Caustics in Arnold work but at a cost. I'm sure you guys can find a way to make it better, stronger, faster. The trick is you can't use a traditional light, it has to be an emitter like a piece of geometry.
Bad news, its REALY expensive to render.
Step 1: Make a ground plane and give it an aiStandard. Turn down the defuse color to a dark gray, this helps capture the refraction.
Step 2: Create some geomerty to shine the light through and drop them on the ground plane. Give them an aiStandard and change the settings to a glass like shader. Scroll down to Caustics and check the Enable Refractive Caustics button. I placed a ramp into Transmittance in order to better showcase the effect. Any color will work.
Step 3: Create a second plane, translate and angle it to emit light on the objects, the angle should create long shadowed refractions on the ground plane. Make it a 1x1 plane in the channel box or each subdivision will act as its own light overpowering the scene. Scroll down to Emission and turn up the value, I chose 10. It now works like a light. At this point a nice refractive effect should be spilling across the ground plane.
Share and ideas you may have to improve and clean up the process.