For $6.99 you can get an 'ArcMania SMJLED' replacement bulb for a (2) C/D cell or Mini-mag light. They're not extremely bright but they have a nice white tint and burn for long long time. Definitely a lot brigher than the Nite Ize though. I've got a couple of the PR based bulbs in cheapo 2D garrity flashlights and they're much brighter than the standard incan bulb. Not to mention it'll run for days.

http://www.lighthound.com/index.asp?PageAction=VIEWCATS&Category=181


(Oops, just noticed you said 4D. Nevermind)





As far as the Petzl goes, you can get screw based replacement bulbs. But to be useful its gotta be a cluster of 5mm leds (not sure they make it anymore), and not a 1W or 3W side emitter. The reason is that the Petzl reflector isn't optimized to capture the light so you just get a dim flood. I know, I found that out $20 bucks later.