Why don't I see light reflected off a mirror in Cycles? I want to render mirror balls. In the real world you would hit each mirror ball with a spot light.

To test if this would work in Cycles, I made a mirror ball and hit it with two spot lights (shown with red and green arrows) as shown here:


However, although you can see the direct spot light effect on the walls, the mirror balls show no light and no light is reflected onto the walls from the mirror balls.


What I would want to see is light on the other side of the wall (i.e. in the area circled in red) because that is the direction the second spot light is pointing, and directly perpendicular to the normal of a few faces of the sphere.

Why don't I see any light reflected from the balls?

Here is the project file:
Lights are only visible in Cycles when they are mesh lights. If you want a light source to be reflected you need to make it from geometry and create an emission shader for it.

If you wish light to be reflected and illuminate other objects, you need to enable reflective caustics:



These calculations take a lot of time in Cycles and are inefficient, because of the way tehy are calculated. For better caustics one would need to use a render engine that supports bidirectional pathtracing. I think LuxCoreRender can do a better job with this.