Effects Of Light Levels Research Articles

Is Ocular Accommodation Influenced by Dynamic Ambient Illumination and Pupil Size?

Purpose: We investigated ocular accommodative responses and pupil diameters under different light intensities in order to explore whether changes in light intensity aid effective accommodation function training. Methods:A total of 29 emmetropic and myopic subjects (age range: 12–18 years) viewed a target in dynamic ambient light (luminance: 5, 100, 200, 500, 1000, 2000 and 3000 lux) and static ambient light (luminance: 1000 lux) at a 40 cm distance with refractive correction. Accommodation and pupil diameter were recorded using an open-field infrared autorefractor and an ultrasound biological microscope, respectively. Results: The changes in the amplitude of accommodative response and pupil diameter under dynamic lighting were 1.01 ± 0.53 D and 2.80 ± 0.75 mm, respectively, whereas in static lighting, those values were 0.43 ± 0.24 D and 0.77 ± 0.27 mm, respectively. The amplitude of accommodation and pupil diameter change in dynamic lighting (t = 6.097, p < 0.001) was significantly larger than that under static lighting (t = 16.115, p < 0.001).The effects of light level on both accommodation and pupil diameter were significant (p < 0.001). Conclusion: Accommodation was positively correlated with light intensity. The difference was about 1.0 D in the range of 0–3000 lux, which may lay the foundation for accommodative training through light intervention.

Automatic pavement rutting measurement by fusing a high speed-shot camera and a linear laser

This study proposes an inexpensive system using a linear laser and a high speed-shot sports camera to compute the rutting depth in static and dynamic modes with acceptable accuracy. Static and dynamic data collection is performed in a laboratory environment and multiple Bus Rapid Transit (BRT) lanes, respectively. The camera captures the projected laser line on the pavement surface, and this image is processed by applying image quality enhancement filters. A clustering method is used to detect the borders of ruts. Moreover, the effect of light level and the distance from the defect surface are measured. The results illustrate that the system has its best performance in 0.0001 lx light level with a relative error of 4%. Based on the paired sample t-test outputs, the optimal distance between the sensors and the ground should be 1 m. By validating the outputs of the system with the standard measurement method, the results show that this system is capable of computing the rut depth between 0.05 and 5.5 cm with a relative error of 9.31%, which confirms its capability for accurate data collection. Moreover, the replicability tests confirm the capability of using this system as an accurate data collection tool.

Effects of light levels on germination of five Asteraceae species native to the tallgrass prairie

The ability of plants to detect variations of light conditions is an essential mechanism for seed survival and germination. In this experiment, germinability and mean germination time were measured in five species of Asteraceae that are native to the tallgrass prairie in Kansas. Seeds were exposed to four light levels in a greenhouse experiment: 100% of natural light, approximately 50% of light, 10% of light, and dark conditions. Ageratina altissima (White snakeroot), Rudbeckia laciniata (Cutleaf coneflower), and Solidago ulmifolia (Elmleaf goldenrod) were non-photoblastic, as light levels had little effect on germinabilities. Aster drummondii (Drummond's aster) and Eutrochium purpureum (Sweet Joe-Pye weed) were positively photoblastic, as increasing light increased germinabilities. However, there were significant differences among species that might correlate with ecological roles. Ageratina altissima and R. laciniata had fast germinating seeds ( 10 d) in all light levels. A. drummondii and E. purpureum had germination times that ranged from fast to intermediate to slow, depending on light levels. Mean germination times decreased with increased light. Measurements of germinability and mean germination time are essential for understanding establishment, succession, and regeneration processes that occur in prairie communities.

Effect of light level on visual discomfort from flicker

Effect of light level on visual discomfort from flicker

Effects of Light Level and Nitrogen Supply on the Red Clover-Orobanche Minor Host-Parasite Interaction.

Infection by holoparasitic plants typically causes decreases in host mass, thought to be primarily as a result of resource abstraction. Inverse relationships have been noted between the number of Orobanche spp. parasites infecting a host and their mass, suggesting that the parasites compete for a shared resource pool, assumed to be recently fixed carbon (C). In clover, nitrogen (N) fixation requires a high proportion of daily photosynthate and represents a potential competitor for recently fixed C. We grew Trifolium pratense, either singly or parasitised by Orobanche minor, under high or low light levels, and with or without exogenous N supply. Low light and N deficiency led to decreased host biomass, while the damage caused by parasitism was proportionate to host mass. Parasitism caused reductions in host leaf mass, area, photosynthetic rates and shoot N concentration, but did not affect starch accumulation. Parasite mass as a proportion of system biomass was significantly higher when attached to plants grown at high light, which was attributed to higher photoassimilate supply, while the N supply had no effect. While both N limitation and parasitism caused reductions in host growth, little evidence of competition for C between N fixation and the parasites was noted.

The Effect of Light Level and Small Pupils on Presbyopic Reading Performance.

To examine the impact of small pupils and light levels on reading performance of distance-corrected presbyopes. To determine whether small pupils would enable presbyopes to read at near even at low light levels. To establish the lower range of text luminances, we quantified the space-averaged luminance of text in nine different artificially lit interior environments, and examined the impact of the text characters on space-averaged luminance of electronic and printed displays. Distance and near reading speeds of 20 presbyopes (ages 40-60 years) were measured while viewing through artificial pupils (diameters 1-4.5 mm), natural pupils, or with a multifocal contact lens. Space-averaged text luminance levels varied from 0.14 to 140 cd/m2 (including the range of measured environmental text luminances). Adding black text to a white computer display or paper reduces luminance by approximately 15% to 31%, and the lowest encountered environmental text luminance was approximately 2 to 3 cd/m2. For both distance and near reading performance, the 2- to 3-mm small pupil yielded the best overall reading acuity for space-averaged text light levels ≥ 2 cd/m2. The 2- to 3-mm artificial pupils and the multifocal contact lenses both enabled maximum or near-maximum reading speeds for 0.5 logMAR characters at distance and near, but with natural pupils, reading speeds were significantly reduced at near. Although photon noise at low luminance reduces the visual benefits of small pupils, the benefits of 2- to 3-mm artificial pupils are sufficient to enable >80% of distance-corrected presbyopes to read proficiently at near, even at the lowest text luminances found in interior environments.

The effect of light level, CO2 flow rate, and anesthesia on the stress response of mice during CO2 euthanasia.

Euthanasia protocols are designed to mitigate the stress experienced by animals, and an environment that induces minimal stress helps achieve that goal. A protocol that is efficient and practical in a typical animal research facility is also important. Light intensity, isoflurane, and CO2 flow rate were studied for their impact on the stress response of mice during CO2 euthanasia. Behavior was observed and scored during euthanasia and serum corticosterone was measured immediately after death. Unsurprisingly, animals euthanized with a high-flow rate of CO2 became unconscious in the least amount of time, while animals euthanized with a low-flow rate required the most time to reach unconsciousness. There was a significant increase in anxious behaviors in animals in the isoflurane group (F1,12 = 6.67, P = 0.024), the high-flow rate CO2 group (F1,12 = 10.24, P = 0.007), and bright chamber group (F1,12 = 7.27, P = 0.019). Serum corticosterone was highest in the isoflurane group (124.72 ± 83.98 ng/ml), however there was no significant difference in corticosterone levels observed for the other study variables of light and flow-rate. A darkened chamber and low CO2 flow rates help to decrease stress experienced during CO2 euthanasia, while the use of isoflurane was observed to increase the stress response during euthanasia.

Effect of light level and salinity on the composition and accumulation of free and ester-type carotenoids in the aerial microalga Scenedesmus sp. (Chlorophyceae)

Composition and accumulation of stress-induced carotenoids were characterized in the aerial microalga Scenedesmus sp. KGU-Y002. The specific growth rate was 0.27d−1, in the logarithmic growth phase. Nitrate starvation and varying light levels were applied to determine the effect of stress on the carotenogenesis of the algal cells. Under 200μmolphotonsm−2s−1, the alga accumulated 34.2±3.8mgg−1dryweightcells (dwc) of total carotenoids and 2.5±0.6mgg−1dwc of total chlorophyll content after 13days of culture. Astaxanthin and adonixanthin were the main xanthophylls in the algal cells. These xanthophylls existed as fatty acid esters in the algal cells under the culture conditions. Light level had an important influence on the rate of accumulation. The addition of NaCl was also found to promote the synthesis of these free and ester-type xanthophylls. Higher light and salt stresses synergistically activated carotenogenesis in the algal cells. These results imply that the esterification of astaxanthin and adonixanthin of algal strain KGU-Y002 is modulated by culture conditions such as light level and salinity.

Tackling black leaf streak disease and soil fertility constraints to enable the expansion of plantain production to grassland in the humid tropics

In Central Africa, plantain is traditionally grown after a forest fallow. Given increasing urban demand and a lack of forest fallows near urban centres, as well as poor roads and environmental concerns to reduce pressure on forests, research is needed to identify suitable shade, fertility management and cultivars to shift production of plantain to grasslands and to reduce losses to diseases such as black leaf streak disease (BLSD). Effects of light level (full, 67%, 33% light), and nitrogen (N)-amendment on BLSD-tolerant (FHIA-21) and BLSD-susceptible (Batard) cultivars planted on soil from paired grassland and forest sites were determined. BLSD and growth were monitored until 5 months after planting. Three months after planting, leaf area attacked on cultivar FHIA-21 was less than half that on Batard. Plants grown under 33% and 67% light had less leaf area attacked (2.9% and 4.6%, respectively) than those grown in full light (7.3%). Leaf area and dry matter (DM) were higher under shade and when grown on forest soils. Compared to growing BLSD-susceptible plantain on forested land under shade, a shift onto grasslands and a reduction in shade use is predicted to reduce yields. Using cultivar FHIA-21 may limit, but not eliminate, yield loss.

Effects of light level, time of harvest and position within field on the variability of tissue nitrate concentration in commercial crops of lettuce (Lactuca sativa) and endive (Cichorium endiva)

Seven commercial crops of lettuce and one crop of endive were sampled in order to study the variability in plant tissue nitrate concentration (TNC). Assuming that an appropriate sampling pattern was employed, ten plants were sufficient to give an acceptable estimate of the mean TNC. Short-term shading (24–48 h) had no significant effects on mean TNC, unlike the increase in TNC known to occur following dull periods 10–14 days before harvest. The effect on TNC of time of day harvested was significant, but there was no obvious pattern of diurnal variation. Averaged over all experiments, the coefficient of variation for TNC was in the order of 35%. Increasing the sample size from ten to 40 plants would only be expected to decrease the standard error of measurement of TNC from 16 to 12% of the mean because of the underlying analytical error, which would remain constant.

Effects of Turbidity, Light Level, and Cover on Predation of White Sturgeon Larvae by Prickly Sculpins

AbstractWhite sturgeon Acipenser transmontanus occur in rivers of the western United States and southwestern Canada, but some populations are in decline because of recruitment failure. Many river systems in this area have been altered as a result of development that has caused major environmental changes. Our goal was to examine how three changes—lower turbidity levels, higher light levels, and altered substrates—might affect predation by prickly sculpin Cottus asper on white sturgeon larvae. We experimentally investigated predation at various turbidity levels and found that significantly more white sturgeon yolk sac larvae were eaten at lower turbidity levels. The effects of light level (1–4 and 7–15 lx), the presence or absence of rocks as cover, and prey size (14–17 mm and 20–24 mm total length) on the outcome of predator–prey interactions were also examined. Significantly fewer white sturgeon were eaten during trials that combined the lowest light level, cover, and the smallest larvae. Our results suggest that altered river conditions caused by impoundment and other factors have increased predation on white sturgeon larvae.

Decoupling of light intensity effects on the growth and development of C3 and C4 weed species through sucrose supplementation.

Light availability has a profound effect on plant growth and development. One of the ways to study the effects of light intensity on plant growth and development without the confounding problem of photosynthate availability is sucrose injection/supplementation. A greenhouse experiment was conducted to evaluate the effects of light levels (0% and 75% shade) and sucrose injection (distilled water or 150 g sucrose l(-1)) on three weed species: redroot pigweed (Amaranthus retroflexus L., C4), lambsquarters (Chenopodium album L., C3) and velvetleaf (Abutilon theophrasti Medic., C3). The average total sucrose uptake was 7.6 and 5.9 g per plant for 0% and 75% shading, respectively, representing 47% of the average total weed dry weight. Plants injected with sucrose had greater dry weights and shoot-to-root ratios under both light levels. In spite of sucrose supplementation the reduction in dry matter due to shading was greater for roots and reproductive structures than vegetative shoot tissues, indicating light level regulation of morphological changes resulting in changed C allocation that are independent of photosynthate availability. Dry weights of plants injected with sucrose under 75% shading were not different from distilled water-injected unshaded plants. However, both sucrose-injected and control plants, regardless of their photosynthetic pathways, underwent similar changes in allocation of dry matter and morphology due to shading, suggesting that these effects are strictly due to light intensity and not related to photosynthate availability.

Effects of light levels and plume structure on the orientation manoeuvres of male gypsy moths flying along pheromone plumes

SummaryThe upwind zigzag flights of male gypsy moths (Lymantria dispar L.; Lepidoptera: Lymantriidae) along narrow, ribbon‐like and wide, turbulent plumes of pheromone were examined in a wind tunnel at light levels of 450 and 4 lux. Under all conditions tested males flew upwind zigzag paths. In 450 lux, males flying along turbulent plumes had the highest ground speeds and the widest crosswind excursions between counterturns, compared to slow flight and a narrow zigzag of males along a ribbon plume. In a turbulent plume, males flew more slowly and had narrower zigzags in 4 than in 450 lux. Across most treatments of plume structure and light level, the rate of transverse image flow and the frequency of counterturning remained relatively constant. The effects of light levels on orientation are not readily reconcilable with a model in which moths in low light levels would head more towards crosswind, thereby enhancing the rate of transverse image flow and the perception of wind‐induced drift.

Effects of light level and N:P supply ratio on the competition between Phaeocystis cf. pouchetii (Hariot) Lagerheim (Prymnesiophyceae) and five diatom species

Phaeocystis cf. pouchetii (Hariot) Lagerheim and five winter/spring diatom species from Cape Cod Bay/Massachusetts Bay were grown in semi-continuous culture in order to investigate the effects of irradiance and N:P supply ratio on their competitive ability. Experiments were conducted at two light levels under N- and P-limiting conditions. Phaeocystis grew fastest relative to the other algae when nutrients were non-limiting and irradiance was low, although it was not capable of dominating under these conditions within the time course of the experiment. In general, Phaeocystis was a poor competitor when N or P was limiting; however, its relative abundance under P limitation varied greatly with irradiance. The flagellated form of this organism predominated in these experiments and appeared to have an enhanced ability to compete for P under high light conditions. Differences in the chemical composition of the phytoplankton assemblages at the two light levels indicated an interactive influence of nutrients and irradiance on growth and biovolume. This interactive effect may play an important role in phytoplankton competition, since nutrient requirements may vary in unique ways for different species with changes in irradiance.

The role of vision and color in the close proximity foraging behavior of four coccinellid species.

The role of vision and color in close-proximity foraging behavior was investigated for four species of lady beetles: Coccinella septempunctata, Hippodamia convergens, Harmonia axyridis, and Coleomegilla maculata. The effect of light level and color cues on consumption rates varied among the four predator species. The consumption rates of these predators on the pea aphid Acyrthosiphon pisum (Harris) was measured under light and dark conditions. C. septempunctata,H. convergens, and Ha. axyridis consumed significantly more aphids in the light than in the dark, while the consumption rate of Col. maculata was not affected by light level. Foraging ability was also measured on red and green color morphs of the pea aphid on red, green, and white backgrounds. C. septempunctata consumed significantly more of the aphid morph that contrasted with the background color, and showed no difference between morphs on the white background. H. axyridis consumed significantly more red morph aphids regardless of background. The remaining two species showed no difference in consumption rates on the two color morphs. The variation in the use of visual cues demonstrates how different species of predators can exhibit different foraging behaviors when searching for the same prey.

Effects of light level and growth history on attack distances of visually foraging juvenile salmon in experimental tanks

The effects of light level, developmental pathway, and previous growth history on the foraging attack distances of juvenile Atlantic salmon Salmo salar were examined in circular rearing tanks. Former manipulation of growth rates had no significant influence on distances moved to intercept food items despite the fact that it caused substantial differences in post-treatment growth. Attack distances of fish that were entering a state of overwinter dormancy (lower modal group; LMG) were shorter than those of actively feeding (and growing) fish (upper modal group; UMG). These differences were explained generally by differences in body size between the two groups, suggesting that actual effort per attack was unassociated with growth requirements. Significant differences between growing and non-growing fish in attack distances could contribute to the variation in growth rates through their effect on feeding rates, but were unlikely to have affected energetic costs. This may be due to the fact that attack distances were consistently short throughout the study period as is also evident from the pattern of change between night and daytime. Whereas in the first experiment (daylight v. twilight) fish moved further to reach food during the day, in the second (daylight v. overcast night) nocturnal attack distances matched (LMG fish) or exceeded (UMG fish) diurnal attack distances. Thus diurnal attack distances were probably minimized in the second experiment. These results are interpreted within a framework of overwintering strategies.

Effects of light level and growth history on attack distances of visually foraging juvenile salmon in experimental tanks

The effects of light level, developmental pathway, and previous growth history on the foraging attack distances of juvenile Atlantic salmon Salmo salar were examined in circular rearing tanks. Former manipulation of growth rates had no significant influence on distances moved to intercept food items despite the fact that it caused substantial differences in post‐treatment growth. Attack distances of fish that were entering a state of overwinter dormancy (lower modal group; LMG) were shorter than those of actively feeding (and growing) fish (upper modal group; UMG). These differences were explained generally by differences in body size between the two groups, suggesting that actual effort per attack was unassociated with growth requirements. Significant differences between growing and non‐growing fish in attack distances could contribute to the variation in growth rates through their effect on feeding rates, but were unlikely to have affected energetic costs. This may be due to the fact that attack distances were consistently short throughout the study period as is also evident from the pattern of change between night and daytime. Whereas in the first experiment (daylight v. twilight) fish moved further to reach food during the day, in the second (daylight v. overcast night) nocturnal attack distances matched (LMG fish) or exceeded (UMG fish) diurnal attack distances. Thus diurnal attack distances were probably minimized in the second experiment. These results are interpreted within a framework of overwintering strategies.

The effect of light levels on daily patterns of chlorophyll fluorescence and organic acid accumulation in the tropical CAM treeClusia hilariana

Sandy plains are characteristic of the coastal region of Brazil. We investigated the diel patterns of changes in organic acid levels, leaf conductance and chlorophylla fluorescence for sun-exposed and shaded plants ofClusia hilariana, one of the dominant woody species in the sandy coastal plains of northern Rio de Janeiro state. Both exposed and shaded plants showed a typical CAM pattern with considerable diel oscillations in organic acid levels. The degradation of both malic and citric acids during the midday stomatal closure period could lead to potential CO2 fixation rates of 28 μmol m-2 s-1 in exposed leaves. Moreover, exposed leaves exhibited large increases in total non-photochemical quenching (qN) accompanied by a substantial decrease in effective quantum yield during the course of the day. However, these potential high rates of CO2 fixation and the increases inqn of exposed plants were not enough to maintain the primary electron acceptor of photosystem II (qA) in a low reduction state, similar to that of shaded plants. As a result, there was a moderate increase in the reduction state of qA throughout the day. Most of the decline in photochemical efficiency of exposed leaves ofC. hilariana was reversible, as evidenced by the high levels of pre-dawn potential quantum yields (Fv/Fm) and their rapid recovery after sunset. However, the depletion of the organic acid pool in the afternoon resulted in an accentuated subsequent drop in Fv/Fm, suggesting that prolonged periods of water stress accompanied by high irradiance levels may expose plants ofC. hilariana in unprotected habitats to the danger of photoinhibition.

The effect of light levels on daily patterns of chlorophyll fluorescence and organic acid accumulation in the tropical CAM tree

The effect of light levels on daily patterns of chlorophyll fluorescence and organic acid accumulation in the tropical CAM tree

Growth and Essential Oil Content ofAngelica archangelicaas Influenced by Light Intensity and Growing Media

ABSTRACT The effects of light levels and growing media on growth and essential oil content in Angelica archangelica were investigated under greenhouse conditions. Eight months after seed sowing, the highest shoot and root dry matter yield (810 g/plant and 438 g/plant respectively) was recorded from sand-hydroponic (SH) grown variants under supplemental light (SL). The highest oil yield (4.03 mg/plant) was produced by SH-grown plants under SL, while the lowest oil yield (1.74 mg/plant) was obtained from plants grown under organic culture with natural light (NL). The contribution of SL to dry matter (DM) shoot production under SH culture was 57%, while for root production this was found to be 61%. The DM root and total shoot yields of organically grown plants under SL declined by 11% and 18%, respectively, due to increased light intensity. Significant differences were found in the distribution of oil content in different organs, root sizes and the grinding of angelica samples. Thick and thin roots were foun...