Presence Of Background Illumination Research Articles

Robust beam width estimation with sub-pixel resolution in uncontrolled imaging conditions.

Estimations of laser beam widths can yield vastly different results depending on the used beam width measurement method and the measurement conditions. We expand upon an imaging analysis method, proposed in the field of laser eye safety, to determine a laser's beam width based on the ratio between encircled energy and diameter. We show this method to be highly valuable when determining beam widths in noisy imaging conditions and in the presence of background illumination. Furthermore, this method enables estimations with sub-pixel resolution on beam widths with a spatial extent of a few pixels.

Environmental CW range-resolved S-lidars with Si/InGaAs arrays: limitations and capabilities under sky background.

In this paper, we discuss some features of open-path remote sensing inherent to CW range-resolved S-lidars (S comes from Scheimpflug) as a new, to the best of our knowledge, and promising class of laser instruments for environmental monitoring. In many remote-sensing applications, the accompanying skylight can degrade the sensitivity and overload the photodetectors, which is also very relevant for S-lidars with Si and InGaAs arrays. We paid special attention to the topical problem of predicting the limitations and potential of S-lidars in the VIS and SWIR spectral bands, where the sky background is particularly strongly affected. For this purpose, the index of immunity against external backgrounds as a quantitative indicator of S-lidars' potential insensitivity to the current skylight is introduced. Its evaluation is carried out by comparing the potentially achievable signal-to-noise ratios at the detector output in the presence and absence of external illumination. The detector response to the skylight in the photon-counting mode is normalized to appropriate parameters of the array in order to use dimensionless estimates in describing the variability of conditions. Characteristic spectral and dark-current-related features distinguishing the response of Si and InGaAs array detectors in the presence of background illumination are taken into account. It is then shown how to determine the minimum required full well capacity of the array in order to neglect the skylight contribution and ensure stable operation of S-lidars. The proposed methodology is aimed at providing a rationale for design solutions to expand the applicability of this promising type of remote sensors.

Fluorimeter with Reflecting Optical Elements for Detecting of Simultaneous Reactions in a Microplate

This paper describes the autocollimation optical scheme of a fluorimeter that allows detecting different reactions from multiple wells of a microplate at the same time. The image focusing is implemented a spherical mirror that excludes the presence of background illumination and chromatic aberration. The operation of the fluorimeter is demonstrated by measuring a signal from the microplate with 96 and 384 individual wells.

Stimulatory Effects of Zinc Oxide Nanoparticles on Visual Sensitivity and Electroretinography b-Waves in the Bullfrog Eye

During the last decade, a large number of studies have focused on the development of nanomaterials for medical applications. Therefore, the present study was designed to evaluate the stimulatory effects of zinc oxide nanoparticles in the vertebrate visual system. Zinc oxide nanoparticles were synthesized and characterized through photoluminescence, ultraviolet (UV)-visible spectroscopy, field emission scanning electron microscopy and X-ray diffraction measurements. Furthermore, various electrophysiological recordings were obtained from the bullfrog eyecup preparations under various treatment conditions. Photoluminescence data showed a central peak at 386 nm while the UV-visible spectrum showed a sharp absorption band centered around 367 nm. Field emission scanning electron microscopy and X-ray diffraction measurements showed that synthesized zinc oxide nanoparticles have a polycrystalline wurtzite structure, with a round to oval shape and an average particle size of > 40 nm. Electroretinography (ERG) demonstrated that zinc oxide nanoparticles significantly increased the ERG b-wave amplitude in dark-adapted bullfrog eyecups and in the presence of background illumination. Zinc oxide nanoparticles also improved the visual sensitivity by 0.7 log unit of light intensity and shortened the duration of rhodopsin regeneration. Based on the results obtained, it was concluded that zinc oxide nanoparticles may be used to improve visual functions. The present study may add new dimensions to the biomedical applications of nanomaterials in eye research.

Zn 2+ differentially modulates signals from red- and short wavelength-sensitive cones to horizontal cells in carp retina

The effects of Zn 2+ were studied while recording intracellularly from L-type horizontal cells (LHCs) in the isolated, superfused carp retina. In darkness, 25 μM Zn 2+ hyperpolarized LHCs and potentiated responses of these cells to 500 nm flashes, but decreased those to 680 nm flashes. Zn 2+ did not change photopic electroretinographic P III responses. The differential modulation by Zn 2+ persisted when the Zn 2+-induced membrane hyperpolarization was compensated by lowering Ca 2+ concentration in the perfusate, but it was abolished in the presence of background illumination. Furthermore, the differential modulation no longer existed in the presence of bicuculline, suggesting the involvement of γ-aminobutyric acid A (GABA A) receptors. We speculate that the differential modulation may be a consequence of multiple changes caused by Zn 2+. Decreased glutamate release from the cone terminal by Zn 2+ results in a reduction of cone signals. Zn 2+ antagonizes GABA receptors on LHCs, leading to cone signal reduction. On the other hand, Zn 2+ may reduce the strength of the negative feedback from LHCs to cones by downregulating the activity of GABA receptors on the cone terminal, which causes a potentiation of LHC light responses. Cone- or wavelength-relevance of the Zn 2+-induced feedback strength change may account for the differential modulation.

WAVELENGTH DEPENDENCY OF THE MAXIMUM QUANTUM YIELD OF CARBON FIXATION FOR TWO RED TIDE DINOFLAGELLATES, HETEROCAPSA PYGMAEA AND PROROCENTRUM MINIMUM (PYRROPHYTA): IMPLICATIONS FOR MEASURING PHOTOSYNTHETIC RATES1

ABSTRACTThe influence of photoadaptive state on the spectral dependency of the maximum quantum yield for carbon fixation was determined for two red tide dinoflagellates, Heterocapsa pygmaea Loeblich, Schmidt, et Sherley and Prorocentrum minimum Pavillard. Cultures were acclimated to green, blue, red, and white light. The spectral dependency in the light‐limited slope of the photosynthesis–irradiance curves (α) was measured with carbon action spectra that, when divided by the spectrally weighted absorption coefficient, provided estimates of the maximum quantum yield (φmax) for carbon fixation. Values of φmax varied with wavelength within each culture condition as well as between different culture conditions. The degree to which the spectral dependency in φmax was influenced by the presence of photoprotective carotenoids and/or energy imbalances between photosystems I and II was assessed for both dinoflagellates. The impact of photoprotective pigmentation on the spectral dependency of φmax was most significant for cells grown under high light conditions reflecting the enrichment of diadinoxanthin. Energy imbalances between the photosystems was assessed by quantifying enhancement effects on spectral φmax in the presence of background illumination. Under our experimental conditions, enhancement effects on carbon action spectra were evident for H. pygmaea under nearly all growth conditions but were not detectable for P. minimum under any growth condition. We hypothesize that sensitivity to enhancement effects reflected differences in the structure of the photosynthetic machinery of these two peridinin‐containing dinoflagellates. While measurements of φmax are sensitive to the color of the light within an incubator, the relative impact on the spectral dependency of a was less than the wavelength dependency associated with the cellular absorption properties. Finally we used our data to validate an approach proposed by others to aid in the correction of photosynthetic measurements where the in situ spectral light field cannot be easily mimicked. The average error using this approach was 8%, which was significantly less than the error associated with ignoring the spectral dependency in α.

Effects of light stimuli on the release of dopamine from interplexiform cells in the white perch retina

Interplexiform cells are centrifugal neurons in the retina carrying information from the inner to the outer plexiform layers. In teleost fish, interplexiform cells appear to release dopamine in the outer plexiform layer after prolonged darkness that modulates the receptive-field size and light responsiveness of horizontal cells (Mangel & Dowling, 1985; Yang et al., 1988a, b). It has been proposed that interplexiform cells may also release dopamine upon steady illumination because horizontal cells' receptive fields shrink in the light (Shigematsu & Yamada, 1988). Here, we report the shrinkage of the receptive fields of horizontal cells seen in the presence of background illumination is not blocked by dopamine antagonists, indicating that dopamine does not underlie the receptive-field size changes observed during steady illumination. Flickering light, however, does appear to stimulate the release of dopamine from the interplexiform cells, resulting in a marked reduction of horizontal cell receptive-field size. Taken together, experiments on horizontal cells indicate that dopamine is released from interplexiform cells in the teleost retina after prolonged darkness and during flickering light, but that dopamine release from interplexiform cells during steady retinal illumination is minimal.

Light adaptation in cone photoreceptors of the salamander: a role for cytoplasmic calcium.

1. Light adaptation has been studied in isolated red-sensitive cone photoreceptors of the salamander, using suction pipette recordings of circulating current. 2. In the presence of background illumination, the response to incremental dim flashes became desensitized according to the Weber-Fechner law. The recovery phase of the flash response was accelerated significantly, although the time-to-peak was reduced only slightly, and for dim backgrounds the rising phase was unaltered. 3. The role of cytoplasmic calcium concentration, Cai2+, in mediating cone adaptation was investigated by minimizing light-induced changes in Cai2+, either by incorporating calcium buffer into the cytoplasm or by exposing the outer segment to low-Ca2+, 0-Na+ solution. Both treatments appeared to slow dramatically or even to eliminate the onset of light adaptation in the cone. 4. When the low-Ca2+, 0-Na+ solution was presented in darkness, responses to subsequent illumination were affected in a characteristic manner: (i) the response-intensity relation was steepened and shifted to lower intensities, (ii) the response to a step of light could be predicted by integration and compression of the flash response, and (iii) the flash sensitivity declined steeply as a function of background intensity. 5. After extended exposure of the cone to bright backgrounds, the sensitivity in darkness failed to return to its original level. The flash response kinetics were faster and more biphasic than for dark-adapted responses or for responses desensitized to a comparable degree by exposure to steady background illumination. 6. The results indicate that, in cones isolated from the pigment epithelium, the primary factor influencing the adaptational state of the cell is the cytoplasmic concentration of free calcium, but that at high intensities the effects of pigment bleaching are likely to be significant.

On the duplex nature of the skate retina

The skate retina contains only one type of photoreceptor which has rod-like properties in the dark-adapted state. In the presence of background illumination, the receptors take on cone-like properties, i.e., their photoresponses become much faster, are less sensitive to light, and can be elicited in the presence of very bright backgrounds. Although the transformation is an extremely slow process, the skate retina performs like that of animals with mixed, rod-cone retinae. In this report we examine some postreceptoral features which may relate to this remarkable behavior. We show, for example, that the skate photoreceptor terminals make two kinds of junctions (ribbon synapses and basal junctions) that appear analogous to the two kinds of synaptic contacts made by cone terminals in other species. Furthermore, two types of horizontal cells are seen in the skate retina. Although the light-evoked responses of these horizontal cells are similar, there are differences in their current profiles recorded under voltage clamp, and in the nature of their dendritic processes. We have also observed several unusual postreceptoral structural features that may have some bearing on the response properties of the skate retina. In addition, a comparison of the adaptive properties of the receptor potential with those of intraretinal responses (b-wave, PNR) reveals differences that suggest strongly the presence of a network adaptive mechanism originating within the proximal retina. The network mechanism appears to be controlled to a large extent by the extracellular concentration of potassium [K+]0; i.e., changes in [K+]0 affect significantly the sensitivities of the b-wave and PBR, but have little effect on responses arising in the distal retina.

Calcium regulates some, but not all, aspects of light adaptation in rod photoreceptors.

The role of calcium as a regulator of light adaptation in rod photoreceptors was examined by manipulation of the intracellular Ca2+ concentration through the use of the calcium ionophore A23187 and external Ca2+ buffers. These studies utilized suspensions of isolated and purified frog rod outer segments that retain their mitochondria-rich inner segments (OS-IS). Three criteria of the dark- and light-adapted flash response were characterized as a function of the Ca2+ concentration: (a) the time to peak, (b) the rate of recovery, and (c) the response amplitude or sensitivity. For all Ca2+ concentrations examined, the time to peak of the flash response was accelerated in the presence of background illumination, suggesting that mechanisms controlling this aspect of adaptation are independent of the Ca2+ concentration. The recovery kinetics of the flash response appeared to depend on the Ca2+ concentration. In 1 mM Ca2+-Ringer's and 300 nM Ca2+-Ringer's + A23187, background illumination enhanced the recovery rate of the response; however, in 10 and 100 nM Ca2+-Ringer's + A23187, the recovery rates were the same for dark- and light-adapted responses. This result implies that a critical level of Ca2+ may be necessary for background illumination to accelerate the recovery of the flash response. The sensitivity of the flash response in darkness (SDF) was dependent on the Ca2+ concentration. In 1 mM Ca2+-Ringer's SDF was 0.481 pA per bleached rhodopsin (Rh*); a background of four Rh*/s decreased SDF by half (Io). At 300 nM Ca2+ + A23187, SDF was reduced to 0.0307 pA/Rh* and Io increased to 60 Rh*/s. At 100 nM Ca2+ + A23187, SDF was reduced further to 0.0025 pA/Rh* and Io increased to 220 Rh*/s. In 10 nM Ca2+ + A23187, SDF was lowered to 0.00045 pA/Rh* and Io raised to 760 RhI/s. Using these values of SDF and Io for each respective Ca2+ concentration, the dependence of the flash sensitivity on background intensity could be described by the Weber-Fechner relation. Under low Ca2+ conditions + A23187, bright background illumination could desensitize the flash response. These results are consistent with the idea that the concentration of Ca2+ may set the absolute magnitude of response sensitivity in darkness, and that there exist mechanisms capable of adapting the photoresponse in the absence of significant changes in cytoplasmic Ca2+ concentration.

Effects of background illumination on the horizontal cell responses in the tiger salamander retina

Synaptic transmission between photoreceptors and horizontal cells (HCs) was studied in the flat-mounted isolated retinas of the tiger salamander. Background illumination expedited the rise time of the HC light response, and the HC response rise time (HCRRT) reached steady state about 2 sec after the onset of the background illumination. The change in HCRRT is probably responsible for the background-induced enhancement of the HC responses to short light stimuli. The amplitude of the HC responses to 100 msec light steps in the presence of background illumination was 2-5 times larger than that measured under dark-adapted conditions. Background illumination exerted little effect on the response rise time in cones and bipolar cells, and thus it caused no significant response enhancement in those cells. The background-induced change in HCRRT correlated closely with the rod voltage but not with the HC voltage. These results suggest that the background-induced change in HCRRT is probably mediated by postsynaptic events in HCs because no significant time course change is observed in photoreceptors and bipolar cells (which share the same synapses with the HCs). A suppressive rod action on the cone inputs in HCs may be responsible for modulating the HCRRT. By shortening the HCRRT, background illumination regulates the frequency response of the photoreceptor-HC synapse and alters the capacity of spatial resolution of retinal bipolar cells.

Electrical coupling between rods and cones in the tiger salamander retina.

Electrical coupling between rods and cones was studied in the salamander (Ambystoma tigrinum) retina by measuring the light responses and spectral sensitivities of rods and cones and by measuring the voltage responses from a rod to current pulses injected into a cone. A population of 10-20% of the photoreceptors exhibited a mixed-response waveform of the rod and the cone under dark-adapted conditions, and a response waveform closely resembled that of a cone in the presence of background illumination. Lucifer yellow injection revealed that these cells are morphologically identical to rods, and thus they are named rodcs. Dark-adapted rodcs exhibited a rod-like spectral sensitivity with a peak at approximately 520 nm that shifted to a cone-like spectral sensitivity with a peak at approximately 620 nm in response to background light (Purkinje shift). The voltage response of a rodc to a -1-nA current step injected into an adjacent cone is approximately 3.6 times larger than that of a rod to the same current step. These results indicate that there is a population of rods (rodcs) in the tiger salamander retina that is strongly coupled to the cones and that these cells allow significant mixture of rod and cone signals at the photoreceptor level.

Changes in response waveform of retinal horizontal cells during dark and light adaptation.

Changes in response waveform of retinal horizontal cells during dark and light adaptation were examined in the tiger salamander retina. In addition to sensitivity changes, the response waveform of HC was altered during visual adaptation: following bleaching or in the presence of background illumination, a transient depolarizing overshoot was observed at the cessation of the test flash. In contrast to the hyperpolarizing light responses, the depolarizing off-overshoots do not follow the standard threshold recovery time course during dark adaptation, neither do they obey Weber's law for increment thresholds during light adaptation. Simultaneous intracellular recordings from photoreceptors and HC revealed that the off-overshoot responses in light-adapted HC are probably originated from a population of cells in the photoreceptor layer which are strongly coupled with the cones.

Kinetics of the flash-induced electrochromic absorbance change in the presence of background illumination. Turnover rate of the electron transport. II. Higher plant leaves

The flash-induced electrochromic absorbance change (ΔA515) was measured in leaves of higher plants in the absence and presence of continuous monochromatic background illumination of different intensities and wavelengths. The variation of the amplitude of ΔA515 in background light was used to estimate the steady-state turnover time of the electron transport. In red light we obtained about 5 msec which was accounted for by the turnover of the linear electron transport. With far red background illumination or in the presence of the photosystem 2 inhibitor, DCMU, the steady-state turnover time tentatively assigned to photosystem 1 cyclic electron transport was much larger (≥100 msec).

Kinetics of the flash-induced electrochromic absorbance change in the presence of background illumination. Turnover rate of the electron transport. I. Isolated intact chloroplasts

We investigated the flash-induced electrochromic absorbance change, ΔA515, of isolated intact chloroplasts in continuous monochromatic background light of different intensities and wavelengths. From the variation of the amplitude of ΔA515 in background illumination the steady-state turnover time of electron transport was found to be around 100 msec and the slowest process could be assigned to a photosystem 1 driven cycle. The change of ΔpH induced by nigericin, ATP, or ADP did not modify substantially the turnover time.

Comparison of frequency characteristics of photopic and scotopic S-potentials in the carp.

Frequency characteristics of photopic and scotopic L-type S-potentials were studied in the carp retina, using either an impulse or a sinusoidal light input superimposed on a steady background light of various intensities. The photopic type responses were faster than the scotopic responses if their frequency characteristics were compared without background illumination. However, the difference was not absolute. Both types of responses became faster in the presence of background illumination. The stronger the background, the faster was the response. At relatively high background intensities, the response to a flash became diphasic due to the rebound effect which corresponds to a low frequency attenuation in the gain characteristics. The main difference between the two types of responses was found in the phase relation; the scotopic units showed more phase lag indicating an extra delay even under a condition in which the time course of their response was faster than that of the photopic units.

The responses of the retinal ganglion cells of the frog

Three groupsofunitswere recorded from theretinaof Rana esculenta. These were: (a)Units which responded to a square wave modulated light stimulus and these were of three types: ON units, ON-OFF units and OFF units. Stimulus-response curves for both a stimulating central spot and an annulus were constructed and the effects of increasing the background illumination on these curves were investigated. (b) Movement sensitive neurones. Units were recorded which responded preferentially to slow movement of the stimulus while some units responded to movement of the stimulus along one particular axis only (axis sensitive neurones). (c) Spontaneously discharging units whose discharge frequency was affected by the presence of background illumination. In one group, the discharge frequency fell whilst in the other group, the discharge frequency increased in the presence of background illumination.

A late component of flash-evoked potentials in the cat's optic chiasma and superior colliculus: its appearance due to background illumination

Flash-evoked potentials (FEPs) in the cat's optic chiasma and superior colliculus were recorded under the following two conditions: complete darkness and background illumination. Special attention was paid to a specific late component of FEPs and comparison in the behavior of the late component was made between the two conditions. It was found that a late component of FEPs in the optic chiasma appeared in the presence of background illumination while it was not observed under the condition of complete darkness. A corresponding late component of FEPs was detected in the superior colliculus. The late component might be supposed to be driven from a class of W-cells in the cat's retina.

Effects of background illumination on the receptive field organization of single cortical cells in area 18 of the immobilized cat.

Averaged responses to photic stimuli were recorded from single cortical cells in a circumscribed small region of the nonstriate area (F0-3 and L2-3 in H-C coordinates) of cats. The retinas were stimulated monocularly by various stimuli, such as a diffuse light flash, an intermittent light spot, or a moving light slit, of different sizes and shapes under various conditions of dark and light adaptations. Studies were made on a total of 86 units.1) The cortical cells had relatively large receptive fields, usually about 20°C×20°C. They were responsive to a diffuse flash, and responsiveness was influenced by background illumination.2) The responses of 27 units to a moving slit were suppressed and those of 13 units were facilitated by background illumination.3) Four units showed a reversal of the preferred direction.4) Three units that had no preferred orientation in the dark developed it in the presence of background illumination.5) The response patterns of 39 units were unaltered by background illumination.

Energy- and electron-transfer systems in algal photosynthesis. I. Actions of two photochemical systems in oxidation-reduction reactions of cytochrome in Porphyra.

Abstract 1. 1. The light-induced oxidation-reduction reactions of Porphyra-cytochrome-553 in the living thalli and isolated particles of three species of Porphyra ( P. yezoensis, P. tenera and P. suborbiculata ) were studied. 2. 2. The action spectrum of cytochrome oxidation had a maximum at 685–690 mμ. In the presence of background illumination of 680–700 mμ, photochemical reduction by a second light of wavelengths shorter than 650 mμ was observed. The maxima of the action spectrum for the reduction were located at 565 mμ and 615–620 mμ. This reduction of cytochrome by light absorbed by phycobilins was inhibited by 5-bromo-3-isopropyl-6-methyluracil 3(4′-chlorophenyl)-1,1-dimethylurea, 2-chloro-4,6-bis-(ethylamino)-1,3,5-triazine, 3,4-dichloropropionanilide and o -phenanthroline. These substances neither inhibited the light-induced oxidation of cytochrome, nor the dark reduction of cytochrome. In the presence of these substances, light-induced oxidation of cytochrome was observed on illumination of the light absorbed by phycobilins as well as by chlorophyll a . 3. 3. Effects of incident light intensity, dark period, inhibitors, gas phase, etc. on the rates and the steady-state change of the cytochrome reactions were investigated. 4. 4. Comparison of the observed amounts of cytochrome change and the amounts of cytochrome-553 extracted from the thalli indicated that the major portion of the cytochrome-553 present in the thalli changed its oxidation-reduction state on illumination. 5. 5. The quantum yield of cytochrome oxidation by light absorbed by chlorophyll a was about 0.14. In the presence of 5-bromo-3-isopropyl-6-methyluracil, quantum yields with light absorbed by chlorophyll a and with light absorbed by phycobilins were about 0.15 and 0.11, respectively.