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ANSI E1.48-2014 (R2019)
A Recommended Luminous Efficiency Function for Stage and Studio Luminaire Photometry
ANSI E1.48 specifies an luminous efficiency function V(lambda) that more accurately represents human eye response than many other V(lambda) functions often used when measuring light energy and then expressing it in units that represent the human eye response, such as lux, lumens, and candela. The function recommended in E1.48 results in a more accurate rendering of perceived brightness, particularly with narrow-band sources that have significant energy at the extreme ends of the spectrum, than do other commonly used V(lambda) functions.
Entertainment Services and Technology Association [esta]