Glow is also caused by a number of optical phenomena. One of them is particles in the air. You can create these in mentalray by using the parti_volume shader.

Another few things you can play with:

1) Put a physical lens shader on your camera, which will help "blow out" areas correctly.
2) Attach an mib_blackbody shader to the additional color attribute of the filament's additional color. This will allow you to specify a physical color temperature for an incandescent bulb. (Usually around 3300K) You'll need to push the intensity to some stupid number (something like 1000000) in order to see it properly.