lumen (lm)
Lumen (lm) is the unit of measurement for the luminous flux incident on a given projection surface. The luminous power is measured, which refers to a unit area and is specified in lux
The suffix ANSI refers to the American Standards Institute and a measurement method standardized by it. The ANSI lumen was defined in 1993 and is more accurate than the undefined lumen. When measured in ANSI lumens, the projection screen is illuminated with white light. The entire surface is divided into 9 equal sized fields and in the center of each field the illuminance is measured in lux and multiplied by the area of the screen. The individual values and the average value from the 9 individual values characterize the properties of the projectors and offer comparability of the projection techniques among each other and are also independent of the size of the projection screen and the distance between the projector and the projection screen.
Smaller screens have between 150 to 200 ANSI lumens, larger screens have 200 to 250, and LCD anddigital light processing( DLP) projectors range from 1,000 to over 10,000 ANSI lumens. The ANSI lumen is thus a measure of projector luminous intensity and is directly related to reference picture bright ness(RHB) and room brightness.