Question about photon power

[2H0U]

In function PhotonShootingTask::Run, the photon power is initiated by function Light::Sample_L which gives radiance instead of flux. In this case, the result of function EPhoton will have a wrong unit. Any explanation?

[mmp]

The way that photon mapping is introduced in Physically Based Rendering isn't in terms of the traditional differential flux stuff, but in terms of measurement equations (see section 15.6.1). In that framework, it actually is radiance that's emitted by the light sources.

An alternate answer would be that if you want to think about it in terms of differential flux, then it's the same computations as pbrt has implemented, just with various unit conversions happening at different times. But IMHO the PBR approach is a bit more rigorous, and also leads to a foundation that works better for understanding things like the recent vertex connection and merging work...