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Glare is one of the most important factors threating expressway traffic safety an night. The most commonly way to prevent glaring night is to set anti-glare plate. Different from the straight sections of expressway, the relationship between the front light of vehicles and the distance of anti-glare plate on the horizontal curved section has some-what changed. Through a lot of tests and finite element simulation, the relationship between the distance of anti-glare plate, horizontal curve radius and anti-glare effect were analyzed systematically. Distance calculation formula of anti-glare plate in horizontal curve sections was revised in this paper. The anti-glare plate distance requirement under different expressway alignment design indexes and its calculation formula was proposed. The achievement was beneficial to confirm the anti-glare effect and improve traffic safety. It can provide us with a reference and a supplement of the specification.

Purpose. Many parameters of visual performance (e.g., contrast sensitivity) are compromised under glaring light conditions. Recent data indicate that macular pigment (MP) is strongly related to improvements in glare disability and photostress recovery based on a filtering mechanism. In this study, we assessed the causality of this relation by supplementing lutein and zeaxanthin for 6 months while measuring MP, glare disability, and photostress recovery. Methods. Forty healthy subjects (mean age 23.9) participated in the study. Subjects were followed for 6 months and assessed at baseline, 1, 2, 4, and 6 months. Spatial density profiles of MP were measured using heterochromatic flicker photometry. Disability glare was measured using a 1 degree-diameter circular grating surrounded by a broadband glare source (a xenon-white annulus). The intensity of the annulus (11 degree inner and 12 degree outer diameters) was adjusted by the subject until the grating target was no longer seen. For the photostress recovery experiment, the time required to detect a 1 degree-diameter grating stimulus after a 5-s exposure to a 2.5 W/cm 2 , 5 degree-diameter disk was recorded. Subjects were tested under central viewing and eccentric viewing (10 degree temporal retina) conditions. Results. At the baseline time point, MP optical density (OD) at 30 eccentricity ranged from 0.08 to 1.04, and was strongly correlated with improved visual performance in the two glare tasks. After 6 months of lutein (L) and zeaxanthin (Z) supplementation, average MPOD (at 30 eccentricity) had increased from 0.41 to 0.57, and was shown to significantly reduce the deleterious effects of glare for both the visual performance tasks assessed. Conclusions. MP is strongly related to improvements in glare disability and photostress recovery in a manner strongly consistent with its spectral absorption and spatial profile. Four to 6 months of 12 mg daily L Z supplementation significantly increases MPOD and improves visual performance in glare for most subjects. (Optom Vis Sci 2008;85:82–88)

A pilot study for investigating the effect of six coated glazing materials on visual perception of the interior and of the view out in scaled rooms is presented. The study, which involved 18 subjects, is carried out in Hørsholm (Denmark, lat. 55.4°N), under overcast skies and a north orientation. The methodology involves subjective ratings using a questionnaire and seven grade bipolar scales. The results of the statistical analysis (ANOVA) show that despite significant amplitude in daylight transmittance (50%—79%), the glazing type did not have any statistically significant effect on the perception of the sharpness of shadows in the room. It is also found that higher transmittance glazing (77%—79%) resulted in views that are more glaring compared with the views obtained with the other glazing types. In terms of light level, the reference glazing (which contained an iron-free pane) results in statistically significant differences in the ratings (brighter room) compared with the ratings from all glazing types, including glazing types of similar transmittance. Finally, it is found that higher transmittance glazing types result in more positive ratings for factors, such as naturalness, beauty, and pleasantness and sharpness.

An experiment was performed to investigate the influence of sparkling luminous elements on overall brightness impressions. Evaluations of overall brightness impressions were carried out under various lighting conditions in which the luminance, size, shape and background luminance of the luminous element were varied. Subjective appraisals of the impression (sparkling, glaring or merely bright) of luminous elements were also carried out. The results suggested that the overall brightness impression of a room with a sparkling luminous element is often about 1.2-1.3 times higher than that without a luminous element The optimum lighting conditions that increased the overall brightness impression were elucidated.

This study evaluated the influences of lamp separation and lamp intensity on the effectiveness of daytime running lights. Subjects performed two tasks. They rated discomfort glare from a pair of lamps, and evaluated the conspicuity of the same lamps. The same nine stimuli were used in both the glare and conspicuity portions of the study. These nine stimuli were obtained by the orthogonal combination of three levels of luminous intensity directed towards the subject's eyes from the two lamps (14,000, 3,500, and 875 cd), and three levels of lamp separation (1.05, 0.65, and 0.25 m-edge to edge). The study was performed outdoors, on bright, sunny days. The viewing distance was 20 m. As expected, lamp intensity had strong effects on both discomfort glare and conspicuity. On the other hand, in the case of lamp separation, there was more evidence for an effect on conspicuity (narrowly separated lamps being more noticeable) than on discomfort glare (a statistically nonsignificant trend for narrowly separated lamps to be only slightly more discomforting). Consequently, if the possible increase in discomfort from narrowly separated lamps is counteracted by a slight reduction in intensity, there is still a net benefit for narrowly separated lamps in terms of conspicuity. Conversely, narrowly separated lamps that are as noticeable as widely separated lamps of higher intensity would be less glaring. The present findings imply that there is a small net benefit in using narrowly separated daytime running lights.

Purpose When a person is confronted with a bright light source against a dim background, scattered light can cause visual discomfort in addition to reducing object contrast on the retina. Previous work addressing the effect of glare on visual performance has focused mainly on the reduction in retinal image contrast (known as disability glare) rather than the often accompanying experience of discomfort glare. This study examines how parallel processing of visual information is affected under conditions of discomfort glare. Methods Light scatter sources surrounded a monitor on which the subject carried out standard contrast acuity (CA) tasks. All CA tasks were carried out with and without discomfort glare (estimated in a prior experiment). In the parallel task, a fovea target (Landolt C) and four peripheral stimuli (three distractors and one target) were presented concurrently; the subject had to indicate both the orientation of the gap for the foveal target and the quadrant containing the peripheral target. The size of the peripheral target was increased relative to the foveal target to ensure that all targets were equally detectable. This was done separately with and without discomfort glare, thus negating any influence of disability glare. Results The presence of discomfort glare degrades visual performance in the parallel processing task even when adjustments are made to cancel out the effects of disability glare. Conclusion Studies that have focused only on disability glare may be underestimating the adverse effect glaring light sources can have on visual performance, particularly in real world scenarios where attention to objects in both the fovea and periphery is often required.

An analytic theory is developed for dynamical-diffraction effects in x-ray radiation from a relativistic electron traversing a thin single crystal. It is shown that such dynamical effects may be responsible for a glaring discrepancy between recent experimental data and the traditional theory of parametric x-ray radiation.

In this article we will introduce a Light Emitting Diode (LED) lighting diffuser plate which diffuses light by optical microstructure. In LED lighting, LED array is the most popular method to attain the illuminance requirement, but this method will produce the glaring and non-uniform illuminance problems. Traditionally, diffuser, which is comprised of diffuser particles, is used to solve the above problems, but it also produces another problem which is low lighting efficiency. Therefore, we use optical microstructure to replace the diffuser particles to solve the problems of LED lighting but only reduce a little lighting efficiency. Moreover, we could control the lighting area of the LED lamp by designing the optical microstructure.

The recovery time of the human eye after brief exposures to monochromatic glare was measured as a function of wavelength and exposure time. The test stimulus and the glare stimulus were of the same frequency and bandwidth. The measurements were performed with approximately constant irradiance over the range from 475 nm to 650 nm in steps of 25 nm.

This study investigates the optical design of planar curved LED end-lit light bars using v cuts as light-diverting structures. The application of LEDs in automotive lighting has become popular, especially in signal lamps and daytime running lamps. Most designs adopt a direct back light using arrays of LEDs with diffusive coupling optics, which often causes problems such as low uniformity, glaring, and excessive LEDs. Edge-lit LED light guides in automotive applications share a similar principle with the light-guide plates in back-light models of LCD but with much more complicated geometry. However, related literature on the optical design of nonrectangular light-guide plates is very limited. This study addresses the design of planar curved LED end-lit light bars and the optimization scheme for illuminance uniformity. V cuts are used as the optical coupling features, and the lead angles of the v cuts are varied to achieve optimum axial luminous intensity. This study presents a solution to reduce the illuminance difference between the inner and the outer portions of curved light bars by introducing gradual taper v cuts across the curved section. A line graph with preselected anchor points is proposed to define the size distribution of evenly spaced v cuts along the light bar. A fuzzy optimization scheme is then applied to iterate the anchor size to achieve illuminance uniformity. The designs of a planar curve light bar with a rectangular cross section and a light-guide ring with a circular cross section are presented to illustrate the design scheme.

This paper discusses the evidence that yellow headlights might be less distracting and glaring than white headlights when driving during snowfall at night. Yellow headlights appear to reduce the negative effects of backscattered light during night driving, and during a snowfall.

Bright light can temporarily reduce the visual capacity of the human eye. Especially in traffic or in dealing with lasers disability glare can considerably reduce the visual faculty and lead to accidents. Even after the glare light has disappeared out of the field of vision, the visual capacity can still remain reduced for seconds or even minutes. It is therefore indispensable to investigate the recovery time of the human eye after glaring and to determine limiting exposures in order to avoid accidents or possible eye damage. We report on measurements of the recovery time in the range from 475 nm to 650 nm performed with thermal sources. Experiments are reported on the influence of varying intensities of test and glare light applied in the line of sight or extrafoveally. These studies allow us to give an empirical formula for the recovery time. In the present contribution we also report on measurements as a function of the duration of glaring. The range from 20 microsecond(s) to 1 s has been covered with an Argon laser at 488 nm as glare source. The resulting recovery time in different regions of this very large time scale will be discussed.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The influence of intraocular light scatter on letter identification in the absence and presence of glaring light is studied through computer simulations and simple experiments on healthy test subjects wearing diffusive glasses with known light scattering properties. An explicit expression for the point-spread function of a cataractous eye is used to calculate retinal images. For estimating resolution in the calculated images an assumed neural contrast sensitivity function is needed. The function used is derived from measurements by Campbell and Green. Experimental results are in agreement with theory. The analysis shows that visual acuity is quite insensitive even to substantial diffusive scattering provided that glare sources are not present in the field of view. Comparing measurements of `letter size' with measurements of `letter contrast' the latter method is found to measure intraocular light scattering more sensitively.

When an exposed light source is present in the field of view, the visibility of neighbouring objects is impaired owing to what may be called the glare effect of the light source. This glare effect has been studied by several investigators, who have measured the increase in the smallest perceptible brightness difference (brightness difference threshold) when the glare source is introduced in such manner that the brightness distribution in the field remains otherwise unchanged. In all the earlier work attention was confined to the case when the subject viewed the brightness difference to be perceived, by direct or foveal vision. For this case the investigations of Luckiesh and Holladay (1925) and of Stiles (1929) have shown that if the field has a uniform brightness of B c./sq. ft. and if a point source, located θ ° from the test object, produces an illumination of E ft. c. on the pupillary plane at the subject’s eye, then the brightness difference threshold T is raised from the value T 0 appropriate to the field brightness B , to the value T G appropriate to a field brightness β , where β = B + kE / θ n . (1) Thus the effect of the glare source on the brightness difference threshold is reproduced by superposing a uniform brightness γ = kE / θ n on the field brightness B . β is termed the equivalent uniform field brightness, and γ = kE / θ n , the equivalent veiling brightness, of the given glare condition. Various values of the constants k and n have been obtained by different investigators, but the best representative values may be taken as n = approximately 2, k = approximately 10. (See Appendix.) It has (Stiles and Crawford 1932) that the value of β for a given glare condition is independent of the size, colour and exposure time of the brightness difference used in the determination of the difference threshold.

Bright light sources can cause glaring effects which may impair visual efficiency. This may be brought about by a directly disabling effect, or it may result indirectly from irritation and discomfo...

By the brightness difference threshold is ordinarily understood the least perceptible difference of brightness of two contiguous test-fields when the brightness of one of these has a given value. It is well known, however, that this critical brightness difference depends not only on the given test-field brightness but also on the brightness in the remaining parts of the visual field. A change in the latter is accomplished in general by a change in the threshold. When an unshielded light source is introduced into the field of view, thee field brightness being otherwise unchanged, the threshold is found experimentally to increase. The observed increase in this case may be regarded as one of the things intended when the unshielded light source is described as "glaring." The researches of Bordoni and others have shown that the change in the threshold varies continuously with the intensity of the glare source and with its position in the field of view. The important conclusion has also been arrived at that provided the linear dimensions of the glare source do not exceed a certain limit, the effect on the threshold depends only on the candle-power in the direction of the subject's eyes and not explicitly on the size or brightness of the source. When such is the case, we may speak of a point source of glare and specify it merely by its position in the visual field and its candle-power. In the present paper an account is given of the determination of the threshold in the presence of a point source of glare for various values of the general brightness level in the field, and for different positions and intensities of the glare source. The ranges of the variables have been chosen with a view to the application of the results in practical illumination problems, such as the design of street lighting installations to give best visibility conditions. The method of measurement is chosen to correspond as far as possible to normal vision conditions, the subject having the unrestricted use of both eyes. In a number of the earlier threshold determinations, notably those of König and Brodhun, the chief interest was the retinal sensitivity, and pupillary accommodation and binocular effects were eliminated by using one eye only and an artificial pupil. The threshold appropriate to these conditions will not necessarily be the same as that for normal vision conditions.

Since higher levels of illumination can now be applied, the distribution of brightness in the visual field asks for special attention. Most studies on this subject are based on the classic formula of Holladay concerning comfortable lighting. In the experiments of Holladay the criterion was taken from the feeling of comfort or discomfort during the first seconds after the momentary shock experienced by an observer who is suddenly exposed to a glaring source. In our opinion it is questionable if such a criterion applies to the feeling of comfort or discomfort of a person who is present and working in a lighted interior for a long time. Therefore we made investigations on a rather small scale on the admissible brightness of lighting fixtures under circumstances as usual for interior lighting. A laboratory model of lighting fixtures was observed in a room, the surrounding brightness of which could be changed from 4.10-5 sb to 5.10-3 sb. The fixture was represented by a rectangular diffusing surface, the dimensions of which could be varied. The observations were made at various distances. From this resulted a solid angle subtended at the eye by the source of 10-5 to 10-1 steradians, whereas the angle at which the source was located above the line of vision varied from 10 to 40 degrees. By twelve observers the brightness of the fixture was adjusted to values that they considered to be the limit above which an increase would cause a transition from comfort to discomfort. The results of these investigations have been compared with the values that can be determined from the work of other investigators. Although there is agreement in some parts of the investigated regions, the deviations between our results and the values that can be computed from other work are considerable. It appeared that the influence of elongated sources on the feeling of comfort or discomfort is quite different from what is found in case of rectangular or circular sources. Tests of limited scope proved that in certain cases discomfort decreases with increasing length of the source when observed crosswise. Similar indications were obtained from observations on an interrupted linear source. These results cannot be understood from Harrison’s glare rating method.

Publisher Summary This chapter discusses adaptation time after glare. Glare from an approaching car in night traffic can give rise to two negative effects on the drivers' ability to detect objects on the road. One is the reduction of the contrast ratio between light from the object and light from the road on the retinas of the driver. The other effect is that the approaching light temporarily changes the adaptation level of the eye, thus, causing a decreased light sensitivity. The adaptation changes are of major importance. The redetection time after glare consists of readaptation time and simple reaction time (RT). The reaction time of the subjects is measured under the different treatments. A subtraction of the RT from the comparable redetection time gives the hypothetical readaptation time as a function of the glaring light. Variation of the duration of glaring light gives a more marked effect under threshold conditions. The contrast ratio between background and signal has a strong effect on redetection time.

Publisher Summary This chapter discusses a few problems and findings with polarized headlights, and describes the meeting conditions and the freeway driving conditions of the polarized lights. The efficiency of the polarized light must be much increased to give a good seeing distance by freeway driving. There is no use to take a lamp with higher wattage because a darker polarizer can then be necessary to prevent glaring. A headlamp with a larger diameter gives a better efficiency; however, the only way to get a real increase in efficiency is to make it possible to add the half part of light, which oscillates in right angle to the polarized beam. The chapter presents a comparison of polarized light and conventional light.

Changes in the sensitivity of the fovea of one of the eyes (the right eye) under influence of a glaring source of light shining into that eye can be demonstrated by comparing the visual impression obtained by that eye from a dimly illuminated surface with the impression obtained by the other eye (the left eye) from a similar surface. By adjusting the illumination of one of the surfaces the apparent brightnesses can be made to match exactly. In this way a quantitative method of measuring the sensitivity of the fovea under influence of various conditions of illumination is obtained. When a small area of the retina is illuminated the sensitivity of this area and also of the surroundings drops to a considerably lower level within 0.1 second (α-adaptation). The rate of recovery of the sensitivity after exposure is strongly dependent upon the time of exposure (β-adaptation). α-adaptation can neither be accounted for by assuming a strong adaptive influence of the stray light within the eye, nor by assuming a lateral diffusion of photosensitive substances or of photolytic products over the retina. The hypothesis is put forward that α-adaptation is of electrical origin. This hypothesis accounts for many of the phenomena observed with incandescent lamp light but not for those observed with strongly chromatic light. The only hypothesis presenting itself at present to account for these phenomena seems to be that α-adaptation has its seat in the retinal synapses.

A resume is presented of the results obtained in an extensive research into the many ways in which glare affects visibility.Visibility was studied chiefly by the method of least perceptible contrasts of brightnesses. Results are presented showing the influence of adaptation and of form and size of test-object upon contrast sensitivity.The results of the investigation show that the least perceptible brightness-difference between an object and its background increases directly with the illumination at the eye from the dazzle-source; varies approximately inversely with the square of the angle which the glare-source makes with the line of vision; and is practically independent of the brightness, size, type, distance, etc. of the dazzle-source.Considerable study has been given to the variations of the pupil under steady, fluctuating, and glaring lights and of their influence upon vision. Results of the investigations upon irradiation, after-images, blinding-glare and light-shocks are also presented.