Flicker vertigo, sometimes called the Bucha effect, is "an imbalance in brain-cell activity caused by exposure to low-frequency flickering (or flashing) of a relatively bright light." It is a disorientation-, vertigo-, and nausea-inducing effect of a strobe light flashing at 1 Hz to 20 Hz, approximately the frequency of human brainwaves. The effects are similar to seizures caused by epilepsy (in particular photosensitive epilepsy), but are not restricted to people with histories of epilepsy.
This phenomenon has been observed during helicopter flight; a Dr. Bucha identified the phenomenon in the 1950s when called upon to investigate a series of similar and unexplained helicopter crashes. Flicker vertigo in a helicopter occurs when the pilot or front passenger looks up through the blades of the main rotor as it turns in the sun causing the light to strobe.
The strobe light effect can cause persons who are vulnerable to flicker vertigo to experience symptoms such as:
- Become disoriented and/or nauseated
- Blink rapidly
- Experience rapid eye movements behind closed eyelids
- Lose control of fine motor functions
- Experience muscle rigidity
These effects are typically very minor and will most often subside within seconds once exposure to the strobe effect has ceased, though residual nausea and minor disorientation may be felt for several minutes.
In extremely rare cases, severe reactions can happen including:
- Total persistent loss of bodily functions
- Loss of muscle/motor response
- Loss of control of aircraft or other moving vehicles
This situation can occur whenever flickering light conditions exist. Examples of this include:
- Using electronics on low-light conditions for extended periods
- Sunlight flickering through a tree-lined street
- Sunlight reflecting off of water, especially off of rippling waves
- Fixed wing flight
- Looking at or through a slowly spinning propeller
According to The US Naval Flight Surgeons Manual, flicker vertigo is a rare occurrence.
Flicker vertigo has been considered as a principle for various forms of non-lethal weapons. A related crowd-control device was invented by Charles Bovill, which "employed a combination of ultra-sonic waves and strobe lights to induce acute discomfort, sickness, disorientation and sometimes epilepsy."
- (online article requires logon) Clarence E Rash: Awareness of Causes and Symptoms of Flicker Vertigo Can Limit Ill Effects: Human Factors and Aviation Medicine: Vol 51: Number 2: Mar-Apr 2004: Flight Safety Foundation
- Bunker, Robert J. (July 1997), Nonlethal Weapons: Terms and References, p. 17, ISBN 9781428991934
- Lyell (September 1997), Non-lethal Weapons: Draft General Report (PDF), p. 3
- Ronson, Jon (2005), The men who stare at goats, p. 147, ISBN 9780743241922
- National Aviation Reporting Center on Anomalous Phenomena United States Naval Flight Surgeon's Manual: Third Edition 1991: Chapter 9: Ophthalmology: Perceptual Disorders; Naval Aerospace Medical Institute
- Bertomen, Lindsey (May 2007), "You Strobe, I Strobe, We All Strobe Together", Law Enforcement Technology
- Patel, Prachi (2007-08-06). "The Incapacitating Flashlight; An LED flashlight makes culprits vomit". MIT Technology Review. Retrieved 17 July 2013.
- Charles Bovill Obituary, The Daily Telegraph, November 2001
- Flight Safety Foundation
- Flicker illness: an underrecognized but preventable complication of helicopter transport.
- "LED-based incapacitating apparatus and method", filed in 2005 — a patent for a device based on this phenomenon.
- "New Robo-Weapon: Paralyzing Floodlight", Wired Danger Room blog, February 20, 2007 — a description of a weapon based on a similar phenomenon.