My simple, effective Luxeon brightness test rig

(Down with the flu now and not in the mood for "real work", so I decided to put this together and post it )

I'm sure all of the modders here know what a grand pain it is to eye-sort luxeons (yes, even the known-binned ones) to ensure only the creme-de-la-creme make it into our mods.

We all know you can't always trust the binning info and that the info doesn't tell you which emitter in a reel is the brightest of them all. Worse still - it doesn't tell you which ones are duds or black sheep underperformers.

And while the eyes are the best judge most of the time, sometimes you just plain don't have the time, conditions or repeatability to the testing. So, when you receive a coupla reels of binned luxeons (that's 500 of them), how do you know which ones deserve to go into your personal "keepers", or some other special mod?

Well, there are probably lotsa ways to do this, but here's the method I devised that helps the process along for me (photo essay):



The simple setup above is portable and allows quick, easy and repeatable test conditions.



Never thought I'd use a McFlood reflector this way, but hey - it works!



The emitter is held at a fixed distance and angle from the sensor by the McFlood. Very quick and very easy and works every time.



Instead of the mini-plugs, you can use bare wires if you prefer if you don't mind worrisome accidental shorting every now and then. Banana jacks will do fine too. That's masking tape you see wrapped around the mini-plugs and it was used by me to "shim" the distance between the 2 probe terminals til they were exactly that of the luxeons legs. So, all I need to do is just bring the probes to the mounted emitter and touch it on its legs.

With the above setup, I could sort thru a whole reel in 2-3 hours at a well-lit and crowded workdesk. I had paper cups with my own flux "grades" written on them. After I measured an emitter, I just threw it into the cup which most closely matched its "grade".

Of course, even the sorted ones would go thru additional eye-sorting since the luxmeter doesn't tell you the color of what you test - only its brightness. But at least you'd have a helluva lot fewer emitters to bother with since you already know which are the brightest

Hotfoot,

Very nice, my own sorting method isn't as automated and I had to do it in the dark. Guess I'll have to try the assembly line approach you've got here. Thanks!

Say, you free today?

Great job Leo!! Get over the flu bud!

- Don

Wow, now this is a fabulous setup. And no more blinding! One thing before I run off and try to do this -- have you determined whether brightness increases/decreases proportionately with applied voltage? I realize the purpose for the .75A power supply, but does anyone know if a particular Luxeon, brighter than another at say, 3V, will maintain that same margin of brightness over that same other one at 4.5V?

Because if not, we could be on to something here. In other words it would mean an emitter would need to be sorted at the actual voltage/anticipated current of its final intended use. Because what if a Luxeon that's better at 3V is Not better at 4.5V, and vice versa...?

Mr Bulk, I don't quite get what you mean. But from what I can see, the setup is a constant current driver. That means regardless of voltage, the LS is being driven at 350ma. From all these, I believe it might be possible to find one that needs a lower voltage to get it to be driven at spec. That would use less power, and have more room for overdriving.

Of cos that is if I didn't really mis-interprete Mr Bulk's words.....

Its true flashaholic honor to hear from the likes of Lambda, McGizmo and MR Bulk!

Charlie, the driver I'm using - the Xitanium -automatically adjusts voltage to the Vf of the LED and maintains current at 750ma, whatever the Vf may be. This cool driver scales voltage as needed for any number of LEDs (up to 6) as long as they are connected in series. Looks like I'll need an extra pair of hands to meter voltage for a given LED while I've got power applied. I'll see if I can rig up a extra pair of leads tapping off the mini-plugs and attached to a voltmeter. If we succeed in doing this, then determinining actual drive voltage for the supplied current can be done at the same time as measuring brightness. WOW! That WOULD be handy! Great idea, Charlie! That'll be the next mod I do to this rig after I get over this @#$%^ flu bug.

However, I don't think I directly answered your question about the relative performance of individual LEDs under differing input voltage. The best reply I can think of is that if we can simultaneously measure drive voltage while maintaining current, the brightest performers would be classified as those having the best lux readings while driven at .75A and using the lowest Vf. Hope I'm making sense here

Thanks for the nice words guys - glad ya like it!

I hope this or similar rigs will help save some of us from the nasty eye damage that is ever-lurking while working with high-output LEDs. And I do hope someone can suggest some improvements too - unheatsinked luxeons drop in output so very quickly and this luxmeter won't handle monochromatic wavelengths very well (bad for those sorting non-white luxeons).

If you made a bracket using an aluminum rod the size of the slug, and used epoxy to mount electrical terminals, you could heatsink and power at the same time. Spring-clamp mounting would be even better, if one can find a wimpy clip.

Hey Mandy (it *is* the weekend, isn't it ), that's an idea. It would be nifty to have some sort of little jig, where you'd pull on a lever and a rig consisting of power probes, an aluminum heatsinking rod and voltmeter probes would come down and do all 3 things at the same time, wouldn't it?

And actually, it doesn't sound all that difficult to make either. Maybe one of those Dremel mini-benches would work this way with a little modding. Next week, I'll swing by some hardware outlets to see if they have cheap made-in-China Dremel-bench ripoffs...

How about having a third piece of metal (in the middle) that can sit flush with the LED while when you put the mini-plugs.