is visual impairment during and following exposure to a light flash of extremely high intensity. It may last for a few seconds to a few minutes.
For example, in everyday life, the subject of a flash photograph can be temporarily flash blinded. The bright light overwhelms the eye and only gradually fades. A bright spot or spots may be seen for many minutes. This phenomenon is leveraged in non-lethal weapons such as flash grenades and dazer laser
The Dazer Laser - Light Fighting Technologies is a non-lethal ocular distraction and interruption device, or dazzler, which has been designed and engineered by Laser Energetics, Inc....
Flash blindness is caused by bleaching (oversaturation) of the retinal pigment. As the pigment returns to normal, so too does sight. In daylight the eye's pupil constricts, thus reducing the amount of light entering after a flash. At night, the dark-adapted pupil is wide open so flash blindness has a greater effect and lasts longer.
Temporary vs. permanent
Is flash blindness temporary or permanent?
- Some sources such as NATO and the U.S. Department of Defense
The United States Department of Defense is the U.S...
state that "flash blindness" can be temporary or permanent.
- Other sources restrict the use of the word to temporary, reversible vision loss: "...These are, in order of increasing brightness: dazzle, after image formation, flash blindness, and irreversible damage." The US Federal Aviation Administration
The Federal Aviation Administration is the national aviation authority of the United States. An agency of the United States Department of Transportation, it has authority to regulate and oversee all aspects of civil aviation in the U.S...
in Order 7400.2F (now cancelled) defines it as "Generally, a temporary visual interference effect that persists after the source of the illumination has ceased."
Because there appears to be no consensus definition, one should be especially clear about which sense(s) of the phrase are meant. For example, using the phrase "temporary flash blindness" when discussing everyday flash photography emphasizes that the condition will disappear without ill effect.
Because vision loss is sudden and takes time to recover, flash blindness can be hazardous. At some sporting events such as figure skating
Figure skating is an Olympic sport in which individuals, pairs, or groups perform spins, jumps, footwork and other intricate and challenging moves on ice skates. Figure skaters compete at various levels from beginner up to the Olympic level , and at local, national, and international competitions...
, fans are cautioned to not use flash photography so as to avoid distracting or disorienting the athletes. Also in aviation, there is concern
Under certain conditions, laser light or other bright lights directed at aircraft can be a hazard. The most likely scenario is when a bright visible laser light causes distraction or temporary flash blindness to a pilot, during a critical phase of flight such as landing or takeoff...
about laser pointer
A laser pointer or laser pen is a small portable device with a power source and a laser emitting a very narrow coherent low-powered beam of visible light, intended to be used to highlight something of interest by illuminating it with a small bright spot of colored light...
s and bright searchlights causing temporary flash blindness and other vision-distracting effects in pilots who are in critical phases of flight such as approach and landing.
The bright initial flash of a nuclear weapon
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion. Both reactions release vast quantities of energy from relatively small amounts of matter. The first fission bomb test released the same amount...
is the first indication of a nuclear explosion, traveling faster than the blast wave or sound wave. "A 1-megaton explosion can cause flash blindness at distances as great as 13 miles on a clear day, or 53 miles on a clear night. If the intensity is great enough, a permanent retinal burn will result."
It is unclear whether pain is directly associated with flash blindness. Reaction to flash blindness can be discomforting and disorienting. The retina has no pain receptors, so reports of pain may be due to more psychological reactions.
Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes...
can get a painful condition called arc eye. While it is caused by bright light as is flash blindness, the welder's arc lasts for much longer than a flash, and emits ultraviolet rays that can affect the cornea
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, with the cornea accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is...
. Flash blindness, in contrast, is caused by a single very brief exposure which oversaturates the retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
, and is not usually accompanied by reports of pain.