The Lumen (lm) is the SI unit of Luminous Flux (the perceived power of light). For projectors, output is typically measured in ANSI lumens - a standard set by the American National Standards Institute in which measurements are taken from several positions and averaged together, with the projector under controlled conditions.

The efficacy at which a source produces light is known as its Luminance Efficacy and is measured in lm/W. This is not to be confused with efficiency, which is the percentage of the power converted to visible light.

See Also

• Useful post explaining lumens, lux and light source efficiency

External Links

• Wikipedia article on Lumens
• Wikipedia article on Luminous flux
• Wisegeek article on Lumens

• Discussion