I tried to rerender with different options you guys suggested, but nothing seems to work (except increasing render time ). I think it's the material of the lamp or something. When I move the lightsource down about 1 meter, I don't get the spots (but the light isn't coming from the lamp ofcourse). If I change the color of the lamp housing to black, the spots also disappear. Next, I tried to use a VRay material (plastic) but that didn't help neither. It seems that whenever I change the lamp material to something bright, It shows me the spots. When I use a dark material, the spots disappear. I'm at work now, so I can't show you the results right now. Tnx