electronic flash unit

Definition: Type of light-source which produces light over a short duration from a small flash-tube. * Consists of (a) tube filled with rare gases e.g. xenon (b) electrodes which are connected to (c) electrical condensers which store charge at high voltage. * When electrical charge is released from the condenser into the tube via the electrodes, the gas flashes brilliantly for a brief duration, which depends on the capacitance of the condenser.
You need to know this (well, maybe not)
Flash duration of in microseconds is approximately equal to the condenser capacitance in microfarads. Most flash-units vary the power of the unit by varying capacitance, hence when most studio flash-units are varied in power, the flash duration changes. However, this cannot work with automatic flash units: here the flash-duration is cut short as needed, using thyristors i.e. a pulse of electricity turns the circuit on or off.

Related Terms: strobe

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