I noticed something odd with lighting on a project I'm working on so re-created something simpler that shows the same thing.

With either distant or point lights in Karma, I find that object faces are receiving light when they shouldn't.

As a comparison, mantra renders as aspected and doesn't ‘bleed’ like Karma.

Wondering what's going on here and why the difference between Karma and Mantra.

…so, simply adding a normals to the geo helps Karma to render as expected.

I guess if no normals are present Mantra uses a normal perpendicular to the plane of the prim, pointing opposite for a reversed vertex order, while Karma takes the average direction of all vertices at each point, which gets averaged again accross the prim..something like that?

Mantra will by default add per-vertex normals if the mesh doesn't have any normal attributes (you can change it to point/shared normals by adding “Add Normals To Geometry” object property and and switching to “Point Normals”). Karma will add point normals (there's no equivalent property to switch the default).

Thanks dlee.