[book 3] Is sampling a light from a point where said light can't be seen correct?

[miguelggcc]

As the title says, wouldn't biasing rays towards a light in places located in the shadow of that light significantly increase the variance there, to the point it would need an ridiculous amount of computing time to eventually converge? Shadow rays would easily solve this problem.

Hopefully this image clarifies what I mean:

[trevordblack]

You are correct. Biasing rays toward a light in an area of the scene that does not have visibility of the light will increase variance. You can definitely add shadow rays as an alternative.

With that said, this isn't really something that we can address in the book as the content of book 3 is meant to educate the reader on an underlying understanding of PDFs. We don't have the time to rewrite for variance & shadow rays.

This is something that we are actively thinking about. But I don't know the extent to which we can/will address