How Does a Camera Flash Work?


The Camera Flash Setup

  • It is very difficult for a camera to capture an image without the right amount of light. Usually, this is a significant amount that cannot be had without the help of a flash, unless of course you are shooting outside in direct sunlight. A flash works by charging a tube filled with xenon gas in order to create a brief burst of light. The setup of a camera flash is the tube of xenon gas itself, an electrode on each end, a metal trigger plate behind the tube, and circuitry that provides the necessary voltage to create the flash.

The Flash's Circuitry

  • Before a camera can use a flash, it has to charge up enough voltage to create light. To do this, the power source sends electricity through special circuitry to increase the voltage the battery puts out. It takes about 1,000 to 4,000 volts or so to create a flash, and a battery emits only 1.5 volts. The electricity flows through a transformer made up of two coils, the first smaller than the second. An oscillator breaks up the electric flow in short bursts, which allows the first coil in the transformer to magnetize the second. This magnetization increases the voltage of the electricity to about 200 to 300 volts. This electricity is then stored in a capacitor.

The Final Voltage Boost

  • The capacitor is like a battery in its own right, and it stores the new, higher voltage until it is full. When it fills up, an indicator light shows that the flash is charged. When the camera shutter button is pressed, the energy in the capacitor flows through one more transformer, which boosts the voltage in the same way as the first, up to the necessary 1,000 to 4,000 volts. This electricity then moves from the transformer onto the trigger plate.

Creating the Flash

  • The trigger plate gets a strong positive charge when the electricity powers it. This charge instantly attracts electrons that are attached to atoms in the tube of xenon. Negatively charged electrons are pulled out from the atoms as other free electrons are pumped through both electrodes on the tube. This attraction of electrons is called ionization. When the electrons hit xenon atoms on their way from the tube to the trigger plate, light is created. This light is then focused in one direction, away from the camera, by a reflective surface behind the tube.

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