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Low Light Levels (low + light_level)
Selected AbstractsCharge Generation and Photovoltaic Operation of Solid-State Dye-Sensitized Solar Cells Incorporating a High Extinction Coefficient Indolene-Based SensitizerADVANCED FUNCTIONAL MATERIALS, Issue 11 2009Henry J. Snaith Abstract An investigation of the function of an indolene-based organic dye, termed D149, incorporated in to solid-state dye-sensitized solar cells using 2,2,,7,7,-tetrakis(N,N -di- p -methoxypheny-amine)-9,9,-spirobifluorene (spiro-OMeTAD) as the hole transport material is reported. Solar cell performance characteristics are unprecedented under low light levels, with the solar cells delivering up to 70% incident photon-to-current efficiency (IPCE) and over 6% power conversion efficiency, as measured under simulated air mass (AM) 1.5 sun light at 1 and 10,mW cm,2. However, a considerable nonlinearity in the photocurrent as intensities approach "full sun" conditions is observed and the devices deliver up to 4.2% power conversion efficiency under simulated sun light of 100,mW cm,2. The influence of dye-loading upon solar cell operation is investigated and the thin films are probed via photoinduced absorption (PIA) spectroscopy, time-correlated single-photon counting (TCSPC), and photoluminescence quantum efficiency (PLQE) measurements in order to deduce the cause for the non ideal solar cell performance. The data suggest that electron transfer from the photoexcited sensitizer into the TiO2 is only between 10 to 50% efficient and that ionization of the photo excited dye via hole transfer directly to spiro-OMeTAD dominates the charge generation process. A persistent dye bleaching signal is also observed, and assigned to a remarkably high density of electrons "trapped" within the dye phase, equivalent to 1.8,×,1017,cm,3 under full sun illumination. it is believed that this localized space charge build-up upon the sensitizer is responsible for the non-linearity of photocurrent with intensity and nonoptimum solar cell performance under full sun conditions. [source] Feeding efficiency of white bream at different inorganic turbidities and light climatesJOURNAL OF FISH BIOLOGY, Issue 2 2007Z. Pekcan-Hekim Experiments were conducted to test the effects of turbidity (10,50 NTU) and light (0,2 ,E m,2 s,1) on the feeding efficiency of white bream Abramis björkna preying on Chaoborus flavicans. Increased turbidity and low light levels did not have a significant impact on the feeding of white bream. In total darkness feeding was impeded indicating that white bream depends on vision for feeding. The dominance of white bream in temperate eutrophic lakes could be attributed to their success of feeding in turbid and low light environments. [source] Leaflet Movement of Robinia pseudoacacia in Response to a Changing Light EnvironmentJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 4 2007Cheng-Cheng Liu Abstract Diurnal and nocturnal leaflet movement of black locust (Robinia pseudoacacia L.) was investigated under three light schemes: 100% natural irradiance, 50% shading, and 90% shading. Changes in leaf mid-vein angle were described by measurements of two planes: (i) ,, the angle formed by the bottom of the petiolule and its relation to the horizontal plane; and (ii) ,, the angle between the petiolule and the main leaflet vein. The two highest light regimens had a significant effect on ,. Variation in , tends to make the leaflet more erect, thereby minimizing any negative impact of high irradiance on leaf lamina. Light-dark rhythms induced variation in , (termed nyctinastic movement). Nyctinastic movement is important during the low light levels experienced by leaflets in early morning and late afternoon. At low light levels, the leaflet stopped nyctinastic movement and , was fixed at an angle that may have enabled the leaf lamina to maximize light interception. After the light-dark cycle was reestablished, nyctinastic movement was restored. Taken together, our results suggest that irradiance induces variation in , leading to diurnal leaflet movement (diaheliotropism), whereas the light-dark cycle influences ,, which results in nocturnal leaflet movement. Both angles are important for describing patterns of leaf movement in R. pseudocacia. [source] Distinguishing the effects of light and temperature variations on the growth, development, multiplication potential and ex vitro survival rates of in vitro cassavaANNALS OF APPLIED BIOLOGY, Issue 3 2001M A B JORGE Summary Dissemination of cassava tissue culture plantlets is difficult in the arid tropics due to low eux vitro survival rates. Increased in vitro light intensity has been reported to induce high ex vitro survival rates. The results from earlier experiments suggested that it would be worthwhile to analyse the separate effects of in vitro light and of temperature on the in vitro growth pattern as well as differentiate its relation to ex vitro survival. Accordingly, analysis of a range of in vitro light intensities from 0 to 369 ,mol,1 m,2 photosynthetic photon flux density (PPFD) was conducted both with and without fans to control the heat. Temperature proved stable at low PPFD levels but increased above 204 ,mol s,1 m,2 when no fans were used. Increased PPFD levels induced larger fresh and dry masses as well as stem thickness. PPFD levels affected the developmental index (senescent leaf numbers) in vitro when it rose above 204 ,mol s,1 m,2 PPFD. Raised temperature ranges increased the multiplication index (node numbers) in vitro and ex vitro. It increased root number and leaf development (lobe anatomy). As in vitro temperatures of up to 40°C improve multiplication rates and PPFD levels above 101 ,mol s,1 m,2 were detrimental for ex vitro survival (as low as 60%), it is suggested that simpler and less costly laboratories with low light levels and a wide range of temperature tolerance could be successfully established in the tropics for in vitro cleaning and rapidly multiplying crops like cassava. [source] Determinants of Lichen Diversity in a Rain Forest UnderstoryBIOTROPICA, Issue 4 2007L. A. Dyer ABSTRACT Change in lichen diversity is often used as a bioindicator to estimate effects of atmospheric pollution, but natural variation in lichen cover and species richness can be very high. We examined the top-down effects of spore-consuming ants and the bottom-up effects of nutrient and light availability on lichen diversity associated with the leaf surface of the rain forest understory plant, Piper cenocladum. Plots containing P. cenocladum were randomly assigned to treatments in factorial experiments that included high and low light levels, nutrient enrichment, and presence and absence of the ant mutualist, Pheidole bicornis. At the conclusion of the experiments, plants were harvested and size of leaves, secondary metabolite content (amides), epiphyll cover, and the species richness of the lichens (which comprised 85% of the epiphyll community) were quantified. Epiphyll cover (mosses, liverworts, and lichens) was greater on plants that had ant-mutualists and balanced resources. Lichen species richness was greater for plants with balanced resources, particularly for those with high light availability. Relationships between toxins and lichen cover and richness were weak and unclear. In this system, natural sources of variation were reliable determinants of lichen diversity and both biotic and abiotic influences were important. [source] | ||||||||||