This is a great big ball of tritium inside a polymer body. It's got sort of a mechanism that lets you "turn it off" by twisting the handle to hide the lamp source from the lens. I've had this for about 7 or 8 years, and it's still glowing pretty brightly.
Note: This is not "flashlight" bright. This is low low LOW light illumination. In total darkness, with night adjusted eyes, this will light things up that are less than a foot away from the lamp. Don't buy this thinking it's an always on low beam flashlight, you'll be sorely disappointed. Buy this if your M1 Abrams tank needs a front night sight. That's about what it feels like. Anyways, this is far and away the largest single piece of GITD tritium I've ever seen. And it's not exactly something that's easy to get here in the states. This was given to me by friend who's from somewhere in Northern Europe.