Ambient light

A measurement of ambient light.

Many cameras now have a built-in flash that is used to take pictures inside when the light levels are low. The camera detects when flash is needed and automatically fires it, there are usually several other modes to increase the flash's versatility. Red eye reduction fires a pre-flash to prevent large red eye pupils appearing. 'Off' turns an automatic flash off so that the camera can be used with a long shutter speed for night photography. 'On' forces the flash to fire as a fill-in for daylight pictures that have harsh shadows or to illuminate a close subject in a night scene. Slow sync fires flash and records the ambient exposure, which is great for creating image trails and creative subject movement.