Strobe Lights and Epilepsy

Strobe lighting can trigger seizures in photosensitive epilepsy. Thus, most strobe lights on sale to the public are factory-limited to about 10-12 flashes per second in their internal oscillators, although externally triggered strobe lights will often flash as frequently as possible. At a frequency of 10 Hz, 65% of affected people are still at risk. The British Health and Safety Executive recommend that a net flash rate for a bank of strobe lights does not exceed 5 flashes per second, at which only 5% of photosensitive epileptics are at risk. It also recommends that no strobing effect continue for more than 30 seconds due to the potential for discomfort and disorientation.

Dennō Senshi Polygon, a 1997 episode of the Japanese animated television program Pokémon was involved in an incident in which reportedly 685 young viewers were taken to hospitals by ambulances after experiencing epileptic seizures (most of the patients recovered on the way to hospitals, although over 150 children were admitted to hospital care). The seizures were provoked by a scene in the episode of an explosion during which solid red and blue patterns blinked at a rate of about 12 Hz for about 6 seconds. Currently, the episode is banned worldwide, including in Japan.

It has been reported that the launch video for the London 2012 logo induced epileptic seizures in some people. The section of the video responsible has been removed.

Parabolic Aluminized Reflector (PAR) Lights

A Parabolic Aluminized Reflector luminare, or PAR light, is a stage lighting fixture widely used in theatre, concerts and motion picture production when a substantial amount of flat lighting is required for a scene.

They are nearly identical in principle to the old-style sealed beam automobile headlight. They are frequently used in patterns of multiple lights such as 3 by 3 (known as a "nine light") when large areas are to be lighted. In situations where sunlight or other specular light is available, a white foam reflector is often used to accomplish the same effect as a PAR array.

Construction

PAR lights possess a lens and reflector that are integral parts of the lamp, the position of which cannot be altered relative to the filament. A notable exception is ETC's Source Four PAR, which uses the same halogen lamp as their Source Four ERS. In this case, the lens is a separate piece from the lamp. The relative position of lamp and lens remains unalterable.

In PAR 64s, Raylite reflectors and two pin base lamps are often used as a cheaper alternative as the lamp is replaced but the reflector remains. Lamps such as the 500 watt A1/244 can be as much as half the price of the sealed beam units. Narrow, medium and wide Raylite refectors are quite readily available. The 2 blade (pin)Mogul lamp connector need not be replaced - this is integral to the Raylite reflector, Although some Raylite reflectors have "tails" which then require connection to the mains flex with the use of a ceramic connector block (ideally fixed to the can's body).

Effects

The sealed beam lamp produces an intense oval pool of light with unfocused edges. The only focus adjustment is a knob that allows the lamp/lens unit to be rotated within its casing, thus changing the orientation of the oval. With some models this control is via the mogul ceramic connector which connects directly to the Mogul prongs of the lamp. With the SourceFour PAR, the interchangeable lens is what is rotated. The type of lamp may be changed, and options include extra-wide flood (XWFL), wide flood (WFL), medium flood (MFL), narrow spot (NSP), and very narrow spot (VNSP).

These types of instruments come in varying diameters, the most common being designated PAR56 and PAR64. The number indicates the diameter of the housing in eighths of an inch (so a PAR64 is eight inches (~20cm) in diameter).

Uses

PAR lights are often used in theatrical or live music shows. Commonly they are used to generate colours by fitting them with transparent colored sheets called Gels, the cans are arranged into rows of different colours and identical rows placed on different sides of the stage. Due to their fast flash time and affordability, they are ideal for color washes in several different colours which can be chased through quickly or blended. However, because of the lack of control over the beam diameter, shape and sharpness, PARs are rarely used as front of house lights or general wash lights but can be used for special effect lighting such as lighting from directly above or from extreme angles.

( Information Source: Wikipedia )