What unit is used for measuring the brightness of projection devices?

The appropriate unit for measuring the brightness of projection devices is lumens. This measurement indicates the total amount of visible light emitted by a source, such as a projector, and is critical for assessing how well an image can be seen in various lighting conditions. A higher lumen rating generally means a brighter image, which can result in better visibility even in well-lit environments.

In contrast, megawatts measure electrical power; rays do not serve as an accepted unit of brightness in optical equipment; pixels refer to the smallest unit of a digital image and do not directly relate to the brightness but rather the resolution and detail of an image. Understanding that lumens specifically quantify light output makes it the clear and relevant choice for this question.