A flash is an artificial light-filling device. Its working principle is to store high-voltage electricity through a capacitor and trigger the pulse to discharge the flash tube. After the instant flash flash is fully charged, the flash synchronization contact on the camera turns on the flash circuit. During the flash, the light is emitted from the flash to the subject, reflected from the subject and enters the camera (for exposure) and the flash metering element. This photometric element quickly converts the light energy into an electrical signal and inputs it into the integration circuit. The integration circuit then outputs an electrical signal proportional to the amount of flash light. The output of the electrical signal causes the control circuit to trigger the flash stop circuit, thereby causing the flash to go out.