This is a great cheat for low cost 'dynamic' lights. If you bake lightmaps in passes, this is a very easy effect to author.

Essentially I combine two lightmaps; adding the dynamic map over the base map. For this demo, I do exactly that. In practical application, you would not want to double your lightmap textures space for a whole level. Instead, create a pass where duplicate chunks of localized geometry will hold low resolution dynamic maps (or even make a larger texture sheet for all the dynamic maps in your level, a 512x512 will do) and bake to a new set of UVs.

There is a lot of flexibilty, production time-savings, and specific look development which can be gained by building lightmaps (for realtime engines) in passes. Using mental ray, these passes are fairly easy to setup and bake. However, while final gathering (FG) works great (result-wise) for radiosity sampling, it is only single threaded when used for rendermapping. Seeing as how FG is a screen space method for sampling, I don't know if this can be called a bug (definitely an oversight). This limitation is made worse when several computers are used via satellite rendering to generate a single lightmap (or lightmap pass). The other systems sit idle, while one machine (using one core) calculates the FG prepass.
To avoid this production slow down and get your systems rendering with full CPU power, an environment sampling shader can do the work FG would normally calculate. Using mental ray's ambient occlusion shader with the below parameters, I generated the environment sampling with satellite rendering using 100% of 24 cores.

Use this sampling method with interactive IBL light domes for a fast and iterative lighting solution.

Here is the collection I use the most; feel free to download the .zip file. I took the liberty of giving the IES files artist friendly names. Using IES profiles to scatter indirect light energy into a scene gives a certain legitimacy to the render; even if the profile isn't used for light scatter effects directly. You can accomplish indirect scatter by setting up photon only lights with an IES profiles.

Wired-up an interesting glass shader.

 Streaming many 128 x 128 pre-baked textures on a consumer mobile device to push very highend looking graphics on limited hardware. Textures are loaded based on the viewers location; a 'poor man's' mega-texturing system. Fun to use all the cheats and lessons learned from the past to manipulate the phone's capabilities.

Render test (mental ray) to simulate radiosity from a moving light source. This technique requires a prepass to cache final gather maps into a single archive before the pixels are rendered. The prepass is painless in Softimage, but renderers like Arnold make caching and prepasses obsolete.

Using an intergrated compositor (Blender, Softimage, Houdini) it is possible to create an interactive studio environment to drive the IBL in a 3d scene. By wiring a couple vector paint nodes together in Softimage I can create an interactive environment map; then I use the map as the source image for the final-gathering or environment sampling.  HDR Light Studio is a standalone product that does just that. Read about the setup in Softimage here.

This environment sampling setup was used in two, full-scale production, Tony Hawk video game projects. 

Volume lighting tests with mental ray. Found this book very helpful. Its not an easy read (gets very technical) but contains an abundance of condensed knowledge that is difficult to find. If you use a version of Softimage prior to version 2011, download the .spdl files below for the required shaders.