exposure meter 
noun Photography
A light meter.Adams couldn't find his exposure meter in his hurry to make the shot before the sun set behind him....
- If the window is smaller or farther away, switch to a spot-metering exposure mode in which the camera's exposure meter reads only a tiny area in the center of the frame.
- You see, the exposure meter built in to your camera is trying to ‘average out’ the light levels that are coming through the lens.