ANSI lumens
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ANSI lumens are a brightness unit from the withdrawn standard ANSI/NAPM IT7.228 (1997). To measure it, use a full-white field in the brightest mode, with calibration that is close to correct. Measure the illuminance (lux) at the 9 points of a 3×3 grid. Calculate the average. Then multiply the average by the image area in m².
"ANSI lumens" is still the term that people cite most. The standard behind it no longer exists.