ghostship2 posted at 6:10PM Sat, 30 May 2020 - #4390604

not a problem with your lighting but a problem with the shader you are using for the wood. post your material settings so we can see them.

Pretty standard PBR sort of setup:

I've used this exact shader on other things and not had this happen.

ghostship2 posted at 6:12PM Sat, 30 May 2020 - #4390605

what happens when you rotate the object so that the horizontal grain is running vertical?

No difference apart from the change in direction. The dark parts are still dark, the light parts are still light.