I believe that the corresponding SI unit could be the becquerel which is defined in the SI brochure as the unit of activity (Wikipedia [wrongly?] states radioactivity).
_____ From: [email protected] [mailto:[email protected]] On Behalf Of John M. Steele Sent: 27 September 2011 02:07 To: U.S. Metric Association Subject: [USMA:51162] Re: The Rayleigh and SI I'm not familiar with the unit, but the Wikipedia article seems more "consistent." http://en.wikipedia.org/wiki/Rayleigh_(unit) The rayleigh is a unit of photon <http://en.wikipedia.org/wiki/Photon> flux <http://en.wikipedia.org/wiki/Flux> , used to measure air <http://en.wikipedia.org/wiki/Air_glow> glow (auroras <http://en.wikipedia.org/wiki/Aurora_(astronomy)> , for example). It was first proposed in 1956 by D. M. Hunten, Franklin E. Roach, and J. W. Chamberlain. <http://en.wikipedia.org/wiki/Rayleigh_(unit)#cite_note-0> [1] It is named for Robert John Strutt, 4th Baron <http://en.wikipedia.org/wiki/Robert_John_Strutt,_4th_Baron_Rayleigh> Rayleigh (18751947). <http://en.wikipedia.org/wiki/Rayleigh_(unit)#cite_note-1> [2] Its symbol is R (also used for the röntgen <http://en.wikipedia.org/wiki/R%C3%B6ntgen> , an unrelated unit). SI prefixes <http://en.wikipedia.org/wiki/SI_prefix> are used with the rayleigh. One rayleigh (1 R) is defined as a column emission rate of 1010 photons per square metre <http://en.wikipedia.org/wiki/Square_metre> per column per second <http://en.wikipedia.org/wiki/Second> . Note that rayleigh is an apparent emission rate, as no allowances have been made for scattering or absorption. The night sky has an intensity of about 250 R, while auroras can reach values of 1000 kR. The relationship between photon radiance, L, (in units of photons per square metre per second per steradian <http://en.wikipedia.org/wiki/Steradian> ) and I (in units of rayleighs) is simply L = I \frac{10^{10}}{4\pi} <http://upload.wikimedia.org/math/2/3/8/23880c078e12078378a924ebb6c229ae.png > --- On Mon, 9/26/11, Bill Hooper <[email protected]> wrote: From: Bill Hooper <[email protected]> Subject: [USMA:51161] The Rayleigh and SI To: "U.S. Metric Association" <[email protected]> Date: Monday, September 26, 2011, 8:32 PM I just ran across this cgs unit, the Rayleigh, and wonder if there is a corresponding SI unit. Also, is the given equivalence correct? The article notes that the Rayleigh is equal to a given number of photons per square metre per steradian. It does't seem to be correct to me. If one of the two units includes "per unit time" (per second) mustn't the other also involve "per unit time"? Similarly, if one unit involves "per unit solid angle" (per steradian), mustn't the other also include "per unit solid angle"? Otherwise, the two measures do not have dimensional consistency. Am I right, or am I overlooking something. ==================================== Here is the definition I found: Rayleighs 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 <http://www.unc.edu/~rowlett/units/sipm.html> units, 795.775 x 106 per square meter per steradian <http://www.unc.edu/~rowlett/units/dictS.html#steradian> (m-2·sr-1). >From the web site: http://www.scribd.com/doc/32965079/A-Dictionary-of-Units-of-Measurement (Click on R and scroll down to find the Rayleigh.)
