The concept of brightness is easy to understand. Projector specification sheets
rate brightness in the form of lumens. What is a lumen? A lumen is a unit of
measurement for the total light output from a specific source. The higher the
lumen count, the more light the source is able to produce.
The brightness controls found in the menu of all projectors control the brightness
in the dark areas of the image (functionally opposite of the contrast controls).
Brightness and contrast controls are usually the two controls that are most likely
to be set incorrectly. As we mentioned in the contrast section, the key to
adjusting these two controls is to have a frame of reference like a home theater
calibration DVD.