High Illumination Levels Research Articles

光照强度和肥力变化对对垂穗披碱草生长的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 光照强度和肥力变化对垂穗披碱草生长的影响 DOI: 10.5846/stxb201211241667 作者: 作者单位: 河西学院农业与生物技术学院,兰州大学干旱与草地生态教育部重点实验室,兰州大学干旱与草地生态教育部重点实验室 作者简介: 通讯作者: 中图分类号: 基金项目: 甘肃省科技计划资助项目（1304FKCG080）；河西学院校长基金（XZ2011-04） The effects of light intensity and fertilization on the growth of Elymus nutans Author: Affiliation: Biology Department of Hexi University,Key Laboratory of arid and grassland ecology of Ministry of Education,Lanzhou University,Key Laboratory of arid and grassland ecology of Ministry of Education,Lanzhou University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:在野外条件下，采用析因设计，对光照和肥力变化影响下垂穗披碱草的生长参数进行测定，评估垂穗披碱草对异质环境的适应特性。光照分为高光照（100%光照强度）、中度光照（43.5%光照强度）与低光照（6.74%光照强度）；肥力分为施肥与不施肥。结果表明，垂穗披碱草在光照强度由高光照（100%）向中度光照（43.5%）变化情况下，地上生物量、分蘖数无变化，株高增大，光照强度减小到6.74%时，地上生物量、分蘖数、株高均减小。比叶面积（SLA）随光照强度的减弱而增加，相对生长率（RGR）随光照强度的减弱而减小，施肥对SLA和RGR无影响。根冠比在中度光照和低光照下各处理之间差异均不显著，高光照（100%）下增加肥力，根冠比增大。施肥时，叶分配随光照强度的减弱而增加，繁殖分配减小，不施肥时，叶分配与繁殖分配在高光照（100%）和中度光照（43.5%）下无差异，低光照（6.74%）下，叶分配增大，繁殖分配减小。施肥时茎分配在中度光照强度（43.5%）下最大，高光照强度（100%）下次之，低光照强度（6.74%）下最小，不施肥时，茎分配在高光照（100%）和中度光照（43.5%）下无差异，低光照（6.74%）下减小。研究表明：垂穗披碱草是一个光照耐受型物种，光照强度减小到全光照一半时仍可正常生长。在低光环境中，垂穗披碱草通过增加株高和大而薄的叶片，来适应环境，资源主要在叶分配、茎分配、繁殖分配之间进行了权衡。 Abstract:Elymus nutans Griseb. (Poaceae: Triticeae) is a tall (shoot height usually 60-120 cm) sparse bunchgrass with broad leaves that is native to the alpine meadows of the Qinghai-Tibetan plateau, China. The study was conducted in the Hezuo Sub-alpine Meadow Ecosystem Field Station of Lanzhou University. Field experiments based on a factorial design were used to measure the effects of illumination and fertilization on the growth parameters of E. nutans to assess the ability of E. nutans to adapt to heterogeneous environments. The experiment began in April, 2006 as part of mowing trials and included eighteen 1.3 m × 0.8 m plots with a total of six treatment combinations of light and fertilization, 80 of plants per plot, 30 that were marked. The plots were separated by 0.5 m. To simulate the effects of attenuated light beneath the canopy on plant growth, green shade nets that did not fundamentally change the spectral composition of sunlight were used in this trial to create three illumination conditions similar to those in the natural environment. The three light intensities were high (100% illumination), moderate (43.5%), and low (6.74%), and plots were either fertilized with diammonium hydrogen phosphate (50 g/m2) or left unfertilized. On 10th October, we harvested 15 individual plants (five marked individuals per plot) from each treatment. Harvested plants were dug up and washed. For each plant, the number of tillers (including withered ones) was recorded, and it was separated into leaves, stem (including leaf sheaths), inflorescences, and roots. Separated plant tissues were dried in an oven (80 ℃) for 48 h and then weighed. The results show that as illumination intensities decreased from high to moderate, the above-ground biomass and number of tillers of E. nutans did not change, while plant height increased. However, as the light intensity declined to 6.74%, the above-ground biomass, number of tillers, and plant height were all reduced. The specific leaf area increased as illumination intensity was attenuated, while the relative growth rate decreased, which suggested that fertilization had no effect on either specific leaf area or relative growth rate. The differences in root-to-shoot ratios at moderate and low illumination levels were not significant, while the root-to-shoot ratios increased with the application of fertilizer under high illumination. After fertilization, allocation to leaf biomass increased while allocation to reproductive structures decreased as the light intensity was attenuated. Without fertilization, there were no significant differences in biomass allocations to either leaves or inflorescences at high and moderate illumination levels, while allocations to leaves and to reproductive structures decreased at the low illumination level. After fertilization, the stem allocations were highest at the moderate illumination intensity, intermediate at the high illumination intensity, and lowest at the low illumination intensity. Without fertilization, there were no differences in the stem allocations at the high and moderate illumination levels, while the allocation to stem tissue decreased under low illumination. The results of this study show that E. nutans is an illumination-tolerate grass species that can grow normally even when the light intensity is reduced to half of full sun exposure. Elymus nutans adapts to low-illumination environments by increasing its height and by producing large thin leaves, and its resources are balanced through altered allocations to leaf biomass, stem tissue, and reproductive structures. 参考文献 相似文献 引证文献

An Evaluation of Light Distribution in the Exhibition Areas of the Mimesis Art Museum Designed by Alvaro Siza

The works of Alvaro Siza have been referred that they were not the theoretical architecture but the sensual and experiential one. His works were designed on the base of their locality that each of them located. For the study, I selected a work of him, which was the Mimesis Art Museum at Paju in South Korea, and reviewed existing literatures to understand how he controlled the light and created the architectural spaces and forms in relation with the light, and I measured the illumination levels of the inside areas of the Mimesis Art Museum, and then, I surveyed the visitors’ responses on the lighting conditions of the Mimesis Art Museum. The results of the measurements showed that the illumination levels of the Mimesis Art museum on the first floor were effectively controlled to display the art works. The illumination levels on the third floor, however, were much higher than recommended illumination values for museum because of less controlled natural light. Therefore, more considerations to control the natural light are needed to secure stable environment in the exhibition spaces. Meanwhile, the answers of questionnaires concerning the quality of lighting conditions in the Mimesis Art Museum showed that the natural light was so effective to light the museum although the natural light illuminated some areas of the museum with high illumination levels.

Exploring of Light Fastness of Inkjet Prints under High Intensity Level of Illumination

Nowadays, inkjet prints have been universally used in packaging, posters and window show promotional items. The quality of the inkjet prints attracts more attentions, especially for posters and window promotional item generally require bright colors, saturation, and a long print life. Generally, the color of inkjet prints fade gradually when being placed outside and radiated directly by sunlight or under lamp, meanwhile, the density decreases and color difference increases. All these phenomena happened make inkjet print cannot meet the requirements of customers to color within the time of use. Light fastness of inkjet prints under high intensity level of illumination is studied in this research. Ten different brands of papers were exploited to print a special design test target by EPSON inkjet printer and the printing test samples were irradiated under high level of illumination so that the aging process can be accelerated. After being irradiated for different time intervals, then color differences were measured by using spectrophotometer. The results show: the color differences of prints printed by using the brands Kodak and Xiongguan papers changed greatly after prolonged exposure to light. These conclusions are very useful for the correct choosing of inkjet materials under suitable inkjet printing condition.

The effect of ambient illumination on handheld display image quality.

Handheld devices such as smartphones and tablets are becoming useful in the medical field, as they allow physicians, radiologists, and researchers to analyze images with the benefit of mobile accessibility. However, for handheld devices to be effective, the display must be able to perform well in a wide range of ambient illumination conditions. We conducted visual experiments to quantify user performance for testing the image quality of two current-generation devices in different ambient illumination conditions while measuring ambient light levels with a real-time illuminance meter. We found and quantified that due to the high reflectivity of handheld devices, performance deteriorates as the user moves from dark areas into environments of greater ambient illumination. The quantitative analysis suggests that differences in display reflection coefficients do not affect the low illumination performance of the device but rather the performance at higher levels of illumination.

Factors affecting parents' presence with their extremely preterm infants in a neonatal intensive care room

To describe parents' experiences of factors that influenced their stay with their extremely preterm infants in a neonatal intensive care unit (NICU). This study has a qualitative descriptive design based on semistructured interviews conducted with seven mothers and six fathers. Opportunities to stay overnight together with their infant facilitated parental presence, and opportunities for taking over their infant's care empowered the parents in their parental role and increased their motivation to stay. Kangaroo mother care helped them to feel in control and feel needed, which increased their presence. High levels of illumination and noise rendered it difficult for parents to sleep and stay overnight with the infant. Low staffing levels limited their use of kangaroo mother care when they had to wait for assistance to transfer the infant from the incubator. Several participants perceived the performance of painful procedures on their child as stressful and as an obstacle to their presence. Kangaroo mother care and active involvement in the infant's care gave parents a sense of control and strengthened their motivation to be with their infant. High levels of noise and illumination and a dismissive staff attitude were obstacles to parents' presence.

User Preferences in Office Lighting: A Case Study Comparing LED and T5 Lighting

Lighting quality parameters were studied in an office lighting setting for three different luminaire types: 1) square LED panel luminaire (Sq_LED); 2) round LED downlight luminaire (Ro_LED); and 3) rectangular recessed T5 fluorescent lamp luminaire (Re_T5). The lighting conditions were evaluated with subjective assessments and horizontal desktop illuminance measurement in the middle of the task area. Re_T5 lighting was compared to Sq_LED lighting at 300, 600 and 1000 lx. Ro_LED lighting was studied at three different color temperatures: 3000, 4500 and 6000 K. Subjects responded to all nine conditions using identical questionnaires, which contained questions regarding glare, reading task ease, detail distinction from the wall, color naturalness and pleasantness, illuminance level sufficiency and pleasantness, general pleasantness of the lighting, naturalness of the shadows, and the appearance of the luminaires. Subjects also set three lighting conditions: 1) minimum illuminance for brief duration office work using Re_T5 lighting; 2) optimal illuminance for long-time office work using Re_T5 lighting; and 3) optimal illuminance and color temperature using Ro_LED lighting. The illuminance in the test room was preset at 300 lx before a subject entered the room and started these adjustment. The illuminance adjustment ranges were 0-1142 lx for the Re_T5 lighting and 0-738 lx for the Ro_LED lighting. In the CCT adjustment task CCT was preset to 3000, 4500, or 6000 K.Subjects evaluated 600 lx to be equally pleasant to 1000 lx and the reading task was evaluated to be equally easy at these two illuminance levels. However, 1000 lx caused slightly more glare. 300 lx was considered to be less pleasant and the reading and detail distinction from the wall was considered to be more difficult at 300 lx than at higher illuminance levels. At 600 lx the amount of light was considered to be more optimal than at 300 or 1000 lx. There were no significant differences in the user answers between the Re_T5 and Sq_LED lightings at equal illuminance levels. The Ro_LED lighting was considered less pleasant at 6000 K than at 3000 or 4500 K. However, CCT did not have a statistically significant effect on user answers to other questions. When the users adjusted illuminance the overall average preferred illuminance was 648 lx for Re_T5 lighting and 517 lx for the LED lighting; there were large variations in the preferred illuminances between subjects. The Re_T5 lighting had larger illuminance adjustment range than the Ro_LED lighting, which may have affected the preferred settings. The overall mean preferred CCT of the Ro_LED lighting was 4150 K. There were signs that preset CCT affected the user set CCT.

Melanopsin Gene Polymorphism I394T Is Associated with Pupillary Light Responses in a Dose-Dependent Manner

BackgroundMelanopsin-containing intrinsically photosensitive retinal ganglion cells (ipRGCs) play an important role in non-image forming responses to light, such as circadian photoentrainment, light-induced melatonin suppression, and pupillary light response. Although it is known that there are some single nucleotide polymorphisms (SNPs) in the melanopsin (OPN4) gene in humans, the associations of the SNPs with non-image forming responses to light remains unclear. In the present study, we examined the associations of melanopsin gene polymorphisms with pupillary light response.MethodsJapanese university students (mean age: 21.0±1.7 years) with the genotypes of TT (n = 38), TC (n = 28) and CC (n = 7) at rs1079610 (I394T) located in the coding region participated in the present study. They were matched by age and sex ratio. Dark-adapted pupil size (<1 lx) was first measured. Then steady-state pupil size was measured during exposure to five lighting conditions (10 lx, 100 lx, 1000 lx, 3000 lx, 6000 lx in the vertical direction at eye level).ResultsSignificant interaction between the genotype of I394T (TT versus TC+CC) and luminance levels was found in pupil size. Under high illuminance levels (1000 lx, 3000 lx and 6000 lx), pupil sizes in subjects with the C allele were significantly smaller than those in subjects with the TT genotype. On the other hand, pupil size in subjects with the C allele under low illuminance (<1 lx) was significantly larger than that in subjects with the TT genotype. Percentages of pupil constriction under high illuminance levels were significantly greater in subjects with the C allele than in subjects with the TT genotype.ConclusionsHuman melanopsin gene polymorphism I394T interacted with irradiance in association with pupil size. This is the first evidence suggesting a functional connection between melanopsin gene polymorphism and pupillary light response as an index of non-image forming response to light.

Effects of Background Lighting and Retinal Illuminance on Spontaneous Eyeblink Activity of Human Subjects in Primary Eye Gaze

To further evaluate possible effects of lighting conditions on the spontaneous eyeblink rate (SEBR) of normal young adult human subjects. A baseline 5 min video recording was made followed by a second recording under test conditions in 7 different groups of 10 subjects. These test conditions were a simple repeat recording under reference conditions (subjects maintaining silence, with gaze directed towards a target on a 2 m distant whiteboard with the luminance of the reflected light of 35 cd/m, recording under lower (5 cd/m), higher (75 cd/m) and floodlit (150 cd/m) levels, after pupil dilation with phenylephrine 2.5 %, after sudden increase with floodlights (to 200 cd/m), as compared subjects engaged in conversation. The overall SEBR values ranged from 8.4 to 15.8 eyeblinks per minute (mean 12.3 ± 2.8 eyeblinks per minute). These did not significantly change with repeated assessments, no significant changes were seen comparing lower or higher illumination levels or after pupil dilation, but an increase to 20.0 ± 4.6 eyeblinks per minute was seen with a sudden increase in illumination. Conversation increased SEBR to 22.2 ± 6.4 eyeblinks per minute. Spontaneous eyeblink activity in silence may be slightly affected by background lighting conditions, but such effects are notably less than SEBR changes that can occur when there is a sudden increase in lighting levels (as a glare stimulus) or when assessments are made during conversation.

DAYLIGHT PERFORMANCE OF SINGLE PEDENTIVE DOME MOSQUE DESIGN DURING WINTER SOLSTICE

In this study, the analysis is to measure lighting performance of single pendentive dome type and pyramid roof type in mosque design built during the Ottoman Empire in Istanbul, Turkey and Mostar, BosniaHerzegovina. The selected case studies are the Firu zaga and Orhan Gazi Mosques as single pendentive dome styl and Neziraga Mosque as case study for the pyramid roof type. This analysis aims to have a research finding to show that Turkish style’s peden tive dome mosque design provides efficient indoor daylighting in the Orhan Gazi Mosque in comparison with the Firuzaga Mosque and Neziraga. This assessment is simulated during winter solstice occu rred when the sun is perimetering at its most south ern position along the Tropic of Capricorn. This study applies simulation analysis using Autodesk software known as 3D Studio Max Design 2011 programme. The simulations were done by the program using weather data file to provide the weather informatio n and climate changes of the study area. The analys is shows that both mosques have mostly an evenly distr ibuted illuminance level with Scales 1 to 5. The Or han Gazi Mosque has slightly higher illuminance levels compared to those of the Firuzaga Mosque and bothe of the pendentive dome mosques have butter illuminance level than the pyramid roof mosque. The study concludes that the pedentive dome mosque design has an effect on the mosque indoor daylighting. Having excellent illuminance level distributed at all the locations is one of the crucial reasons why the mos ques with pedentive dome roof cover are built by Ottoman master builders.

Shedding light on light: benefits of anthropogenic illumination to a nocturnally foraging shorebird

Intertidal habitats provide important feeding areas for migratory shorebirds. Anthropogenic developments along coasts can increase ambient light levels at night across adjacent inter-tidal zones. Here, we report the effects of elevated nocturnal light levels upon the foraging strategy of a migratory shorebird (common redshank Tringa totanus) overwintering on an industrialised estuary in Northern Europe. To monitor behaviour across the full intertidal area, individuals were located by day and night using VHF transmitters, and foraging behaviour was inferred from inbuilt posture sensors. Natural light was scored using moon-phase and cloud cover information and nocturnal artificial light levels were obtained using geo-referenced DMSP/OLS night-time satellite imagery at a 1-km resolution. Under high illumination levels, the commonest and apparently preferred foraging behaviour was sight-based. Conversely, birds feeding in areas with low levels of artificial light had an elevated foraging time and fed by touch, but switched to visual rather than tactile foraging behaviour on bright moonlit nights in the absence of cloud cover. Individuals occupying areas which were illuminated continuously by lighting from a large petrochemical complex invariably exhibited a visually based foraging behaviour independently of lunar phase and cloud cover. We show that ambient light levels affect the timing and distribution of foraging opportunities for redshank. We argue that light emitted from an industrial complex improved nocturnal visibility. This allowed sight-based foraging in place of tactile foraging, implying both a preference for sight-feeding and enhanced night-time foraging opportunities under these conditions. The study highlights the value of integrating remotely sensed data and telemetry techniques to assess the effect of anthropogenic change upon nocturnal behaviour and habitat use.

Studi evaluasi Pencahayaan Alami Pada Gedung Kuliah Bersama Iii Universitas Muhammadiyah Malang

In Gedung Kuliah Bersama (GKB) III at University Muhammadiyah of Malang, at the first floor with a low-level of illumination should be used for audio-visual rooms or meeting, or it’s not used to read, write a long time (often), and for a thorough job, so it does not require a high level of illumination, because the majority of rooms on the first floor level of 30 lux illumination only and the maximum light level is only about 300 lux at the window. On the second floor with office functions majors and computer labs are appropriate to the level of illumination most of the rooms reached 200 lux, at the window level to 500 lux maximum lighting. Lecture room on 3 and 4 floors have a very high level of illumination, on the third floor reached 120-240 lux in the most of the rooms and around the window to 1200 lux, the uneven illumination very disturbing visual comfort of user room. On the fourth floor most of the rooms have lighting levels of 200-400 lux and 1800 lux maximum reached around the windows.Key Words: Lighting levels or level of illumination, GKB ( Gedung Kuliah Bersama )

Mechanism of current transport in Schottky barrier diodes based on coarse-grained CdTe films

The possibility of fabricating a Schottky barrier on Al-p-CdTe structures with the lowest density of surface states has been demonstrated and confirmed by the results obtained from the capacitance-voltage and photoelectric measurements of the potential barrier height. It has been established that, at different forward bias voltages, there are different exponential dependences of the electric current on the voltage, which are related to the changes in kinetic parameters of the base of the Al-p-CdTe-Mo structure. It has been shown that the Al-p-CdTe-Mo structure at a forward current and high illumination levels operates as an injection photodiode. This injection photodiode has a high current sensitivity. When the current is switched on in the reverse direction, after the complete coverage of the base of the structure by the space charge, electrons responsible for the charge transfer mechanism and noise characteristics of the structure are injected from the rear contact.

자연채광 유도공간에의한 전시공간내 채광에 관한 연구

In recent years, it clearly shows the tendency toward the utilization of daylight in many exhibitory buildings such as museum since the expectation of visitors for whom high illuminance levels are preferable to perceive the details of the works of art. Shading devices and special glazings are often used as the tool to control the amount of light and heat which should be avoided for the presentation of high-light sensitive art works such as paintings. Another way of controling the light is to provide the space for inducing and attenuating light in the exhibitory building. This study aims to investigate the illuminance on the exhibitory space when the space for inducing and attenuating light is applied. Interaction between the daylight and the space was simulated by Lumen Micro program with variation of the size of the exhibitory space, the length of inner wall, surface reflectivity, area of windows to obtain the illumination of the wall surface. This study shows that those variables affect the illumination on the wall surfaces. By comparing the results with suggestive illumination of KS and ICOM, available wall for display on natural lighting are suggested for the seasons and time.

Injection photodiode based on p-CdTe film

Photosensitive large-block p-type cadmium telluride (p-CdTe) film with a resistivity of ρ ≈ 106−107 Ω cm has been used to create an Al-p-CdTe-Mo structure with a Schottky barrier, which exhibits the properties of an injection photodiode. Being switched in the forward current passage direction (with “+” on the Mo contact) at high illumination levels, the proposed structure exhibits a responsivity of Sλ ≈ 2.6 A/W at a wavelength of λ = 0.625 μm, which is about five times the spectral response of the ideal photodetector for this wavelength range.

An Algorithm for Designing Dynamic Solar Shading System

The present study aims to define and validate an analytical procedure for determining the optimal movement profile for dynamic shading system based on the horizontal mobile blinds for high level of illumination and visual comfort in indoor environments. The algorithm is developed to design a dynamic solar shading system for an office building (Ergo Tower) situated in Milan, Italy. The calculations take into account variables such as geographic location, date, time, surface orientations and geometrical and functional characteristics of shading system. In the first step the solar coordinates and the variation of solar incidence angle on the building surfaces have been defined. Using the equations of solar geometry the typical solar path (sun position e.g. solar altitude, azimuth etc.) corresponding to the specific location for the entire year and also the variation of the incidence angle with which the direct radiation affect the building surfaces are described. Based on the geometry of shading system, the optimal values of inclination of the profiles can be calculated.Finally, due to the technical limitations of the systems, the feasible configuration has been determined corresponding to an angle close to the optimal values of inclination for ensuring appropriate shading. This test system allows the definition of the movement of dynamic solar shading systems based on a specific location and geometrical/mechanical characteristics of a certain technical solution.

Responses of the photosynthetic electron transport system to excess light energy caused by water deficit in wild watermelon

In plants, drought stress coupled with high levels of illumination causes not only dehydration of tissues, but also oxidative damage resulting from excess absorbed light energy. In this study, we analyzed the regulation of electron transport under drought/high-light stress conditions in wild watermelon, a xerophyte that shows strong resistance to this type of stress. Under drought/high-light conditions that completely suppressed CO(2) fixation, the linear electron flow was diminished between photosystem (PS) II and PS I, there was no photoinhibitory damage to PS II and PS I and no decrease in the abundance of the two PSs. Proteome analyses revealed changes in the abundance of protein spots representing the Rieske-type iron-sulfur protein (ISP) and I and K subunits of NAD(P)H dehydrogenase in response to drought stress. Two-dimensional electrophoresis and immunoblot analyses revealed new ISP protein spots with more acidic isoelectric points in plants under drought stress. Our findings suggest that the modified ISPs depress the linear electron transport activity under stress conditions to protect PS I from photoinhibition. The qualitative changes in photosynthetic proteins may switch the photosynthetic electron transport from normal photosynthesis mode to stress-tolerance mode.

An Investigation of the Reciprocity Principle of Light Exposures Using Microfading Spectrometry

ABSTRACT It is frequently assumed that sensitive museum materials follow the reciprocity principle of light exposures. Thus, equivalent exposure doses obtained by using either high-illuminance levels for short periods of time or lower illumination for longer exhibition periods are believed to cause similar degrees of damage to an object. Microfading spectrometry permitted the investigation of this phenomenon by evaluation of light-induced changes in a series of samples. The effects of equivalent exposure doses on materials such as Blue Wool 1, LightCheck Ultra, and various dyed silks from a reference collection were compared. The results indicate that reciprocity is obeyed by the most stable colorants, while materials with lower stability to light may experience deviations that are proportional to the intensity of illumination. This study confirms that reciprocity failure is associated with the use of high-intensity lamps during accelerated-aging trials. Therefore only those tests conducted at low-illumination intensity ranges where reciprocity holds should be employed when one estimates the extent of damage occurring in a museum environment.

Digital Holography at Shot Noise Level

By a proper arrangement of a digital holography setup, that combines off-axis geometry with phase-shifting recording conditions, it is possible to reach the theoretical shot noise limit, in real-time experiments.We studied this limit, and we show that it corresponds to 1 photo-electron per pixel within the whole frame sequence that is used to reconstruct the holographic image. We also show that Monte Carlo noise synthesis onto holograms measured at high illumination levels enables accurate representation of the experimental holograms measured at very weak illumination levels. An experimental validation of these results is done.

Effect of short-term simulated daylight exposure on optically brightened papers

Two optically brightened commercial papers were subjected to 72 hours continuous exposure to graphic arts daylight simulating fluorescent lamps at 1.4 and 4.4 klux. At the higher illuminance level, a CIELAB colour difference of 1.0 was reached in approximately 3 and 50 hours for the two papers. The colour differences produced by the 1.4 klux exposure were greater than that predicted by assuming a linear relationship between intensity and colour change, by a factor of 1.8.

Simultaneous determination of carrier lifetime and electron density-of-states in P3HT:PCBM organic solar cells under illumination by impedance spectroscopy

We report new insights into recombination kinetics in poly(3-hexylthiophene):methanofullerene (P3HT:PCBM) bulk heterojunction (BHJ) solar cells, based on simultaneous determination of the density of states (DOS), internal recombination resistance, and carrier lifetime, at different steady states, by impedance spectroscopy. A set of measurements at open circuit under illumination was performed aiming to better understand the limitations to the photovoltage, which in this class of solar cells remains far below the theoretical limit which is the difference between the LUMO level of PCBM and the HOMO of P3HT (∼1.1 eV). Recombination kinetics follows a bimolecular law, being the recombination time (lifetime) inversely proportional to the density of photogenerated charges and the recombination coefficient γ=6×10 −13 cm 3 s −1. We find that the open-circuit photovoltage is governed by the carrier ability of occupying the DOS, which results in Gaussian shape and spreads in energy σ≈125–140 meV. The energy position of the Gaussian DOS center ( E L=0.75–0.80 eV), which corresponds to half occupation of the electron DOS, approximates LUMO(PCBM)–HOMO(P3HT) difference. But the recombination rate is strongly enhanced at high illumination levels, what produces the photogenerated charge to remain in the tail of the DOS. Consequently, the electron and hole Fermi levels are unable to reach the center of the DOS, then substantially limiting the photovoltage. Detailed theoretical analysis of the lifetime dependence on photovoltage is provided.