Incident Light Levels Research Articles

Crystal Growth of LiNbO3:Fe and Its Photorefractive Properties

We have grown LiNbO3:Fe single crystals with different doping concentrations (0.09-0.27 mol%). The homogeneity of Fe in the material was investigated by X-ray microanalysis(XMA) and inductively coupled plasma (ICP) analysis. The optical absorption coefficient increased with doping concentration in the entire wavelength region, and the characteristic band centered around 480 nm was observed. The amplitudes of refractive index change produced by photorefractive two-wave mixing were measured in the initial stage (short-time limit) with respect to the wavelength, the direction of polarization, the intensity of incident laser light and doping levels of crystals.

An Evaluation of the Effects of Ethylene on Carbon Assimilation inLycopersicon esculentumMill

Leaf and whole plant gas exchange rates of Lycopersicon esculentum Mill, were studied during several days of continuous exposure to ethylene. Steady-state photosynthesis and transpiration rates of control and ethylene-treated individual leaves were equivalent. However, the photosynthesis and transpiration rates of treated leaves required at least five times longer to reach 50% of the steady-state rate. This induction lag was attributed to ethylene—induced leaf epinasty and temporary acclimation to lower incident light levels immediately prior to measurement of gas exchange. The whole plant net carbon exchange rate (NCER) of a representative treated plant was also reduced by 51% after 24 h exposure to ethylene relative to both its pre-treatment rate and that of the control. Ethylene exposure reduced the growth rate of the treated plant by 50% when expressed as carbon (C) gain. The inhibition of NCER and growth rate associated with epinasty was completely reversed when the epinastic leaves were returned to their original positions and light interception was re-established. The results demonstrate that the inhibition of whole plant CO2 assimilation is indirect and due to reduced light interception by epinastic leaves. Morphological changes caused by environmental ethylene are thus shown to reduce plant C accumulation without inhibiting leaf photosynthesis processes per se.

Photosynthetic responses of Ulva lactuca at very low light

Changes in photosynthetic variables and dark respiration were measured in Ulva lactuca acchmated to continuous photon f l u densities between 0 and 55prnol n ~ ~ s ' at ?OC for up to 80d. Photosynthetic light harvesting efficiency (a ) was lughest in U. lactuca acclimated to intermedate light levels of 8.8 and 25 prnol m-2s-1 and was associated with maximum chlorophyll density and light absorptance. Below 2.5 pm01 m-'s-', energy capture was insufficient to maintan the maximum light harvesting apparatus and at 55 pm01 m-2s-i, light was no longer fully lirnihng to photosynthesis. The light harvesting efficiency (m) was linearly related to light absorptance (A). The quantum efficiency (0, = a ~ ' ) was, therefore, relatively constant and independent of the light acclimation level (0.045 to 0.059 m01 C [m01 photon absorbed]-'). The light compensation point for photosynthesis (I,) is given by the ratio between dark respiration (r) and light harvesting efficiency (a). Dark respiration rates increased with incident light level. As a result of combined changes in r and a, I, had minimum values (1.5 to 2.3 pm01 m-2s') in plants acclimated to 8.8 vmol m-2s' and it increased in the dark and particularly in the high light acclimated plants (5.3 to 7.6 pm01 m-2s' ) . Photosynthetic capacity (P,) was lmearly related to light harvesting efficiency (cc) , suggesting that photoadaptation mainly occurred by changes in number of photosynthetic units. U. lactuca growing in continuous low light possessed a photosynthetic capacity in excess of photosynthetic performance and would benefit from short-term exposure to high light. This may be of selective advantage, considering that natural light levels are widely fluctuating.

Solar Powered Cathodic Protection Using Residual Potential

Solar panels are a viable economical source of power for cathodic protection installations where grid power is not readily available. First those installations where alternative power sources are feasible are discussed. Then solar panel operation is investigated. This includes an overview of the semiconductor construction of the solar cells as well as the effect of incident light levels on the power output. A description of cathodic protection fundamentals outlines a typical configuration including the need for backup power. Because of the hysteresis effect of direct current on the well casing, a method of protecting the well without using batteries for the backup is demonstrated.

Light interception and its relation to structural differences in three Australian rainforest canopies

AbstractRelative differences in the seasonality of light penetrating the canopies of three Australian rainforests were measured directly with a quantum meter and indirectly using hemispherical photographs. The mossy microphyll fern forest had higher incident light levels (100–200 μEinstein m−2 per s) and more sky visible (21.8%) at ground level than the simple (5–20 μEinstein m−2 per s with 11.2% skylight) and complex (5–10 μEinstein m−2 per s with 10.8% skylight) notophyll vine forests. There were no significant changes in amounts of sky visible through the canopy over time (10 months) for any canopy, despite the fact that leaf‐fall was a seasonal event. Profile diagrams were constructed at each site to illustrate the depth and stratification of the canopy, and the differences in these structural features were related to the variation in light attenuation. Ecological aspects of light interception through rainforest canopies are discussed, including tree branch growth patterns and leafing phenologies, and seedling regeneration on the forest floor.

Quasielastic light scattering in silicon

An investigation of the origin of quasielastic light scattering from silicon surfaces, first observed by Sandercock (1972, 1978) is described. Measurements have been made of the dependence of the quasielastic spectrum upon temperature, wavevector, doping level, and polarisation and intensity of incident light. The results rule out the possibilities of scattering by free electrons or by entropy fluctuations in a collision-dominated phonon regime. A simplified calculation suggests that two-phonon difference scattering may be the origin of the observed spectrum with the main contribution coming from pairs of optic phonons on the same dispersion branch.

A simple, steady state description of phytoplankton growth based on absorption cross section and quantum efficiency1

We present a simple, quantitative formulation of steady state growth and metabolic regulation by phytoplankton, which describes well the nutrient‐limited and light‐limited growth of Thalassiosira weissflogii. The specific growth rate is a function of the quantum efficiency of carbon assimilation, the absorption cross section of cellular carbon, the incident light level, and the specific rate of respiration. The quantum efficiency is solely a function of light level, the absorption cross section is a function of light level and nutrient supply, and the respiration rate is a function of specific growth rate. The formulation, which resembles those proposed by Bannister and Shuter, is consistent with the thermodynamic model of Kiefer and the principle of optimization of energy conversion.

Comparative Foraging Behavior of Light- versus Shade-Seeking Adult Damselflies in a Lowland Neotropical Forest (Odonata: Zygoptera)

The damselflies Heteragrion erythrogastrum and Argia difficilis selected markedly different perching sites within the same forest. Heteragrion erythrogastrum perched only in deep shade and exhibited thoracic temperatures that were within 1.0 C of ambient. Conversely, A. difficilis perched in the most brightly lit areas and on sunny days exhibited thoracic temperatures between 4.4 and 8.4 C above ambient. During sunny conditions A. difficilis foraged approximately five times more frequently than H. erythrogastrum and made longer foraging flights as well. Subsequent observations of A. difficilis under varying conditions of light, however, revealed that thoracic temperature, foraging rate, and foraging flight distance all varied directly with incident light level. Thus, during overcast conditions A. difficilis exhibited thoracic temperatures and foraging behavior much like H. erythrogastrum. These results suggest that, for these ectothermic predators, foraging rate primarily reflects the energy demand associ...

A novel MOS compatible light intensity-to-frequency converter suited for monolithic integration

A novel circuit for light intensity-to-frequency conversion (LFC) suited for monolithic integration in MOS technologies is presented. The function is based on an R~S~ flip-flop whose toggle frequency is controlled by the discharge of a capacitance at the inputs of the R~S~ FF. For homogeneous illumination, the output frequency is proportional to the incident light level. For an implemented device, a dynamic range of more than six decades (approximately 0.2 lux up to >2/spl times/10/SUP 5/ lux) and a range of linearity of five decades were found.

OLISTHODISCUS LUTEUS (CHRYSOPHYCEAE). V. ITS OCCURRENCE, ABUNDANCE AND DYNAMICS IN NARRAGANSETT BAY, RHODE ISLAND1

ABSTRACTThe distribution and abundance of the flagellate Olisthodiscus luteus Carter were examined over a 17 yr period (1959–75) at one station in lower Narragansett Bay, Rhode Island, and at many stations throughout the Bay during the 1974, 1975 summer bloom periods. A bimodal pattern of maximum abundance characterized the 17 yr data set. Maxima (103–104 cells·ml−1) occurred during June–July and October–November separated by a mid summer (August) minimum of <102 cells·ml−1. This species was also absent from surface waters during the winter months (January–February) of each year. Regional abundances reached maximal densities of >105 cells·ml−1 during June 1974 and were confined to the northern and western regions of Narragansett Bay. Incident light, temperature, salinity and nutrient (NH4+, NO3−, NO2−, PO43‐) levels were also determined. The abundance cycle appears to be strongly effected by temperature, life cycle, motility, excreted substances and, to lesser extent, by light intensity, salinity, and nutrient dynamics. Regional distribution is affected by motility, wind forced water movements and benthic stage formation. The autecological data for O. luteus, pertinent observations of herbivorous zooplankton and the field observations are used to assess causative factors regulating the dynamics of O. luteus populations in Narragansett Bay. Pratt's hypothesis on the interaction between this species and Skeletonema costatum (Grev.) Cleve is reexamined.

Focusing method for nondestructive measurement of optical fiber index profiles

A new method to determine the refractive-index distributions of the cores of optical fibers is presented. The fiber is immersed in index matching oil to eliminate light refraction at the outer core boundary. Collimated light is passed transversely through the fiber core and is detected with a microscope focused just above the plane of the core boundary. The intensity distribution in the image plane is recorded with the aid of a computer-controlled video-analysis system. The refractive-index profile of the fiber core is then computed from this intensity distribution. In this paper we present error estimates and show how well the focusing method agrees with the interferometric slab method. The repeatability of the index measurement is approximately 2%, an error which is easily attributable to incident light level fluctuations.

Poly(carbon suboxide): A photosensitive paramagnetic ladder polymer

AbstractCarbon suboxide was found to give, on photo‐ and thermal‐polymerization, a photosensitive paramagnetic polymer. Studies of the kinetics of the ESR signal growth accompanying the polymerization process complement documented results obtained from monitoring the rate of polymer production and monomer disappearance. The spin concentration of the polymer increases with higher reaction temperature, reaching 2 × 1019 spin/g at a polymerization temperature of 105°C. The paramagnetism of poly(carbon suboxide) follows the Curie—Weiss law. Relaxation behavior at room temperature and g values for the spin systems have been obtained. The 105°C polymer shows a Weiss constant equal to 17°K and an extremely narrow ESR line width, ca. 10 mG, at 5°K. The 13C coupling constant from the selectively labeled polymer indicates π‐electron delocalization over the ladder polymer. The polymer paramagnetism can be further reversibly enhanced by visible light irradiation. The steady‐state concentration of the photo‐ESR signal is proportional to the square root of incident light intensity, with a quantum yield at room temperature for charge accumulation equal to 5% at an incident light level of 1015 photons/sec‐cm2. Fluorescence and excitation spectra of the soluble fraction of poly(carbon suboxide) are presented together with the quantum yield. The polymer has also been found to be an effective photopolymerization initiator at wavelengths longer than 340 nm.

Some recent developments in remote sensing

In recent years electronic instruments have been developed which increase very considerably our ability to view the nocturnal scene at otherwise critically low incident light levels, by using the available reflected radiation more efficiently with the aid of image intensifiers. Still other instruments employ sensors which are sensitive in the infrared and convert the natural thermal radiation of any object in the scene into visible pictures. In this article recent technological developments in image intensification and thermal image conversion are briefly discussed.

Effects of incident light levels on photosynthetic membrane polypeptide composition and assembly in Rhodopseudomonas sphaeroides.

Cells of Rhodopseudomonas sphaeroides were grown anaerobically with incident light levels ranging between 4,500 and 400 footcandles (ca. 48,420 and 4,304 lux). Cells grown with the higher light levels had lower contents of total bacteriochlorophyll and incorporated L-[U-14C]leucine into membrane protein at higher rates than cells grown with lower light levels. The former cells also contained relatively lower amounts of light-harvesting membrane polypeptides as compared with the latter cells. In contrast, the relative amounts of reaction center membrane polypeptides were approximately the same with varying incident light levels. The relative amounts of these membrane polypeptides were correlated with differences in rates of synthesis and assembly of the polypeptides into membrane by measuring the rates of incorporation of L-[U-14C]leucine into the membrane-bound polypeptides. No significant differences in rates of turnover of these polypeptides were detected under the varying incident light levels as measured in pulse-chase radioactive labeling experiments.

Fonction chromatrope de la pars intercerebralis chez l'acridien Oedipoda coerulescens

The median neurosecretory cells of the protocerebrum of fifth instar larvae and 1- or 2-day-old adults of Oedipoda coerulescens produced more fuchsinophilic material when reared on dark backgrounds than on pale ones. In the latter case, the neurosecretory cell bodies were almost completely devoid of neurosecretion. The same differences were found in the anterior lobes of the corpora cardiaca. Individuals implanted with pars intercerebralis from donors reared on a dark background showed dark pigmentation no matter what their own background colour (and conversely). Black or red pigmentation appeared on absorbent grounds whereas a pale one was produced on reflecting grounds with high levels of incident light predominantly between 576 and 588 mμ. The significance of these results is discussed. A possible scheme for the interaction of environmental factors and pigmentation is suggested.

Limitations in Optical Imaging Devices at Low Light Levels

An examination is made of the influence of objective lens parameters on the resolution capabilities of low light level imaging devices. From the resulting characteristics the dependence of the perception range of a given target on the incident light level is deduced. The restrictions imposed by larger lenses on the depth of field of acceptable focus are investigated, and comparisons made with the thresholds set by quantum-noise and optical resolution limitations. Degradations in the performance of image intensifiers due to different levels of image tube dark noise are also discussed.

Some photoelectric observations of lightning

During the summer of 1965, a calibrated silicon photodiode and an oscilloscope were used as a fast-response lightning photometer covering the visible and near-infrared regions of the spectrum from 0.4 to 1.1 μ. Simultaneous still photographs of the discharge channels were taken to determine how the photoelectric pulse profiles depend on the type of lightning (i.e., cloud-to-ground versus cloud-to-cloud) and the geometry of the channels. These observations represent the first attempt at a photometric study of lightning with correlated photographs of the discharge channels. The photodiode detector consisted of an Edgerton, Germeshausen & Grier model 560-561 ‘lite-mike’ and ‘detector head’ This system provided a voltage output, proportional to the light flux input, which was recorded as a function of time on a fast oscilloscope (Tektronix type 555). The photodiode and associated circuitry were linear over a wide range of incident light levels (within 5% over 7 decades) and had a response time of less than 1 μsec. The relative spectral response of the detector was calibrated by the manufacturer and is shown in Figure 1. The manufacturer also provided a pulse calibration factor of 7.7 mv/mw of incident light power at 800 mμ. The area of the photosensitive detector was 0.0728 cm2.

A hysteresis effect in photoconductive cadmium selenide and its use in a solid-state image storage device

A brief description of a new hysteresis effect in cadmium selenide photoconductive powder will be given. Photocurrent plotted as a function of voltage has the form of a hysteresis loop, with triggering from low to high currents occurring at a voltage depending on the incident light level. At a suitably chosen voltage, triggering from low to high currents occurs with light pulse excitation. Return to the condition of low current flow is brought about by brief interruption of the supply voltage. Since the triggering is present with ac or dc operation, it is possible to use the effect in a series circuit of photoconductor and ac operated electroluminescent panel. If this is done on an area basis with due attention paid to the impedance match of the photoconductor and electroluminescent layer, it is possible to make an image storage device having no optical feedback. The construction and operation of such a device is described, and a photograph of a stored image on a 3-inch panel is shown.

The Effect of Various Lighting Conditions on the Efficiency of "Candling" Cod Fillets for Detection of Parasites

The efficiency of candling cod fillets was studied using various values and colours of light transmitted through the cod flesh and various values of incident light. It was found that there was no advantage gained in using other than white light for transmission through the fillet. It was also found that a low level of incident light was desirable if the maximum number of parasites is to be detected.