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High Power LED lights
Despite the falling costs of LED 'light engines'and the increasing use of them in the auto industry the price of good, powerful, bicycle lights remains very high.
LEDs from Cree, Luxeon, Philips, Osram, Nichia etc. are routinely able to deliver 200 lumens and, provided that the source is adequately cooled, the LED colour temperature and output can be sustained for 1,000's of hours.
These devices rely upon being driven by a constant current (not constant voltage) and the electronics to do this can be bought separately or are increasingly incoporated within the 'light engine'. A circuit known as a Buck/Boost regulator is widely used and, as its name suggests, it can actually boost the voltage necessary to deliver the required current (3-4V, depending on the LED) as well as drop it from 12-24V.
Cree Q5 R2 torch replacement 'bulb'
These are sold as replacements for Solarforce/Spiderfire torches and incorporate a reflector, regulator and heatsink. This device can deliver 250 lumens and run from 3V to 18V, depending on the exact model. 12V is perhaps more common.
The basic unit has a beamwidth of about 15°, but this can be modified by using a fresnel lens in front:
3W LED 15° at 4 Metres
3W LED 15° at 8 Metres
3W LED Fan beam
An important consideration when using these units on their own is to provide a good mass of thermally-conducting metal - aluminium is ideal - as a housing and then to keep the water out. I will describe the simplest form I have made to arrive at
The shell is made using 28mm copper plumbing pipe - yes, 28mm: not usually stocked at DIY stores, it is used in the primary circuit of sealed heating systems, but it can be hard to find. A couple of sellers on ebay supply 50cm or 100cm lengths, rather than commercial 3m lengths. This inside diameter is slightly smaller than the reflector, but it is just right to PRESS the reflector in with a vice, thus making a good thermal contact.
I have had no success in using small toggle switches that rust after a few months: see my 'SoftSwitch' how-to page
Unscrew the brass heatsink and refit it tighty with silicone heat-conducting goo. I have had 2 failures over 2-3 years and I think that there may have been insufficient heat conduction away from the emitter. You can use heat-conducting epoxy for a permanent job, (this is loaded with metal) but not ordinary epoxy.