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A unit of measurement of the amount of brightness that comes from a light source. Lumens define "luminous flux," which is energy within the range of frequencies we perceive as light. For example, a wax candle generates 13 lumens; a 100 watt bulb generates 1,200 lumens.

Lumen Ratings for Data Projectors
When choosing a data projector, the lumen rating is an important specification. In a darkened room, 500 lumens may be ample; however, in a conference room with normal lighting, 1,000 lumens would be better. In a room with daylight, 2,000 lumens is preferred. The standard lumen rating of a data projector is the average of photometer readings at several points on a full white image on the screen. See ANSI lumen, candela and spectrum.