Making a light source invisible to everything except shadow rays

Question

I saw this in another answer and I would like to know how to do it:

"Making a light source invisible to everything except shadow rays will cause it to only block light from other light sources and not influence anything else."

Thank you!

Answer 1

There are two ways to do this.

Materials nodes:

Ray visibility:

Using these ray visibility checkboxes instead of nodes will speed up render times a little, however you lose the flexibility of nodes.