When someone wants to take a photograph in dim light or darkness, he makes use of a flash-gun with his camera. As soon as the shutter of the camera is pressed, flash gun produces its own light and illuminates the object. Do you know how does a camera’s flashlight work?
A modern flash-gun consists of a light source which is usually a xenon flash lamp. To operate the flash lamp there are electrical circuits and an electric source which gives energy to the flash lamp. Electric source is usually a dry battery.
A xenon flash lamp is a glass tube – usually two inch long with quarter inch diameter. Two tungsten electrodes are sealed at the ends of this glass tube. This tube is evacuated and filled with xenon gas at a pressure of 400 to 500 mm of mercury. A thin wire is wound around the tube which acts as the third electrode and is known as trigger electrode. The two electrodes of the lamp are connected to the electric circuit which consists of a capacitor bank to store the electrical energy. When shutter is pressed, the electric switch is also pressed and a high voltage pulse comes on the third electrode. This high voltage pulse ionizes the xenon gas by which it becomes electrically conducting. At this point, the energy stored in the capacitor bank gets discharged through the xenon lamp. As a result light is produced which illuminates the object to be photographed? At the back of the xenon lamp, a reflector is mounted which directs the light towards the object.
Unlike a flash bulb, an electronic flash can be used again and again. The flash contains a tube that gives out a bright flash of white light when a strong electric charge passes through it.
The light emitted from the flash gun is in the form of a pulse. Its duration is about one millisecond but the light is very intense. Nowadays almost all cameras are fitted with the electronic flash devices.
