Long Exposure To Light Research Articles

Assessing light performance of vertical greenery shading in tropical climate

Natural light is abundant in tropical climates and advantageous for incorporating daylighting into building designs. However, this daylight intensity often leads to excessive brightness indoors, specifically in high-rise buildings with glass façades. In addressing sustainability concerns, incorporating greenery outside glass façades can effectively shade and alleviate eyestrain for building occupants. Therefore, this study aimed to investigate the effectiveness of plant leaves in reducing the high light intensity on glass facades. An experiment was conducted using the Vernonia elliptica plant, which thrives in medium to high sunlight in tropical climates. Three different leaf area indexes (LAI) were examined in this study as the independent variables, while light illuminance and luminance served as the dependent variables. Two identical box models measuring 1 m × 1 m × 1 m were utilized for the experiment. The two models were oriented towards the west and north, representing intense and longer light exposure. The first, the base case, featured a glass façade without any other additional element, whereas the other incorporated greenery on its glass façade. The obtained results indicated that the impact of leaf density on illuminance and luminance is significant, specifically when the LAI is doubled. It was also found that denser foliage with longer leaf strands produced better results, specifically at low altitudes. These results can be used to implement vertical greenery shading in high-rise office buildings.

Investigation on the Effects of Additive on Performance and Photostability of PCDTBT:PC71BM Solar Cells

In this work, the effect of DIM on the PCE and photostability of PCDTBT:PC71BM PSCs was investigated. DIM is an effective additive in a BHJ PCDTBT:PC71BM solar cell since it fulfills the requirement of a selective PC71BM dissolution. PCE of the device based on PCDTBT:PC71BM processed with DIM is higher than that of the reference device. In terms of the device stability, the PSCs processed with DIM showed poor stability at longer light exposure time. For the device without DIM especially as the light exposure time was increased, the device stability was better because the PCDTBT could be shielded from air by an aggregated PC71BM layer. For the PCDTBT:PC71BM device processed with DIM, the results obtained from J‐V measurement indicates that it has a lower recombination rate. The result from IS measurement shows that for pristine PCDTBT:PC71BM devices with 3% DIM, the active layer resistance is lower compared to the device without DIM. However, after irradiating the device for 5 hr, the resistance of the device processed with DIM is higher and it is consistent with decreased PCE of the aged device.

Protective effect of chitosan oligosaccharides on blue light light-emitting diode induced retinal pigment epithelial cell damage

Excessive blue light light-emitting diode (LED) exposure and consequent oxidative stress causes damage to retinal pigment epithelial (RPE) cells. Chitosan oligosaccharides (COSs) are the hydrolyzed products of chitin, which is abundant in the exoskeleton of crustaceans and cell walls of fungi. We investigated the protective effect of COSs on blue light LED-induced RPE cell damage. These cells were treated with various concentrations of COSs and then exposed to blue light LED. Our results confirmed that RPE cell apoptosis increased significantly with longer light exposure. Treatment with COSs significantly reduced apoptosis in a dose-dependent manner. These molecules also suppressed the production of reactive oxygen species and the expression of inflammation- and apoptosis-related proteins. Moreover, COSs stabilized the mitochondrial membrane potential of cells and down-regulated the NF-κB pathway. In this study, the protective effects of COSs on blue light LED-induced RPE cell damage, as well as the associated mechanisms, were demonstrated.

Comparative bonding ability to dentin of a universal adhesive system and monomer conversion as functions of extended light curing times and storage.

The purpose of this in vitro study was to evaluate the bonding ability and monomer conversion of a universal adhesive system applied to dentin as functions of different curing times and storage. The results were compared among a variety of commercial adhesives. Flat superficial dentin surfaces were exposed on human molars and assigned into one of the following adhesives (n = 15): total-etch Adper Single Bond 2 (SB) and Optibond Solo Plus (OS), self-etch Optibond All in One (OA) and Clearfil SE Bond (CSE), and Scotchbond Universal Adhesive in self-etch mode (SU). The adhesives were applied following the manufacturers' instructions and cured for 10, 20, or 40s. Specimens were processed for the microtensile bond strength (µTBS) test in accordance with the non-trimming technique and tested after 24h and 2 years. The fractured specimens were classified under scanning electron microscopy (SEM). Infrared (IR) spectra were obtained and monomer conversion (%) was calculated by comparing the aliphatic-to-aromatic IR absorption peak ratio before and after polymerization (n=5). Data were analyzed by 2-way ANOVA/Tukey's tests (α = 0.05). At 24-h evaluation, OA and CSE presented similar bond strength means irrespective of the curing time, whereas SB and SU exhibited significantly higher means when cured for 40s as did OS when cured for 20 or 40s (p < 0.05). At 2-year evaluation, only OA exhibited significantly higher bond strength when cured for 20 and 40s (p < 0.05). When the evaluation times were compared, OA also exhibited the same bonding ability when cured for longer periods of time (20 and 40s). All of the adhesives tested exhibited significantly lower monomer conversion when photoactivated according to the manufacturers' instructions (10s). Higher monomer conversions obtained with longer light exposure allow only higher immediate bond strength for most of the adhesives tested. After 2-year storage, only the self-etching adhesive Optibond All-In-One exhibited the same bonding ability when cured for longer periods of time.

Modeling the ferrochelatase c.315-48C modifier mutation for erythropoietic protoporphyria (EPP) in mice.

ABSTRACTErythropoietic protoporphyria (EPP) is caused by deficiency of ferrochelatase (FECH), which incorporates iron into protoporphyrin IX (PPIX) to form heme. Excitation of accumulated PPIX by light generates oxygen radicals that evoke excessive pain and, after longer light exposure, cause ulcerations in exposed skin areas of individuals with EPP. Moreover, ∼5% of the patients develop a liver dysfunction as a result of PPIX accumulation. Most patients (∼97%) have a severe FECH mutation (Mut) in trans to an intronic polymorphism (c.315-48C), which reduces ferrochelatase synthesis by stimulating the use of an aberrant 3′ splice site 63 nt upstream of the normal site for exon 4. In contrast, with the predominant c.315-48T allele, the correct splice site is mostly used, and individuals with a T/Mut genotype do not develop EPP symptoms. Thus, the C allele is a potential target for therapeutic approaches that modify this splicing decision. To provide a model for pre-clinical studies of such approaches, we engineered a mouse containing a partly humanized Fech gene with the c.315-48C polymorphism. F1 hybrids obtained by crossing these mice with another inbred line carrying a severe Fech mutation (named m1Pas) show a very strong EPP phenotype that includes elevated PPIX in the blood, enlargement of liver and spleen, anemia, as well as strong pain reactions and skin lesions after a short period of light exposure. In addition to the expected use of the aberrant splice site, the mice also show a strong skipping of the partly humanized exon 3. This will limit the use of this model for certain applications and illustrates that engineering of a hybrid gene may have unforeseeable consequences on its splicing.

Regulation of Conidiation by Light in Aspergillus nidulans

Light regulates several aspects of the biology of many organisms, including the balance between asexual and sexual development in some fungi. To understand how light regulates fungal development at the molecular level we have used Aspergillus nidulans as a model. We have performed a genome-wide expression analysis that has allowed us to identify >400 genes upregulated and >100 genes downregulated by light in developmentally competent mycelium. Among the upregulated genes were genes required for the regulation of asexual development, one of the major biological responses to light in A. nidulans, which is a pathway controlled by the master regulatory gene brlA. The expression of brlA, like conidiation, is induced by light. A detailed analysis of brlA light regulation revealed increased expression after short exposures with a maximum after 60 min of light followed by photoadaptation with longer light exposures. In addition to brlA, genes flbA-C and fluG are also light regulated, and flbA-C are required for the correct light-dependent regulation of the upstream regulator fluG. We have found that light induction of brlA required the photoreceptor complex composed of a phytochrome FphA, and the white-collar homologs LreA and LreB, and the fluffy genes flbA-C. We propose that the activation of regulatory genes by light is the key event in the activation of asexual development by light in A. nidulans.

Two Open States with Progressive Proton Selectivities in the Branched Channelrhodopsin-2 Photocycle

Channelrhodopsins are light-gated ion channels that mediate vision in phototactic green algae like Chlamydomonas. In neurosciences, channelrhodopsins are widely used to light-trigger action potentials in transfected cells. All known channelrhodopsins preferentially conduct H+. Previous studies have indicated the existence of an early and a late conducting state within the channelrhodopsin photocycle. Here, we show that for channelrhodopsin-2 expressed in Xenopus oocytes and HEK cells, the two open states have different ion selectivities that cause changes in the channelrhodopsin-2 reversal voltage during a light pulse. An enzyme kinetic algorithm was applied to convert the reversal voltages in various ionic conditions to conductance ratios for H+ and divalent cations (Ca2+ and/or Mg2+), as compared to monovalent cations (Na+ and/or K+). Compared to monovalent cation conductance, the H+ conductance, α, is ∼3 × 106 and the divalent cation conductance, β, is ∼0.01 in the early conducting state. In the stationary mixture of the early and late states, α is larger and β smaller, both by a factor of ∼2. The results suggest that the ionic basis of light perception in Chlamydomonas is relatively nonspecific in the beginning of a light pulse but becomes more selective for protons during longer light exposures.

The flexible interrelation between AOX respiratory pathway and photosynthesis in rice leaves

Alternative respiratory pathway was investigated in rice seedlings grown under total darkness, light/dark cycle, or continuous light. The capacity of the alternative pathway was relatively higher in leaves that had longer light exposure. An analysis of rice AOX1 multigene family revealed that AOX1c, but not AOX1a and AOX1b, had a light-independent expression. The alternative oxidase (AOX) inhibitor, salicylhydroxamic acid (SHAM, 1 mM), inhibited nearly 68% of the capacity of the alternative pathway in leaves grown under different light conditions. The plants grown under different light periods were treated with SHAM and then were exposed to illumination for 4 h. The transition from dark to 4 h of light stimulated the capacity of alternative pathway in etiolated rice seedlings and in those grown under light/dark cycle, whereas the capacity of the alternative pathway was constant in seedlings grown under continuous light with additional 4 h of illumination. Etiolated leaves did not show any CO 2 fixation after 4 h of illumination, and the increase in chlorophyll content was delayed by the SHAM pretreatment. When seedlings grown under light/dark cycle were moved from dark and exposed to 4 h of light, increases in chlorophyll content and CO 2 fixation rate were reduced by SHAM. Although these parameters were stable in plants grown under continuous light, SHAM decreased CO 2 fixation rate but not the chlorophyll content. These results indicate that the role and regulation of AOX in light are determined by the developmental stage of plant photosynthetic apparatus.

Nonmonotonic Redox Conversions of P700 in Leaves Irradiated with Far-Red Light Originate from Variable Contributions of Several Alternative Electron Transport Pathways during the Induction Period

The origin of nonmonotonic changes in the redox state of P700, the primary electron donor of PSI, was investigated on predarkened barley (Hordeum vulgare L.) leaves exposed to far-red light. To accomplish this, the relaxation kinetics of absorbance changes at 830 nm, reflecting the dark reduction of P700+, were measured at different stages of the induction curve. The onset of far-red light resulted in rapid oxidation of P700, which was followed by its partial reduction and subsequent slow oxidation of P700 to a steady-state level. This steady-state level was usually attained within 10 s under far-red light. The relative contribution of the slow kinetic component of P700+ reduction decreased in parallel with the transient photoreduction of P700+ and increased upon a subsequent stage of P700 photooxidation. The contribution of the middle component to the dark reduction of P700+ increased monotonically with the length of far-red light irradiation. The relative amplitude of the fast component of P700+ reduction increased sharply during the first 3 s of irradiation and decreased upon longer light exposures. The rates of fast and slow components of dark reduction of P700+ remained constant upon illumination of dark-adapted leaves with far-red light for 1 s and longer periods. Thus, nonmonotonic changes in the redox state of P700 in barley leaves exposed to far-red light reflect variable contributions of few alternative electron transport pathways characterized by different rates of electron donation to PSI. The results show the principle possibility of switching-over between alternative pathways of PSI-related electron transfer within one complex of this photosystem. Such switching may occur irrespective of active operation or inhibition of ferredoxin-dependent electron transport.

Three Cases of Large Retinal Capillary Hemangiomas Treated With Verteporfin and Photodynamic Therapy

To investigate the efficacy of verteporfin and photodynamic therapy in the treatment of large retinal capillary hemangiomas. Case reports of 3 patients with large retinal capillary hemangiomas treated with photodynamic therapy using verteporfin. Standard verteporfin dosages (6 mg/m(2) of body surface area) were given. Both standard and modified photodynamic protocols were followed. Modified protocols included shorter verteporfin infusion times and longer light exposure times. Pretreatment best-corrected Snellen visual acuity of the 3 affected eyes were 20/100, 20/50, and 2/200, respectively. All cases had associated exudative retinal detachments involving the macula. Cases 1 and 2 were classic endophytic retinal capillary hemangiomas. Case 3 was a reactive retinal capillary hemangioma. Case 1 had 2 photodynamic therapy treatments, and after 8 months, visual acuity improved to 20/40. Two years after initiating photodynamic therapy, the visual acuity was 20/30 and there was no reperfusion of the hemangioma. Case 2 had 3 photodynamic therapy treatments. The hemangioma was fibrotic, and 20 months after initiating photodynamic therapy visual acuity improved to 20/30. Case 3 had 1 treatment, 11 weeks later and visual acuity improved to 20/400. Four months after treatment, visual acuity returned to counting fingers because of tractional elevation of the macula as the capillary hemangioma fibrosed. Vitrectomy surgery was performed, and choroidal and retinal neovascularization was discovered. Three months after vitrectomy visual acuity was 20/400. In cases 1 and 2, the capillary hemangioma ultimately regressed, and the exudative detachment resolved. Verteporfin and photodynamic therapy were effective in achieving closure of large retinal capillary hemangiomas. In all cases, the hemangioma underwent fibrosis with consequent macular puckering due to retinal traction. In all cases, the visual acuity improved.

Calcium released by photolysis of DM-nitrophen triggers transmitter release at the crayfish neuromuscular junction.

1. Spontaneous and evoked transmitter release at the crayfish neuromuscular junction were potentiated in response to photolytic release of calcium from the 'caged' calcium compound DM-nitrophen, which had previously been injected into presynaptic terminals. 2. The amount of calcium released from DM-nitrophen photolysis depends on the concentration of DM-nitrophen, its photoproducts, Ca2+, Mg2+, H+, ATP and the cell's native buffer. Since none of these are known in the crayfish terminal, the study was conducted in a qualitative fashion. 3. Photolytic release of calcium from DM-nitrophen increased excitatory junctional potentials (EJPs) by a range of 2-31 times over control values and the miniature excitatory junctional potential (MEJP) frequency increased from resting values of 1-10 quanta/s to 3000-11,000 quanta/s. 4. Extracellular calcium was not required for the light-evoked asynchronous release of transmitter. Calcium-bound DM-nitrophen previously pressure injected into crayfish presynaptic terminals increased the MEJP frequency from resting values of 1-8 quanta/s to 800-10,000 quanta/s during photolysis in a calcium-free cobalt Ringer solution. 5. Iontophoresis of calcium-free DM-nitrophen into presynaptic terminals released transmitter upon photolysis, but only in a calcium-containing Ringer solution. This suggests that DM-nitrophen is capable of binding calcium once injected into terminals, but this is dependent on the presence of external calcium. 6. Photolysis of DM-nitrophen at lower light intensities produced a slower rate of transmitter release. 7. Brief light exposures, i.e. those which photolysed 5-20% of the DM-nitrophen, resulted in a rapid decay of postsynaptic responses on extinguishing the light, due to rebinding of photolytically released calcium to unphotolysed DM-nitrophen. Longer light exposures which completely photolysed DM-nitrophen, leaving only the low affinity photoproducts, produced a slow decay of transmitter release after the light pulse, presumably due to the active extrusion of calcium from the presynaptic terminals. 8. During photolysis of DM-nitrophen, the time courses of changes in EJP amplitude and MEJP frequency were different, indicating that the two measures of transmitter release were not linearly related. 9. MEJP frequency and EJP amplitudes during DM-nitrophen photolysis were fitted to a 'non-linear summation model' in which photolytically released calcium sums with calcium entering during an action potential to evoke transmitter release with a calcium co-operativity of five.

Towards understanding persistent photoconductance in doping modulated amorphous silicon

Abstract We present a simple model to explain the origin of the persistent photoconductance (PPC) in p–n–p–n multilayers made of hydrogenated amorphous silicon: brief light exposures create metastable Staebler-Wronski defects in the p-type material, making it more intrinsic. This in turn pushes the Fermi level of the whole multilayer closer to the conduction band, thus causing the observed metastable increase of the electron dominated coplanar conductance of the multilayer. Much longer light exposures are needed to shift the Fermi level towards midgap due to Staebler-Wronski defects in the n-type layers, leading to a consequent decrease in the PPC effect. In support of our model we present experimental results on the creation rate and annealing kinetics of the light-induced metastable conductance changes in a multilayer and in p-type and n-type single layers.

The combined effect of haematoporphyrin derivative and light on the normal mouse retina.

Combined treatment with haematoporphyrin derivative (Hpd) and light irradiation has been reported to be an effective method of killing cancer cells. This would be a very suitable treatment of intraocular tumours because the light can be controlled by the refractive media of the eye. Light and electron microscopy of Hpd and light treated normal mouse retina showed that only the irradiated area was damaged. Tissue destruction increased with greater concentrations of Hpd and longer light exposure. The outer layers of the retina were most sensitive. Hpd was retained in the tissue for 6 days.

The Influence of Ultraviolet Light and Carbohydrate Nutrition on Pycnidium Formation in Phyllosticta Antirrhini

Long wave ultraviolet light, peaking at 366 nm, inhibits pycnidium development. The extent of this inhibition is related to: (1) the duration of the ultraviolet light exposure, (2) the intensity of ultraviolet light, (3) the carbohydrate in the substrate, and (4) the concentration of the carbohydrate. At low concentration of the carbohydrate (0.6 g C/liter) inhibition occurred on all the substrates within 15 min. Longer light exposures, up to 40 min, were required to inhibit pycnidia at the high carbohydrate level (6.0 g C/liter). When the ultraviolet light intensity was increased from 100 gW/cm2 to 320 AuW/cm2, shorter exposures inhibited pycnidium formation. Identical dosages of ultraviolet light inhibited pycnidium formation on some substrates but not on others. When cultures were irradiated, inhibition occurred readily on maltose media at both concentrations. Inhibition on other substrates and substrate concentrations generally required exposures of a longer duration.

Interactions between photosynthesis and respiration in Chlorella I. Types of transients of oxygen exchange after short light exposures

1. Synchronous Chlorella fusca was exposed to light for periods of 0.1 sec-15 min. Subsequent to the illumination, the rate of O 2 exchange passes through a series of transient phenomena. These transients vary greatly with cellular age and depend also upon conditions prior to and during the experiment. However, the individual maxima and minima of O 2 exchange specified as T 1, T 2, T 3..., occur at reproducible times provided that algae of the same developmental stage and pretreatment are used. 2. At least 5 individual components are involved in the complex changes: (a) A sudden photosynthetic O 2 evolution ( T 1) which, after darkening, declines rapidly and without oscillations. (b) A brief and distinct O 2 uptake ( T 2) immediately after switching off the light, which is only observed under special conditions. (c) The next maxima and minima T 3, T 4, T 5, and partly also T 6 obviously are damped oscillations of the respiratory O 2 uptake, started by an inhibition of some respiratory step by photosynthesis. (d) A slow declining stimulation of O 2 uptake superimposed on the foregoing transients occurs after longer light exposures. (e) A very strong stimulation of respiratory O 2 consumption ( T 8), culminating not until 6 to 8 min after the start of illumination, is induced only by irradiation with short-wave light (< 540 nm) after longer dark periods. 3. The individual components differ with respect to their dependence on intensity, wavelength and duration of the light exposure and their sensitivity to several inhibitors. According to their characteristics all transients except T 8 depend on, but in different ways, the function of the photosynthetic apparatus. The components b and c seem to be closely connected with System I.

Electron diffraction, a new tool for research

Excessive blue light light-emitting diode (LED) exposure and consequent oxidative stress causes damage to retinal pigment epithelial (RPE) cells. Chitosan oligosaccharides (COSs) are the hydrolyzed products of chitin, which is abundant in the exoskeleton of crustaceans and cell walls of fungi. We investigated the protective effect of COSs on blue light LED-induced RPE cell damage. These cells were treated with various concentrations of COSs and then exposed to blue light LED. Our results confirmed that RPE cell apoptosis increased significantly with longer light exposure. Treatment with COSs significantly reduced apoptosis in a dose-dependent manner. These molecules also suppressed the production of reactive oxygen species and the expression of inflammation- and apoptosis-related proteins. Moreover, COSs stabilized the mitochondrial membrane potential of cells and down-regulated the NF-κB pathway. In this study, the protective effects of COSs on blue light LED-induced RPE cell damage, as well as the associated mechanisms, were demonstrated.