Is It Difficult to Center an Emitter?

I see a lot of discussion about off-center emitters lately. Many people seem to obsess over this, and regard even the slightest bit of disparity in die centering as an egregious manufacturing error indicative of a careless QC department and completely unacceptable.

I'd be interested to hear from modders and Custom builders who have experience: Is it challenging to perfectly center an LED? What makes it difficult to do so? Is it purely technique or do component design/manufacture play into it as well? Is it reasonable to expect a perfectly centered emitter every time? What sort of variance should be expected and what is truly poor manufacturing?

Thanks for your thoughts!

I've always have trouble centering an emitter...The problem lies in my lack of proper alignment tools. I've always make a complete pill with the hole bored out perfectly for the mpcb board to sit in. That said, an emitter is never aligned perfectly this way due to the reflow soldering process.

A steady hand and plenty of light helps. Whenever I make P60 dropins I have around 5 minutes max before the arctic alumina thermal epoxy sets. I can also use the emiiter hole opening of the reflector to help center the led.

I agree Nick, there does seem to be an obsession going on up there. I believe there are factors that may not be considered when an emitter "looks" to be off-center. I'll preface that I'm basing this on both investigating my own production lights and from assembling my own P60 drop-ins.

The first factor I consider that can cause the appearance of an off-center emitter is simply due to the reflector having been tightened under the lens and bezel/ring a hair out of plumb. Second, although the emitter is dead center on its MCPCB, perhaps the board was installed onto the pill/heatsink a tad off-center. And the last possibility that came to mind from reflowing, is that the solder pads may not be perfectly centered onto the MCPCB. So even if the emitter has been properly reflowed, well then it's still going to be off-center. Now combine two or more of just those factors and the emitter is going to "look" as if it was not centered instead of other factors. There's probably other factors to consider, but that's all I have for now.

Some will say, "what difference does it make if the emitter was not centered onto the MCPCB, or whatever the case may be, it's "off-center" nonetheless". My response would be to remind them of the fact that several factors could be at play, and as such, occasionally one is going to slip through the five hole. So if it's an issue of any sort, then return it and start over. Tolerance begins with us!

With peace,
John

So it would seem from your replies that it actually IS fairly difficult to perfectly center an emitter.

By hand, you have the disadvantages of human error coupled with component imperfections, but the advantage of adjusting til it looks right.

Mass produced lights alleviate some of the inconsistencies but you still have the possibility of component inperfections such as poorly printed or shaped PCBs. You also don't have the opportunity to inspect and adjust each unit prior to packaging.

In that case, it would seem that there is the potential for a good percentage of lights to have slightly off center dies. That brings the question then: how much is tolerable? What should be accepted and what should not? Is it really reasonable to expect manufacturers to disassemble lights and replace parts to center LEDs perfectly when they are only "defective" to the eye and performance is not affected?

I've found that the emitter can be off-center and it doesn't make a big difference in the light output. The best method for me is using screws so you can adjust the mcpcb and then lock it in place.

For the custom-builder of either primarily drop-ins or complete lights, who by nature are likely very particular about every element of the build, eventually the refinement of emitter placement techniques, the addition of alignment augmentation devices, and good old repetition, steady hands, and patience will result in a very high quality result. Otherwise, again by nature of the custom builder, their product wouldn't leave the workshop.

For mass production, I'll assume the process is mostly automated, at least for reflowing the emitter to the MCPCB. Also assuming all other aspects of production have met tolerance standards, I would think the occasional malalignment is just a matter of statistics. That's the nature of mass manufacturing and the need for tolerances.

For those of us that swap emitters, or make our own drop-ins, that don't have the same level of resources as the others, speaking for myself at least, getting proper alignment requires practice and testing new ideas, or sharing in others successful techniques. To loosely paraphrase what Gene Malkoff told me, "you just have to get started and be willing to make mistakes. It's in the failures that you really learn what works and what doesn't". In following this advice, I developed a rudimentary bench top set-up for reflowing that allows me to follow manufacturer recommended procedures such as pre-heating, ramp-up, placement, then cool down. Cree"s "Soldering and Handling Guidelines" is a wealth of information to help develop "home-made means" to a properly aligned emitter. What I put together for the reflow process cost around $100-$120, more than half of the total was for a magnifier lamp to compensate for deteriorating eyesight.

So how much is tolerable, well that all depends on the individual. Honestly, until I started reading the thread in the LED sub forum regarding this topic, I never even thought to look. In fact I still haven't as I write this. Every light I own seems to provide the expected beam of light, so I've had no reason to consider there was any issue. However, looking at the head-on photos I've seen on here of emitters that appear to be "off-center", I can understand how that would bother some. Undoubtedly, there will also be a direct correlation with tolerance of perceived imperfections, and relative cost of the offending product.

What should be accepted, again depends on the tolerance of the individual. As a recovering perfectionist, I can honestly say that as long as the projection of light is unobstructed, then I'm good to go.

As to your last question Nick, my answer is no. If such would be an issue for someone, I suspect checking the alignment of the emitter will happen the day they get their new light. Even if it doesn't impact the light's performance in the least, if an individual prefers to send it back to the source for refund or replacement, that is certainly their prerogative. Who am I to suggest to another what's good for them, other than my children of course.

With P60 drop-ins, a factor that can also influence emitter centering is the amount of "Play" in the threading on the pill and reflector. A third of a turn can make the difference between centered and not centered. If you are trying to get the right focus for your LED and keep the emitter centered it can be a tedious process. High thread count (TPI) pills are easier to work with IMO.

and i would liek to add an experience of mine.
I hada case where the LED was just a bit off-center but the reflector had a small hole for the XPG. Upon assembly and tests i rescrewed the reflector which got caught on the LED dome and pulled it off

Quite easy with a lathe:

Energie said:

Quite easy with a lathe:

Click to expand...

How do you align that jig to the reflector?

I make fixtures for all of my lights so they all should be pretty much perfectly centered. Even when I purchase LED's pre-mounted to PCB's I turn the PCB slightly down in the lathe to be sure the LED will be centered. I see many cheap lights have horribly aligned emmiters and don't understand A simple fixture that can be made in minutes (if you have a lathe) is all thats needed. My friend picked up a free 511 tactical light with a jacket purchase last week and the LED is so off center it's amazing!

I think I need to do more research on how a light engine is assembled. It will probably help in understanding the challenges, and also the remedies, when placing emitters, PCBs, etc. in a light.