I'd be surprised if you get an absolute answer to that question. I've had my E2e since probably 2002 (or before) and have used it hiking, camping, kayaking, fishing, and it rides daily in my briefcase. It's still using the original lamp. So what's that? Well over 3 years and going. On the other hand, I've changed the bulb on my E1 (oldschool one) and the bulb lasted a few seconds before fizzling out.

It seems like, to me at least, if you get a good one it'll last a long time. Conversely, if you get a bad one it's usually quickly evident. I'm sure you've seen a standard filament bulb burn out when dropped but my E2e has been downright abused and still goes on. (Watch, it'll blow out tonight) <img src="/images/graemlins/tongue.gif" alt="" />

PS I've heard that the light quality degrades over time and should be replaced to keep it at its peak performance. Maybe some CPF'ers will chime in if there's been any bulb tests. Which I imagine would be difficult to apply to real life use since noone keeps their lights on, runs the batteries down, inserts new batteries, runs the light down, etc.)