What Is an AF Assist Lamp and What Is It Used for in Photography?

An AF assist lamp is a small light, usually built into a camera body above the lens mount. It is used to assist the camera in focusing on a subject in low light conditions by lighting up the subject area while the camera focuses. AF Assist lamps only work at very short distances due to the low power of their output and in order to work correctly they must only be lit whilst the camera focuses. Were an AF assist lamp to remain on whilst a camera was metering an image it could cause the camera to read a scene to be brighter than it actually is therefore leading to unwanted underexposure.