Dark Polymerization Following Partial Radical Photocuring: Effect of Light Intensity and Exposure Duration

Ohadi S, Rahimian Mashhadi H, Tavakkol‐Afshari R & Beheshtian Mesgaran M (2010). Modelling the effect of light intensity and duration of exposure on seed germination of Phalaris minor and Poa annua. Weed Research50, 209–217.SummaryPhotocontrol of weeds requires a better understanding of the effect of light on seed germination. Therefore, the effect of light intensity and exposure duration was tested on seed germination of two winter annual weeds, Phalaris minor and Poa annua. Photo‐sensitised seeds of both species were subjected to four light intensities, including 130, 250, 500 and 1000 μmol m−2 s−1, each at six exposure durations of 0.1, 1, 10, 100, 1000 and 10 000 s. Light stimulated the germination of both weeds. A modelling approach was used to describe the relationship between light intensity and exposure duration with the germination of weed seeds. A combination of logistic and Gaussian models provided good fits to P. minor percentage germination data, whereas in the case of P. annua, the incorporation of logistic and quadratic models better described the relationships. According to the model, increasing light intensity from 0 (full darkness) to 1000 μmol m−2 s−1 increased the germination of P. minor and P. annua from 28% to 57% and from 0% to 35% respectively. The seed germination of both weed species increased with exposure duration, but declined at duration periods longer than 100 s in P. minor or 1000 s in P. annua. The model predicted a trade‐off between light intensity and light duration for both weeds. That is, a high light intensity irradiated for a short time exposure may result in the same percentage germination as one with a low light intensity, but at longer exposure duration.

The phase resetting response of the human circadian pacemaker to light depends on the timing of exposure and is described by a phase response curve (PRC). The current study aimed to construct a PRC for a 1 h exposure to bright white light (∼8000 lux) and to compare this PRC to a <3 lux dim background light PRC. These data were also compared to a previously completed 6.7 h bright white light PRC and a <15 lux dim background light PRC constructed under similar conditions. Participants were randomized for exposure to 1 h of either bright white light (n=18) or <3 lux dim background light (n=18) scheduled at 1 of 18 circadian phases. Participants completed constant routine (CR) procedures in dim light (<3 lux) before and after the light exposure to assess circadian phase. Phase shifts were calculated as the difference in timing of dim light melatonin onset (DLMO) during pre- and post-stimulus CRs. Exposure to 1 h of bright white light induced a Type 1 PRC with a fitted peak-to-trough amplitude of 2.20 h. No discernible PRC was observed in the <3 lux dim background light PRC. The fitted peak-to-trough amplitude of the 1 h bright light PRC was ∼40% of that for the 6.7 h PRC despite representing only 15% of the light exposure duration, consistent with previous studies showing a non-linear duration–response function for the effects of light on circadian resetting.

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.

ntroduction: The use of computers is increasing these days. The use of computer cause serious eye complaints in the form of Computer vision syndrome (CVS) symptoms. CVS is a disease associated with symptoms of watery eyes, blurred vision, eye redness, eye strain, etc. Consequences of these symptoms can reduce working productivity or efficiency. Allegedly one of the factors that trigger CVS symptoms is the duration of computer’s light exposure. Purpose: To determined whether there is association between duration of computer light exposure with Computer Vision Syndrome (CVS)’s incidence in employees who use computers. Method: This study was an observational analytic study with cross-sectional design. The sampling method used was purposive sampling. The total sample in this study was 85 people. The duration of light exposure was measured by interview while the CVS was measured using the CVS-q questionnaire. Data analysis was performed using the SPSS program with chi-square test. Results:The results of this study found that people who work more than 4 hours were more likely to experienced symptoms of CVS compared to people who work less than 4 hours. The results showed that there was a significant association between the duration of computer light exposure with computer vision syndrome (CVS) incidences in employees who are using computers. Conclusion: There was an association between the duration of computer light exposure with computer vision syndrome (CVS) incidences in employees that using computers

Effect of light exposure on the accumulation and depletion of retinyl ester in the chicken retina

The human circadian system is primarily regulated by the 24-h LD cycle incident on the retina, and nocturnal melatonin suppression is a primary outcome measure for characterizing the biological clock's response to those light exposures. A limited amount of data related to the combined effects of light level, spectrum, and exposure duration on nocturnal melatonin suppression has impeded the development of circadian-effective lighting recommendations and light-treatment methods. The study's primary goal was to measure nocturnal melatonin suppression for a wide range of light levels (40 to 1000 lux), 2 white light spectra (2700 K and 6500 K), and an extended range of nighttime light exposure durations (0.5 to 3.0 h). The study's second purpose was to examine whether differences existed between adolescents' and adults' circadian sensitivity to these lighting characteristics. The third purpose was to provide an estimate of the absolute threshold for the impact of light on acute melatonin suppression. Eighteen adolescents (age range, 13 to 18 years) and 23 adults (age range, 24 to 55 years) participated in the study. Results showed significant main effects of light level, spectrum, and exposure duration on melatonin suppression. Moreover, the data also showed that the relative suppressing effect of light on melatonin diminishes with increasing exposure duration for both age groups and both spectra. The present results do not corroborate our hypothesis that adolescents exhibit greater circadian sensitivity to short-wavelength radiation compared with adults. As for threshold, it takes longer to observe significant melatonin suppression at lower CS levels than at higher CS levels. Dose-response curves (amount and duration) for both white-light spectra and both age groups can guide lighting recommendations when considering circadian-effective light in applications such as offices, schools, residences, and healthcare facilities.

Introduction One in three American adults are sleep deprived in the United States (US). Racial/ethnic minorities are more likely to experience shorter sleep duration than are whites. Light exposure is associated with sleep duration. However, whether this association is independent of individuals’ race/ethnicity has not been studied in a nationally representative sample of the US adult population. We examined associations between ambient light exposure and sleep duration and between race/ethnicity and sleep duration. We also assessed whether associations between light exposure and sleep duration are independent of participants’ race/ethnicity. Methods We used data from the National Health and Nutrition Examination Survey (n=4,277 adults; 2013-2014). Participants (≥ 18 years old) wore an actigraph that collected 24-hour sleep/wake and light data for 7 consecutive days. Objective measurements in our analyses included sleep duration (valid minutes) and light exposure (lux). To determine the associations between light exposure and sleep duration, a weighted mixed-effects linear model was estimated controlling for age, sex, family income to poverty ratio, education, employment, marital status, homeownership status, birthplace, household size, vitamin D, smoking, physical activity, sedentary lifestyle, health status, body mass index, depression, chronic conditions, and time in days. A product term between lux and race/ethnicity was included in a second regression model. Results Participants had a mean sleep duration of 468.2 minutes. On average, White adults had the longest sleep duration (mean=478.8), followed by other/multiple races (mean=458.6), Asians (mean=449.1); Blacks (mean=445.0), and Hispanics (mean=444.7). Overall, light exposure was negatively associated with sleep duration (= -0.08 lux; p&amp;lt;0.001). Black slept significantly less than did Whites (= -37.1 p&amp;lt;0.001) followed by Asians ( = -26.5; p&amp;lt;0.01) and Hispanics (= -24.6; p&amp;lt;0.01). The association between light exposure and sleep duration did not significantly differ across all race/ethnic groupings, except for Blacks (= -0.05; p&amp;lt;0.01). Conclusion To our knowledge, this is the first study that used national data to assess racial/ethnic disparities in objectively measured light exposure. Future research is needed to shed more light on racial/ethnic disparities in the light-exposure-sleep-duration link. Support (If Any) R01HL142066, R01HL095799, RO1MD004113, R01HL152453, R25HL105444

Light‐induced melatonin suppression data from 29 peer‐reviewed publications was analysed by means of a machine‐learning approach to establish which light exposure characteristics (ie photopic illuminance, five α‐opic equivalent daylight illuminances [EDIs], duration and timing of the light exposure, and the dichotomous variables pharmacological pupil dilation and narrowband light source) are the main determinants of melatonin suppression. Melatonin suppression in the data set was dominated by four light exposure characteristics: (1) melanopic EDI, (2) light exposure duration, (3) pupil dilation and (4) S‐cone‐opic EDI. A logistic model was used to evaluate the influence of each of these parameters on the melatonin suppression response. The final logistic model was only based on the first three parameters, since melanopic EDI was the best single (photoreceptor) predictor that was only outperformed by S‐cone‐opic EDI for (photopic) illuminances below 21 lux. This confirms and extends findings on the importance of the metric melanopic EDI for predicting biological effects of light in integrative (human‐centric) lighting applications. The model provides initial and general guidance to lighting practitioners on how to combine spectrum, duration and amount of light exposure when controlling non‐visual responses to light, especially melatonin suppression. The model is a starting tool for developing hypotheses on photoreceptors’ contributions to light's non‐visual responses and helps identifying areas where more data are needed, like on the S‐cone contribution at low illuminances.

The present study was undertaken to evaluate the effects of daily duration, intensity, and spectral composition of light exposure on the sexual maturation of female rats. Pregnant rats (Holtzman) delivered their young in a controlled environment with various illuminations of defined duration, intensity, and spectral composition. Pups were weaned at 22 days of age and separated by sex. Only females were used in the present study. They were checked for vaginal opening twice daily starting at 29 days of age. A group of 5–6 rats was sacrificed from each experimental condition 2–3 days prior to and after the expected date of vaginal opening. Results indicate that exposure to either 22 or 24 h of light/day significantly advanced vaginal opening when compared to 14-h/day exposure. No difference was obtained between animals in 6- and 14-h/day exposure. Light intensity was a significant variable at 14-h/day exposure, but not at 24 h/day. Animals exposed to 14 h of light at 100 lm/m2 matured faster than those at 30 or 600 lm/m2, but not significantly earlier than those at 2400 lm/m2. Animals in blue light exhibited vaginal opening significantly earlier than in red light if exposure was provided for 14 h/day. In continuous exposure, red light was more stimulating. No significant differences between yellow and green light were detected either with 14- or 24-h/day exposure, except for a small population of rats in continuous green light in which vaginal opening was significantly delayed. A significant seasonal variation was also detected in animals raised in white fluorescent light of 14-h/day exposure. Rats raised in the summer months showed vaginal opening significantly earlier than those in the winter. Examination of ovarian and uterine weights prior to vaginal opening revealed no significant differences with increased daily duration but equal intensity of illumination. Increasing intensity between 30 and 600 lm/m2, on the other hand, produced significantly heavier weights prior to vaginal opening. Uterine weights were heaviest at 100 lm/m2. Animals exposed to blue light had significantly heavier ovarian weights before vaginal opening than those in red light, regardless of the duration of exposure. No other differences were detected with various spectral compositions. After vaginal opening, ovarian weights were greater in 22-h/day light exposure than in either 6 or 14 h/day. However, one of two experiments revealed significantly smaller ovaries in rats kept in continuous light than in rats kept in 14 h of daily light exposure. No differences in uterine weights were noted. No differences in ovarian weights were observed following vaginal opening in animals raised in various light intensities. A significant difference in uterine weights was detected between animals raised in 30 and 100 lm/m2 of light intensity at continuous exposure. Differences in spectral composition did not result in significant differences in either ovarian or uterine weights following vaginal opening. Results are interpreted to indicate, first, that variations in the daily duration, intensity, and spectral composition of light exposure can significantly influence the age at which vaginal opening occurs and, therefore, suggest that light can play a significant role in the timing of sexual maturation and should be carefully controlled in studying the role of photoperiods in reproductive function. Secondly, the present data suggest that while in long exposures, intensity may not play a significant role, in 14-h/day-exposure intensity can be a highly significant factor. Finally, our data give no evidence for a chronic stimulation of gonadotropin release as a result of increased photoperiods, but, in the case of increased light intensity, early maturation may have resulted from increased FSH and/or LH release, as evidenced by increased ovarian and uterine weights.

&lt;p&gt;Circadian dysrhythmia, commonly known as jet lag, is a prevalent condition affecting travelers who cross multiple time zones, which leads to significant physiological and cognitive disruptions. This thesis explores the design and optimization of light exposure schedules as a non-invasive intervention to mitigate jet lag symptoms by inducing controlled shifts in the human circadian rhythm. Using established mathematical models—specifically the Forger99 and Jewett99 models—this research quantifies circadian phase shifts in response to variations in light intensity and exposure duration over a 24-hour cycle. Through computational simulations and comparative analysis with empirical data from clinical trials, the study evaluates the effectiveness of different light exposure parameters. Key findings reveal that while both light intensity and duration significantly influence circadian phase shifts, duration has a unique effect on altering the phase&lt;/p&gt; &lt;p&gt;response curve’s structure. The results inform the development of optimal periods to stimulate measured changes to circadian phase, and reveal the limitations of current mathematical circadian models. This research will contribute to the optimization of light therapy as a method of combatting jet lag, aiding in the development of effective in-flight interventions for circadian realignment.&lt;/p&gt;

&lt;p&gt;Circadian dysrhythmia, commonly known as jet lag, is a prevalent condition affecting travelers who cross multiple time zones, which leads to significant physiological and cognitive disruptions. This thesis explores the design and optimization of light exposure schedules as a non-invasive intervention to mitigate jet lag symptoms by inducing controlled shifts in the human circadian rhythm. Using established mathematical models—specifically the Forger99 and Jewett99 models—this research quantifies circadian phase shifts in response to variations in light intensity and exposure duration over a 24-hour cycle. Through computational simulations and comparative analysis with empirical data from clinical trials, the study evaluates the effectiveness of different light exposure parameters. Key findings reveal that while both light intensity and duration significantly influence circadian phase shifts, duration has a unique effect on altering the phase&lt;/p&gt; &lt;p&gt;response curve’s structure. The results inform the development of optimal periods to stimulate measured changes to circadian phase, and reveal the limitations of current mathematical circadian models. This research will contribute to the optimization of light therapy as a method of combatting jet lag, aiding in the development of effective in-flight interventions for circadian realignment.&lt;/p&gt;

Light energy is an important factor affecting plant growth. The hypothesis of &quot;light-cold and heat property&quot; holds that the original plants of traditional Chinese medicines(TCM) with cold property can obtain more energy to maintain growth in high light intensity environment, whereas the original plants of TCM with heat property prefer weak light environment. The current experiment investigated the effects of different light intensities on primary metabolites levels, energy levels, cell apoptosis, and leaves ultrastructure of Viola yedoensis, the original plants of TCM Violae Herba with cold property. There were five treatment groups of V. yedoensis, which was planted under Li1(8 500 lx),Li2(7 250 lx),Li3(6 000 lx),Li4(4 750 lx),Li5(3 500 lx)LEDs light intensity conditions, respectively. After harvest, primary metabolites levels, contents of ATP, ADP, AMP, activities of ATP synthesis and hydrolysis related enzyme, as well as cell apoptosis activation degree were measured, and transmission electron microscopy technique was used to observe leaves ultrastructure. The results showed that the total sugar, total protein, contents of ATP, ADP and AMP, activities of NADH dehydrogenase, cytochrome C reductase, ATP synthase and ATP hydrolase were positively correlated with light intensities(P&lt;0.05). The crude fat content, activities of SDH and CCO enzyme showed a trend of increasing first and then decreasing, the highest value were found in Li2 group and Li3 group respectively(P&lt;0.05). The vitality of caspase-3 and caspase-9 was negatively correlated with light intensities(P&lt;0.05). The structure of chloroplast and mitochondria were normal and intact in Li1-Li3 groups, and the damage degree of Li4 and Li5 groups increased with the decrease of light intensities. The analysis of results indicated that the structure of chloroplast and mitochondria of V. yedoensis is normal under the light intensity of 6 000-8 500 lx, which can obtain more energy to maintain its growth and metabolism. When the light intensity is lower than 4 750 lx, the chloroplast morphology and mitochondrial membrane are damaged, affecting the metabolism of material and energy. There was no significant difference in energy charge of V. yedoensis in the light intensity range of 3 500～8 500 lx. The effect of light intensity on energy metabolism of V. yedoensis accords with the hypothesis of &quot;light-cold and heat property&quot;.

The effects of light intensity on embryonic development of fertilized eggs of Sepia lycidas were investigated to determine the best light conditions for the embryos’ development. A single-factor experiment was performed to examine the effects of different light intensities (dark or 4.3, 10.2, 29.6, or 50.7 μmol/(m2·s)) on the embryonic development. The hatching rate, incubation period, hatching period and weight, and survival of hatchling cuttlefish were significantly affected by the light intensities (P < 0.05). When light intensity exceeds 10.2 μmol/(m2·s), the weight of hatchling cuttlefish and incubation period gradually decreased with the increase of light intensity, while the hatching rate first increased and later decreased. The sensitivity to light clearly varies among stages of embryonic development; the impact of light intensity on embryonic development appeared from the red-bead stage to hatching. High light intensities can interfere with the development of embryos and lead to abnormal development and premature hatching, reduced hatchability, decreased vitality of cuttlefish hatchlings, and asynchronous hatching, especially at light intensities exceeding 10.2 μmol/(m2·s). Low light intensities are better for embryonic development of S. lycidas than high light, and the light intensity as 10.2 μmol/(m2·s) was thus recommended. During incubation of paralarvae, fertilized eggs should be kept out of direct sunlight, and shading measures should be taken to keep the eggs in low light intensities.

We examined the effects of photoperiod and light intensity on survival and growth of kuruma shrimp ( Marsupenaeus japonicus ) across developmental stages from the zoea–mysis (ZM) to the postlarval (PL) stage, as well as the effect of light intensity on phototactic behaviour. During the ZM stage, growth tended to be higher ( p = 0.052) under photoperiods including a dark phase (12L:12D and 18L:6D) than under continuous light (24L:0D) and tended to be higher ( p = 0.059) under low to medium light intensities (200 and 1000 lx) than under the highest intensity (5000 lx). In contrast, during the PL stage, growth was not strongly affected by photoperiod but was significantly greater ( p &lt; 0.001) at 5000 lx than at 200 or 1000 lx. Although the optimal photoperiod and light intensity differed markedly among developmental stages, survival was not significantly affected by the light environment. In behavioural experiments using a projector to generate different light intensities, larvae at the ZM stage showed strong positive phototactic behaviour ( p &lt; 0.05), whereas this behaviour was weaker at the PL stage. These results suggest that kuruma shrimp growth during the ZM stage is enhanced under photoperiods including a dark phase and low-to-medium light intensities. Overall, our findings suggest that the optimal photoperiod and light intensity for M. japonicus shift during development: light regimes including a dark phase and low to medium intensities may favour early larval growth, whereas high light intensity enhances growth at later stages.

Effects of Light Intensity from Photostimulation in Four Strains of Commercial Egg Layers: 2. Egg Production Parameters