Strange lighting effect

I have created a spiral staircase with grille steps. The scene is lit with one spot directly above.

Problem is that whether I use smooth or flat shading, the front faces of the steps are split in half (just visually of course) and in flat shading even the light seems to come from below!

Subdividing the mesh didn’t help at all and the scene has already over 100 000 faces with just the stairs and the stairwell.

Are you model normals really facing outside? Fid you check it?

It would be great if you could share a blend file with the mesh to inspect.

It is eevee, right?
Looks like “Contact shadows” option is not checked at the light.

This is not exactly the same file (I altered it after the original post), but very close to it.

How can I check the normals and how can I change them? (1.9 MB)

Nope, it’s cycles.

The normals are messed up. You can apply “Weighted Normal” Modifier to fix it.
Or reset vectors.

Nope, normals are fine and the file you shared is working as it should work.

Oh, yes, the shade flat is not. I will give a look and say something in a bit.

The problem in your model is that, for some reason, the autosmooth is affecting the the model even in the shade flat mode. So you go and disable the autosmooth there.

I believe the reason for that is that your modeling is a bit messy. It’s really not important if the model is just for your own use but if you want to keep it as a good asset you should be more precise on that. That would help also to avoid lots of issues, like this one you had.

Thanks, now the shading works as it should. And yes, the model could be more simple and even “lighter” without losing any visual aspects.

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Not just that, there are some parts where it as supposed to be solid, but you just have faces there. If you want, I could show you how to model that in a very simple and absolutely clean way.

It would take 3 minutes for you to model that.

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