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The latter is commonly measured in W⋅sr −1⋅m −2⋅nm −1. Radiance of a surface per unit frequency or wavelength. Watt per steradian per square metre per hertz This is sometimes also confusingly called "intensity". Radiant flux emitted, reflected, transmitted or received by a surface, per unit solid angle per unit projected area. The latter is commonly measured in W⋅sr −1⋅nm −1. Radiant intensity per unit frequency or wavelength. Radiant flux emitted, reflected, transmitted or received, per unit solid angle. The latter is commonly measured in W⋅nm −1. Radiant flux per unit frequency or wavelength. This is sometimes also called "radiant power", and called luminosity in Astronomy. Radiant energy emitted, reflected, transmitted or received, per unit time. Unlike power density, radiant intensity does not depend on distance: because radiant intensity is defined as the power through a solid angle, the decreasing power density over distance due to the inverse-square law is offset by the increase in area with distance. Radiant intensity, denoted I e,Ω ("e" for "energetic", to avoid confusion with photometric quantities, and "Ω" to indicate this is a directional quantity), is defined as I e, Ω = ∂ Φ e ∂ Ω, Mathematical definitions Radiant intensity In radio-frequency engineering, radiant intensity is sometimes called radiation intensity. Radiant intensity is distinct from irradiance and radiant exitance, which are often called intensity in branches of physics other than radiometry. m −1)-commonly the watt per steradian per nanometre ( W.Hz −1) and that of spectral intensity in wavelength is the watt per steradian per metre ( W.

The SI unit of radiant intensity is the watt per steradian ( W/sr), while that of spectral intensity in frequency is the watt per steradian per hertz ( W In radiometry, radiant intensity is the radiant flux emitted, reflected, transmitted or received, per unit solid angle, and spectral intensity is the radiant intensity per unit frequency or wavelength, depending on whether the spectrum is taken as a function of frequency or of wavelength. For other measures of electromagnetic radiation, see Light intensity (disambiguation). For ionizing radiation, see Radiation flux.