The Light Cannon is a nice light, but as others have suggested it won't take you far in cave diving.
Just to throw in another idea in with the already good ones, I would take a look at this:
http://www.cnsales.net/photontorpedopage.htm
The LED version of the Photon Torpedo light costs less than the Light Cannon, but puts out a ton of light, and it lighter, not as bulky, and easier to use imo. It would be good enough to use as your primary light in cavern, and make a perfect to transition to a backup light as you progress further into your cave training. I have owned about 11 different lights, and tried out a few more, and this is the nicest light I have used that is not a can light.
If you are looking for another scout style light, EE has the older version of the scout light on sale for $50, and they are new and come with a warranty:
http://shop.extreme-exposure.com/news/
Near the bottom of the page.
If it were me, I would get 1 of the Photon Torpedo LED lights and one of the scout or other scout style light. That will give you all the light you need for cavern, and both will work perfectly for cave in the future.
Good Luck