Brightness is measured in ANSI lumens. For home theater projectors, brightness typically ranges from 700 – 2000 lumens or more. Your viewing environment will be a big part of determining how bright your projector needs to be:
– home theaters need 1000 lumens or better.
– rooms with some ambient light should have at least 1200 lumens.
– big spaces with high ambient light need about 2000 lumens.
Suggested projector lamp brightness

Image courtesy Benq.
LCD and DLP lamp life
LCD and DLP projectors typically have a lamp life between 2000-4000 hours. This specification is actually referring to the ‘half-life’ of the lamp. The half-life is the point where the lamp is half as bright as it was new. The lamp will still work at its half-life, but it will continue to gradually lose brightness. Longer lamp life means less expense in maintaining your projector.
Run your projector for two weeks and/or 20 hours shortly after your purchase. If the lamp is going to fail, it will usually occur within the first ten hours of operation.