Influence of different light intensities on the daily grooming distribution of common marmosets Callithrix jacchus

The daily distribution of autogrooming was evaluated in adult marmosets submitted to different illumination intensities in the light phase of the light-dark cycle. Autogrooming and locomotor activity were monitored and the faecal cortisol level assessed as a stress indicator. The distribution of autogrooming showed two distinct tendencies: when the light intensity varied from 500 to 200 lux, a slight increase in frequency and duration was observed, while a significant decrease in both variables occurred at 10 lux. Varying light intensities did not inhibit rhythm synchronization. The daily profile of autogrooming was mainly unimodal with an acrophase in the first half of the light phase. Faecal cortisol levels tended to increase in animals submitted to 100 and 10 lux, but these results are not conclusive. We suggest keeping captive marmosets in light intensities of at least 200 lux in the light phase, allowing animals to maintain autogrooming levels in order to reduce the discomfort caused by captivity and isolation.     

Temporal dynamics of late-night photic stimulation of the human circadian timing system

The light-dark cycle is the primary synchronizing factor that keeps the internal circadian pacemaker appropriately aligned with the environmental 24-h day. Although it is known that ocular light exposure can effectively shift the human circadian pacemaker and do so in an intensity-dependent manner, the curve that describes the relationship between light intensity and pacemaker response has not been fully characterized for light exposure in the late biological night. We exposed subjects to 3 consecutive days of 5 h of experimental light, centered 1.5 h after the timing of the fitted minimum of core body temperature, and show that such light can phase advance shift the human circadian pacemaker in an intensity-dependent manner, with a logistic model best describing the relationship between light intensity and phase shift. A similar sigmoidal relationship is also observed between light intensity and the suppression of plasma melatonin concentrations that occurs during the experimental light exposure. As with a simpler, 1-day light exposure during the early biological night, our data indicate that the human circadian pacemaker is highly sensitive even to typical room light intensities during the late biological night, with approximately 100 lux evoking half of the effects observed with light 10 times as bright.     

Effects of psi-mutations on the Oviposition Rhythm of Drosophila rajasekari

The psi -mutations affected the circadian rhythm of locomotor activity in the early and late strains of Drosophila rajasekari (Joshi, 1999a). The present study was designed to determine the effects of psi -mutations on the oviposition rhythm of the early and late strains. Oviposition rhythms were studied in light-dark cycles of 12 :12 h in which the light intensity of photophase was 0.001, 0.01, 0.1, 1, 10, 100 or 1000 lux. The oviposition rhythm of wild type was unimodal at or above 10 lux with a peak before lights-off, while it was bimodal at lower light intensities. The early strain was unimodal at all light intensities with a peak after lights-on at or above 10 lux, and around the mid-day at or below 1lux. The late strain was rhythmic at 100 and 1000 lux with a peak after the lights-off, weakly rhythmic at 10 lux and arrhythmic at or below 1 lux. Free running period in constant darkness was shortest in the early and longest in the late strain. Threshold light intensity of constant light to generate arrhythmicity was lowest in the early and highest in the late strain, apparently the photic sensitivity of the clock photoreceptors was differentially altered by these mutations. Thus the psi -mutations for locomotor rhythmicity affected the oviposition rhythm too, suggesting that the same circadian oscillator might be controlling these both rhythms.     

Effects of psi-mutations on the Oviposition Rhythm of Drosophila rajasekari

The psi -mutations affected the circadian rhythm of locomotor activity in the early and late strains of Drosophila rajasekari (Joshi, 1999a). The present study was designed to determine the effects of psi -mutations on the oviposition rhythm of the early and late strains. Oviposition rhythms were studied in light-dark cycles of 12 :12 h in which the light intensity of photophase was 0.001, 0.01, 0.1, 1, 10, 100 or 1000 lux. The oviposition rhythm of wild type was unimodal at or above 10 lux with a peak before lights-off, while it was bimodal at lower light intensities. The early strain was unimodal at all light intensities with a peak after lights-on at or above 10 lux, and around the mid-day at or below 1lux. The late strain was rhythmic at 100 and 1000 lux with a peak after the lights-off, weakly rhythmic at 10 lux and arrhythmic at or below 1 lux. Free running period in constant darkness was shortest in the early and longest in the late strain. Threshold light intensity of constant light to generate arrhythmicity was lowest in the early and highest in the late strain, apparently the photic sensitivity of the clock photoreceptors was differentially altered by these mutations. Thus the psi -mutations for locomotor rhythmicity affected the oviposition rhythm too, suggesting that the same circadian oscillator might be controlling these both rhythms.     

Zeitgebers for animals in the continuous daylight of high arctic summer

Summary To find out which of daily oscillating environmental factors in the continuous daylight of arctic summer are responsable for synchronization of animal activity period with the rotation of the earth, in Spitsbergen (78° N) a whole summer continuous measurements of temperature (°C), light intensity (lux) and spectral composition of the light (colour temperature in °K) were done. With a daily amplitude of 4–5° C in the air, resp. 10° C at the ground surface, temperature can only act as a Zeitgeber for heterothermic animals. Measurements of light intensity (with a photocell directed vertical upward to the zenith) showed relatively large daily oscillations. But since light intensity depends on the cosine of the angle of incidence of the light (Lambert's cosine law) and in high latitudes the angle of incidence of the sun is always very great, in fact measurements have to be done with the photocell directed to the sun or, as the latter meets with mechanical problems, all dates got with the photocell vertical upward must be converted after Lambert's cosine law. Converted dates of light intensity oscillate not nearly as intense as measured dates. This small daily amplitude of light intensity, which in addition is strongly influenced by sudden changes of the wheather, can hardly come into consideration as a Zeitgeber of animal activity period. Colour temperature however showed large and regular daily oscillations and therefore could be a Zeitgeber of animal activity period in high arctic summer, particularly because in the laboratory the synchroniing effect of an artificial daily alternation of colour temperature is already proved. Nest (feeding) activity of local snowbuntings and perch hopping activity of greenfinches, brought from Germany, were registrated with light traps. Activity period of both bird species was clearly synchronized with the rotation of the earth. In a narrow valley the activity pattern of greenfinches was identical as in open country, in spite of temporarily total other conditions of light intensity (shading by mountains). Apparently even the activity period of non arctic animals can be synchronized by weak Zeitgebers like colour temperature.     

Retinal cyclic light damage threshold for albino rats

This study determined the minimum cyclic [12L:12D] light intensity which produces retinal damage in albino (Sprague-Dawley) rats raised from birth to 15 weeks of age under a cyclic light intensity of 6 lux. Four experimental light intensities were tested, including: 1345, 270, 130 and 65 lux. Control animals remained under 6 lux. For each of the intensities tested, the retinas of groups of six rats were evaluated after various durations of light exposure for physiological and morphological evidence of light damage. The indices of damage were (a) histological and morphometric changes in the retina and (b) changes in the amplitude of the b-wave of the electroretinogram. The data indicated that light intensities of 1345 or 270 lux severely damaged retinas of albino rats within 3-7 days of the initiation of light exposure. Exposure to 130 or 65 lux produced much less dramatic changes in the responsiveness and morphology of the retina which did not appear to be permanent. Based on these results, a reasonable estimate for the threshold cyclic light intensity which produces damage to retinas of albino rats raised under 6 lux lies between 130 and 270 lux, or approximately 1.3 log units above the light intensity under which the animals were raised.     

Circadian Rhythms and time Measurement in Locomotor Activity of the Scorpion Leiurus Quinquestriatus (Buthidae)

The circadian rhythms of locomotor activity of the scorpion Leiurus quinqueslriatus were examined under different light-dark cycles and in free-running conditions. The circadian rhythm is bimodal in LD 12:12 with alternating cycles of temperature (35°-25°C) with high intensity (1300 lux) or in LD 12: 12 with constant temperature 35° C with 300 lux. In LD 12:12 (1300 lux), in long or in short light spans with constant temperature, the bimodal pattern is slightly changed with the appearance of a third minor peak of activity. In free-running conditions, the bimodal rhythm of locomotor activity persists in DD with T about 24 hr, but in LL the rhythm becomes unimodal with T about 24 hr. Cosinor and power spectrum analysis showed the presence of more than one periodic component. It seems that there is a correlation between the range of light regimens, temperature, light intensity and the coincidence of these components. These components are independently entrained by the environmental light cycle. The mechanism of entrainment of components is discussed.     

Modeling light adaptation in circadian clock: prediction of the response that stabilizes entrainment

Periods of biological clocks are close to but often different from the rotation period of the earth. Thus, the clocks of organisms must be adjusted to synchronize with day-night cycles. The primary signal that adjusts the clocks is light. In Neurospora, light transiently up-regulates the expression of specific clock genes. This molecular response to light is called light adaptation. Does light adaptation occur in other organisms? Using published experimental data, we first estimated the time course of the up-regulation rate of gene expression by light. Intriguingly, the estimated up-regulation rate was transient during light period in mice as well as Neurospora. Next, we constructed a computational model to consider how light adaptation had an effect on the entrainment of circadian oscillation to 24-h light-dark cycles. We found that cellular oscillations are more likely to be destabilized without light adaption especially when light intensity is very high. From the present results, we predict that the instability of circadian oscillations under 24-h light-dark cycles can be experimentally observed if light adaptation is altered. We conclude that the functional consequence of light adaptation is to increase the adjustability to 24-h light-dark cycles and then adapt to fluctuating environments in nature.     

Effect of light intensity on the oviposition rhythm of the altitudinal strains of Drosophila ananassae

The sensitivity of the circadian photoreceptors mediating entrainment of the eclosion rhythm and phase shifts of oviposition rhythm of the high altitude (HA) strain of Drosophila ananassae originating from Badrinath (5123 m above sea level) in the Himalayas was compared with the low altitude (LA) strain from Firozpur (179 m above sea level). Reduced photic sensitivity of the HA strain is regarded as the result of natural selection, which led to the weakening of the coupling mechanism between the circadian pacemaker and light at the high altitude of origin. The present study was designed to determine whether or not the photic entrainment of the oviposition rhythm of the HA strain of D. ananassae is also altered by the high altitude of its origin, and the results are compared with those of the LA strain. The effects of light intensity on the phase angle difference (Ψ), degree of rhythmicity (R), the percent oviposition in photophase, the threshold light intensity (i.e., the intensity at which stable entrainment occurred), and the saturation light intensity (i.e., the intensity beyond which the values of Ψ or amplitude of rhythm remained unaltered) were determined. Entrainment was studied in light-dark cycles in which the light intensity of 12 h of photophase varied from 1 to 1000 lux, and complete darkness prevailed in all scotophases. The oviposition rhythm of the HA strain was arrhythmic from 1 to 90 lux, weakly rhythmic at 95 lux, but rhythmic at or above 100 lux, while that of the LA strain was weakly rhythmic at 1 lux but rhythmic at or above 2 lux. Oviposition of the HA strain occurred mostly in the photophase, while that of the LA strain occurred in the scotophase; as a result, the oviposition medians of the HA strain were around the subjective forenoons while those of the LA strain were around the subjective evenings. The percent of oviposition in photophase increased from 68 to 98 in the HA strain and from 5 to 33 in the LA strain as light intensity increased from 1 to 1000 lux. In the HA strain, the Ψ values were significantly less and values of R and percent oviposition in photophase were significantly more than those of the LA strain at each level of light intensity. Threshold and saturation intensities for Ψ were 100 and 700 lux, respectively, for the HA strain, but just 2 and 45 lux, respectively, for the LA strain. The saturation intensity for R was 650 and 700 lux for the HA and LA strains, respectively. These results extend the confirmation that the reduced photic sensitivity of the HA strain might have been acquired through natural selection in response to environmental conditions at the high altitude of its origin.     

Light intensity preferences of broiler chickens: implications for welfare

There is considerable debate as to the optimal light intensities for growing chickens. This is influencing regulations and industry practices. The present study examines the preference of broiler chickens for light intensity. A choice system was developed to allow determination of the preferences of broiler chickens for light intensity. This system had three light proof pens each with feeders or waterers but different light intensities. There was a connecting transit pen with a light intensity of 1 to 2 lux. This allowed birds access to the pens each with feeders or waterers. There were markedly more chickens observed in the pens each with feeders or waterers and a light intensity of 20 lux than 5 lux. Moreover, more feed was consumed in the 20 lux pens than 5 pens. There were also high numbers of chickens in the transit compartment with its low light intensity (1 to 2 lux) and no feeders or waterers. Broiler chickens exhibited a preference for 20 lux light intensity for feeding compared to 5 lux light intensity. The present study supports the view that there should be a light intensity of at least 20 lux for the areas around the feeders and also suggests that light intensity may be reduced in other areas for resting and other activities.     

The effect of light intensity on the breeding and development of rats and golden hamsters

The growth, gestation and lactation of rats and hamsters subjected to different light intensities (15-2,000 lux) have been investigated. In the male rat, adrenal, testis and kidney weights were higher with increased light intensity, and there was an optimal light intensity (250 lux) for number of litters born, and a different optimum (60 lux) for the number of young per litter. In the hamster there were no differences related to light intensity, apart from an increase in the incidence of anoestrus where light intensities were below 60 lux.     

Effect of different light intensities on growth,amino-acid,fat and sugar concentrations inCaulerpa prolifera (Foerskal) Lamouroux

The effect of different light intensities on growth, and the amino acid, fat and sugar concentrations ofCaulerpa prolifera (Foerskal) Lamouroux were studied. The results showed that 2,500 lux was the optimum light intensity for growth coupled with a minimum in total free amino acids and maximum in peptides, total soluble sugars and total lipids. Any deviations above or below the optimum light intensity caused a drop in all components studied.     

Effect of light intensity on the locomotor activity rhythm of Talitrus saltator (Montagu 1808) from Korba Beach

In this work, we investigate the locomotor behaviour of Talitrus saltator (Montagu 1808) for a population collected from the supralittoral zone of Korba beach. The locomotor activity rhythm was recorded for adult individuals during 10 summer days under continuous light with four different luminous intensities: 5 lux (N = 30), 35 lux (N = 30), 75 lux (N = 30) and 140 lux (N = 15). By the end of the experiments, 100% of the considered individuals were found alive under light intensities of 35 and 140 lux, whereas only 86 and 90% were found alive under light intensity of 5 and 75 lux, respectively. Furthermore, whatever the imposed luminous intensity is, actograms showed a clear drift to the right lengthening day after day the circadian period. Moreover, we found that by raising the light intensity, the drift becomes increasingly important. Actograms as well as activity curves, results showed that the locomotor activity profiles are mainly unimodal and their percentage increases when increasing the light intensity. Furthermore, periodogram analysis highlighted the presence of ultradian and circadian components where the longest periods were observed with the highest luminous intensity. In addition, the locomotor activity rhythm was statistically more defined and individuals of Talitrus saltator were significantly more active under the lowest luminous intensity.     

Assessment of lighting needs by W-36 laying hens via preference test

Light intensity, spectrum and pattern may affect laying hen behaviors and production performance. However, requirements of these lighting parameters from the hens’ standpoint are not fully understood. This study was conducted to investigate hens’ needs for light intensity and circadian rhythm using a light tunnel with five identical compartments each at a different fluorescent light intensity of <1, 5, 15, 30 or 100 lux. The hens were able to move freely among the respective compartments. A group of four W-36 laying hens (23 to 30 weeks of age) were tested each time, and six groups or replicates were conducted. Behaviors of the hens were continuously recorded, yielding data on daily time spent, daily feed intake, daily feeding time, and eggs laid under each light intensity and daily inter-compartment movement. The results show that the hens generally spent more time in lower light intensities. Specifically, the hens spent 6.4 h (45.4%) at 5 lux, 3.0 h (22.1%) at 15 lux, 3.1 h (22.2%) at 30 lux and 1.5 h (10.3%) at 100 lux under light condition; and an accumulation of 10.0 h in darkness (<1 lux) per day. The 10-h dark period was distributed intermittently throughout the day, averaging 25.0±0.4 min per hour. This hourly light-dark rhythm differs from the typical commercial practice of providing continuous dark period for certain part of the day (e.g. 8 h at night). Distributions of daily feed intake (87.3 g/hen) among the different light conditions mirrored the trend of time spent in the respective light intensity, that is, highest at 5 lux (28.4 g/hen, 32.5% daily total) and lowest at 100 lux (5.8 g/hen, 6.7%). Hen-day egg production rate was 96.0%. Most of the eggs were laid in <1 lux (61.9% of total) which was significantly higher than under other light intensities (P<0.05). Findings from this study offer insights into preference of fluorescent light intensity by the laying hens. Further studies to assess or verify welfare and performance responses of the hens to the preferred lighting conditions and rhythm over extended periods are recommended.     

Effect of light periodicity and intensity on the growth and survival of Heterobranchus longifilis Val. 1840 (Teleostei: Clariidae) larvae after 14 days of rearing

Heterobranchus longifilis Val. 1840 larvae were reared under two light intensities, 30 lux and 915 lux, and at varying photoperiods. Results show that maximum survival (82.5 ± 6.5% respectively) at 30 lux was obtained at continuous illumination [24 h light (L)], while the minimum (65 ± 21.2%) was at the 6 h L : 18 h dark (D) treatment. Survival at 24 h D averaged 71.3 ± 6.3%, with no significant difference (P < 0.05) in growth of larvae. Maximum larval survival at 915 lux was 87.5 ± 17.7% at the 18 h L treatment. Growth was not significantly different (P < 0.05) in the treatments. Comparison of the two light intensities showed that survival was better at a photoperiod above 12 h irrespective of intensity, while growth was significantly better at the 915 lux intensity.     

Effects of different light intensities in the morning on dim light melatonin onset

The present study evaluated the effects of exposure to light intensity in the morning on dim light melatonin onset (DLMO). The tested light intensities were 750 lux, 150 lux, 3000 lux, 6000 lux and 12,000 lux (horizontal illuminance at cornea), using commercial 5000 K fluorescent lamps. Eleven healthy males aged 21-31 participated in 2-day experiments for each light condition. On the first experimental day (day 1), subjects were exposed to dim light (<30 lux) for 3 h in the morning (09:00-12:00). On the same day, saliva samples were taken in dim light (<30 lux) every 30 min from 21:00 to 01:00 to determine the DLMO phase. The subjects were allowed to sleep from 01:00 to 08:00. On the second experimental day (day 2), the subjects were exposed to experimental light conditions for 3 h in the morning. The experimental schedule after light exposure was the same as on day 1. On comparing day 2 with day 1, significant phase advances of DLMO were obtained at 3000 lux, 6000 lux and 12,000 lux. These findings indicate that exposure to a necessary intensity from an ordinary light source, such as a fluorescent lamp, in the morning within one day affects melatonin secretion.     

Paradoxical masking effects of bright photophase and high temperature in Drosophila malerkotliana

Synergic contribution of light and temperature is known to cause a paradoxical masking effect (inhibition of activity by bright light and high temperature) on various rhythms of animals. The present study reports the paradoxical masking effects of 1000-lux photophase at 25°C on the locomotor activity rhythm of Drosophila malerkotliana. Flies were subjected to light (L)-dark (D) 12:12 cycles wherein the photophase was varied from 10 to 1000 lux, whereas the scotophase was set to 0 lux in these and subsequent LD cycles. At 10, 100, and 500 lux, the flies were diurnal; however, at 1000 lux they were nocturnal. Transfer from LD 12:12 cycles to continuous darkness (DD) initiated free-running rhythmicity in all flies. Free-running rhythms of the flies switched from the 10-lux to the 500-lux groups started from the last activity-onset phase of the rhythm following 3-5 transient cycles, suggesting involvement of the circadian pacemaker. In contrast, the free-running rhythm of the flies of the 1000-lux group began abruptly from the last lights-on phase of the LD cycle, indicating noninvolvement of the pacemaker. Furthermore, all flies showed nocturnal activity in the two types of LD 12:12 cycles when the photophase was 1000 lux. The first type of LD cycles had three succeeding photophases of 100, 1000, and again 100 lux, whereas the second type of LD cycles had only one photophase of 1000 lux, but the LD 12:12 cycles were reversed to DL 12:12 cycles. Apparently, the combined effects of light and temperature caused such paradoxical masking effects. This hypothesis was tested by repeating the above experiments at 20°C. Flies in all experiments exhibited a diurnal activity pattern, even when the photophase was 1000 lux. Thus, the present study demonstrates that the paradoxical masking effect in D. malerkotliana was caused by the additive influence of light intensity and temperature. This strategy appears to have physiological significance, i.e., to shun and thus protect against the bright photophase at high temperature in the field.     

Quantifying human circadian pacemaker response to brief, extended, and repeated light stimuli over the phototopic range

The authors' previous models have been able to describe accurately the effects of extended (approximately 5 h) bright-light (>4000 lux) stimuli on the phase and amplitude of the human circadian pacemaker, but they are not sufficient to represent the surprising human sensitivity to both brief pulses of bright light and light of more moderate intensities. Therefore, the authors have devised a new model in which a dynamic stimulus processor (Process L) intervenes between the light stimuli and the traditional representation of the circadian pacemaker as a self-sustaining limit-cycle oscillator (Process P). The overall model incorporating Process L and Process P is intended to allow the prediction of phase shifts to photic stimuli of any temporal pattern (extended and brief light episodes) and any light intensity in the photopic range. Two time constants emerge in the Process L model: the characteristic duration for necessary bright-light pulses to achieve their full effect (5-10 min) and the characteristic stimulus-free (dark) interval that can be tolerated without incurring an excessive penalty in phase shifting (30-80 min). The effect of reducing light intensity is incorporated in Process L as an extension of the time necessary for the light pulse to be fully realized (a power-law relation between time and intensity). This new model generates a number of new testable hypotheses, including the surprising prediction that 24-h cycles consisting of 8 h of darkness and 16 h of only approximately 3.5 lux would be capable of entraining a large fraction of the adult population (approximately 45%). Experimental data on the response of the human circadian system to lower light intensities and briefer stimuli are needed to allow for further refinement and validation of the model proposed here.     

Noise-Induced Coherence in Multicellular Circadian Clocks

In higher organisms, circadian rhythms are generated by a multicellular genetic clock that is entrained very efficiently to the 24-h light-dark cycle. Most studies done so far of these circadian oscillators have considered a perfectly periodic driving by light, in the form of either a square wave or a sinusoidal modulation. However, in natural conditions, organisms are subject to nonnegligible fluctuations in the light level all through the daily cycle. In this article, we investigate how the interplay between light fluctuations and intercellular coupling affects the dynamics of the collective rhythm in a large ensemble of nonidentical, globally coupled cellular clocks modeled as Goodwin oscillators. On the basis of experimental considerations, we assume an inverse dependence of the cell-cell coupling strength on the light intensity, in such a way that the larger the light intensity, the weaker the coupling. Our results show a noise-induced rhythm generation for constant light intensities at which the clock is arrhythmic in the noise-free case. Importantly, the rhythm shows a resonancelike phenomenon as a function of the noise intensity. Such improved coherence can be only observed at the level of the overt rhythm and not at the level of the individual oscillators, thus suggesting a cooperative effect of noise, coupling, and the emerging synchronization between the oscillators.     

A laboratory experiment to determine the dispersal response of Atlantic salmon (Salmo salar) fry to street light intensity

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