Lighting/shadow problems in RunTime

Hello, some faces end up darker or blacked out then the others, I try ctrl+n and checking the UV Face setting, but it shows nothing is wrong, I figure out how to correct this by mirroring the face or rotating them to the opposite side, Is there a better way to do this ?

Maybe you just need a few more lights in the scene.

Use radiosity.

Well, seem to figure out the problem, which was enabling draw normal and flipping them, it’s alot like how the texture face in Doom map editing.

Doubles or duplicates also can cause this problem.