Flash blindness is an either temporary or permanent

visual impairment Visual or vision impairment (VI or VIP) is the partial or total inability of visual perception. In the absence of treatment such as corrective eyewear, assistive devices, and medical treatment, visual impairment may cause the individual difficul ...

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, th ...

, flash photograph,

lightning Lightning is a natural phenomenon consisting of electrostatic discharges occurring through the atmosphere between two electrically charged regions. One or both regions are within the atmosphere, with the second region sometimes occurring on ...

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

searchlight A searchlight (or spotlight) is an apparatus that combines an extremely luminosity, 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 part ...

laser pointer A laser pointer or laser pen is a (typically battery-powered) handheld device that uses a laser diode to emit a narrow low-power visible laser beam (i.e. Coherence (physics), coherent light) to highlight something of interest with a small brigh ...

, landing lights,

the sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot Plasma (physics), plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as ...

, or

ultraviolet light Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of th ...

. The bright light overwhelms the

retina The retina (; or retinas) is the innermost, photosensitivity, light-sensitive layer of tissue (biology), tissue of the eye of most vertebrates and some Mollusca, molluscs. The optics of the eye create a focus (optics), focused two-dimensional ...

s of the

eye An eye is a sensory organ that allows an organism to perceive visual information. It detects light and converts it into electro-chemical impulses in neurons (neurones). It is part of an organism's visual system. In higher organisms, the ey ...

s 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

, the

blindness Visual or vision impairment (VI or VIP) is the partial or total inability of visual perception. In the absence of treatment such as corrective eyewear, assistive devices, and medical treatment, visual impairment may cause the individual difficul ...

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 convention ...

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 ...

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 The pupil is a hole located in the center of the iris of the eye that allows light to strike the retina.Cassin, B. and Solomon, S. (1990) ''Dictionary of Eye Terminology''. Gainesville, Florida: Triad Publishing Company. It appears black becau ...

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, the term "flash blindness" 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 ; , OTAN), also called the North Atlantic Alliance, is an intergovernmental organization, intergovernmental Transnationalism, transnational military alliance of 32 Member states of NATO, member s ...

and the

U.S. Department of Defense The United States Department of Defense (DoD, USDOD, or DOD) is an executive department of the U.S. federal government charged with coordinating and supervising the six U.S. armed services: the Army, Navy, Marines, Air Force, Space Force, t ...

, state that "flash blindness" can be temporary or permanent. Other sources restrict the use of the word to temporary, reversible vision loss, distinguishing it from permanent blindness in a hierarchy of effects: "when the eye perceives bright light one of four reactions may take place. These are, in order of increasing brightness: dazzle, after image formation, flash blindness, and irreversible damage. ..Flash blindness occurs when an extremely bright flash is discharged, usually at night, and again vision is temporarily lost." The United States

Federal Aviation Administration The Federal Aviation Administration (FAA) is a Federal government of the United States, U.S. federal government agency within the United States Department of Transportation, U.S. Department of Transportation that regulates civil aviation in t ...

defines flash blindness in Order JO 7400.2 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, with its introduction occurring at the Figure skating at the 1908 Summer Olympi ...

, 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 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, H ...

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 or atomic bomb) or a combination of fission and fusion reactions (thermonuclear weapon), producing a nuclear exp ...

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) will result."

Pain

It is unclear whether pain is directly associated with flash blindness. Reaction to flash blindness can be discomforting and disorienting, but the retina itself has no

pain receptors In physiology, nociception , also nocioception; ) is the sensory nervous system's process of encoding noxious stimuli. It deals with a series of events and processes required for an organism to receive a painful stimulus, convert it to a molecular ...

,BBC NEWS Tuesday, 17 August, 1999, 16:13 GMT 17:13 UK Safety in sight total eclipse 300
/ref> unlike the

cornea The cornea is the transparency (optics), transparent front part of the eyeball which covers the Iris (anatomy), iris, pupil, and Anterior chamber of eyeball, anterior chamber. Along with the anterior chamber and Lens (anatomy), lens, the cornea ...

. However,

psychological pain Psychological pain, mental pain, or emotional pain is an unpleasant feeling (a suffering) of a psychological, mental origin. A pioneer in the field of suicidology, Edwin S. Shneidman, described it as "how much you hurt as a human being. It is m ...

could potentially occur in response to loss of vision. This can cause amplified stress levels, but such effects usually fade over time.

Related conditions

Welders A welder is a person or equipment that fuses materials together. The term welder refers to the operator, the machine is referred to as the welding power supply. The materials to be joined can be metals (such as steel, aluminum, brass, stainles ...

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

. 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