Luminous efficacy
- Dominant language
- C++
- Stars
- 20.5k
- Forks
- 2.3k
- Avg merge
- 2d 16h
- Merged PRs (30d)
- 74
Description
Filament uses 683 in some places to convert from physical luminosity (watts) to perceptual luminous flux (lumens). 683lm/W is the peak luminous efficacy of monochromatic 555nm green light, and sometimes used as a simplification.
https://github.com/google/filament/blob/74b09c708a71a934b192fbfd1fd14e032b00f9ae/docs/Filament.md.html#L1246-L1260
https://github.com/google/filament/blob/74b09c708a71a934b192fbfd1fd14e032b00f9ae/filament/include/filament/LightManager.h#L814-L816
https://github.com/search?q=repo%3Agoogle%2Ffilament+683+NOT+language%3ACSV+NOT+language%3ASVG+NOT+language%3A%22Wavefront+Object%22+NOT+language%3AText&type=code
FYI There is an open discussion about this constant in the Blender and Khronos GLTF repositories. Apparently the correct number is 177.83, not 683, and can be calculated using the spectral distribution of the D65 standard illuminant from Rec.709 specified for GLTF.
https://github.com/KhronosGroup/glTF-Blender-IO/issues/2493#issuecomment-2687469019
https://github.com/KhronosGroup/glTF/issues/2473#issuecomment-2688156071
Contributor guide
Assessment
This issue has not been assessed yet.