Beware! Unpredictable results when mirroring area lights

I am modelling an interior spacing including a rectanglular space.
The ceiling of that spaced is step and there is light along the perimeter edges.
I created lights by mirroring the area light objects I created : Left to Right and Front to Back,mirrored about the room center. All lights pointing in the room.
Despite the light graphic indication showing the area light pointing into the room the two mirrored lights lit the rendering as if pointing the other way!
It took me a while to figure it out. I mirrored the mirrored lights again around their own center (this made them point out but their mirror setting was reversed meaning they were now unmirrored). Then I rotated them 180deg to point back into the room and all was ok.

I am sure that was the problem since the recessed light pattern was repeated in my model in 3 rooms, all had 2 area lights created then mirrored about the room center to form the remaining two lights. In all rooms the mirrored lights (2 out of 4 edges) were lit wrong. All were repaired as above.


  • all the problematic area lights had a negative Z scale value (Euler). So maybe you can mirror lights with no problem UNLESS it’s the pointing direction that is mirrored, meaning mirroring in X and Y maybe ok. Did not test.
  • Also I wonder if there is a difference between scaling the dimension (X or Y , not Z) of an area light vs actually modifying it’s dimensions from the light properties panel: does created 1X1 and scaled double (Euler 2) have the same lighting effect as one created 2X2