Radiance
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:
“Miracles occur,
if you care to call those spasmodic
Tricks of radiance miracles. The wait’s begun again,
The long wait for the angel,
For that rare, random descent.”
—Sylvia Plath (1932–1963)
“Give me your poppies,
let their radiance spill
rapture
for ever;
love me,
O love me.”
—Hilda Doolittle (1886–1961)
“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)