solid angle factor, Q

[] A function of the solid angle (ω), given in steradians, that is subtended by a source.* Solid angle factor is given by:

Q=20.4\left ( \omega \right )+ 1.52\left ( \omega \right )^{0.2}- 0.75

See index of sensation (M) (of a source).

* Recommended Practice for Photobiological Safety for Lamps and Lamp Systems — General Requirements, ANSI/IESNA RP-27.1-05. New York: Illuminating Engineering Society of North America; 2005. 

‡ McGowan TK, Guth SK. Extending and applying the IES visual comfort rating procedure. Illuminating Engineering. Apr 1969;64(4):253. 

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