I was going to say "an illumination device" because I couldn't decide if I should call it a light or a lamp, but I figured that would be overcomplicating things.
From my time doing am-dram stage teching:
The
lamp is the bulb/tube/etc that is housed in a
lantern (or
luminaire if you're feeling fancy, or
instrument if you're feeling American) and is the source of the
light that shines out of the front
(the stuff that the director will never be entirely happy with, the cast will complain is getting in their eyes, and the lighting director will want to make into ultimate violet at every opportunity :roll
Of course, the terminology
(& outrageous stereotypes) in other industries may differ...