Lighting issues (weird lines/circles on 3D objects)

This is an effect called 'banding'. It occurs particularly in areas of low light/little contrast in colour, as the gaps are so small that the computer can't 'distinguish' between them. You have, however, stumbled upon the fix for your own problem. In practically every context, the way in which you deal with banding is to simply add noise to your scene, as you have done here. This works because the human eye is surprisingly lenient towards noise, and as the colours have been 'jittered' together, your brain fills in the gaps. In actual fact, there is still just as much banding happening, its just that you can't perceive it.