If you want to do it in Mental ray, create an mia_material, and under advanced, map a mia_light_surface node. In the color, map an mib_blackbody. In the blackbody, set the temperature to 7500 (cool-white) and leave the intensity at 1. Go back and map this blackbody to the mia_material's color as well. Go back to the mia_light_surface node, and turn the Fg Contrib to 1. To make your light brighter, play with the intensity and the Fg Contrib. (It goes without saying that you'll need to enable final gather)

If you want your light to glow, and you don't want to do it in post, you can map the output value of the mia_material into the color of a surface shader, assign the surface shader to the object, then use the glow there.

Hope this helps.