I am killing some time waiting for my lighting programmer to complete his work down here in Denver, so i'll address your questions.
First, you should see my book where each of the light sources are explained in detail. The book also explains in detail how to build light fixtures. No one using Archicad and LightWorks and seeking passable work would use the lamp objects to illuminate a scene since they take so long to adjust. Lamps are mere props in a photographic scene lit by photographic lighting: mainly the general light source.
Think like a photographer.
Yes, you can build any fixture and place a light source in it, but this often causes sharp, shadows. One places the light source in close proximity to the fixture, not necessarily in it.
The lamp glass is a constant glowing material that immitates a lamp turned on. It is fake. But it does lead us to emulating vast ceilings of fluorescent fixtures that appear to be "on" but don't add to rendering time.
Lastly: the spot light is obsolete - use a tightly focused light cone instead.
Dwight Atkinson