Help with my D.I.Y. Sphere Calibration

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djozz
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I think it is great that you made these video’s, I will watch them tonight.

The PVC-pipe device does not suffer much from entrance hole effects indeed because not much light is not coming back, it does not integrate very well. In fact: how better the integrating properties of the device the bigger the entrance hole effects, so improving integration creates an extra problem to be solved :-/

garrybunk
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Thanks djozz. I’m liking the idea to “keep it simple” and have a calibration factor calculated for a medium sized light which should be within reason on smaller or larger lights. I’m okay with readings staying within about 10% range. I’ll have to read up on your Sphere #3 soon.

djozz wrote:
[

It looks like you use a standard chinese luxmeter, if I’m correct it measures down to 1 lux.

I’m using the LX1330B which reads down to 0.1 lux (not saying it’s accurate that low though).

mhanlen has graciously agreed to swap some lights (I send some of mine to be tested and he sends me some of his that have been tested) with me so that I have measurements in common with another user to compare my calibration against. I know what will happen though, I’ll get these measurements and then will change my sphere thereby negating all the measurements!

BTW djozz, where did your signature go?

Thanks,
-Garry

My Bike Lights Thread, Optics (TIR) Comparison Beamshots, Diffusion Techniques


NOTE: Moving my photos from PhotoBucket to Flickr. PM me or post in the thread if you can’t see my images and need me to fix or send a gallery link. PhotoBucket images should remain visible until November 2018.
djozz
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No idea where the signature has gone, it is there in my account information. Sad

edit: I deleted my signature line and then created it again, and it seems to be back now Smile

ToyKeeper
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garrybunk wrote:
BTW – found a link to this thread where someone was given the opportunity to measure 68 lights in a professional sphere (though measurements taken at 5secs not 30secs) and the results are pretty disappointing …

Disappointing is a good word for it. It looks like they only measured the high modes, which are usually the most variable and the least accurate. Would be nice if they had measured low and medium modes too, or perhaps every mode on each light. It looks like a big missed opportunity, using the most-precise equipment only on the least-precise modes.
djozz
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Just watched the video’s, nice work! I’d say the sphere is working convincingly well Smile , it integrates fine even with the fairly large entrance hole, and as expected it is somewhat sensitive to the physical type of flashlight that is measured. I agree that with a mid-size calibration light, the deviation of the multiplier is not that great of a worry.

mhanlen
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djozz wrote:
garrybunk wrote:
djozz wrote:

For improving accuracy for this type of sphere, you can either . . . or you can measure the specific sphere reflectivity for each to be measured light source before doing the actual light measurement (using a constant output light source elsewhere in the sphere) and then adjust the multiplier accordingly.

In my sphere #4 with build-in reflectivity measuring light source, I do not adjust the multiplier, but I have build in a simple device that for each flashlight optically adjusts the reflectivity of the sphere to a constant value.

Is there a link showing how you’ve done this? And/or can you go into some detail on it? Could I do something like create a hole where I tightly fit a Convoy S2/S2+ being certain to always insert to where the light’s bezel is flush with the inside surface, and run the light at a low to medium level on a AMC7135 regulated driver? I guess that requires getting a very good lumen measurement on that S2/S2+ light to begin with. Then my next question is, is that “hassle” worth it? Are we talking narrowing down our overall accuracy from say 10% to 5%? Or is it more like 30% to 5%?

Is there a source where BLF users are posting lumen measurements for guys like me to reference and compare to? Or are they just scattered through posts everywhere?

-Garry

I do not know a single BLF source for measured outputs. I know selfbuilt over at CPF incudes output numbers in his reviews (made with his corrected milk carton device 8-) ), and so does UPz in his reviews, who btw made a very thorough write-down of how his sphere is made and tested (although in spanish).

When you say measured output what are the characteristics of a measures output. I include my measurements for all modes in all the lights I review. So you mean a real ansi measurement from a real integrating sphere?

djozz
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mhanlen wrote:

When you say measured output what are the characteristics of a measures output. I include my measurements for all modes in all the lights I review. So you mean a real ansi measurement from a real integrating sphere?

No, I did not mean to suggest that they are the only ones with valuable lumen information. We are all amateurs with home-made contraptions. I mentioned selfbuilt and UPz because they have written down a thorough explanations of how their methods work and what their flaws are, and I like how Garry has done some characterisation of his sphere (sorry, I’m a bit OCD in testing stuff ;-)) , but there are quite a few others too: you provide your own measurements, Dale does, TomE, manxbuggy, pflexpro to name a few.
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I actually plan on doing a guide on how I do it, for a future video. Thanks!

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djozz was also answering my question about a “single source” – a thread or Google Spreadsheet or somewhere I could go to see where members have collectively posted their measurements. I wouldn’t even know where to go if say I wanted to see what other members measured for a 2D LED Maglite.

Wouldn’t this be a handy reference to put together? At least a thread, but then you might have to scroll through many posts to find various lights.

-Garry

My Bike Lights Thread, Optics (TIR) Comparison Beamshots, Diffusion Techniques


NOTE: Moving my photos from PhotoBucket to Flickr. PM me or post in the thread if you can’t see my images and need me to fix or send a gallery link. PhotoBucket images should remain visible until November 2018.
mhanlen
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garrybunk wrote:
djozz was also answering my question about a “single source” – a thread or Google Spreadsheet or somewhere I could go to see where members have collectively posted their measurements. I wouldn’t even know where to go if say I wanted to see what other members measured for a 2D LED Maglite.

Wouldn’t this be a handy reference to put together? At least a thread, but then you might have to scroll through many posts to find various lights.

-Garry

I have a notebook where I collect my findings, and would be happy to share them if someone were to create it. I don’t have a lot of time to create the document at the time being though.

garrybunk
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Yeah I don’t have a lot of time either, plus I’ll disappear from BLF for 6 months at a time. I am thinking to link to a document in my signature for my own though.

Still contemplating whether or not to mess with the calibration reference light. Part of me says it’s good enough and part of me says I can do better (though usually when I move ahead with trying to do better I screw something up).

-Garry

My Bike Lights Thread, Optics (TIR) Comparison Beamshots, Diffusion Techniques


NOTE: Moving my photos from PhotoBucket to Flickr. PM me or post in the thread if you can’t see my images and need me to fix or send a gallery link. PhotoBucket images should remain visible until November 2018.
djozz
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I call my lumen the ‘djozz-lumen’ because I’m not sure if my SWM D40A on high setting, which is my single calibration source, indeed exactly puts out the specified 550 lumen. But I do know that the D40A gives very repeatably the same output, at various drainage levels of the (Eneloop) batteries. So I take very good care of my D40A (I use it for nothing else than calibrations) and I stick to this as a reference, even though the true lumen may differ somewhat, because it keeps all my measurements repeatable and comparable.

garrybunk
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I was thinking to call my calculated lumens “GBL’s”.

-Garry

My Bike Lights Thread, Optics (TIR) Comparison Beamshots, Diffusion Techniques


NOTE: Moving my photos from PhotoBucket to Flickr. PM me or post in the thread if you can’t see my images and need me to fix or send a gallery link. PhotoBucket images should remain visible until November 2018.
garrybunk
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I’m back to this topic with another question. I’m wanting to buy/build a “calibration check light”. This does not need to be a light that has known ANSI lumen ratings, but rather a light I can calculate lumen output on myself (based on calibrating my sphere from other lights) and then use this 1 light as a “calibration check” prior to any use of my sphere. (Hopefully this made sense.)

So I am thinking to build a Convoy M1 with a 7135 driver and XM-L2 or XP-G2. The M1 would be more “medium sized” for my testing and has more heatsinking than an S2+. Though I’m thinking to retire my old S2 EDC (XM-L2 & 2.1A 7135 driver) and use it for this purpose (check light). Any thoughts? I’m thinking to have 2 or 3 modes but nothing high enough where output isn’t steady. I notice on my current M1 with a 3A 105C 7135 driver that high’s output slowly drops from turn on to 30 seconds, whereas low mode (15% I think) is rock steady. So I’m thinking an M1 w/105C 1.75A driver (5×350mA AMC’s) with an XM-L2 on noctigon with 3 modes around 3%, 30%, 100%. Or should I stick to single mode? Or keep it simpler with 2 modes? There’s no need to change the lens or add diffusing material, right? So long as whatever I calibrate it at stays the same (and the diffusion technique could wear off / scratch). I would dedicate this light to only sphere use to keep it from getting worn, lens scratched, etc. . .

Thanks,
-Garry

My Bike Lights Thread, Optics (TIR) Comparison Beamshots, Diffusion Techniques


NOTE: Moving my photos from PhotoBucket to Flickr. PM me or post in the thread if you can’t see my images and need me to fix or send a gallery link. PhotoBucket images should remain visible until November 2018.
garrybunk
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Repost of what I posted here.

I did a quick test of applying various sphere multipliers to readings I took on a specific date to see how much spread there would be in my readings. I use my “calibration check lights” every session, so I’m actually computing new multipliers each session (remember, I can’t count on my luxmeter being in the same perfect alignment each time, so no perfectly constant “multiplier” to use). In real world use (over the past month now) my multipliers have only ranged from 0.381 to 0.387 with 0.3865 being what seems the most consistent. Even across my measurements last year I only saw a range of 0.38 to 0.405. So here’s what I calc’d up:

Note that my “Expected Lumens” values are not necessarily known with 100% certainty. And of course the “Lumens Multiplier #3” column will closely match those values because that’s a multiplier very close to the one used to determine those values (so don’t let that fool you). This was merely done to see how far off I would be if I determined a “bad” multiplier.

-Garry

My Bike Lights Thread, Optics (TIR) Comparison Beamshots, Diffusion Techniques


NOTE: Moving my photos from PhotoBucket to Flickr. PM me or post in the thread if you can’t see my images and need me to fix or send a gallery link. PhotoBucket images should remain visible until November 2018.

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