With most of the work done of Steve’s light, I am free once again to tinker on my own devices. … and what do I do? I build more lights. Sometimes I wonder the overall healthiness of dedicating all of ones available time doggedly pursuing one thing. LIGHTS. I’ve discovered recently that the LED’s I’ve been using in my Dynamo powered lights actually can get significantly brighter than I had previously realized. They are Luxeon K2′s w/ TFFC. The emitters I have are a couple of series old (I bought them back in June), so they are only capable of 180 Lumens @ 1A (the newest ones are up to 220 lumen, I think). The max drive they can handle is 1.5A, which pumps out well over 200 Lumens. (for reference, a 60w lightbulb is about 800 lumens of unfocused light) Dynamo’s can only produce so much current, which limits how bright a light can be. However, when you step beyond that mode of power generation and look at batteries or even the ol’ Wall Wart as a source of DC current, whole new possibilities open up.
The end result I’m aiming for is to have a functional and BRIGHT headlight/helmet light combo for Mountain Biking at night. Photos behind the cut.
The constant current driver (more on this later). A mosfet, a transistor, and two resistors (in practicality).
This circuit produces a lot of heat, hence the enormous heatsinks on the mosfet and the LED. The Mosfet actually produces more heat than the LED, that little bit of copper heats up hotter than you'd believe.
Notice the splotchy color. That's what happens when you put too much power into an LED. I was having fun to see what would happen, putting 1.6A into it. It discolors.
brightness comparison: my 2 bulb incandescent light on in my ceiling.
The LED on. Dimmer, yes, but 3watts of power, instead of 120. 