1. Radiance to Irradiance Conversion Training Level: Intermediate
Dr. Richard Young
Optronic Laboratories, Inc.

2. Geometry Source Detector
Let us start off with a source of radiance, e.g. a sphere source, and a detector

3. Geometry Source Detector
Each point on the detector is illuminated by light within the solid angle (cone) to the source

4. Geometry Source Detector
A large distance between source and detector is required for even illumination.

5. Geometry Source Detector Area = Distance = d A
The solid angle is calculated by A/d² when d²>>A

6. Geometry
Although it is a simple formula, it works well at d>10 x source diameter

7. Geometry Source Detector
If the source is uniform, then the light in the solid angle to the source…

8. Geometry Source Detector
…is equal to the light in the same solid angle from the source.

9. Geometry Source Detector x sr Irradiance from Radiance: E = L * A/d²
L [W/(cm² sr)]
E [W/(cm²)]
x sr
Irradiance from Radiance: E = L * A/d²
Radiance from Irradiance: L = E * d²/A