new LED lights for this night commuting season?


Kevin McMurtrie

In article <[email protected]>,
Victor Kan <[email protected]> wrote:

> On Sep 20, 1:28 am, Kevin McMurtrie <[email protected]> wrote:
> ...
> > I'm building a light using 12 Luxeon Rebel LXML-PWC1-0100 LEDs.

> What current level are you going to run them at? I can't imagine what
> 12 Rebel-100 LEDs would be like as a bike light if you ran them near
> max. Are you going to run them at lower power for max efficiency with
> the high number of emitters making up the difference in output?

The power output of LEDs is somewhat logarithmic. 5W coming from 12
LEDs is much brighter than 5W coming from 3 LEDs. Using 12 LEDs gives
me a boost of efficiency plus the ability to momentarily go blazing
bright downhill.

I built a new power supply board and LED assembly. So far it looks
good. The switching power supply adjusts smoothly from ~4V with voltage
regulation to ~6A with current regulation. There were no major
soldering issues with the new LED array. I don't know the continuous
power ability of the LEDs is yet. I'm testing the power supply on an
older LED array design attempt that didn't work so well. It handles
about 3W continuously. Based on a better design of the new array, I
estimate it will handle up to 10W continuously.

Just for amusement, I put a low-grade Rebel on a small tab of copper and
drove it at 1.2 amps. It dims as it heats then unsolders itself.
Solder it back on and it's OK again! I remember the old days when LEDs
had a half-life of 1-5 seconds at soldering temperature.

> I recently got a Fenix L2DCE, single CREE XRE LED flashlight and find
> it pretty good so far, if a little narrow, for road riding.

CREE makes some very good LEDs too. It was hard to pick the LED type to
use in my project. I think Luxeon has an advantage in high-current
ability, in that it's good for moments where brightness matters more
than efficiency.