Apple Color 1.0 - Manual (Page 150)

150 Chapter 8 Video Scopes
Luma
The Luma scope shows you the relative levels of brightness within the image. Spikes or
drops in the displayed waveform make it easy to see hot spots or dark areas in your
picture.
The difference between the highest peak and the lowest dip of the Luma scope’s
graticule shows you the total contrast ratio of the shot, and the average thickness of
the waveform shows its average exposure. Waveforms that are too low are indicative of
images that are dark, while waveforms that are too high may indicate overexposure.
If you’re doing a QC pass of a program with the Broadcast Safe settings turned off, you
can also use the scale to easily spot video levels that are over and under the
recommended limits.
Overexposed waveform
Underexposed waveform Well-exposed waveform