The luminance of radiation refers to the light flux per unit area, usually described in terms of the solid angle (in radians) per unit area. The luminance of radiation can be calculated using the following formula:

 

L = dΦ / (cosθ dA dΩ)

 

where L is the light flux per unit area, dΦ is the light flux passing through a small surface element dA, dΩ is the solid angle of the surface element, θ is the angle between the normal to the surface element and the line of sight of the observer.

 

In practical applications, illuminometers or radiometers are commonly used to measure the luminance of radiation. If the light flux and emitting area of the light source are known, the luminance of radiation per unit area can be calculated by dividing the light flux by the emitting area, and then the luminance of radiation can be calculated using the above formula.

 

It should be noted that the luminance of radiation is related to the direction and position of the light source, so specific calculations and adjustments need to be made for practical applications.