I just got a new booklight that will take NiMH or NiCD recharable batteries. Any advice as to which is better and/or longer lasting?
NiMH have a higher capacity, are easier to maintain and are more tolerant of poor charging habits. They are slightly more expensive and require chargers specifically designed to charge them (charging NiMH batteries with a NiCd charger will shorten their lifespan) but those are minor issues over the long term. Go with the NiMH.
Spend the extra money and get Sanyo Eneloops or the equivalent. These are low-self-discharge NiMHs, and will and up lasting much, much longer between recharges.
I believe NiMH are a newer technology than NiCD.
Thanks, guys for the good advice. NiMH it is for me.
NiCads are also more polluting.
The best battery information I’ve ever seen is here:
If it’s a modern LED booklight, and assuming you don’t use them for many hours every day, I wouldn’t use standard NiMH or NiCD batteries. They both have high levels of self-discharge. On a low-power device such as a book light, you’ll be charging the batteries every couple of weeks - not because you’ve used up the charge, but because the batteries have discharged by themselves. Use low self-discharge rechargeable batteries such as Sanyo Eneloop, or just use standard (non-rechargeable) alkaline batteries.
NiMHs have been known to help old ladies cross the street.
Yes, but they’ll also beat you up and take your lunch money.
Those are in the minority. In fact they’re probably NiCads in disguise.
Outside of specialized uses there’s no real reason to use nicad. They underperform and have terrible memory issues compared to more modern materials.
Ya’ really gotta love the Dope. I ask a question and get good answers within minutes. Then it generates other posts that make me LOL. Or degenerates into humor, whatever. What a place!
Not a lot of places you can go for genuinely funny rechargeable battery humor. 
The big difference, far as I can tell is NiCDs don’t have a secret.
Oh yes they do! Like do they really have a memory?
OK, I don’t get this reference.
Boyscouts.
Probably why Mrs. Frisby doesn’t use 'em.
OK, then what do Boyscouts have to do with NiMHs?