  Radiant intensity - is the radiant flux radiated from a point on a light source into a unit solid angle in a particular direction. Radiance - Radiance is the radiant intensity per unit projected surface area, where projected surface area is the real surface area multiplied with the cosinus of the angle between the direction of the radiation and the surface normal. &nbsp;Standard unit of radiance is watts per steradian and square meter (W/sr&nbsp;m2) Radiant exitance - is the total amount of radiative flux leaving a point on a surface into all directions above the surface.
Irradiance (usually Ei in formulas) is the total amount of radiative flux incident upon a point on a surface from all directions above the surface. Reflectance / Albedo – the ratio of incident luminous flux upon a surface which is reradiated in the visual spectrum Luminous - Emitting light, especially, emitting self-generated light (as opposed to reflected light). 
