Generally, the → radiant energy
per unit → solid angle per unit of
→ projected area of the → source.
It is usually expressed in → watt per
→ steradian per → square
→ meter (W m-2 sr-1). Same as
steradiancy.
Of any particular → wavelength within the interval
covered by a → spectral line, the → energy
per unit → surface per steradian,
per wavelength; denoted Iλ. The term radiance is often loosely
replaced by “→ intensity.” The radiance of the whole line is given by
I = ∫ Iλ dλ. The radiance of an
→ emission line depends, among other things, upon the
→ number of → atoms
per unit area in the → line of sight (the
→ column density) in the
→ upper level of the line.
Etymology (EN): From radia(nt), → radiant, +
→ -ance.
Etymology (PE): Tâbešmandi, noun from tâbešmand “possessing radiation,”
from tâbeš, → radiation, + -mand a suffix denoting
possession; Mid.Pers. -ômand suffix forming adjectives of quality.
