About three years ago I started commuting on a bicycle thinking I would save a bundle on traveling expenses and get fitter and healthier, imagine to my horror that with the cycle lamp that I bought ( a cheapish one, krypton bulb, alkaline cells etc) that I was getting through about £10 in bateries each week over winter.  Plus with a conventional bulb as the battery voltage drops the light output rapidly becomes useless ( and these things get safety endorsements! ).

So I got to working on the idea, just about that time high output white leds were becoming available at reasonable prices,  what I came up with is now probably quite old hat and expensive to manufacture but it's still working very well after 2.5 years with no problems at all.  The led light will run for about a week between charges doing about 1.5 hours per day.

The circuit is based upon a LM2577T switching regulator that is used to boost and regulate the battery supply voltage of 7.2v upto about 24v to drive three strings of 6 leds each giving around 176,400 mCd.  The datasheet for the LM2577T is here.

Below are some photographs of the unit compared to the original krypton bulb based unit, krypton bulb based unit on left, led based unit on right.

The two photos below show just how more visible the led based lamp is on the right hand picture over that of the krypton bulb on the right.  The large lamp is a 400W halogen flood, I guess this should give some idea as to what it must be like with oncoming headlights next to a bicycle.  The led light is noticibly blue-white over the krypton bulb.

  Here is the led cluster with a pp3 battery connector whilst testing the unit.

  Here is the finished unit built into a bicycle light.