I thought I would post this for others who may be interested in a very high efficiency brake light. I currently use three 7.2v nicad batteries to power my lights, two wired in series for my headlight and one for my brake light. My headlight is powered by a high efficiency 60 led bulb that draws 5w and at my current voltage, less than 0.5A. I can't remember exactly what capacity the batteries powering my headlight are, but I did know at one time and I figured out that my headlight could run for about 4 hours on a single charge. I used an incandescent bulb in my brake light, figuring that because its not on ALL the time, the battery should still last awhile. But I was wrong. My battery that powers my brake light constantly needs charged ( I opted not to attempt building a charge circuit and/or some type of generator and instead I wall charge). Well today I finally figured out why. I looked at the package that my bulbs (two pack of 1129, which when cross referenced is 1156 or BA15s) came in, and they are a whopping 16.8W! At 7.2v, that's 2.3A! My battery that powers my brake light I believe has a capacity of 2.6Ah, so that would only power the light for about one hour solid. Even though the brake lights are not on constantly, that still is not very efficient to me. If my brake light is on for 30 seconds at a time, that means after about 120 times of braking, my battery is dead. There are about 10 traffic lights or stops on my way to work, and there are also times I have to slow down for traffic, so let's say conservatively I pull my brake lever 30 times going back and forth, that's maybe 4 days worth of light from a single charge. 30 seconds is a hypothetical and liberal estimate, so it could be a little longer, but still. Anyway, on to the upgrade. Today I grabbed another battery from a buddy, and this one has a capacity of 1.8Ah. I plan to wire it in series to the current battery that powers my brake light, and use this bulb: http://www.ledwholesalers.com/store/index.php?act=viewProd&productId=758 Which has a 1.3W power consumption and can be powered by anything from 10-30VDC. At 14.4V, it will only draw 0.09A, and with a 1.8Ah battery capacity, that is roughly 20 hours of light! This will literally make my brake light 20 times more efficient! My current bulb only puts out 21 lumen, and the led replacement puts out 90 lumen, so it will also be about 4 times as bright! Wishing I had the motivation to do this sooner! lol.
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