How to Focus Led in Reflector - Do I need a light meter?

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mountainair26
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How to Focus Led in Reflector - Do I need a light meter?

Hi all, in the past I’ve simply put a small piece of copper under the pcb if the beam was disappointing after a mod on the few lights I’ve done so far. I’m totally new to modding, but after searching the forums I haven’t found a good method to focus an led in a reflector other than just trial and error of moving it deeper into the reflector. Basically all I do currently is move the led as much as I can to eliminate a “donut” in the middle of the hotspot, but I don’t really know how to focus it for best throw or the best beam possible. Can anyone offer a quick sketch of how to focus an led in a reflector? What about lights (often cheap onces of course) that have the pcb sitting inside the reflector itself instead of the reflector on top of the pcb? I’ve never had one that has this setup and has mutliple led’s on the pcb. If multiple leds are used, do they all focus and make on beam or is it a scattered mess? Is there a different process when using dedomed leds like an xp-l hi or homebrew dedomes? Is it much different when using something with a huge dome like an mt-g2? Does having a light meter reduce the time it takes to focus the led, or does it just make it more reliable? Im not looking for the trade secrets of those who build and sell such amazing lights on this forum, just a very basic outline of what the goal is in using a light meter or not using one to focus the led. I don’t have a problem getting a meter, they seem to be around for $20 or less. I just wouldn’t even know how to use the thing once I get it. I’m mainly talking about lights like a basic C8. Could someone please briefly go over how they’d focus something like an xp-l hi, or a smaller xp-e2? Are there significant differences in the process when dealing with different size leds and with/without domes please? I’m sorry if this question’s already been covered elsewhere, I feel like this might be a common question, but I appreciate the responses and direction. Thanks.

Edited by: mountainair26 on 03/17/2017 - 23:54
FmC
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A lot of related questions there, but basically you will end up having to either sand down centering rings &/or make some shims of varying thickness to obtain the best focus.

In some cases, just a few thousandths of an inch can make a significant difference, when you are trying to get the most throw from a given led/reflector combination.

I went through a bit of testing a while back, which you may be able to benefit from.

Flintrock
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As for a light meter, the one in my phone seems pretty good.  Of course I don't know how it relates to real lux or if it's even very linear or how even the color response is, but none of that is too important for what you're doing.  How to use it?  Bigger number=you did better?

djburkes
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Sanding the centering ring is the easiest way as a lot of them are taller than the emitter itself…especially in C8s. I usually start with the underside of the spacer to lower the reflector as close to the mcpcb as possible then finish with the top to make sure it’s not obstructing the path of the light coming from the emitter.

mountainair26
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Thanks you guys, that thread has already helped a lot, and believe it or not, the “bigger number=you did better” was actually informative for me. Just keep adjusting till I get the most Lux I can I assume?
However, in looking at many of old lumens threads concerning the mt-g2, he always said he wanted the reflector lower than the substrate and the led as high in the reflector as possible.
Aside from heatsinking concerns, is it a bad idea to put the led/mcpcb in the reflector when possible? Or, if one is already dremmeling out a reflector to fit a new, larger led, why not just slice off the entire flat bottom of the reflector and sit the mcpcb basically inside of the reflector if design allows?

mountainair26
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I guess a better way of asking my last question is: in lights like this mining LOL headlamp where the led is inside the reflector, what are you giving up by having the led above the bottom of the reflector instead of below? (all thermal issues aside).

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djburkes wrote:
Sanding the centering ring is the easiest way as a lot of them are taller than the emitter itself…especially in C8s. I usually start with the underside of the spacer to lower the reflector as close to the mcpcb as possible then finish with the top to make sure it’s not obstructing the path of the light coming from the emitter.

Keep your solder joints low to the MPCB board and get some kaptron tape to ensure that you don’t short out the light with the reflector.

Bob

Vegetarian: vejiˈte(ə)rēən/noun: old Indian word for lousy hunter.

Enderman
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mountainair26 wrote:
Thanks you guys, that thread has already helped a lot, and believe it or not, the “bigger number=you did better” was actually informative for me. Just keep adjusting till I get the most Lux I can I assume?
However, in looking at many of old lumens threads concerning the mt-g2, he always said he wanted the reflector lower than the substrate and the led as high in the reflector as possible.
Aside from heatsinking concerns, is it a bad idea to put the led/mcpcb in the reflector when possible? Or, if one is already dremmeling out a reflector to fit a new, larger led, why not just slice off the entire flat bottom of the reflector and sit the mcpcb basically inside of the reflector if design allows?

Actually, if you want the best throw, you want to focus it so that the hotspot projected is as close as possible to the size of your reflector.
This is how you collimate the beam for maximum throw, aka focused at infinity.

If you use a measuring device, they have a very small point where the light is measured, and since usually the measuring device is at only a few meters away you end up with converging light rays that will give you the highest intensity at that distance, but then they diverge farther away. Like this:

Just pretend the lens is the head of your flashlight.
As you can see, you will get the highest intensity at the focal point (where your measuring device is) but when you go past the focal point the light spreads out more giving you less throw.
Ideally, you want the light going straight forward:

Flintrock
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Just understand that lights get dimmer as they get hotter, and the driver output may change as the battery gets lower, so bigger=better is true, but big relative to what might be difficult to determine while things are changing.  If you have a constant power source you can clip to the spring and case that would help, then run it not too bright and wait for readings to stabilize.  

JasonWW
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If you don’t want to burn up the led, you need to make sure it’s always pressed to the flashlight body.

In most lights the reflector is pushing the led star (copper or aluminum) down against the body for good heat transfer. A centering ring is in between the 2 to give it proper spacing (optically and electrically)

If you use a low power setting you can unscrew the head and lift the reflector a little to see if the beam looks better or worse. If it’s worse, then you might need to go the other way. You can put some tape over the contacts and remove the centering ring to move the reflector down and see how it looks.

Depending on the light, the gap between the reflector and the wires/contacts can vary from 0.5mm to 3mm maybe. You’ll need to figure that out if you want to drop the reflector a little. You can usually take the centering ring and rub it across some sandpaper big side down.

If you want to go full custom, you can use screws to hold down the LED star for good heat transfer and then cut off the bottom of the reflector. Then you can move the reflector up and down as much as you want. You can also use shims made of aluminum or copper to raise up the LED for more height.

As far as what the beam pattern looks like, you just have to choose whatever you think looks good. You can make the beam narrow for more throw or make it wider for a larger hotspot. It’s your choice really.

My Convoy L6 thread with XHP70.2, Texas Avenger FET driver, Narsil v1.2 ramping firmware, lighted side switch and cut down SMO reflector. Lots of amp draws on stock driver as well.
http://budgetlightforum.com/node/54477

My Supfire L5-S thread with XHP70, Texas Avenger FET driver, NarsilM ramping firmware and lighted side switch. My mini L6! http://budgetlightforum.com/node/55746

6 NarsilM user videos https://www.youtube.com/user/JasonWW2000

JasonWW
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Most people don’t mess with the reflector unless they are chasing lux. So if you don’t have a meter, just go with what looks good.

I’m currently converting my Convoy L6 into a xhp70 thrower. It’s fun. I’m measuring my lux at 5 meters and calculatin it back to 1 meter. I’ve pretty much doubled it from stock.

You kind of asked too many questions at once. If you can narrow it down to a few, I’ll answer them for you.

My Convoy L6 thread with XHP70.2, Texas Avenger FET driver, Narsil v1.2 ramping firmware, lighted side switch and cut down SMO reflector. Lots of amp draws on stock driver as well.
http://budgetlightforum.com/node/54477

My Supfire L5-S thread with XHP70, Texas Avenger FET driver, NarsilM ramping firmware and lighted side switch. My mini L6! http://budgetlightforum.com/node/55746

6 NarsilM user videos https://www.youtube.com/user/JasonWW2000