https://unitycoder.com/blog/2012/01/24/ray-tracing-photon-mapping-render-unity3d-c/
Ray Tracing & Photon Mapping (Unity3D C#)
An article by mgear 
6 Comments
Converting some ray tracing code from java/processing (original source by Grant Schindler/2007)
1st version works fine already, just missing the user interactions.. (and its quite slow at the moment)
Current progress: v1.0
– 512×512 render: time 23.65258s (got it down to 16.54801s, if disable preview while rendering..)
– 128×128 render: 1.34s
– Didnt manage to make it faster with small changes, giving up for now.
– Its quite fast in low resolution..
– Here is more interesting project, too bad no sources to download? http://forum.unity3d.com/threads/27612-Real-time-global-illumination
Webplayer:
http://unitycoder.com/upload/demos/mRayTracingPhotons1/
Download source: (C#)
RayTracePhoton.unity
Tags: 3D, ambient occlusion, photon, ray tracing, reflections, render, shadows