Drag the cat/square (press space to change) to change the light USE TURBOWARP https://turbowarp.org/1135400497?turbo https://turbowarp.org/1135400497?fps=250 USE TURBO MODE ALSO BY PRESSING SHIFT AND CLICKING THE GREEN FLAG (The link already has turbo on)
The walls reflect about 75% of photons and is speculative reflection, cat/square reflects 10% of photons and is diffusive reflection. (there is also subsurface scattering, but not much)