Originally Posted by
dougmc
500 lumens means at least ten watts for that style of LED (efficiency isn't a big concern, as they're already way better than the incandescents that they replaced.) For that to last 15 hours, that means 150 Watt*Hrs, which means about a 12,500 mAh 3s battery. That's a big honking R/C battery -- about two to three pounds.
Do you really ride with a battery that large? Where do you mount it?
Personally, I've found lights like
these to be pretty good -- have about a meter of them total in various colors around your bike, and nobody will miss you. But at five watts/meter, I generally go for a 2000 mAh 3s battery or so -- it'll power them for about four hours, which is generally enough.
Twin 3W red LED lights that draw less than an amp each tied into a 6,600mAh 3S1P Lipo RC hard case that mounts vertically behind the seat post. Thats only 73.3 Wh. I do have some 5,600mAh packs that are wired to clip together for extra capacity but two of those aren't any bigger than this one. The cell quality specs allow for a smaller lighter build although the packs are more expensive. Two will fit inside a Cage Rocket when I use them to power equally ridiculous front lights.
Alternately it'll mount on the top tube, or on top of the stem, or in a small frame bag.
The problem is that after driving with these now for almost two years - everything else comes up short. Am currently experimenting with shaping the rear light outputs because it'll probably let me use one instead of two rear lights.
What would be REALLY interesting would be a hub dynamo designed to charge a LARGE capacity battery during the daytime, so that higher powered lights could be driven using battery power after dark. Currently the light output associated with a generator system is directly related to the nominal hub wattage output. It doesn't have to be. The time spent spinning a generator with the lights off could also be made usefull storing watts.