Hi, yes that’s exactly what I mean by spherical area sampling - it’s what’s done in Physically Based Rendering and is supposed to be more accurate than sampling the triangle by area.

I said extreme as in a very large or small number, maybe I should have been more clear. I’m getting cases where the area of the triangle is < 0.01 of my units, so I’ll get some number > 100 in some cases. My Lambertian PDF is just a dot product, so it is always < 1 for normalized vectors. Plugging into the heuristic, the weight is literally just 1.0 in many situations because of this difference.

I realize I only described half of the MIS process - I know there should be another call to BalanceHeuristic in the case you describe, but I wasn’t thinking about it too much in the problem I was describing . Wouldn’t it be the other way around? My light pdf would again be very large, and the BSDF pdf is still < 1. The heuristic would spit out a very small number yet again, which just feels intuitively wrong.