Underpowering a 5 watt Luxeon

I had an interesting observation yesterday. Since I'd recently received a Vital Gear 2xAA tube to fit my L4 I wanted to see if rechargeable batteries could be used. When I first tried this the head wouldn't even light up. Later I found that I had tried to use a pair of PowerEX 2200's that I'd run flat and not recharged.

Last night I put in a pair that had been charged the previous day. The result was really interesting, they fired up the L4 head with what appeared to be nearly full brightness for about 25 minutes then the output dropped suddenly to about the same as my Inova X5.

Well, that was around 7pm last night and at 4am this morning they were still going, brightness had dropped even more but was still a bit brighter than an ARC AAA. That was 9 hours ago!. I pulled the batteries and ran a quick voltage check, both cells were just slightly over 1 volt.

That's says the head is still operable at 2.1 volts. Pretty impressive for a head designed to take 6 volts.

Another interesting thing about this is that when new, this head would run from a single CR123 for about 40-50 minutes, then dim and run at reduced brightness for another 30 minutes. Now, 6 months later, it will go for 75-90 minutes before dimming. It appears that the electronics have become more tolerant of low voltage with age. Anyone ever heard of this happening?.

Al

I would guess, that the Vf of the LED decreased with time. There was a thread some time ago, which described this observation.I have also seen a decrease of Vf after usage on a 5W star.

Is that a bad thing or good thing. I'm still a newbie to the electronics side.

Actually, I don't know if it's good or bad, perhaps one of our more learned members can advise. I have about 15-20 hours total on the head.

From my standpoint, it's good since I get a lot more life from the batteries. Also, as far as I can tell with my simple measurements, it's just as bright, so it works for me!.

I don't have a lux meter so the only output test I can do is to use my old GossenPro light meter. I shine the L4 on the defuser and it reads the same as when new for each battery setup so there doesn't seem to be any drop in the output, might even be a needle's width brighter than when new.

Al

You may want to doublecheck which luxeon emitter it came with.
Your description closely matched both my rare Led Lenser v2 turbos with early, "earthtone" white L3's in them.
Most of these came with 1 watt Luxeon emitters. /ubbthreads/images/graemlins/sssh.gif
These ran for only 25 minutse with 3 fully charged Radio Shack 360 ma nimh "N" cells in them and were hotter than heck. /ubbthreads/images/graemlins/tongue.gif They now go about 35-40 minutes and run cooler with no apparent loss in brightness. /ubbthreads/images/graemlins/buttrock.gif
They are each still much brighter than both my big "3D" cell, 10 T5 led equipped Lightwave 4000's with fresh batteries running together. /ubbthreads/images/graemlins/grin.gif

A lowering of the forward voltage would be a good thing, usually. Basically, it usually means that your LED has gotten more efficient (if your brightness hasn't suffered).

3rd_shift

Actually, it's a Surefire L4 so it's a 5watt for sure. Interesting though that the leds can become more efficient.

Al