My lumen guesstimate....Am i even close?

Flashlight Modding and DIY Parts
1

Recently I tried working out an average lumen output using the tail cap readings method on a WS CT9t mod as it had become my go to light when anything looked like it needed a lumen tan.

I know there are many variables etc but I took the time on this one to mod it with as little resistance left over in the end result as possible, or not.

That’s where a 2nd, 47th etc, pair of eyes and no doubt much greater knowledge and experience than I hold see something obvious to them, where I probably won’t have a clue about.
Also to see if what my lumen estimate shows to be, is anywhere near the estimate coming from someone who might actually have a clue turns out to be.

Ok, so as stated above it’s a Warsun CT9t.
Mod includes,
*20mm XM-L2 U2 on Noctigon.
*Factory anodising removed in area directly under emitter.
*Screwed down tightly using 2X brass bolts.
*Direct drive using a Keeppower IMR18650 30A HD cell showing 4.8A at the tail.
*Copper braided contact plate and tail switch.
*Heavy gauge copper speaker wire used from contact plate to LED.
*Black plastic spacer between reflector and LED filed down to allow more light to escape (as the Warsun ones seem to be really thick and sit quite high compared to most).

Apart from an AR lens, I don’t think there’s much else left to do, or anything else that I might have missed that would of helped bump the lumen output higher.

So my guess went a bit like this…

XM-L2 U2 1A ON NOCT est =1200lm @ 3A.
est = 1600lm @ 4A

1600lm + est 300lm for the extra 0.8A

1900lm - 5% loss from plastic centering ring
=est 1800lm

1800lm - 15% loss from reflector.

= est 1530lm.

Rounded off to 1500lm guesstimated output.

Obvliously I don’t expect to add any vadility to the estimated figure, just curious to see if “generally speaking” the above number holds any vadility at all, in the slightest.

To also see how close said number is to estimated general opinion.

If nothing else, to at least give me a reason to pick some brains, take advice, learn and hear some well respected opinions.

Cheers.
Paul.

2

Just get a luxmeter… :wink:

3

… and an integrating sphere! :smiley:

4

Theoretically yes you are right on the money. If all your assumptions are right on the money. Things like.

Emitter is up to spec.

losses from centering ring and reflector and lens. Oh no. you did not have losses from lens? They are ~4 to 15%

And then there is the...

Wait. No. No you are likely far from it.

Even those of us that have luxmeters and lightboxes and integrating spheres are at a loss as to how much a lumen is. Or how to reliably measure it and translate that to real world usefulness. A while ago this site almost hosted the worlds first international integrating sphere and luxmeter war of "scientifically unproven method to measure light that I will fight to the death over - on the internet" but it was avoided only because another great sk68 deal that was too good to pass up on was posted in the deals alert thread.

So take it easy and know that you done all that you could do. Which it really sounds like.

Next is a AR lens. The easiest way to gain 4~15% on all modes.

Oh by the way. You did use some thermal grease/compound of some type under the star I hope. You may have forgotten to mention it in the OP but not in the light :-)

And welcome to the BLF. I hope you also have fun here. Actually it sounds like you already did ;-)

5

Welcome to BLF!

Thing is, with all the uncertainties and inaccuracies involved in light-measurements-the-amateur-way as we do here at BLF and on CPF, your way of getting to the light output is probably just as valid as sending the flashlight to one of the CPF/BLF pro's for measurement :bigsmile:

6

^This

Dad, what’s the best way to just get an average of final cost for all these products without using a calculator?

“Just get a calculator son”
Thanks dad, very helpful.

:bigsmile:

A ball park figure is obviously all I’m after, but yes agreed, there a few variables to consider.
Which is why the final lumen output is clearly a rough, but calculated average that should be fairly close.

It was never intended to be a deadly accurate exact lumen calculation.
I’m not going to worry about a difference that wouldn’t even be noticeable to the human eye.

Just something a little closer to the specs given by some, not all of our Oriental friends
in the business of flashlight sales. :beer:

7

Thanks djozz, appreciated.

Well that’s where I was going initially actually.
Was wondering if there are any members that provide that who are based in Aus.

Then I would most likely compare it to my estimated (and surely inflated figures) leading me to the conclusion that I should have just listened to dad and used a calculator lol.

8

Dunno, the text on the side of my light says 13,800 lumens, its in writing so it must be right! :stuck_out_tongue:

9

ROTFL!

-Garry

10

Hehe like a squirrel. A nut… where! My brain is exactly like this, hate to admit… It’s a side effect of drinking and being with the same girl forever

11

Seems way too high. Based on the tests I have seen, I would expect around 1400 LED lumen at 4.8A (you can’t assume perfect heat dissipation in a flashlight).

Best case is around 80% efficiency (OTF vs. LED lumen) with a perfect reflector and coated lens (no blocked light). So you can probably expect 60 - 70% for your light.

Assuming 65%, you get about 900 OTF lumen @ 4.8A.

15% is rather high. It should be less than 10% for an uncoated lens (4% per surface, plus a very small material loss).

12

I know it is not a scientific answer you are after but I think Djozz summed it up. We don't know. Even if you send it to me. We don't know. If I then send it to Djozz then there are just more people who don't know.

@ BofL: The lens losses are measured losses from flashlights, window glass, coated glass and wine glasses I measured once.

I was always fascinated with how my eye glasses casts a shadow. So when I had nothing to do one day I measured a lot of diffenrent lenses and other glass items.

The flashlight with highest loss was 15%. It was a C10 light I bough off e-bay a while ago. And as far as I recall it was after cleaning.

13

I have a bike light where the original glass lens was measured at 18% loss.

-Garry