Please correct me if I'm wrong. Does Le(p,w0) here means the irradiance emitted from point p on surface when not considering light?
(eg. When not considering light, we can consider surface point p as a point light source if the surface is shining. If the surface does not shine, then Le(p, w0) can be considered as 0)
I think slide 36 can answer this question.
@Nina. It is radiance emitted from point p in direction w_o. (But this is very much "considering light"! I think you mean when not considering reflected light.)
Why don't we also need to weight the emitted light from point p by a cosine? The light emitted from p does not necessary hit the lens at an angle perpendicular to the lens' surface.
I think its because we're trying to compute the amount of output radiance from point p in the direction wo. The Le term we are considering is already giving us the radiance along wo, so there's no need to multiply by cosine.