**Default unit:** watt per steradian per square metre per nm (W·sr-1·m-2·nm-1)    
**Opt. unit:** watt per steradian per meter3 (W·sr-1·m-3) (1), watt per steradian per square metre per hertz (W·sr-1·m-3) (2)

Radiance of a surface per unit frequency or wavelength.

                        
