In
radiometry,
radiosity is the
radiant flux leaving (emitted, reflected and transmitted by) a
surface per unit area, and
spectral radiosity is the radiosity of a
surface per unit
frequency or
wavelength, depending on whether the
spectrum is taken as a function of frequency or of wavelength. The
SI unit of radiosity is the
watt per square metre , while that of spectral radiosity in frequency is the watt per square metre per
hertz (W·m
-2·Hz
-1) and that of spectral radiosity in wavelength is the watt per square metre per metre (W·m
-3)—commonly the watt per square metre per nanometre . The
CGS unit erg per square centimeter per second is often used in
astronomy. Radiosity is often called "intensity" in branches of physics other than radiometry, but in radiometry this usage leads to confusion with
radiant intensity.