L4 longevity test – 50 hours

Since I got my beloved Surefire L4 I've been using it almost every night (for 1-1½ hours) for walking in the woods. Right from the beginning I decided to take some relative light measurements to see if the output degrades over time, as it has been discussed many times on CPF. I'm using an LDR resistor that I've put in a polystyrene foam box, and in the other end of the box I made a hole the size of my L4 bezel. I know this is a rather crude instrument, but for relative measurements I think it's okay, simple and reliable. For readout I'm using my digital multimeter on ohm setting.

So far (50 hours) there is no measurable degradation of the output from the L4 what so ever.

The running conditions are in the L4's favour though, because I walk with the light, and consequently flowing air over the bezel, thereby cooling it. Also this is done in a rather cold climate (wintertime in Denmark) so this has to be taken into account too.

However I think it speaks well for the design of the L4, and I'm no longer so concerned about the health of the 5 watter in this light.

Jan

Is this the first test of this type? Thanks for taking it on.

Jon, IIRC it is the first, but others may have more info on it.

BTW something that might be of interest (perhaps especially to you Jon), is that the performance of my two Pila 168s has only degraded very little if anything. They started out by giving me 55 min. runtime, and after approx. 40 hours on each (been using them for a KL1 head too) they are now at about 52 min. on the L4. The 3 min. difference could be caused by factors other than battery wear such as contact resistance and so on, so one shouldn't conclude too much on it.

Jan

Hello Jan,

That is excellent information.

I am very curious as to when the degradation actually begins. It seems to me that if 75% brightness remains after 500 hours, you should start to see some reduction early on. However, rough calculations indicate that at 200 hours, you would only be down 10% (if the loss is linear).

I believe that if you can keep things cool, you should see a very long life.

Tom

Here is my runtime plot for my L4 (s/n A500942).

Jan,

Keep us posted. This is the first reported longevity test I've read about. At your rate of burn, you ought to reach 500 hours in a short time. Hope you got rechargeables /ubbthreads/images/graemlins/smile.gif And when that LED finally degrades, you could probably replace it with an Z bin 5W that will be rated 20000 hours /ubbthreads/images/graemlins/grin.gif

[ QUOTE ]
Roy said:
Here is my runtime plot for my L4 (s/n A500942).

[/ QUOTE ]

i think they're referring to the led's output over the time of sets of batteries changed. original out of the box output vs 50+ hours on it.

Sure CM - I'll keep you posted /ubbthreads/images/graemlins/smile.gif. The days are getting longer now though, so my "rate of burn" will probably decrease a bit during the summer, and some of my night walks will be converted into some SCUBA diving (using a Green Force 10 watt HID, BTW).

Yes, I'm using Pilas in my L4 and the KL1 you modded. Guilt free lumens! /ubbthreads/images/graemlins/buttrock.gif /ubbthreads/images/graemlins/grin.gif

Jan