February 13, 2002
The problem of glare affects all individuals. Although it is usually only a fleeting annoyance, glare can have grave consequences. For instance, problems caused by glare from computer screens account for 10 million optometrist examinations per year (Berman, 1998). There are two types of glare: discomfort glare and disability glare. The types of glare are distinguished by their origin. Discomfort glare comes from an external source; it is the physical sensation one experiences in the presence of a light source that is too bright. An example of discomfort glare is the experience of stepping outside on a bright day just after leaving a dark movie theater. Surfaces such as snow and sidewalks can cause discomfort glare (Ludt, 1997). Discomfort glare affects everyone. Disability glare, however, has an internal source. It is intrinsic to the individual due to aging or disease. Disability glare refers to intraocular scattering of light that interferes with normal visual functioning by decreasing image contrast on the retina. These individuals have a debilitating sensitivity to high levels of illumination. Streetlamps, floodlights, and the sun are examples of everyday encounters that can induce, and require recovery time from, disability glare. The pervasive and insidious nature of glare demands additional research. This paper examines discomfort glare, disability glare, the reasons why they warrant further research, and the direction of this research.
Because discomfort glare refers to reflection sources in the field of vision, the most simple way to guard against discomfort glare is to modify the environment. Some of the sources of discomfort glare are the sun, unshielded streetlamps, floodlights, computer screens, and parabolic luminaires. When the sun is low on the horizon, early in the morning and at dusk, discomfort glare peaks because the sunís illumination is much brighter than other objects and these objects become difficult to see. (Ludt, 1997). Protective gear may be sufficient to counteract the overhead rays of the sun in between dusk and dawn. A remedy for discomfort glare caused by the sun is simply to wear a visor while outdoors. A brim that extends 3 inches forward should block light from entering the pupil. Sunglasses with yellow, orange, or red tinted lenses may decrease discomfort glare (Ludt, 1997).
Unshielded streetlamps, or semi-cutoff luminaires, fail to make streets safer because their high-wattage bulbs shine light throughout the entire surrounding area. Full cutoff optics are a less bright and ultimately safer alternative. Full cutoff optics use flat glass lenses and external shielding to direct light to the roadway (Ngai & Boyce, 2000).
Floodlights are lamps fitted with reflectors and mounted outside the home to ward off intruders. Floodlights with bright bulbs can, however, be a source of glare for neighbors, a condition referred to as light trespass. Top and side shielding control the broadcast of illumination (Miller, 2001).
Glare from computer screens may be a source of nuisance for workers. Computer screens may reflect light and thus adversely affect display legibility; therefore, glare may reduce worker productivity. A simple way to reduce glare from computer screens is to display a light background on the screen rather than a dark background. Glare increases the luminance of both the background and the images of the screen and therefore reduces the contrast between them. Light backgrounds are preferable because of the sharper contrast between image and background. If possible, use high luminance displays and avoid shiny screens. A glare guard, a screen placed in front of a computer monitor, reduces glare. Also, good quality screens reduce glare. If the previous options are not feasible, then less direct modifications may yet be helpful. For example, a shield that covers overhead illumination makes the light indirect. Also, one can cover the windows with blinds and use dark-colored paint or wallpaper (Ngai & Boyce, 2000).
Overhead glare refers to the physical sensation of being in the presence of a bright source of illumination that is above the line of sight. Businesses are increasingly using parabolic luminaires, which are unshielded, bright bulbs. Overhead glare from parabolics can cause distraction when light reflects from the nose, eyebrows, and spectacles into the eyes. Ambient illuminance counteracts these effects. Parabolics placed at angles that are greater than the line of sight, however, reduce discomfort glare. Rubino, Cruz, Garcia, & Hita (1994) recommend a position of 180 degrees from the line of sight.
All of the sources of discomfort glare are exacerbating to those with disability glare. While discomfort glare is uncomfortable but does not disrupt visibility, disability glare is much more debilitating. Disability glare decreases visual acuity and prolongs reaction time. The light scatters in front of the retina, where an image is focused, and therefore reduces visual acuity. Some of the risk factors for disability glare are advanced age, cataracts, albinism, corneal edema, vitreous opacities, and migraine headaches (Ludt, 1997). Those with cataracts are less sensitive to glare after surgery to remove the lens. Individuals who experience disability glare can also benefit from visors and sunglasses (Ludt, 1997). Old age is a factor because the intraocular scattering of light, increases with age and creates a veil of luminance around the retinal image that reduces target visibility (Guirao et al., 1999). Older eyes are also slower to react to changes in illumination levels. With age the pupil becomes smaller and less flexible; as a result light scatters more and reduces clarity. (Miller, 2001). Brabyn, Haegerstrom-Portnoy, & Schneck (2000) conducted a study that compared visual assessments of the elderly in clinical and realistic conditions. The results indicated that clinical assessments, in particular the Snellen test for visual acuity, do not necessarily predict performance of daily tasks. Individuals with acceptable Snellen acuities nevertheless experience problems with everyday tasks such as walking and driving. Brabyn et al. (2000) used the Berkeley Glare Test and the SKILL Glare Recovery test to simulate more realistic conditions of the effect of glare on acuity. The results showed that 90% of the 70-75 year-old subjects had acuities below 20/70 and 70% of subjects in the over-85 group had acuities of 20/200 under conditions of glare. Although glare decreases acuity in everyone, it is much more debilitating to older eyes than to younger eyes because of increased intraocular scattering of light. The subjectsí recovery time ranged from 13-90 seconds. Glare recovery time measures how quickly the visual system regains function after exposure to a bright light. The disease and age factors that affect glare recovery time also affect light and dark adaptation. Therefore, it takes longer to become accustomed to varying levels of illumination. In this instance, glare can occur when a source of luminance is much brighter than that to which the observer is adapted.
Current research, such as that by Miller (2001), focuses on how to modify the environment to reduce glare and improve contrast. The emphasis is on practicality to reduce discomfort glare. The pressure is on businesses and public institutions to become more responsible about choices of illumination. There is an outcry against parabolics by Ngai & Boyce (2001), Miller (2001) and many others. According to Ngai & Boyce (2001) workers complained about overhead parabolics ever since their introduction and even when they were not located in the line of sight. The employees at Advanced Technology Laboratories complained about vision problems and headaches from glare and parabolic lights. This system was replaced by an indirect, linear lighting system that focuses light upward and reduces glare because there are no visible lamps (Berman, 1998). There needs to be more research on the adverse effects of parabolics.
Similarly, Miller (2001) argues that gas station canopy lights should be directed downward instead of at glare-producing high angles. There is a general consensus that bare lamps should always be covered. There is a need for more research that focuses on glare problems found in the everyday environment. These conditions include, for example, low lighting, glare, and shifting levels of illumination. The clinical setting, with high acuity, contrast, and bright luminance does not generalize to real life. Additionally, Miller (2001) notes that some of the tests used to measure glare, such as the Visual Comfort Probability or Unified Glare Rating, assume that the light source is uniform, bright, and in the field of view. A range of various intensities would more accurately reflect the real world. Thus, research concerning the effect of illumination on glare should be qualitative rather than quantitative.
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