Which LED would you use for an aspheric Mag mod?

Bimmerboy

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Posting in this particular sub-forum for some of the expert advice to be found here. My request is part technical, but I'm also looking for opinions to help me make a subjective choice.

Planning a 2D Mag aspheric build using a Wavien collar, and the recommended lens that came with it. I have an idea for easily getting the collar aligned properly without driving myself nuts, but that's another subject. First is choosing what I want this thing to be... the tightest thrower I can possibly make with the smallest die but less lumens than possible, or a still really good thrower with more lumens to light a larger area downrange. What will look more impressive and/or useful to the naked eye at a distance?

I think I have the LED's narrowed to two choices, both de-domed. The Osram CSLNM1.TG FLAT at 2.5A - 3A, or the CREE XP-L HI V3 at perhaps 4A - 4.5A. Here's where I could use a little time saving technical help. Is there much difference in surface brightness at those amp figures? The answer to that may factor heavily into the final decision. If fairly similar lux can be had while lighting a larger area, I'll go with the CREE. But if the smaller die produces a brighter spot at any distance, I'll go with the Osram. Also open to suggestions as to amp settings for either LED.

Hopefully that all made sense.
 

DIWdiver

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Others have convincingly argued that throw is all about surface brightness, which you seem to know.

I can't produce the math, but I'm pretty sure that also means the the longest thrower will product the brightest spot at any distance, at least beyond very short distances.

To pick the best LED, it's a fairly simple calculation once you have the data you need. That is:
1. Die size. Since both de-domed, it's actual die size.
2. Total lumens at expected drive current. This can be a bit tricky to calculate from the datasheet. LMK if you need help.
Then it's just lumens/unit area.

I would expect the wavien collar would make the viewing angle of the LED to be of little or no impact.

Have you looked at the latest XRE and XPG2 data sheets? The efficacies are way up. I think the XPG3 is a bigger die than the G2. The XRE used to be the best for throwers, but that's some years back.
 

Bimmerboy

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Thank you, DIWdiver! Your response is highly appreciated.

I've been having fun screwing around in other threads, and avoiding the harder thinking over here. Was hoping someone would let me get away with the laziness, but realized after posting my "cough cough" last night that I need to do more of my own work if I'm going to consider myself a true hobbyist, and also not waste other people's time without some more effort on my part. I've got a lot to think about to make this build right the first time, with little to no experimentation. Though I've been carving out time lately due to a desire to get back in touch with the hobby again, time is at a premium as "life" hasn't let up whatsoever.

The lumens/area to surface brightness math is easy, but I'll take you up on the help to calculate lumens at expected drive current! That sounds like it would be a great help, and I'll start looking at data sheets to provide whatever numbers you might need.

Could I ask for more clarification on what you mean by the viewing angle with the collar, and its impact?

What?? The XRE is still being made, and at higher efficacy?! This could be good. Not as surprised about the XPG2, and am going to look into that emitter as well. Wasn't considering either as I assumed there MUST be something better after all this time. Perhaps not.
 

DIWdiver

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Okay, let's do an example. I don't see a domeless XPL-HI V3 in the data sheet. Only the Hi Density (with dome) does a V3. So lets do the V2. I'm looking at this: https://www.cree.com/led-components/media/documents/ds-XPL.pdf

At the top of page 9 we see that at 1050 mA, the 5000K V2 does 400 lm at 85C, 446 at 25C. Since you are pushing hard on this thing, let's start with 400. Conveniently Cree has already done the measurements on a hot emitter. If they had only given us 446 lm at 25C, we would have to go to the graph at the bottom of page 12. There we see that at 25C we should have 110% of rated lumens, while at 85C we should get about 100%.

So if 446 lm is 110%, then what is 100%? 100/110 * 446 = 405. Close enough for government work.

Now we're going to do the same thing to get from 1050 mA to 4000 mA. For that we need the graph at the bottom of page 13. It shows that at 1050 mA, we get 100%. We'll have to extrapolate the curve to 4000 mA, because the graph only goes to 3000 mA. I'm going to say it would be around 260%. So we'd get about 260/100 * 405 = 1170 lm. Beyond 3000 mA we are (literally) in uncharted territory, so this is only going to be an estimate. It doesn't look like the curve is going to do something wonky between 3000 and 4000, so maybe a pretty reasonable estimate.

About the viewing angle. With a reflector, some of the light will go straight out the front without hitting the reflector. This gives you your spill. Some of the light, which comes less straight out of the emitter, will hit the reflector. This will be focused by the reflector to form the hotspot. With a lens, the reverse is true. The light coming more straight out the emitter will hit the lens and get focused into the hotspot, while the light at a wider angle misses the lens and becomes spill (or just lost).

The reason for using domeless LEDs is twofold. One is that the apparent emitter size is smaller and the other is that the viewing angle is narrower (more light hits your lens). The total lumens are less because there is more internal reflection in the die. That's why domes are better for illumination, while domeless are better for throwers.

The wavien collar helps mitigate the viewing angle effect by catching some of the spill and throwing it back at the die, where some of it gets re-radiated out toward the lens.

Come to think of it, I'm guessing that the collar will be significantly less effective on a domeless emitter, for two reasons. One, there is less spill to start with. Two, the flat surface of the die will tend to reflect more of the wavien light (it's actually not because it's flat, but because of the angle at which the light hits it).
 

DIWdiver

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Sorry, I did say XRE, but I meant XPE. I just looked again, and it's neither of those that have the high efficacies, only the XPG. The XPG2 goes up to 171 lm/W. The XPG3 is up to 185 lm/W, but I think the die is bigger, and they don't make it domeless.
 

Bimmerboy

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Done a TON of reading and thinking the last few days, to the detriment of practically everything else aside from work, and a family medical emergency... lol. Were I planning a reflector build, one could say I've been sucked into the donut hole of throw. Lucky I've taken out half the Sunday night garbage so far.

Thanks again, DIWdiver. Along with learning/cramming as much as I can beyond the point of buffer overload, your responses have been helpful in multiple ways.

In the meantime, I'm coming across info on die sizes, and people measuring lumens (taken with a grain of salt) at drive currents beyond spec.

Funny you mention domed vs. domeless, especially with regard to the collar. The conglomeration of reading has led me to wonder about which way to go. Yet more factors I need to figure out.

This is an exciting, but time consuming, and initially confusing adventure if you want to do it properly to get good results. The way I see it, most anyone can haphazardly throw (no pun intended) together an aspheric mod without knowing much. But, the results may not be satisfying, and/or nowhere near what they could be.
 

Bimmerboy

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I think the thing to do at this point is to get a handful of different LEDs, a few drivers, and make a test platform to experiment with the intended optics.

It's gonna' take a while, but I won't forget this thread, and will report back. Got a thrower to make!
 
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