Brightness

سطوع (Ar); Luminosité (Fr); Helligkeit (Ge); Luminosità (It); 明度 (Ja); Яркость (Ru); Brillo (Sp).

Brightness is defined as the flux per unit of solid angle of the radiation cone. It takes thus the beam divergence into account. The unit is p.p.s. $\times$mra². Brightness is an appropriate parameter to use when comparing two X-ray sources with identical focal spot size, as the definition does not contain a unit area.