abstract: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."(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 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.