Projector brightness is measured in ANSI lumens. LCD, DLP, and LCoS projectors start as low as 750 lumens (best for lights-off presentations), and go beyond 3500 lumens. Low lighting presentations are generally not desirable, as you may be inviting a few to doze during your presentation. A projector with at least 800 lumens is desirable for use in rooms where there will be some ambient light that cannot be eliminated. The size of your audience will also factor into how bright your projector should be. Larger audiences require larger images, which also require higher lumen output.
Fast and easy guide:
   - 750 lumens for small presentations with low ambient light.
   - 900 lumens for small presentations with some ambient light.
   - 1700 lumens in conference room setting with high ambient light.
   - 2500 lumens for large venues with some ambient light.