Glare Angle Research Articles

Optical instrument for the study of time recovery from total disability glare vision.

Disability glare is defined as the loss of contrast sensitivity of the retinal image due to intraocular straylight originated from the presence of an intense and broad bright light in the field of vision. This loss of vision can range between vision loss at high spatial frequencies or total temporal blindness. If the extreme case occurs, the recovery time is crucial in night driving conditions or those professional activities in which maximum visual acuity is required at any moment. The recovery time depends mainly on the intensity and glare angle of the light source, ocular straylight, and the photoreceptor response at the retina. The recovery time can also be affected by ocular pathologies, aging, or physiological factors that increase ocular straylight. The aim of this work is to develop a new optical instrument based on psychophysical methodology as well as to investigate the recovery time from total disability glare (photobleaching) as a function of the contrast of the visual target and the glare angle of the source in healthy volunteers. Results showed significant exponential correlation between recovery time and contrast of the visual target and linear correlation between contrast sensitivity and the glare angle. Those findings allowed to obtain an empirical expression to compute the recovery time required to restore contrast sensitivity baseline vision after photobleaching. Finally, a statistical dependence of recovery time with age was found for short glare angles that disappear as the glare angle increases.

Electronic System of Counteraction to Laser Means of Location and Destruction

The work is devoted to the development of a device for counteracting laser means of location and destruction. The analysis of data from open literature on similar systems and technologies have been performed. Theoretical calculations of the effectiveness of protecting the human eye or optical device from laser damage with various types of protection have been carried out.Laser technology has been used by the military since the mid-1950s. The military uses lasers in systems of direct thermal destruction of the object, pointers, detection systems of snipers, systems of interference with snipers, rangefinders, etc. In the late 1970s and early 1980s, military-experimental blinding self-propelled complexes were created in the USSR. The development of laser and computer technology has significantly reduced the dimensions of the devices, as well as their cost. Now such systems are widely used in combat operations.On the other hand, there is a challenge to counteract such complexes. Systems are needed that can hide optical systems from detection, as well as prevent them from being destroyed by blinding complexes.The purpose of the work is to develop a system to counteract the laser complexes of location and damage. Its task is to hide the optical device from laser scanning systems and prevent the damage of the optical device or the human eye by blinding laser radiation.The relevance of this article is due to the need to create new and improve existing electronic systems to counteract the laser means of location and destruction. Despite the fact that studies in this area are conducted for more than one year, the choice of such systems is very small.To minimize the probability of detecting an optical device, mechanical means of narrowing the beam glare angle are commonly used. One example is cellular blinds. The length of one cell must be much higher than its diameter. The surface of the cell tubes should be blackened to reduce the reflection of light rays. For more accurate narrowing of the flare angle, it possible to set several cellular blends in a row - the number depends on their optical qualities.Optical means include optical filters that absorb, block, or scatter the infrared spectrum, because laser detectors of optical devices are in it. Such a filter should be placed on the optical sight between the lens and the lens hood. After all, it reflects the infrared rays, working as a mirror. Therefore, this angle of reflection should be reduced by all means, in particular tubular blinds, as described above.However, these methods cannot fully protect the operator of the optical observation device from the powerful laser radiation directed to the device. To solve this problem, you can use technology that completely blocks the optical channel when you receive high-power laser radiation on an optical device. The radiation sensors respond to the high-power laser radiation of the destruction and transmit the signal to an electronic circuit, which turn on a liquid crystal filter that covers the optical channel. Under the influence of electric current, liquid crystals become a special structure in such a way that infrared radiation does not pass through the filter. When the radiation is lost, the electronic system returns the liquid crystal filter to a transparent state.The power impulse of laser means of location and destruction can significantly damage a person's vision, and at large lens diameters or at short distances between a these means and an observer, a person may lose it completely. The same applies to light-sensitive arrays of optoelectronic devices. As shown in the calculations, the maximum permissible level of radiation energy density in unprotected optics is much lower than the radiation energy density provided by laser means of location and destruction.The opto-electronic protection system reduces the time of laser radiation to the human eye or the light-sensitive matrix of the optoelectronic device to safe limits. As shown by the calculations, this increased the maximum allowable level of radiation energy density above the level provided by power lasers for their entire range of use and lenses with diameters from 24 mm to 100 mm, which will protect them from the blinding effect of laser means of location and destruction.

Local susceptibility of the retina, formation and duration of afterimages in the case of Class 1 laser products, and disability glare arising from high-brightness light emitting diodes

According to the new European Directive on Artificial Optical Radiation, the employer has to determine the exposure and the assessment of risks and in addition, he shall give particular attention to any indirect effects, such as temporary blinding, when carrying out the risk assessment. Up to now, secondary effects such as temporary blinding have not been regarded in safety standards and there exist but a few data on this topic as far as modern artificial high-brightness (HB) light sources are concerned. Temporary blinding from a Class 1 laser and a white high-brightness light emitting diode (LED) in the visual field has been investigated as a function of the glare angle and of the amount of the emitted optical energy. In an extensive study with a He-Ne laser at a wavelength of 632.8 nm, it was found that even for output powers of 5 to 30 μW, the tested subjects reported intense glare effects and felt uncomfortable due to the high brightness. The durations of afterimages ranged up to 300 s and have been measured as a function of the angle between the line of sight and the laser beam direction for an exposure duration up to 10 s. The maximum afterimage duration was found for the foveal pit. In the case of a HB-LED, the investigated power level was between 0.0045 and 3.96 mW measured in a 7 mm aperture, and the exposure durations were limited to 20 s. The annoyance duration, i.e., the capability to read after an irradiation, was between about 10 and 25 s and relatively independent of the applied power, but interindividually different. As a result of the investigations instructions for users of Class 1 lasers and HB-LEDs should be given in order to take into account temporary impairment of visual tasks due to dazzling and glare effects which are accompanied with relatively long lasting afterimages.

Glare and contrast sensitivity before and after Nd:YAG laser capsulotomy

The benefits of Nd:YAG laser capsulotomy on visual performance were evaluated in 13 patients with after-cataract following extracapsular cataract extraction. Besides clinical evaluation we measured: visual acuity, letter contrast sensitivity with and without the presence of a circular glare source (glare angle: 8 degrees). Finally, the patients were asked to evaluate their subjective glare problems. In all patients, visual acuity had decreased markedly compared to measurements 2 months after cataract surgery. Before capsulotomy we observed impaired letter contrast sensitivity and increased intraocular light scatter compared to normals. Following capsulotomy, VA and contrast sensitivity both improved by a factor of 2. The subjective glare problems diminished, although most patients showed minor decreases in intraocular light scatter. The limited glare induced loss of letter contrast sensitivity, present before capsulotomy, remained after treatment. Our study indicates that after-cataract impairs resolution and contrast sensitivity without necessarily causing a marked increase in light scatter as measured at a large angle.

Light scatter in the normal young, elderly, and cataractous eye demonstrates little wavelength dependency.

The purpose of the study was to investigate whether light scatter in normal young, elderly, and cataractous eyes exhibits significant wavelength dependency. Straylight was quantified by calculating light scatter factors (LSF's) based upon the reduction in contrast sensitivity produced by a glare source. The angle of the glare source relative to fixation was varied (3.25 to 26 degrees), as was its wavelength (460 to 660 nm). LSF's increased as a function of age an especially in the presence of media opacities. However, the relation between LSF and glare angle remained approximately the same for each group. Our results suggest that wavelength dependency in normal young, elderly, or cataractous eyes is rather unimportant relative to other factors.

Intraocular light scatter in normal vision loss with age

Comparisons of contrast sensitivity functions between young (20–30-yrs) and old (60–70-yrs) subjects show that, on the average, the older subjects require about twice the contrast as the younger to detect gratings of high and intermediate spatial frequencies. The question of the source of this visual loss is addressed by calculating the loss of contrast due to intraocular light scatter. This, in turn, is estimated using measurements of disability glare as a function of glare angle and observer age. It is shown that the measured loss of vision with age is consistent with the hypothesis that it is due to increased intraocular light scatter.

Nighttime legibility of traffic signs: conditions eliminating the effects of driver age and disability glare

The effects of observer age and environmental glare on nighttime legibility of traffic signs were investigated in two field experiments with the subjects driving or riding in a car towards a sign. Experiment 1 showed that equating older and younger subjects in terms of their low luminance/high contrast visual acuity resulted in elimination of any age effects on legibility. Furthermore, the presence of a glare source with an illuminance of 0.17 or 0.017 lux offset 2° from the sign legend improved legibility distance significantly. The results of Experiment 2 indicated that a glare source with an illuminance of 0.0098 lux had no effect on legibility when presented at an offset angle of 1.5° or 0.6°, but it had a significant detrimental effect at an offset angle of 0.2°. The present findings suggest that (1) the usually observed age-related performance decrement on nighttime legibility tasks is the result of visual-acuity deficits, and not shortcomings in information-processing ability; (2) legibility is relatively unaffected by glare, unless the glare angle is very small or glare level very high; and (3) glare sources positioned outside of the fovea might improve nighttime legibility performance under certain conditions.

Effect of glare angle on the brightness function for a small target

The effect of a small, intense glare source (118 dB) on the brightness of a small target was measured as a function of glare angle and target luminance. Using an interocular matching procedure the observer adjusted the brightness of a match field (seen by the right eye) to equal the depressed brightness of the target under the influence of the glare (seen by the left eye). Glare angle was varied from 13.2 to 274 min. Target luminance was varied from 58 to 93 dB relative to 10 −10 Lambert. For all target luminances, the apparent brightness of the target was shown to be directly related to the logarithm of the glare angle. At a given glare angle the brightness grows as a power function of the luminance, and the exponent of the power function is largest when the glare angle is smallest. In double logarithmic coordinates the functions relating the luminance of the match field to that of an equally bright target become straight lines that converge at a common point, equal to the luminance of the glare (118 dB).

Rapid changes in foveal sensitivity resulting from direct and indirect adapting stimuli.

It is well known that an intense stimulus imaged upon one part of the retina has the capacity to reduce the sensitivity of a spatially remote area. Controversy has long existed regarding the interpretation of this effect—whether it is the result of stray light in the eye or of some kind of indirect inhibition. A method first used by Crawford makes it possible to measure sensitivity changes associated with the onset of an adapting stimulus by determining the threshold of a test flash at various times near the onset of the adapting stimulus. Two adapting stimuli were used alternately within each experimental session. The “direct” adapting stimulus was concentric with and larger than the foveal test flash; the “indirect” or glare-adapting stimulus was presented at a glare angle of 18°. When the luminances of these radically different adapting stimuli were suitably adjusted, the resulting foveal sensitivity changes, as a function of time after onset of adapting stimulus, were found to be identical. The equivalence held when the luminance of each adapting stimulus was reduced 1 log unit. The results are interpreted as favoring the stray-light hypothesis.

A brightness difference threshold meter for the evaluation of glare from light sources

An instrument for the evaluation of glare from light sources has been further developed and is here described in its final form. The method of use is described, with the necessary precautions. Results are given of a number of determinations with the glaremeter of the constants in the relation between glare effect (equivalent background brightness), glare intensity and glare angle. Values for the instantaneous probable errors of a single threshold reading and of a determination of equivalent background are deduced. The value for the probable error of a single reading agreed well with values found in other investigations by other methods.

The scattering theory of the effect of glare on the brightness difference threshold

The introduction of light sources into the visual field results, as is well known, in an increase in the brightness difference threshold for foveal vision. Several extensive investigations of this effect have been carried out in the last few years, and the values of the threshold under different conditions of glare have been related to the physical variables, such as the angular seperation between glare source and test object. Holladay, to whom one of these experimental investigations is due, puts forward the theory, following a suggestion of Raman, that the threshold is raised owing to an increased illumination of the fovea centralis by light scattered in the media of the eye, by the pencil of light from the glare source, in its passage from cornea to retina. Holladay applies Rayleigh's scattering formula to compute the illumination scattered onto the fovea in this way, and argues therefrom as to the way in which the threshold will vary with change of glare angle. Holladay's discussion is subject to criticism on the following grounds: (1) it fails to make clear the part played by the pupil aperture; (2) it treats white light as monochromatic in applying Rayleigh's formula; (3) it neglects to make a collateral deduction of the magnitude of the scattering coefficient which the eye media must posses in order to produce enough scattered light to explain the observed increases in the threshold. The object of the present paper is to give a brief sketch of the scattering theory, with the above defects removed, and to compare the results of recent experimental measurements, with the predictions of the theory.