer to the equator have an advantage in utilizing solar-powered UAVs; where smaller and lighter solar-powered UAV can be designed.

Diurnal and seasonal variation of the brain serotonin system in healthy male subjects

The mammalian circadian clock underlies both diurnal and seasonal changes in physiology, and its function is thought to be disturbed in both seasonal and non-seasonal depression. In humans, molecular imaging studies have reported seasonal changes in the serotonin system. Despite the role of the circadian clock in generating seasonal physiological changes, however, diurnal variation of serotonin receptors and transporters has never been directly studied in humans. We used positron emission tomography to examine diurnal and seasonal changes in the serotonin 5-HT1A receptor and serotonin transporter in two large cohorts of healthy male subjects, employing a cross-sectional design. In 56 subjects measured with [11C]WAY-100635, we observed diurnal increases in the availability of 5-HT1A receptors in the cortex. In 40 subjects measured with [11C]MADAM, a decrease in 5-HTT was observed in the midbrain across the day. We also found seasonal changes in the 5-HT1A receptor in serotonin projection regions, with higher availability on days with a longer duration of daylight. Our observation that serotonin receptor and transporter levels may change across the day in humans is corroborated by experimental research in rodents. These findings have important implications for understanding the relationship between the circadian and serotonin systems in both the healthy brain and in affective disorders, as well as for the design of future molecular imaging studies.

Thyroid hormone divergence between two closely related but ecologically diverse cyprinid fish species (Cyprinidae)

Thyroid hormones (THs) are involved in regulation of many life history traits of fishes. Development, growth, reproduction and shaping the adult phenotypes were found to be regulated by THs. Regulatory evolution is one of the main factors driving morpho-ecological diversification and speciation. We tested a hypothesis whether closely related but ecologically diverged species may have a diverse level of THs. We compared seasonal levels of plasma concentrations of triiodothyronine (T3) in two cyprinid species, benthophagous bream Abramis brama and zooplanktivorous blue bream Ballerus ballerus. Significant differences in T3 concentrations were detected. B. ballerus had substantially reduced T3 levels as compared to most other species of fish. Two hypotheses explaining the thyroid divergence are discussed. Despite differences in absolute T3 concentrations, both species manifest similar seasonal cycling with increased plasma T3 levels in warmer seasons and decreased T3 in colder seasons. Several peaks of plasma T3 level were registered: at pre-spawning periods, at mid-summer and in the early autumn. The pre-spawning peak noted in cyprinids was a novel observation. Significant positive correlations were detected between water temperature and plasma T3 concentrations, as well as between the duration of daylight and T3 plasma concentrations in both species.

Seasonal Variation in Paroxysmal Atrial Fibrillation: A Systematic Review.

A variety of cardiovascular diseases have been demonstrated to have seasonal variations with peaks in the winter and troughs in the summer. Studies regarding atrial fibrillation (AF) have had varying results and this review describes the current data regarding the seasonal variation of AF and mechanisms mediating this seasonal fluctuation. A systematic review was conducted of PubMed, EBSCO and OVID for manuscripts describing the association between seasonal variation and the occurrence of AF. Studies meeting eligibility criteria were assessed for quality and reporting bias. Data was extracted in regards to the following associations: seasonal variation and AF paroxysms, temperature and AFparoxysms, duration of daylight and AF paroxysms, barometric pressure and AF paroxysms, alcohol and AF paroxysms, as well as seasonal variation and AF related stroke. A total of 15 studies were identified for inclusion. Of these, 11 studies assessed seasonal variation and the remaining 4 studies assessed seasonal variation in AF related stroke. AF paroxysms peaked in winter with a trough in summer. There was an inverse correlation between temperatures as well barometric pressure and the occurrence of AF paroxysms and a positive correlation with duration of daylight. The rate of occurrence of paroxysmal AF varies by seasons and is greatest during winter and least in summer.

Some adaptations of aquatic organisms to high latitudes (brief overview)

The adaptations of aquatic organisms to high latitudes are primarily concerned with an adjustment to low temperatures and seasonal changes in illumination, including an alteration of Polar Night and Day. The adaptations always involve multiple aspects and levels – from the molecular to the behavioral. The most important adaptations to low temperatures are: the movement of water from the intracellular to the extracellular compartments, so that the molecular weight of the intracellular fluid increases and its freezing point shifts downwards, preventing an intracellular freezing, ensured by the synthesis of anti-freeze compounds; the transition from saturated to unsaturated fatty acids, which is a critical mechanism for the membrane lipids functioning; as well as the synthesis of more flexible proteins. The most crucial component of the algae adaptation is their variable thermal resistance and an increase in the content of photosynthetic pigments as the daylight duration decreases. The reserves necessary for survival during the Polar Night are accumulated in the summer season. Cryoflora adaptations are studied. Some essential adaptations occur in oogenesis. The synthesis of fats in the yolk increases considerably, enabling a transition from the primitive ontogeny in the larval stage to a more advanced, direct ontogeny, which meets the conditions of high latitudes better. An asynchronous type of oogenesis remains during the transition from a repeat to single spawning.

Diurnal and Seasonal Occurrence of Febrile Seizures

BackgroundFebrile seizures are the most common seizures in children, but their pathogenesis remains unknown. Some studies have suggested an association between the light-dependent secretion of melatonin and the occurrence of febrile seizures. The diurnal and seasonal occurrence of febrile seizures could clarify the role daylight plays in febrile seizures. MethodsIn Finland, summer days are long and bright and winter days are short and dark. We evaluated the diurnal and seasonal occurrence of the first febrile seizures in 461 children and adjusted them according to the epidemiology of the febrile episodes in a population-based study of 1522 children. ResultsThe first febrile seizure most often occurred in the evening, peaking between 6 and 10 PM (31%), and least often at night, in the early morning hours between 2 and 6 AM (8%) (P < 0.001). This diurnal pattern repeated itself in different seasons according to variance in daylight duration. Febrile seizures occurred irregularly throughout the year, most frequently in winter, concurrently with the febrile episodes, and least frequently in summer; this seasonal variation in the occurrence of febrile seizures disappeared however when adjusted for the number of febrile events. ConclusionsWe found clear diurnal and seasonal variations in the occurrence of febrile seizures, even though they did not follow the amount of daylight. Our findings do not support the hypothesis that the diurnal and seasonal variation of daylight explains the occurrence of febrile seizures. Moreover, febrile events associated strongly with the occurrence of febrile seizures.

Activity patterns of Eurasian lynx are modulated by light regime and individual traits over a wide latitudinal range.

The activity patterns of most terrestrial animals are regarded as being primarily influenced by light, although other factors, such as sexual cycle and climatic conditions, can modify the underlying patterns. However, most activity studies have been limited to a single study area, which in turn limit the variability of light conditions and other factors. Here we considered a range of variables that might potentially influence the activity of a large carnivore, the Eurasian lynx, in a network of studies conducted with identical methodology in different areas spanning latitudes from 49°7′N in central Europe to 70°00′N in northern Scandinavia. The variables considered both light conditions, ranging from a day with a complete day–night cycle to polar night and polar day, as well as individual traits of the animals. We analysed activity data of 38 individual free-ranging lynx equipped with GPS-collars with acceleration sensors, covering more than 11,000 lynx days. Mixed linear additive models revealed that the lynx activity level was not influenced by the daily daylight duration and the activity pattern was bimodal, even during polar night and polar day. The duration of the active phase of the activity cycle varied with the widening and narrowing of the photoperiod. Activity varied significantly with moonlight. Among adults, males were more active than females, and subadult lynx were more active than adults. In polar regions, the amplitude of the lynx daily activity pattern was low, likely as a result of the polycyclic activity pattern of their main prey, reindeer. At lower latitudes, the basic lynx activity pattern peaked during twilight, corresponding to the crepuscular activity pattern of the main prey, roe deer. Our results indicated that the basic activity of lynx is independent of light conditions, but is modified by both individual traits and the activity pattern of the locally most important prey.

Seasonal changes in the apparent position of the Sun as elementary applications of vector operations

Many introductory courses in physics face an unpleasant chicken-and-egg problem. One might choose to introduce students to physical quantities such as velocity, acceleration, and momentum in over-simplified one-dimensional applications before introducing vectors and their manipulation; or one might first introduce vectors as mathematical objects and defer demonstration of their physical utility. This paper offers a solution to this pedagogical problem: elementary vector operations can be used without mechanics concepts to understand variations in the solar latitude, duration of daylight, and orientation of the rising and setting Sun. I show how sunrise and sunset phenomena lend themselves to exercises with scalar products, vector products, unit vectors, and vector projections that can be useful for introducing vector analysis in the context of physics.

Modeling and Simulation of Solar Irradiance and Daylight Duration for a High-Power-Output Solar Module System

Solar energy is the largest available renewable energy for enhancing the endurance of a solar-powered unmanned aerial vehicle (UAV). However, harnessing solar energy is a great challenge because the power output efficiency of solar module systems is only 15% to 30%. A solar-powered UAV has the potential to outperform a battery-powered UAV, particularly in tasks involving a pseudo satellite that requires long operating hours. Atmospheric conditions and geographical location are the main causes of the poor performance of solar modules. Despite the improvements in solar cell efficiency over the years, solar module systems can still barely convert half of the sun’s power into electricity. This limitation hinders the use of current solar module systems for harvesting solar energy. Recent studies have focused not only on the type of solar cells but also on the positioning system. However, understanding and research on the solar irradiance intensity, as well as on the effect of daylight duration on the power output, remain lacking. A comprehensive model was developed to address this gap and investigate how the movement of the sun movement affects the performance of solar module systems. This simulation model found that daylight duration is more important than available solar irradiance. Higher solar irradiance and daylight duration corresponds to a higher power output of the solar module system. Daylight duration also depends on latitude where higher latitudes lead to longer daylight duration. On the other hand, longitudinal coordinates and elevation have minor effects on the estimation of daylight duration. Therefore, the northern hemisphere has more advantages than southern hemisphere during summer and vice versa.

Changes in Chinese hair growth along a full year.

To confirm the existence of seasonal hair growth cycle among Chinese subjects and objectivize the seasonal effect of hair loss; the hair growth parameters of Chinese volunteers were followed monthly for an entire year on the same area of vertex. The hair growth parameters of 41 Chinese volunteers (women and men), free from alopecia, were recorded monthly along an entire year using the phototrichogram technique. Results show an increased rate of telogen hairs (growing arrest) around August-September in the study group, as previously reported in European subjects albeit of a lower extent and remaining within the normal range of healthy head hair parameters. The possible effects of latitude and daylight duration are discussed. Data confirm that Chinese hairs present characteristics of the most developed and fast growing terminal fibres, as compared to other non-Asian ethnics.

Assessing the Effect of Weather States on Crash Severity and Type by Use of Full Bayesian Multivariate Safety Models

Rather than investigate the isolated effects of individual weather elements on crash occurrence, this study investigated the aggregated effect of weather states, defined as a combination of various weather elements (e.g., temperature, snow, rain, and wind speed), on crash occurrence. The main argument was that a combination of weather elements might better represent a particular weather condition and subsequent safety outcome. Therefore, to explore the effect of various weather states on crash severity and type, this study defined 12 weather states, based on temperature, snow, rain, and wind speed, and developed multivariate safety models by using 11 years of daily weather and crash data for Edmonton, Alberta, Canada. The proposed models were estimated in a full Bayesian context via a Markov chain Monte Carlo simulation, while a posterior predictive approach assessed the models’ goodness of fit. Results suggested that property-damage-only (PDO) crashes increased by 4.5% to 45% because of adverse weather states and showed that PDO crashes were more affected by adverse weather states than were severe (injury and fatal) crashes. For crash type, adverse weather states were associated with an increase of 9% to 73.7% for all crash types, with the highest increase for run-off-the-road crashes. Duration of daylight was found to be significant and negatively related to all crash types and PDO crashes. Sudden weather changes of major snow or rain were statistically significant and positively related to all crash types. Days of the week and seasons of the year were used as dummy variables and were statistically significant in relation to crash occurrence.

Trade‐offs between global warming and day length on the start of the carbon uptake period in seasonally cold ecosystems

[1] It is well established that warming leads to longer growing seasons in seasonally cold ecosystems. Whether this goes along with an increase in the net ecosystem carbon dioxide (CO2) uptake is much more controversial. We studied the effects of warming on the start of the carbon uptake period (CUP) of three mountain grasslands situated along an elevational gradient in the Alps. To this end, we used a simple empirical model of the net ecosystem CO2 exchange, calibrated, and forced with multiyear empirical data from each site. We show that reductions in the quantity and duration of daylight associated with earlier snowmelts were responsible for diminishing returns, in terms of carbon gain, from longer growing seasons caused by reductions in daytime photosynthetic uptake and increases in nighttime losses of CO2. This effect was less pronounced at high, compared to low, elevations, where the start of the CUP occurred closer to the summer solstice when changes in day length and incident radiation are minimal.

Efficient venetian blind control strategies considering daylight utilization and glare protection

This paper presents the development of new venetian blind control strategies considering daylight provision, lighting energy use and visual comfort. A hybrid ray-tracing and radiosity method is used to calculate transmission through the window-blind system and interior illuminance distributions taking into account specular and diffuse material properties. Work plane illuminances are used to extract daylighting metrics, while directional light distribution and respective luminance values are used to calculate glare potential. Four types of control strategies were evaluated – a cut-off angle control, a daylight-redirecting control, and two glare protection control modes. Using the common “cut-off” angle may result in a strong second reflection that might significantly affect visual discomfort depending on view direction and profile angle. Proper rotation of the tilt angle and consideration of specular characteristics can minimize this effect and redistribute daylight deeper into the space, although glare problems cannot be eliminated in some cases. Moreover, two additional control strategies were developed based on glare probability and sky conditions: the first is a model-based control derived from real time glare simulation results. The second is a “simplified” control that uses pre-calculated correlations between glare probability and transmitted illuminance to establish binary set points that can be used in model-predictive control algorithms.A detailed daylighting analysis was performed in order to evaluate set points for blind control actions, annual daylighting metrics, lighting energy use and daylight glare probability and duration. Different room sizes, glazing properties, blind material characteristics and orientations were studied. The results showed that diffuse blinds do not reduce the risk of glare when light redirection is desired; double-sided slats with a diffuse top and a specular bottom surface are better in this regard. Fixed angles at 60° or higher provide satisfactory results for most cases, although there is a penalty in daylighting efficiency. The two glare protection control algorithms proved to be efficient in providing high daylight autonomy values without the risk of glare for all studied cases.

CHANGES OF SETTINGS OF BRAIN BIOELECTRICAL ACTIVITY IN NORTHERN SCHOOLCHILDREN AGED 16-17 IN DIFFERENT AMBIENT LIGHT CONDITIONS

A study of frequency characteristics of electroencephalograms (EEG) in high school students during increasing, maximum, decreasing and minimum duration of daylight has been conducted. In the paper, dynamics of the main EEG rhythms has been presented, their relationship with periods of daylight has been established. There has been revealed dominance of alpha and delta activity in contrasting seasons, periods favorable for the brain functioning and development of higher mental functions have been defined.

Multi-objective optimization of building envelope for energy consumption and daylight

The objective of this article is to provide a methodology for optimizing the envelope of a building with respect to the triple objective of heating load, cooling load and daylight. The variables to optimize are the window to wall area ratio (WWR) and the window type characterized by its visual and thermal characteristics (visual and solar transmittance, and U-value). Energy load is computed using building performance simulation software (TRNSYS). A criterion of daylight is defined as the integrated time when the illuminance is below a threshold and artificial light is required. This criterion was calculated using the software Daysim. The variables have antagonistic effects on the objectives: WWR and window type may have opposite effects by increasing solar gain and daylight duration during winter, which would be beneficial, but could lead to overheating during summer. Therefore, an easy-to-set up methodology is proposed to find the optimal solutions of such a problem. A multi-objective optimization was performed in order to find the optimal variables leading to the minimization of the energy load and the maximization of the indoor daylight duration. The method was applied to a dormitory retrofitting. Optimal solutions are the best compromise among antagonistic objectives and would offer guidance to designers in making construction decisions.

The Sun’s position in the sky

We express the position of the Sun in the sky as a function of time and the observer’s geographic coordinates. Our method is based on applying rotation matrices to vectors describing points on the celestial sphere. We also derive direct expressions, as functions of date of the year and geographic latitude, for the duration of daylight, the maximum and minimum altitudes of the Sun, and the cardinal directions to sunrise and sunset. We discuss how to account for the eccentricity of the Earth’s orbit, the precessions of the equinoxes and the perihelion, the size of the solar disc and atmospheric refraction. We illustrate these results by computing the dates of ‘Manhattanhenge’ (when sunset aligns with the east–west streets on the main traffic grid for Manhattan, in New York City), by plotting the altitude of the Sun over representative cities as a function of time, and by showing plots (‘analemmas’) for the position of the Sun in the sky at a given hour of the day.