Radiance and spectral radiance are measures of the quantity of radiation that passes through or is emitted from a surface and falls within a given solid angle in a specified direction. They are used in radiometry to characterize diffuse emission and reflection of electromagnetic radiation. In astrophysics, radiance is also used to quantify emission of neutrinos and other particles. The SI unit of radiance is watts per steradian per square metre (W·sr−1·m−2), while that of spectral radiance is W·sr−1·m−2·Hz−1 or W·sr−1·m−3 depending on if the spectrum is a function of frequency or of wavelength.
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Famous quotes containing the word radiance:
“The radiance was that of the full, setting, and blood-red moon, which now shone vividly through that once barely- discernible fissure,... extending from the roof of the building, in a zigzag direction, to the base. While I gazed, this fissure rapidly widened.”
—Edgar Allan Poe (1809–1849)
“The complete life, the perfect pattern, includes old age as well as youth and maturity. The beauty of the morning and the radiance of noon are good, but it would be a very silly person who drew the curtains and turned on the light in order to shut out the tranquillity of the evening. Old age has its pleasures, which, though different, are not less than the pleasures of youth.”
—W. Somerset Maugham (1874–1965)
“What though the radiance which was once so bright
Be now for ever taken from my sight,
Though nothing can bring back the hour
Of splendour in the grass, of glory in the flower;
We will grieve not, rather find
Strength in what remains behind.”
—William Wordsworth (1770–1850)