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The Visual Environment: Measurement and Design
Published in R. S. Bridger, Introduction to Human Factors and Ergonomics, 2017
Certain visual phenomena are more difficult to explain using simple color mixing theories. If a bright light is fixated for several seconds, a retinal afterimage remains when the viewer looks away. Blue lights produce yellow afterimages and vice versa and red lights green ones. It has been suggested that at the retinal level, a component process exists with functionally different cones responding maximally to different wavelengths. The outputs of this system are thought to fire into a so-called opponent process system. There are said to be three opponent process systems—a blue/yellow system, a red/green system, and a light/dark system. When long wavelengths are incident, the red/green system increases its firing rate above its spontaneous level and red is perceived. As the incident wavelength is shortened, the system is inhibited and its firing rate decreases until it drops below the spontaneous level and green is perceived. Thus, after viewing a bright red light for several seconds, a green afterimage of the object is seen due to a sudden drop in the output of the opponent process system. Certain cells in the brain appear to act like opponent process cells, increasing and decreasing their firing rate in this way.
Laser Eyewear
Published in Ken Barat, Understanding Laser Accidents, 2018
At exposure levels below the maximum permissible exposure (MPE), several adverse visual effects from visible laser exposure may occur. The degree of each visual effect is strongest at night and may not be disturbing in daylight. These visual effects are: Afterimage. A reverse contrast, shadow image left in the visual field after a direct exposure to a bright light, such as a photographic flash. Afterimages may persist for several minutes, depending upon the level of adaptation of the eye (that is, the ambient lighting).Flashblindness. A temporary visual interference effect that persists after the source of illumination has been removed. This is similar to the effect produced by a photographic flash and can occur at exposure levels below those that cause eye injury. In other words, flashblindness is a severe afterimage.Glare. A reduction or total loss of visibility in the central field of vision, such as that produced by an intense light from oncoming headlights or from a momentary laser pointer exposure. These visual effects last only as long as the light is actually present. Visible laser light can produce glare and can interfere with vision even at exposure levels well below those that produce eye injury.Dazzle. A temporary loss of vision or a temporary reduction in visual acuity.Startle. Refers to an interruption of a critical task due to the unexpected appearance of a bright light, such as a laser beam.
Laser Eyewear
Published in Barat Ken, Laser Safety Tools and Training, 2017
Afterimage. A reverse contrast, shadow image left in the visual field after a direct exposure to a bright light, such as a photographic flash. Afterimages may persist for several minutes, depending upon the level of adaptation of the eye (i.e., the ambient lighting).
Discomfort Glare from Small, High-Luminance Light Sources When Viewed against a Dark Surround
Published in LEUKOS, 2018
Yulia Tyukhova, Clarence E. Waters
For the visual system to be able to function well, it has to be adapted to the prevailing lighting environment [DiLaura and others 2011]. The duration of afterimages and the total experiment length were considered while determining the adaption time. An afterimage is a visible trace of a primary stimulus that appears even though the stimulus is no longer present [Virsu and Laurinen 1977]. If the glare luminance is too high, then potential carryover effects may exist that affect subsequent discomfort glare assessments. If the experiment is too long, it might cause fatigue in subjects [Bennett 1979]. In each experimental condition, the adaptation time (49.2 s), the time between the start of each experimental condition and the flashing sequence, was a compromise between sufficient time for adaptation and minimal fatigue.