Low Illumination Conditions Research Articles

Design and Characterization of 1×128 In0.53Ga0.47As/InP Photodetector Linear Array with Improved Optical Sensitivity and Shunt Resistance

An InGaAs/InP heterojunction phototransistor (HPT) 1×128 one dimensional array chip with an improved optical sensitivity and shunt resistance has been designed and characterized for the detection of a low light signal intensity. We also present epitaxial structures and an equivalent model for optimizing the optical gain and shunt resistance characteristics. The device operation mechanism and experimental results are discussed. The experimental results show that our device has an optical sensitivity of 46 A/W, which is significantly higher than that of a conventional PIN photodetector with the same light absorbing area. This high sensitivity originates from the optical gain-enhanced device structure. The typical optical gain is approximately 94, indicating that HPTs are 94 times more sensitive than PIN photodetectors. The proposed HPT also has over 100–200 of kΩ shunt resistance and a high optical sensitivity under a low illumination condition, which is sufficient for effective signal conversion through a trans-impedance amplifier circuit. In addition, we also discuss a high-power optical-stress-induced dark current reduction effect that is similar to a thermal-annealing-induced dark current reduction effect. of An optical-stress-induced dark current reduction of approximately 1 order is observed in our experiments.

A Review of Technologies for Studying Visual Perception under Low-Illumination Conditions

A method for replicating low-illumination scenes with photography is critical to studying and understanding how people perceive poorly lit environments. The method can be used for post hoc accident analyses as well as ad hoc evaluations of safety in dark areas. The ability to photographically replicate conditions at such scenes for subsequent scrutiny is useful for accident reconstruction and safety analysis. This paper reviews the past, present and future of these methodologies from film photography to digital photography to digital video, including high-definition and high-definition 3D formats. Pros and cons of various methods and technologies are discussed.

Vigamox: How good is its self-preservation?

and is not dependent on the calculation method. In clinical practice, the transition zone is known to cause visual disturbances at low-illumination conditions, especially when localized light sources are present. The severity of these symptoms is dependent on the actual pupil diameter and its relation to the functional optical zone of the cornea and on the amount of dioptric difference between the central (treated) and peripheral (untreated) cornea. However, these visual effects result from aberrations originating from the actual corneal geometry, which cannot be adequately approximated by low-order (eg, up to the 4th order) Zernike polynomials. We strongly believe that in postoperative eyes, especially after correction of high refractive errors, the optical system should be divided into 2 parts: the central part, including the uniform part of the cornea, that can be measured using commercial instruments and approximated with Zernike polynomials and the peripheral part, involving the transition zone and the untreated cornea, which is not suitable for sharp image formation. Conventional optical analysis of postoperative eyes should be restricted to pupil diameters including the central part only. It is therefore suggested that the transition zone should not interfere with the sampled pupil if a limited set of Zernike polynomials are used to approximate the wavefront. Furthermore, the statistical evaluation of isolated Zernike coefficients (eg, C4 ) may lead to erroneous conclusions because they exhibit high intrasubject variability and because their true impact may be balanced by other higher-order coefficients, possibly neglected at wavefront reconstruction.

夜間走行を想定した低照度環境下における物体の認識率と認識時間の年代差

To determine the differences in the visual characteristics between people in their twenties and those in their sixties under low-illuminance conditions, assuming night driving conditions, we measured the recognition ratios and recognition time of subjects by changing the presentation position, the size, the luminance, and the contrast of a Landolt. A Landolt is the circle which is cut off like alphabet “C”, and is used as the eye testing chart. By analyzing the data, we found that the recognition ratio of both age groups increased as the background luminance increased with a constant contrast, or as the contrast increased with a constant background luminance.

A new approach for image enhancement applied to low-contrast–low-illumination IC and document images

Machine vision has become an integral part of today’s electronic industry. Digital images capturing low contrast and low illumination conditions often cause serious problems in optical character recognition systems. This paper uses poorly digitized images of integrated circuits and documents to demonstrate the effectiveness of using the Generalized Fuzzy Operator with Histogram Equalization and Partially Overlapped Sub-Block Histogram Equalization in reducing background noise and increasing the readability of text by contrast enhancement.

Far‐infrared absorption due to shallow acceptors in semi‐insulating GaAs in dependence on EL2 bleaching

AbstractFar‐infrared absorption in semi‐insulating GaAs due to electronic transitions of shallow acceptors was measured in dependence on conditions of bleaching the GaAs intrinsic defect EL2. The far‐infrared spectra were compared with the results of near‐infrared spectroscopy of EL2 fundamental state. It was found that under conditions of low intensity illumination the neutral acceptors can coexist with the neutral EL2 defect. The model is proposed which explains the effects that were not observed previously, such as depopulation of neutral shallow acceptors at low temperature, and the charge redistribution between different shallow acceptor levels at increasing temperature for the samples co‐doped with zinc and carbon. It is shown that far‐infrared spectroscopy is suitable for quantitative evaluation of the shallow acceptor concentration in GaAs material. The corresponding calibration factors are given. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Different Patterns of Parental Effort During Chick-Rearing by Female and Male Thick-Billed Murres (Uria Lomvia) at a Low-Arctic Colony

Abstract Using temperature loggers and radio telemetry, foraging and brooding behaviors of female and male Thick-billed Murres (Uria lomvia) were measured during chick rearing at the Gannet Islands, Labrador, to quantify parental roles during this crucial stage of reproduction. We recorded 2,725 foraging dives by 10 females and 7 males during 1,416 bird-hours of monitoring. Our study birds made between 21 and 107 dives per day between 0327 and 2220 hours, with 54% of females' dives and <1% of males' dives occurring in conditions of low illumination between sunset and sunrise. Males foraged mostly at midday and, overall, made longer and presumably deeper dives (mean duration 116.2 ± 37.6 s) than females (mean duration 84.1 ± 46.0 s). The maximum dive duration recorded was 240 s. Final dives of foraging trips were inferred to include dives during which chick meals (∼95% by number daubed shanny [Lumpenus maculatus]) were obtained. Those dives (mean duration 134.0 ± 36.1 s) and dives in final diving bouts prior to return to the breeding site (mean duration 139.1 ± 40.2 s) averaged longer than other dives, and longer in males than in females, but there was no difference between the sexes in their daily frequency. The modal travel time from the last dive in a feeding trip to arrival at the breeding site was 8 min (no difference between sexes), which represents a maximum travel distance at 65 km h−1 of 8.7 km, suggesting that foraging occurred close to the colony. Females spent 9 h day−1 (38% of day, mostly diurnal brooding) at breeding sites whereas males spent 16 h (67% of day, mostly nocturnal brooding). Taken together, these data indicated drastic differences in patterns of foraging and brooding behavior between male and female Thick-billed Murres, but suggest that individual and intercolony variation were also significant.

Electro-Optic Sensors to Aid Tower Air Traffic Controllers

Background: Tower air traffic controllers separate aircraft to assure safety and expedite the flow of traffic. During poor visibility (e.g., fog) the aircraft landing and departure rate decreases significantly which can result in flight delays. The purpose of this study was to investigate the feasibility of using electro-optic sensors to enhance tower controller visual capabilities during poor atmospheric or low-illumination conditions. Methods: Day and nighttime visible, mid-and long-wave infrared digital imagery were collected at an airfield. To validate the collected imagery, a human-in-the-loop analytic model was used to predict an average military observer's visual discrimination of a target on the airport surface. Results: The field data collection and model results found that electro-optic sensors, in particular long-wave infrared, improved operators nighttime detection, recognition, and identification of targets on the airfield surface. Conclusions: Actual or potential applications of this research include integrating electro-optic sensors into the tower to improve aircraft movement during poor visibility.

Increased anxiety-related behavior in mice deficient for metabotropic glutamate 8 (mGlu8) receptor

Pre-synaptic metabotropic glutamate (mGlu) receptors modulate neuronal excitability by controlling glutamate and gamma-aminobutyric acid (GABA) release. The mGlu8 receptor is predominantly found in pre-synaptic terminals and its expression is highly restricted. To study the role of this receptor, mGlu8 receptor-deficient mice were generated. Here we report that naïve mGlu8 receptor-deficient mice showed increased anxiety-related behavior in the elevated plus maze in low illumination conditions (red light). Open arm avoidance and risk assessment behavior were both significantly increased in mutant mice. Increased stressfulness of the testing conditions abolished this behavioral difference. Fluorescent light or prior restraint stress decreased the open arm activity of wild-type mice, while the open arm activity of mutant mice was essentially unaffected, leading to similar values in both strains. The total number of arm entries or closed arm entries was not significantly different between strains, indicating that the lack of mGlu8 receptor does not affect locomotor activity. No gross behavioral changes, or changes in the function of the autonomic nervous system or somatomotor systems were observed in mutant mice. Moreover, no significant differences in seizure susceptibility were detected between strains. Our results suggest that mGlu8 receptor may play a role in responses to novel stressful environment.

Behavioral profile of rats submitted to session 1-session 2 in the elevated plus-maze during diurnal/nocturnal phases and under different illumination conditions

The elevated plus-maze (EPM) model usually employs nocturnal species (e.g. rats and mice) and the tests are almost exclusively performed during the diurnal phase (lights on), leading some laboratories to perform experiments with animals under a reversed light cycle to overcome this problem. However, it is questionable whether the artificial reversal of the light cycle for short periods guarantees modifications in all the physiological parameters found in normal subjects. The present study evaluated the session 1-session 2 (S1-S2) EPM profile in rats during their normal diurnal or nocturnal phase using different illumination conditions. Prior exposure to the EPM decreased open arm exploration for all groups in S2, regardless of the circadian phase and illumination condition; however, this behavior was decreased in subjects tested during the nocturnal phase, when compared to the diurnal phase. Risk assessment (RA) behavior was decreased under high illumination for both circadian phases in S1 and increased in the first minute of S2, when compared to the last minute of S1. Although open arm exploration and RA behavior were decreased under high illumination, when compared to low illumination conditions in both circadian phases, general locomotor activity was only decreased during the nocturnal phase. The results are discussed in terms of circadian variations in the behavioral profile and as a possible source of variability in pre-clinical models of anxiety.

Amorphous silicon phototransistor as nonlinear optical device for high dynamic range imagers

An amorphous silicon bulk barrier phototransistor is studied as a basic element for the pixel of high dynamic photosensor arrays. The device is an n-i-/spl delta/p-i-n structure whose optical gain shows a nonlinear dependence on the illumination intensity. For each applied bias voltage, a quasi-hyperbolic decrease of the optical gain as a function of the incident power is found. This behavior can be explained taking into account both the material characteristics (defect distribution, dopant concentration), and the structure properties. Our measurements lead to a minimum detectable signal of about 0.7 nW/cm/sup 2/ independently on the applied voltage, making the device suitable for low illumination conditions. On the other hand, by increasing the input power up to 35 mW/cm/sup 2/, we did not find saturation of output photocurrent leading to a dynamic range of at least of 120 dB. This value can be further increased by using as basic cell of the pixel the phototransistor and a resistor connected between the voltage supply and the collector electrode.

DIFFERENT PATTERNS OF PARENTAL EFFORT DURING CHICK-REARING BY FEMALE AND MALE THICK-BILLED MURRES (URIA LOMVIA) AT A LOW-ARCTIC COLONY

Abstract Using temperature loggers and radio telemetry, foraging and brooding behaviors of female and male Thick-billed Murres (Uria lomvia) were measured during chick rearing at the Gannet Islands, Labrador, to quantify parental roles during this crucial stage of reproduction. We recorded 2,725 foraging dives by 10 females and 7 males during 1,416 bird-hours of monitoring. Our study birds made between 21 and 107 dives per day between 0327 and 2220 hours, with 54% of females' dives and <1% of males' dives occurring in conditions of low illumination between sunset and sunrise. Males foraged mostly at midday and, overall, made longer and presumably deeper dives (mean duration 116.2 ± 37.6 s) than females (mean duration 84.1 ± 46.0 s). The maximum dive duration recorded was 240 s. Final dives of foraging trips were inferred to include dives during which chick meals (∼95% by number daubed shanny [Lumpenus maculatus]) were obtained. Those dives (mean duration 134.0 ± 36.1 s) and dives in final diving bouts pri...

低照度レベルにおける周辺視野でのカテゴリカル色知覚の特性

We measured the characteristics of categorical color perception in the peripheral visual field under low illumination conditions and compared with those under 2000 lx illuminance in our previous study [J. Illum. Engng. Inst. Jpn. 83 (1999)]. OSA color chips, simulated by the LCD projector, were presented at the fovea (0 deg), at eccentricities of 30 and 50 deg in the nasal visual field, and at 30, 50, 70, and 80 deg in the temporal visual field. A large gray surrounding field, made with a hemisphere, was illuminated by D65 fluorescent lamps at 5 or 0.1 lx. The stimulus was subtended 4 deg and presented for 3 s. The observer reported the color appearance of the stimulus with 1 of 11 basic color terms. The response of color categories at the fovea showed almost no difference to the 50 deg temporal under 5 lx illuminance. Beyond the 30 deg nasal and the 70 deg temporal, the response of achromatic categories increased, and that of green, purple, and pink categories decreased. Under 0.1 lx the response of achromatic categories dominated. Our results show that categorical color perception in the central visual field is constant across a large visual area under a wide range of illumination conditions.

Germination of Important East African Mountain Forest Trees

The germination ecology of 25 tree species of the montane forests of Mount Kenya (Kenya) was studied. Five different germination strategies could be observed under similar ecological conditions. Pioneer species often required mechanical scarification before germinating, but did not react to different light conditions. Many species germinated without scarification, but were strongly influenced by the duration of seed storage. An equally high number of species positively reacted to bright illumination. Primary forest species mainly germinated under low illumination or dark conditions and showed a very short seed viability. The storage temperature did not influence viability, whereas the maturity of the seeds collected had a considerable influence on the germination success.

Evaluation of two new soft contact lenses for correction of presbyopia: the Focus Progressives multifocal and the Acuvue Bifocal

The clinical performance of Focus Progressives multifocal contact lenses and Acuvue Bifocal contact lenses was evaluated in a group of 42 presbyopes, with equal numbers of individuals having low, medium, and high spectacle add requirements. Following visual performance assessment with an optimal sphero-cylinder spectacle refractive correction, each individual wore each of the two types of contact lenses in successive random order. Each type of lens was used in a daily-wear mode for a period of 7 to 12 days, with follow-up and/or refitting visits occurring after 2 to 5 days, and again after 4 to 7 days of attempted wear. Testing for all three forms of refractive correction encompassed Snellen acuities at distance and near, Bailey-Lovie acuities under high and/or low ambient illumination conditions at near, intermediate, and far viewing distances, stereoacuity, a timed visuomotor task (needle threading), apparent glare/flare, and the nearwork range of subjectively clear binocular vision. The contact lenses also were evaluated for handling, comfort, distance and near ghosting, subjective visual quality, acceptability for common tasks (e.g., using a phone directory), and personal preferences. As might be expected, distance and near acuity, stereoacuity, and visuomotor task performance were somewhat better with sphero-cylinder spectacle correction than with either of the two types of contact lenses. However, several performance differences between the multifocal and bifocal lenses were noted. The Focus Progressives lenses provided significantly better distance acuity under both high and low illumination conditions, and received significantly higher ratings for visual quality (overall and at distance), comfort, and handling. The Focus Progressives lenses were preferred 5:1 over the Acuvue Bifocal lenses. No differences existed between the lenses with respect to near visual acuities, the perceived quality of the near vision, the nearpoint binocular range, stereoacuity, or the acceptability of vision for common nearwork tasks. The results suggest that although both types of lenses afford presbyopes a viable alternative to spectacles, the Focus Progressives lens is superior in many ways to the Acuvue Bifocal lens.

Photomineralisation of 4-chlorophenol sensitised by TiO 2 thin films

The results of a study of the oxidative mineralisation of 4-CP by oxygen, sensitised by thin films of Degussa P25 TiO 2, are reported. The films are used under conditions in which the kinetics of photomineralisation are independent of mass transfer effects and stable towards repeated irradiation. Using a TiO 2 film, the process goes through the same mechanism as a TiO 2 dispersion, generating the same intermediates, namely: 4-chlorocatechol and hydroquinone. The kinetics of photomineralisation show clear differences between a TiO 2 film and a dispersion. With TiO 2 films the initial rate of photomineralisation is strongly dependent upon photocatalyst loading, (units; g dm −3) reaching a distinct maximum, which appears to be associated with the formation of a monolayer of aggregated particles – the diameter of the aggregated particles is estimated as 0.44 μm. A simple 2D model is presented to help illustrate the features of such a system. With TiO 2 dispersions the rate usually reaches a plateau at ca. 0.5 g dm −3 of TiO 2. For TiO 2 films the initial rate depends directly upon the incident light intensity, implying that the photocatalytically active particles are under low illumination conditions, partially shielded by the other particles making up each aggregated particle. In contrast, with TiO 2 dispersions R i depends upon I 0.64, implying that the different light intensities used spanned both the high ( R i ∝I 1/2) and low ( R i ∝I) intensity kinetic regions. The kinetics of photomineralisation of 4-CP, sensitised by TiO 2 films obey the same Langmuir–Hinshelwood expressions as found in most semiconductor photocatalyst work conducted with TiO 2 dispersions. However, in a study of the variation R i as a function of [4-CP] and [O 2] the values for the maximum rates were larger, and those for the apparent Langmuir adsorption coefficients were smaller, than those found for TiO 2 dispersions.

Light/dark cycles in the growth of the red microalga porphyridium sp

The effect of light/dark cycles on the growth of the red microalga Porphyridium sp. was studied in a tubular loop bioreactor with light/dark cycles of different frequencies and in two 35-L reactors: a bubble column reactor and an air-lift reactor. Photon flux densities were in the range of 50 to 300 μE m-2 s-1, and flow rates were 1 to 10 L min-1. Under conditions of low illumination and high flow rates, similar results were obtained for the bubble column and air-lift reactors. However, higher productivities-in terms of biomass and polysaccharide-were recorded in the air-lift reactor under high light intensity and low gas flow rates. The interactions of both photosynthesis and photoinhibition with the fluid dynamics in the bioreactors was taken as the main element that allowed us to interpret the differences in performance of the bubble column and the air-lift reactor. It is suggested that the cyclic distribution of dark periods in the air-lift reactor facilitates better recovery from the photoinhibition damage suffered by the cells. Copyright 1998 John Wiley & Sons, Inc.

Assessment of high and low contrast visual acuity after photorefractive keratectomy for myopia.

Our aim was to assess visual acuity using standardized charts and illumination conditions after photorefractive keratectomy. High and low contrast visual acuity were measured on Bailey-Lovie logarithm of the minimum angle of resolution (LogMAR) charts under high and low illumination conditions on 105 photorefractive keratectomy patients who had been treated with the Summit (N = 60) or the VISX (N = 45) excimer laser. Best corrected visual acuity was reduced in the treated eye compared with the untreated control eye under all test conditions, with the greatest differences under conditions of low contrast and low illumination. Reduction of acuity under low contrast and low illumination was related to small optic zone sizes and steep ablation edge profiles found in Summit-treated eyes. In the VISX-treated eyes, high contrast acuity was reduced in the presence of central topographical irregularities, subepithelial haze, and higher myopic corrections. Testing conditions such as those described here may be useful in quantifying vision degradation in suboptimal viewing conditions and among patients with vague complaints.

Quantal processing of visual information in the brain

In order to test if vision is a continuous processing system that analyses information immediately after it arrives at the retina or a discontinuous system that accumulates information and periodically analyses a data quantum, the time required by 38 healthy adults to solve simple visual tasks was accurately quantified. The main finding of the present study was that the processing time for visual tasks is always a multiple of a basic unit whose duration was 30–40 ms. Present data support the hypothesis that visual information is processed in the brain with a discontinuous flow of discrete-time quanta. Data suggest two processing ways for the visual system, one that with a high time-resolution (30–40 ms) operates under high-illumination conditions, and the other that with a low time-resolution (100–120 ms) is put into operation in low-illumination conditions.

Relative effects of turbidity and light intensity on reactive distance and feeding of an estuarine fish

Gulf killifish Fundulus grandis were allowed to prey on daggerblade grass shrimp Palaemonetes pugio in clear water with bright light, turbid water containing bentonite clay, and clear water treatments where the light intensity was adjusted to match that in the bottom of the turbid tanks. Significantly fewer shrimp were consumed in the turbid tanks relative to the clear and shade treatments where predation rates did not differ significantly. The results suggested that the influence of suspended particles on predation rates was a consequence of light scattering and was not related to a decrease in light intensity. Reactive distances were subsequently determined for human observers viewing a small target in elongated tanks containing turbid water (7.3–60.5 NTU) under conditions of both low (8-10 μE m−2 s−1) and high illumination (153–1249 μE M−2 s−1). Reactive distance was primarily governed by turbidity while light intensity had little influence except at low turbidities. The shape of the relationship between reactive distance and turbidity for humans resembled curves reported for a variety of fish species.