Photons do not work properly with true inverse power fading

[CousinRicky]

Photon mapping does not work properly with true inverse power fading. When true inverse power fading was introduced, the photon mapping code was apparently not updated to use the new feature.

POV-Ray version: 3.8.0-beta.2.unofficial (self-compiled) OS: openSUSE 15.3 GNU/Linux Hardware: Lenovo Ideapad Slim 7 Architecture: x86-64 CPU: Intel Core i7

See attached example scene file. invsq_photons.pov.zip

These scene has 4 animation frames.

1. Frame 1 uses the old light fading formula without photons.
2. Frame 2 uses true inverse square fading without photons.
3. Frame 3 uses the old light fading formula with photons.
4. Frame 4 uses true inverse square fading with photons. Frame 4 should look similar to frame 3; instead, it has hyper-white caustics as if no light fading was used at all.

User wfpokorny has proposed a solution, but I do not know if it has been implemented.

[CousinRicky]

See thread Photons are broken with true inverse squared lighting in povray.beta-test.