A unit of luminous flux used to measure air glow, for example of aurora, first proposed in 1956.1 Symbol, R. The SI prefixes are used with this unit. One rayleigh is 1010/4pi quanta per square meter per second per steradian.

The night sky has a luminous intensity of about 250 rayleigh, while auroras can reach values of 1000 kilorayleigh.

The unit is named for Robert John Strutt, fourth Lord Rayleigh (1875 – 1947).

D. M. Hunter, F.E. Roach, and J.W. Chamberlaine.
Journal of Atmospheric and Terrestrial Physics (GB) volume 8, page 345 (1956).

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