To follow up on MultiBiker's comments, voltage regulation is an excellent advanced-geek technique for all battery-powered lights. Here's an interesting article that tells more: http://www.cs.indiana.edu/~willie/lvr.html . If you don't need multiple power levels I think a simple regulator would work as well as the fancy microprocessor system in the article, at a cost of less than $2.

I'm hoping to get a regulated system geeked up before daylight savings time ends, although it appears less likely with every passing day...