Rayleigh (R)
Rayleigh (R) :
A CGS unit of light intensity used in astronomy and physics to measure the brightness of the night sky, auroras, etc. One rayleigh represents the light intensity of one million photons of light emitted in all directions per square centimeter of receiver per second, or, in SI units, 795.775 x 106 per square meter per steradian (m-2·sr-1). A dark night sky has a light intensity of roughly 250 rayleighs. The unit honors the English mathematician and physicist John William Strutt, the third Lord Rayleigh (1842-1919)
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