Flash blindness is an either temporary or permanent

visual impairment Visual impairment, also known as vision impairment, is a medical definition primarily measured based on an individual's better eye visual acuity; in the absence of treatment such as correctable eyewear, assistive devices, and medical treatment� ...

during and following exposure of a varying length of time to a light flash of extremely high intensity, such as a

nuclear explosion A nuclear explosion is an explosion that occurs as a result of the rapid release of energy from a high-speed nuclear reaction. The driving reaction may be nuclear fission or nuclear fusion or a multi-stage cascading combination of the two, t ...

, flash photograph,

lightning Lightning is a naturally occurring electrostatic discharge during which two electric charge, electrically charged regions, both in the atmosphere or with one on the land, ground, temporarily neutralize themselves, causing the instantaneous ...

strike, or extremely bright light, i.e. a

searchlight A searchlight (or spotlight) is an apparatus that combines an extremely bright source (traditionally a carbon arc lamp) with a mirrored parabolic reflector to project a powerful beam of light of approximately parallel rays in a particular direc ...

laser pointer A laser pointer or laser pen is a small handheld device with a power source (usually a battery) and a laser diode emitting a very narrow coherent low-powered laser beam of visible light, intended to be used to highlight something of interest by ...

landing lights Landing lights are lights, mounted on aircraft, that illuminate the terrain and runway ahead during takeoff and landing, as well as being used as a collision avoidance measure against other aircraft and bird strikes. Overview Almost all moder ...

ultraviolet light Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...

. The bright light overwhelms the

retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then ...

s 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 weapon Non-lethal weapons, also called nonlethal weapons, less-lethal weapons, less-than-lethal weapons, non-deadly weapons, compliance weapons, or pain-inducing weapons are weapons intended to be less likely to kill a living target than conventional ...

s such as flash grenades and

laser dazzler A dazzler is a non-lethal weapon which uses intense directed radiation to temporarily disorient its target with flash blindness. They can effectively deter further advances, regardless of language or cultural barriers, but can also be used for h ...

Cause

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

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 The North Atlantic Treaty Organization (NATO, ; french: Organisation du traité de l'Atlantique nord, ), also called the North Atlantic Alliance, is an intergovernmental military alliance between 30 member states – 28 European and two No ...

and the

U.S. Department of Defense The United States Department of Defense (DoD, USDOD or DOD) is an executive branch department of the federal government charged with coordinating and supervising all agencies and functions of the government directly related to national secur ...

, 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 United States

Federal Aviation Administration The Federal Aviation Administration (FAA) is the largest transportation agency of the U.S. government and regulates all aspects of civil aviation in the country as well as over surrounding international waters. Its powers include air traffic m ...

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."

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 Figure skating is a sport in which individuals, pairs, or groups perform on figure skates on ice. It was the first winter sport to be included in the Olympic Games, when contested at the 1908 Olympics in London. The Olympic disciplines are me ...

, fans are cautioned to not use flash photography so as to avoid distracting or disorienting the athletes. Also in aviation, there is concern about

s and bright

searchlights A searchlight (or spotlight) is an apparatus that combines an extremely bright source (traditionally a carbon arc lamp) with a mirrored parabolic reflector to project a powerful beam of light of approximately parallel rays in a particular dire ...

causing temporary flash blindness and other vision-distracting effects to pilots who are in critical phases of flight such as

approach Approach may refer to: Aviation *Visual approach *Instrument approach *Final approach Music * ''Approach'' (album), by Von Hertzen Brothers * ''The Approach'', an album by I:Scintilla Other uses *Approach Beach, a gazetted beach in Ting Kau, Ho ...

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 (fission bomb) or a combination of fission and fusion reactions ( thermonuclear bomb), producing a nuclear explosion. Both bom ...

is the first indication of a

, traveling faster than the blast wave or sound wave. "A 1-megaton explosion can cause flash blindness at distances as great as on a clear day, or on a clear night. If the intensity is great enough, a permanent retinal burn (

photic retinopathy Photic retinopathy is damage to the eye's retina, particularly the macula, from prolonged exposure to solar radiation or other bright light, e.g., lasers or arc welders. The term includes solar, laser, and welder's retinopathy and is synonymous ...

) will result."

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.BBC NEWS Tuesday, 17 August, 1999, 16:13 GMT 17:13 UK Safety in sight total eclipse 300
/ref> Nonetheless, psychological pain may very well be present. It can cause amplified stress levels but usually fades.

Related conditions

Welders In a broad sense, a welder is anyone, amateur or professional, who uses welding equipment, perhaps especially one who uses such equipment fairly often. In a narrower sense, a welder is a tradesperson who specializes in fusing materials together ...

can get a painful condition called

arc eye Photokeratitis or ultraviolet keratitis is a painful eye condition caused by exposure of insufficiently protected eyes to the ultraviolet (UV) rays from either natural (e.g. intense sunlight) or artificial (e.g. the electric arc during welding) ...

. 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 The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Along with the anterior chamber and lens, the cornea refracts light, accounting for approximately two-thirds of the eye's total optical power ...

. Flash blindness, in contrast, is caused by a single, very brief exposure which oversaturates the

, and is not usually accompanied by reports of pain.

References