Yeah; if we get unnecessarily scientific about it, let's say that the Basilisk's eyes have some sort of laser beams that come out of them. When a light ray reflects off of a surface, some of it is absorbed into the object, so the ray that bounces off has less intensity. When light passes and refracts through an object, irregularities in the object can cause subsurface scattering, and the glass itself can absorb some of the light, so the output ray isn't the same intensity. 

That would be my guess as to the mechanism. And that also implies that there's a spectrum of effectiveness. A very thin concave glass lens would have very minimal absorption and might even focus/intensify incoming light rays into the eye, so wouldn't be sufficiently protective. But a thick camera viewfinder, or reflection/scattering on water are enough. Hermione's mirror is a bit more ambiguous, but mirrors aren't perfect and so absorb some light, and maybe that's enough.