The amount of light emitted through a projection system lens is TYPICALLY specified and measured

The light output of a projection system is typically measured in lumens, which quantify the total amount of visible light emitted by the projector. Lumens measure the projector's brightness, making it a standard metric for comparing different projectors' output capacities.

Lux is used to measure illuminance or the amount of light falling on a surface.

Footcandles is another unit of illuminance, similar to lux but based on the imperial system.

Contrast ratio describes the difference in luminance between the brightest white and the darkest black a projector can produce, not the brightness itself.

CTS Technology Specialist Reference

According to CTS training materials, projector brightness should be specified in lumens, which provides a clear indication of the projector's suitability for different environments and screen sizes.