When shooting green screen, it is incredibly important to have a backing that has a consistent color temperature and brightness. This balance is monitored in the field by either a waveform monitor(video), or an incident light meter(film.) Waveform Monitor - An instrument that displays the luminance information in a video signal. The waveform displays the luminance information in IRE. The visible portion of the signal is between 40 and 100 units on the graticule. A good backing should display as a thin horizontal line, with no fluctuation at roughly 60IRE. Incident Light Meter - An instrument used to measure the amount of light falling on or reflected from a subject. The light meter displays the light falling on an object in footcandles, based on the shutter speed of the camera, and the speed of the film. Meter readings on the backing should be equal at every point on the backing.