Devices that create light pulsations at intervals varying from
one flash every few seconds to several flashes per second. They
have become a familiar part of the atmosphere of excitement
at some dance halls and discotheques, but in different situations
they have proved of some assistance in inducing hallucinatory
experiences, especially when seen with half-open or
even closed eyes.
Pierre Janet did pioneering work with stroboscopes. He
flashed lights at mental patients and saw some immediate
breakthroughs in their health. The strobes work by a process
called entrainment, in which the brain tends to align itself with
the frequency of the flashing light. A beam flashed at the right
frequency can induce a more relaxed state and cause the brain
to change its frequency.
Hooper, Judith, and Dick Teresi. Would the Buddha Wear a
Walkman New York Simon and Schuster, 1990.