Weird artifacts on surface

lasersayspew

Initial scene(first pic) has 2 ghost lights at the window and at the ceiling. When I add a meshlight outside(second pic) the floor starts to look weird, how do I avoid/fix this?

Tried moving to the world center, changing shaders on the floor(same artifacts at the same positions no matter the shader or tiling)

 

4blueyes

As a quick and dirty fix, try to raise the floor from the ground a little bit (0.1-0.5) (I assume the floor mesh is flat on the ground of the scene).

lasersayspew

The floor is above the ground. There is one more light source, meshlight that illuminates bg image. When I turn it off those artifacts disappear. Or when I turn the sun-mesh off. So it's like there are too many lightsources, 4. Astronomical number for daz I guess.