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Radiance

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Radiance

The physical quantity that corresponds closely to the visual brightness of a surface. A simple radiometer for measuring the (average) radiance of an incident beam of optical radiation (light, including invisible infrared and ultraviolet radiation) consists of a cylindrical tube, with a hole in each end cap to define the beam cross section there, and with a photocell against one end to measure the total radiated power in the beam of all rays that reach it through both holes (see illustration). If A1 and A2 are the respective areas of the two holes, D is the length of the tube (distance between holes), and is the radiant flux or power measured by the photocell, then the (average) radiance is approximately given by the equation .

A simple radiometerenlarge picture
A simple radiometer


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? Mentioned in ? References in classic literature
 
She and her husband fell asleep with hands tenderly clasped, and awoke from visions of unearthly radiance to meet the more blessed light of one another's eyes.
From Twice Told Tales by Hawthorne, Nathaniel View in context
After many years, on looking back from the middle turn of life's way at the events of the past, which, like a friendly crowd, seem to gaze sadly after us hastening towards the Cimmerian shore, we may see here and there, in the gray throng, some figure glowing with a faint radiance, as though it had caught all the light of our already crepuscular sky.
The Mirror of the Sea by Conrad, Joseph View in context
But high above the flying scud and dark-rolling clouds, there floated a little isle of sunlight, from which beamed forth an angel's face; and this bright face shed a distinct spot of radiance upon the ship's tossed deck, something like that silver plate now inserted into the Victory's plank where Nelson fell.
Moby Dick I-LXVII by Melville, Herman View in context
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