i am assuming it is something like this
http://www.ultimatereptiles.com.au/c...fd951c7060.jpg
Yeah, the light should come on if it is working, regardless of bulb etc.
Some have an on/off switch but other than that, if the light isnt coming on, and it is plugged in then it may not be working.
i assume that the temperature in the enclosure is less than the setting on the dial, obviously if not it isnt going to come on.
Is it all of them or just one that isnt working?