The light is not an ultraviolet light or a laser. Originally, they were a really bright projector bulbs with a loud cooling fan, cords and everything. Now the newer ones are wireless LED's which do not produce much heat. The light travels down a fiberoptic glass bundle to the tooth. (That's the curved rod looking thing). I think most of the cost of the things is making the fiber-optics. They also have reduced the curing times by adjusting the frequency of the light to match the chemical in the material that initiates the reaction-roughly 470nm. Curing times used to be about 40 seconds. The most recent one claims a 5 second cure. That seems a little too short for me, but we will see. They make the thing beep every 10 seconds or so as a timer, so you might hear a mysterious "beep" noise while in the dental office. For all this fancy technology, I tell the kids it's a flashlight, (which it pretty much is).
Oh, this is a short funny video showing the "flat (dead) battery" feature. Of course, I always dress in a tux in the office:
There are some other cool videos out there for different companies version of these lights, especially if you go deeper into their websites. Ivoclar has a Ivoclar James Bond Theme Video-A License to Cure
Light frequency distribution chart courtesy ADA Professional Products Review Vol. 4 Issue 4 2009.