Intensity

The intensity of an emitter in a given direction is the flux it emits per unit of solid angle in the direction considered. The intensity is denoted \(I_{S}\) and is expressed in \(W.sr^{-1}\). We have

I S = dΦ d Ω s size 12{I rSub { size 8{S} } = { {dΦ} over {d %OMEGA rSub { size 8{s} } } } } {}
Figure 2.6 : intensity of a source

A so-called isotropic source is a source whose intensity is independent of the direction of emission. However, this situation is very rare in practice. The angular behavior of radiation is characterized by the intensity indicator or radiation diagram. The indicator of an isotropic source is a sphere.