Music video by Justin Bieber performing Never Let You Go. (C) 2010 The Island Def Jam Music Group. #VEVOCertified on November 9, 2010. http://www.youtube.com/vevocertified.
Lumens are a unit of measurement of the total brightness that comes from a light source, in this case, a projector. One may also see the term ANSI Lumens. ANSI is an acronym for the American National Standards Institute. In general, the more lumens a projector has, the brighter the image on the screen.
For home theater projectors where ambient light is kept to a minimum, you'll need a minimum of 1500 lumens. For classrooms, conference rooms or rooms with windows, a projector with a minimum of 2500 lumens is best. For large auditoriums or lecture halls, you'll need more lumens.