Objects that emit light

This image uses mental ray. We have a spotlight on for all the boxes but the light emitting cluster in the middle. The moral of the story will be: set output to above 1.0 to self illuminate, and turn on FG.

The light emitting object’s material:

This is the setting for the OUTPUT map ... the 2.0 output is for the brightness of the light. The fact that is it ABOVE 1.0 makes it self illuminate if FG is on.

The falloff [could be a gradient ramp, whatever]:

Don’t forget to set your minimum sample to 1, this will eliminate blockiness on relatively flat areas like the floor:

Global Illumination settings enabled:

The Light Properties:

Set Final Gather to 10 for a fast render, or higher for better results: 500, 0r 1,000..

Also, the min/max setting ... use the Message window to get a number:

When you render it WILL complain that there are no photon emitters [light] ... but who cares? Render will be faster. Of course, you have no light rollouts to work with, so you have to love the shadows as they are, or add other lights.