I'm working on something very simple for my dad. He wants me to illuminate something without cords. It seems inefficient to me but that's what he wants. Anyway I'm wondering what the longest last type of battery is and about how long they could last lighting a few white LEDs. It's indoors so solar isn't an option, but perhaps a low powered photoresistor and transistor it turn it off when it's lightish. Would that require more energy than it's worth?

I know this is a pretty broad question, I'm just wondering if its worth attempting so any input is appreciated, thanks.

Oh, and I'm confined to approximately the size of a toilet paper roll, that's probably a pretty important detail.

 

Why build something when you can buy it (then hack it if necessary)? Harbor Freight sells some inexpensive LED lights for closets (I bought a pack of 3 of them for $15 a few years ago and we use them for reading in our RV -- much better than the incandescent bulbs and we don't drain our 12 V battery). Might not fit your size constraint though. But instead you could look at those cheap flashlights that are on sale for a buck each.

 

http://en.wikipedia.org/wiki/Oxford_Electric_Bell

 

Lithium ion and Nickle Metal Halide have the best watt-hours per kilogram, and that probably means the best watt-hours per cubic inch.

All batteries are rated in amp-hours. Calculate the amps you will use and thus find how many hours a battery will last.

 

I can't recommend discount store LED lights. They are horribly inefficient. Try a headlight or hand light from Princeton Tec, Black Diamond or Petzl. They are very long running on their lower settings. If you run them on lithium cells (expensive) they last many times longer than on alkaline. You can use rechargeable nickel metal hydride but the run time is much shorter than alkalines and managing rechargeable batteries for value and efficiency is a big hassle.

I've owned and used several Princeton Tec headlights for more than 15 years and they are a pleasure. You can fall asleep with one of the LED headlights on and keep using it with the same batteries for months afterward. It took me two years of intermittent use to use up the first set of alkaline batteries in my first LED headlight! It wasn't very bright but they've come a long way since then.

http://www.princetontec.com/
http://www.blackdiamondequipment.com/en-us/default/locale/choose/
http://www.petzl.com/