I have a scene with a gi light (Irradiance only). It looks fine without irradiance cache activated but with long render times. If I turn on irradiance cache in the mantra properties I always get white specles but I have no idea which parameter I should change to get rid of these specles.

And what exaclty are the differences of rendering between irradiance, photon mapping and pbr? I have roughly an idea but Im missing the essence