What Are ANSI Lumens?
An ANSI lumen in a particular unit of measurement for the light output of a projector. A lumen (lm) is a unit for measuring luminous flux, or the perceived output of a light source. ANSI is an acronym for the American National Standards Institute. As such, an ANSI lumen is a lumen measured in the specific method defined by the American National Standards Institute.
In 1992, ANSI defined a method for measuring the lumen output of projectors (both film and video). The method involves adjustments of brightness and contrast, measurements of a white field at nine designated spots on the screen, and the averaging of the measurements multiplied by the screen area.
The ANSI method for measuring lumens is very accurate and is therefore used in the marketing of projectors. Manufacturers almost always list the ANSI lumen output of their projectors as a point of comparison.
The lumen is defined as 1 lm = 1 cd·sr = 1 lx·m2 ("cd" is candela, "sr" is steradian, "lx" is lux and "m" is meter).
In the marketing of home theatre projectors, ANSI lumens can be somewhat misleading. The ANSI lumen measurement represents the optimum potential of the projector and does not reflect variables such as screen size, screen material, ambient light and viewer eye fatigue. Some projectors feature video optimization technology which can skew the ANSI lumen rating.
Lumens measure luminous flux, or light that is perceived by the human eye. This is not to be confused with radiant flux, which measures the total power of emitted light. The human eye is more sensitive to certain wavelengths of light.
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