In general, the brighter the image a projector can produce, the more impact your presentation will have. For small groups of people in an office 1000 lumens is fine. As a rough guide under normal office lighting, 500 ANSI lumens per square metre of screen will give a bright and well-contrasted picture. Higher brightness allows larger images for presentations to more people. Bear in mind that the quality of the screen, it's size and the ambient light will have a dramatic effect on the image brightness. A demonstration by your dealer is the best way to make sure the projector will fit the job.