Flash blindness

Flash blindness is an either temporary or permanent visual impairment during and following exposure of a varying length of time to a light flash of extremely high intensity, such as a nuclear explosion, flash photograph, lightning strike, or extremely bright light, i.e. a searchlight, laser pointer, landing lights or ultraviolet light.[1] The bright light overwhelms the retinas of the eyes and generally gradually fades, lasting anywhere from a few seconds to a few minutes. However, if the eyes are exposed to a high enough level of light, such as a nuclear explosion, the blindness can become permanent.

Flash blindness may also occur in everyday life. For example, the subject of a flash photograph can be temporarily flash blinded. This phenomenon is leveraged in non-lethal weapons such as flash grenades and laser dazzlers.

Cause

Flash blindness is caused by bleaching (oversaturation) of the retinal pigment.[2] 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

Depending on the source consulted, term may exclusively refer to a temporary condition or may describe a potentially permanent one. Some sources, such as NATO and the U.S. Department of Defense, state that "flash blindness" can be temporary or permanent.[3] 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."[4] The United States Federal Aviation Administration in Order JO 7400.2 defines flash blindness as "generally, a temporary visual interference effect that persists after the source of the illumination has ceased."[5]

Potential hazards

Because vision loss is sudden and takes time to recover, flash blindness can be hazardous. At some sporting events such as figure skating, fans are cautioned to not use flash photography so as to avoid distracting or disorienting the athletes. Also in aviation, there is concern about laser pointers and bright searchlights causing temporary flash blindness and other vision-distracting effects to pilots who are in critical phases of flight such as approach and landing.

The bright initial flash of a nuclear weapon is the first indication of a nuclear explosion, traveling faster than the blast wave or sound wave.[6] "A 1-megaton explosion can cause flash blindness at distances as great as 13 miles (21 km) on a clear day, or 53 miles (85 km) on a clear night. If the intensity is great enough, a permanent retinal burn (photic retinopathy) will result."[7]

Pain

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.[8] Nonetheless, psychological pain may very well be present. It can cause amplified stress levels but usually fades.

Welders can get a painful condition called arc eye. While it is caused by bright light similar to flash blindness, the welder's arc lasts for much longer than flash blindness and involves exposure to ultraviolet rays that can damage the cornea. Flash blindness, in contrast, is caused by a single, very brief exposure which oversaturates the retina, and is not usually accompanied by reports of pain.

See also
  • Smart glass

References
  1. "Laser Pointers: Their Potential Affects [sic] on Vision and Aviation Safety (April 2001)FAA" (PDF). Archived from the original (PDF) on June 26, 2013. Retrieved September 10, 2006.
  2. Kulur, Malvika. "Causes and Risks of Flash Blindness". buzzle.com. Buzzle. Retrieved 3 March 2018.
  3. first strike(DOD) The first offensive move of a war. (Generally associated with nuclear operations.) Archived September 10, 2005, at the Wayback Machine
  4. BMJ No 7120 Volume 315 Editorial, 29 November 1997 Blinding laser weapons still available on the battlefield
  5. FAA Order JO 7400.2L, Procedures for Handling Airspace Matters, effective 2017-10-12 (with changes), accessed 2017-12-04
  6. Byrnes, V. A. (1953). Flash Blindness. Operation SNAPPER. Nevada Proving Grounds, April–June 1952, Project 4.5. School of Aerospace Medicine. Brooks A.F.B. Texas.
  7. Flashblindness | Effects of Nuclear Weapons | atomicarchive.com
  8. BBC NEWS Tuesday, 17 August, 1999, 16:13 GMT 17:13 UK Safety in sight total eclipse 300
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