The original flash was invented before the 1920s and 1930s to improve the quality of photography in poor light. This flashing device is a magnesium strip placed in front of the reflector. Both ends of the magnesium strip are connected to the high-power battery through a switch, and the switch is linked with the shutter of the camera. When the camera shutter is pressed, the switch is turned on, and the magnesium rod is short-circuited and burned under the action of the battery, resulting in strong flash, and the reflector reflects the flash to the position to be photographed, thus enhancing the flash effect. This flashlight is very troublesome to use. A magnesium rod needs to be replaced every time it is used. The battery power required to ignite the magnesium rod is relatively large, and the battery device is bulky and inconvenient to carry.

Later, people invented xenon lamps. The bulb of xenon lamp is a glow discharge tube filled with low-pressure xenon (the structure is very simple, if you have used an electric pen, its structure is the same as the neon tube on the electric pen). Therefore, xenon lamp should be chosen as the light source, because the color temperature of xenon lamp is very close to sunlight, and the color of photos irradiated by its flash lamp is very natural.

The xenon lamp is connected to a large-capacity electrolytic capacitor for storing electric energy through a circuit device controlled by a shutter. Usually, this capacitor is charged by the control circuit, and its voltage is the same as that of the camera battery (about 3V).

When taking pictures, if the flash is on. When the shutter is pressed, it will trigger the flash control circuit to start, generate high voltage to light the xenon lamp, and then the electric energy stored in the capacitor will be released instantly, which will make the brightness of the xenon lamp rise sharply and also produce a flash effect. The flash goes out until the power of the capacitor runs out or the timing time of the control circuit ends.

After the flash lamp goes out, the control circuit begins to charge the capacitor to store energy. Usually, this process takes several seconds to fully charge the capacitor before continuing to the next flash. Therefore, it is impossible for the flash of an ordinary camera to flash continuously in a short time.

With the progress of science and technology, people invented high-brightness light-emitting diodes, which have the advantages of low voltage, energy saving and environmental protection. At present, the light bulbs of some mobile phones have been replaced by high-brightness light-emitting diodes (LEDs). But at present, the light color of light-emitting diodes is not good enough for xenon lamps, so most cameras and some mobile phones still use xenon lamps as flashlights.

The white flash on the stage is also a xenon lamp, and the circuit principle is similar to that of a camera. However, because the city power is used, the energy is sufficient, and there is no need for capacitor energy storage like a camera, so it can continue to flash intensively.