reflecting direct light on glossy surface in Cycles

Question

Working in Cycles.

Say I have a "disco ball" with a glossy shader. I'm pointing a spot light to it, and I'm trying to have the reflections of that light illuminate the diffuse material on the walls with the patterns from the ball.

I get this:

but I'd like to get something like:

For the illustration I placed a point light inside the ball an removed faces. But what I'd like to do is move the light around the ball so that the light reflected from it changes like it would do in real life.

Is that possible at this point?

EDIT:

Just for the record here's the image rendered in LuxRender (yet another program to learn...)

Answer 1

Unfortunately cycles isn't very good at rendering caustics yet, due to the way it traces rays "backwards", from the camera to the light source; it's very unlikely for a ray to bounce off a diffuse surface, a glossy surface, and then hit a point light source.

However there is a working patch which adds Metropolis Light Transport (MLT) and adaptive sampling based on noise detection.

In the mean time, if you don't want to compile blender with the MLT patch, you might want to try Luxrender, an open source render engine which supports unbiased MLT and Bi-directional sampling. It can also use openCL to render using a GPU.

Answer 2

I had to create a disco ball for a project and I was determined to find a work around for this.

Here is what I came up with.

1. Create a spot light with a very small and sharp light.

2. Then create an object that you want to shoot light (in my case a disco ball)

3. Add a hair particle system and choose the spotlight as the object. You will have to play with the settings for the hair to match your object but the settings below worked well for my disco ball.

Answer 3

Apart from Lux it is worth to check Yafaray (in PM or SPPM) and Mitsuba (in Energy Redistribution PT mode).