Chetal Gazdar shows how to set up and render and RGB light pass in Autodesk Maya, that will be used for compositing in Nuke.
how to render RGB Light Pass in Maya as well as how to compose it in Nuke.
This workflow also applicable when you deal with super white value in your pass.(Specially when you render your image in openexr)
An RGB light pass can be created in any 3D application, where each channel R,G, or B, will contain the lighting information in the scene, from any particular light.
This saves time by having to do separate Render Layers for each light. You can render more than three lights by also setting secondary colors other than RGB. These can be brought out with simple calculations in the compositing application like Nuke.