Radiance to Irradiance Conversion Training Level: Intermediate

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

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

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

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

5. Source Detector Geometry Area = A Distance = d 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. Source Detector Geometry If the source is uniform, then the light in the solid angle to the source…

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

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