Now the sewers are no more magically illuminated. They are pitch black except near the manholes that let the sun light the ground (during daytime). I still have to add artificial lights (torchs) at least in the first levels. Until then, I have to buy a torch each time I go and test the sewers ;)
On this first screenshot, I'm standing between two manholes. We can see the white sun light and the light from my torch which is more yellow.
On this one, I went away from the manholes and there is only the torch light. The white dots represent visible cells, the light gray the cells in penumbra.