Floating lumens II, my second integrating sphere in the make

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djozz
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Floating lumens II, my second integrating sphere in the make

I made a second integrating sphere. I made it because my first sphere (thread about my first sphere here) had some properties and uncertainties that I thought needed improving. The major improvement will be that it makes use of the high quality (DIN 5032-7) class A Mobilux luxmeter, that is very accurate, very well V_lambda-corrected for all light colours, and has a very good range, from 0.01 lux to 200,000 lux. This second sphere is huge (outer size 54x54x54cm, inner diameter 46cm) compared to the first one and I'm not sure where to store it Sad . It is fully functional now apart from the coating on the inside (that will be a four layer 60%/40% BaSO4/latex paint mixture): the inner surface is still bare styrofoam, although sanded carefully with 1000 grit sandpaper to remove most of the direct reflectiveness.

I post about it now, before finishing it, to stimulate myself to carry on with it.

It has three ports, an entrance port on top with 80mm diameter (I made an insert for it, reducing it to a 30mm port), a side port for the luxmeter sensor, and an extra 30mm side port that can be used either as an entrance port (for the conversion factor adjustment light) or as a measuring port. (as a consequence of the 3 ports it has 3 baffles on the inside between the ports, I will add some pictures of that later).

I still have to characterise this sphere. One of the things is that I want to measure carefully is what the influence will be of the coating: on the intergrating properties and on the wavelength response. I made a number of constant output light sources for that: cool white, neutral white, warm white, red, green, blue, basically low output small flashlights that run on one or two 7135 chips.

Below my test plans, just to give an idea; they are mostly notes to myself, I did not write it down with the intention that it is all clearly explained

More later!

EDITS : some progress in post #16 : a conversion factor correction light is added.

             progress in post #38 : six reference flashlights were measured in the still uncoated sphere

            some details of the sphere in post #40.

            start of coating in post #42

            coating finshed and tested in post #45

            an extra accurate test on the integrating properties in post #64

Edited by: djozz on 11/26/2016 - 11:23
DrJones
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Very nice Smile Looks great and with the coating it'll be quite professional... A NIST light source would be great, but probably too pricey.

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For storage, I wonder if there is a way you can use some sore of quick connect/disconnect hardware instead of screws to hold it together?

No one, after lighting a lamp, puts it away in a cellar nor under a basket, but on the lampstand, so that those who enter may see the light.

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djozz
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DrJones wrote:

Very nice Smile Looks great and with the coating it'll be quite professional... A NIST light source would be great, but probably too pricey.

Thanks! Correct, if all else tests well, a calibrated source will make it complete, and is indeed too expensive. Another too expensive dream is a fiber optic spectrometer with appropriate software, to measure tint and CRI :Love:

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kronological wrote:
For storage, I wonder if there is a way you can use some sore of quick connect/disconnect hardware instead of screws to hold it together?

The storage problem is mainly the 154 dm3 that I do not have spare in the entire apartment, my girlfriend's looks when this thing was being assembled already made me feel very uncertain Undecided.

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You can always put a cushion on it, and use it as a stool.

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Xmas tree stand? It looks like you have lots of projects ahead of you next year. What does the girlfriend think of that? Maybe you could put a sub woofer speaker picture on it and tell her its part of the sound system?

 

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                      "My man mousehole needs one too"

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djozz wrote:
I’m not sure where to store it Sad

Just attach a sheet of glass to the top of it… then, it’s a new coffee table, just for her. “Merry Christmas!”

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I love it! 

And I love that you just went ahead with it. You must have known this would be a "stretch" of your hobby that would not necessarily sit well with the missus. 

But here you are, posting a wonderful picture of a nearly lab-grade IS... 

You a mad man. 

But you have my vote. And my confidence in you finishing this and setting a helluva high bar for us amateurs that mess with measuring light in our free time Silly

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I assume you’re building a scale model of the infamously accurate “Integrating bathroom” measuring device. When will you be tiling the walls and installing the miniature bathtub, sink and toilet? Wink

Seriously though, very impressive looking IS. Is the larger size important to it’s accuracy or simply allows you to measure bigger/floodier lights perhaps?
I have no clue about integrating spheres (or rather integrating shipping crates!) so I’m sure I’ll pick up a lot. It actually looks quite attractive to me so stick it in a corner and stack your flashlight collection on top Smile

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djozz wrote:

kronological wrote:
For storage, I wonder if there is a way you can use some sore of quick connect/disconnect hardware instead of screws to hold it together?

The storage problem is mainly the 154 dm3 that I do not have spare in the entire apartment, my girlfriend’s looks when this thing was being assembled already made me feel very uncertain Undecided.

Just let her know you are building the other end table next weekend so you will have a matched pair.

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LinusHofmann wrote:
I assume you're building a scale model of the infamously accurate "Integrating bathroom" measuring device. When will you be tiling the walls and installing the miniature bathtub, sink and toilet? Wink Seriously though, very impressive looking IS. Is the larger size important to it's accuracy or simply allows you to measure bigger/floodier lights perhaps? I have no clue about integrating spheres (or rather integrating shipping crates!) so I'm sure I'll pick up a lot. It actually looks quite attractive to me so stick it in a corner and stack your flashlight collection on top :)

Information on the interiors of my integrating spheres is strictly classified, although I can reveal here that one key to succes is an inbuild jacuzzi.

I'm not sure if the larger size makes for a much better integrating sphere. I have seen an professional integrating sphere (for lasers) with a 2.5cm inner diameter. A rule of thumb is that the total surface area of entrace and exit holes must not exceed 2% of the inner surface (or else you will loose too much reflectance to get a proper integration). With my entrance hole diameter of 80mm the small size of my first sphere would not suffice. But given the size of our three-room apartment and  the need to accomodate a 3-person family life perhaps a 30 or 40 cm sphere would have been a better idea Undecided.

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You cant get an apartment with a garage to accommodate the sphere?Wink

 

djozz quotes, "it came with chinese lettering that is chinese to me".

                      "My man mousehole needs one too"

old4570 said "I'm not an expert , so don't suffer from any such technical restrictions".

Old-Lumens. Highly admired and cherished member of Budget Light Forum. 11.5.2011 - 20.12.16. RIP.

 

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That looks really high tech

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blueb8llz wrote:
That looks really high tech

Well, the tech that I put into it is mainly pretty low: pine wood, plywood, a 50cm styrofoam sphere for hobby use, some glue, screws and some floor lacquer. And a quality luxmeter of course. What I hope will make it stand out is that I try to characterise its performance in as much detail as can be done in a non-lab environment.

Perhaps the result of it all will be that it appears that using a simple and small styrofoam ball with two holes and a cheap chinese luxmeter gives equally accurate measurements as big impressive balls carefully coated with a sophisticated (Wink) bariumsulfate formula and a snobistic top-notch luxmeter. I actually hope that that will be the outcome, it makes life easy for us at BLF Undecided.

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MRsDNF wrote:

You cant get an apartment with a garage to accommodate the sphere?Wink

Hmm, I'd love a garage, it will be especially convenient for the hobby since we do not own a car Laughing. But coincidently we were at our financial adviser today, and I can say with certainty that that is not a probable scenario Wink .

Well, it is if we (city folks) move to Oost-Groningen, which is as rural as it gets in the Netherlands, there's earth quakes ruining houses because of 50 years of natural gas exploitation, and there's no jobs...

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I made a (so I called it) conversion-factor-correction-light for the second sphere (cfc-light from now on), as I did for the first sphere (I called it an adjustment light then). It is a constant output light source in a fixed position inside the sphere of which the luxmeter-reading differs when something (like a flashlight) is positioned at the the entrance hole, because objects in that position alter the overall internal reflectivity of the sphere. This way you can correct the readings for different objects at the entrance hole (every flashlight has a different influence on the reflectivity). This sounds theoretical but different flashlights can make a difference of many percents in the reading, and with your sphere's integrating properties getting better, this variance gets worse. Or the other way around: if your sphere/box/pipe does not suffer from this you can question the integrating qualities. Unless your sphere/box is way bigger than the entrance hole, because that reduces this variance. But I already found that although I hoped not to need a cfc-light in this bigger 46cm sphere with 80mm entrance hole,  the variance can still be several percents of the reading of the sphere, so I made one after all.

While in the first sphere this correction light had to be very tiny and narrow to hang at the side of the top entrance hole together with the to-be-measured light, in this new sphere I have the luxury of an extra entrance hole at the side for it. I already measured that the reading of a constant output flashlight when measured through the top port is within 1% of the reading of the same flashlight from the side port Smile .

The cfc-light that I made is very ugly and has burnt and molten bits from the soldering torch (I even burnt the led dome, so I had to slice most of it off), but everything works, so that's fine by me. It runs on 1 14500 battery, and a nanjg 101-AK-A1 driver with all 7135 chips but one removed (so constant 350mA). The XM-L2 led is on a 10mm Sinkpad directly soldered onto the copper pillar that in turn is soldered to the copper body of the light. The pillar of the light is slid into a hole through the insert that I made for the side-port of the integrating sphere, the body hangs outside the sphere. So although the led is very low-driven, it is very well cooled. Some pictures:

 

So does it pay off making it? How does it perform as a constant light source? Here are some readings when it is in place inside the sphere. I started with a fully charged Efest IMR 14500 750mAh, let the light run for half an hour, taking readings underway (the body gets very slightly warm within half an hour). Then I let it cool for 10 minutes (to see warming-up effects) and let it run for another half hour (actually 50 minutes). Then I took the battery out and charged it again. Two hours later I did another run for half an hour, to see how reproducable the results are (they are Smile ). As you can see the light is not perfect constant output under warming-up and battery-drain effects, but stays within 97.5% of initial output for an hour, and if I'm extra keen on accuracy for a reason, I can use the light between 10 and 30 minutes, the difference is just 1% then. But for its typical use I will take readings just seconds apart so it will do its job fine in any case. A partly drained battery is even better than fully charged.

To be continued...

LinusHofmann
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This is all incredibly impressive looking!
Sounds like every last lumen will be accounted for inside this thing! Smile

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Speechless. Are you doing all this work for us?Smile 

 

djozz quotes, "it came with chinese lettering that is chinese to me".

                      "My man mousehole needs one too"

old4570 said "I'm not an expert , so don't suffer from any such technical restrictions".

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djozz
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MRsDNF wrote:

Speechless. Are you doing all this work for us?Smile 

Eehhmm... in case of this sphere project, perhaps I do it for some folks here, but it is more a challenge for myself than anything else. I do not think that the BLF-community benefits much from it except by making people uncertain now, who were thusfar quite happy about their light measurements Tongue Out.

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I have a proposition for you, when you are satisfied that you have it working to it’s optimum performance let me know. I will send you a light that I have built and tested in my pvc lightbox. Then we can see how my box, and duplicates of mine used by Richard and Tom as well as manxbuggy1 and rdrfronty, stacks up by comparison.

You will be free to keep the light I send you for your efforts.

Then we will all know how to adjust our conversion factors if/as needed. Smile

Or, as you say, we’ll be more confused than ever before. Silly

Oh, let me add my keen observations from this point….You Are F’N Brilliant! That cfc light is impressive too. Amazing.

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Nice! Put four short legs on it and use it as a coffee table, Kramer djozz.

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DBC. I'm going to build a light box sometime in the future and need you to send me a real hot rod light. When I've finished testing I promise I will send it back to you. You can trust me. No seriously you can, just dont ask my wife.Wink

 

djozz quotes, "it came with chinese lettering that is chinese to me".

                      "My man mousehole needs one too"

old4570 said "I'm not an expert , so don't suffer from any such technical restrictions".

Old-Lumens. Highly admired and cherished member of Budget Light Forum. 11.5.2011 - 20.12.16. RIP.

 

DB Custom
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Tracking says it was delivered on…lets see..yeah right here, Dec 3rd. That one is awesome, I clocked it at 4487.34 at start on Efest 35A’s. That particular UI was kind of experimental, hope you like it (or hope your wife likes it, apparently)

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That is a nice looking little cfc light djozz. Even if utilitarian in its design. Looking forward to your progress Smile

 

And never mind my new sig line. That totally made me laugh so hard that I nearly woke everybody up.

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djozz
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I'm honoured to have made it into your sig-line, Ledsmoke Laughing

And Dale, let's make it a swap, you send me a light you measured and I will send you a light that I measured. But I still need to do the coating so let's wait until that is done. But while I try to do everything to characterise this sphere and reduce any possible secondary measuring errors, there's one thing that you and others have done more thoroughly than I have done: the primary calibration of the sphere! Many use a multitude of ANSI-F1 measured flashlights for calibration and take a mean of that, I just define the 'high' output of my SWM D40A (rated 550 lumen) as the holy truth (I do that for very practical reasons btw), if my copy of this light is off, the djozz-lumen is off. As DrJones suggested, in the end I need a NIST-calibrated lightsource to finish the characterisation (or have my D40A measured officially), but that is way too expensive.

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This is very impressive work, i wonder how much this would be worth (materials plus time at reasonable wage)

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Bort wrote:
This is very impressive work, I wonder how much this would be worth (materials plus time at reasonable wage)

There's three answers to the question how much it is worth:

1) materials+wages. It is a hobby so wages are not there, I enjoy the work that is in it. The materials: I guess about 150 euro, this is including 5 new-build test flashlights with constant output. If I ever have a lightsource officially calibrated for it, another 325 euro's is added. (for the luxmeter alone I payed 425 euro's second-hand, new and freshly calibrated this one goes for 1500 euro's. But I had the luxmeter already and use it for other measurements as well, so it was not purchased exclusively for this sphere).

2) the functionality. If this sphere performs close to the performance of a professional sphere, it could be worth over 1000 dollars. A professional sphere goes for many thousands of dollars (think 30), but it comes certified, which will never happen to my DIY-thingy, and it has all kinds of convenient computer-outputs and software.

3) relevance to what we do here at BLF. Well, probably it is worth close to any white-painted cardboard box with a cheap chinese luxmeter (so say: 20 dollars), meaning: if you get within 10 to 15% of the real lumen-value which is what such a box probably achieves if you build and calibrate it carefully (and more accurate if you measure only cool white flashlights with similar beam profiles), the difference is not noticable by eye and therefore good enough. My goal of getting within 1% for all beam profiles (from mule to thrower) and colour temperatures is purely for my own enjoyment (and I must admit that I do enjoy posting about it as well Wink )

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djozz wrote:

Bort wrote:
This is very impressive work, I wonder how much this would be worth (materials plus time at reasonable wage)

There’s three answers to the question how much it is worth:

1) materials+wages. It is a hobby so wages are not there, I enjoy the work that is in it. The materials: I guess about 150 euro, this is including 5 new-build test flashlights with constant output. If I ever have a lightsource officially calibrated for it, another 325 euro’s is added. (for the luxmeter alone I payed 425 euro’s second-hand, new and freshly calibrated this one goes for 1500 euro’s. But I had the luxmeter already and use it for other measurements as well, so it was not purchased exclusively for this sphere).

2) the functionality. If this sphere performs close to the performance of a professional sphere, it could be worth over 1000 dollars. A professional sphere goes for many thousands of dollars (think 30), but it comes certified, which will never happen to my DIY-thingy, and it has all kinds of convenient computer-outputs and software.

3) relevance to what we do here at BLF. Well, probably it is worth close to any white-painted cardboard box with a cheap chinese luxmeter (so say: 20 dollars), meaning: if you get within 10 to 15% of the real lumen-value which is what such a box probably achieves if you build and calibrate it carefully (and more accurate if you measure only cool white flashlights with similar beam profiles), the difference is not noticable by eye and therefore good enough. My goal of getting within 1% for all beam profiles (from mule to thrower) and colour temperatures is purely for my own enjoyment (and I must admit that I do enjoy posting about it as well Wink )


Thanks for the detailed reply Smile
I agree, its not about the money, its a hobby, but i do like to see what goes into a project, especially a hobby one (the watermark software comes to mind from another thread, the writer worked carefully on it instead of corporately produced which values production rate over refinement and bug catching)
You answered my next question about how much the meter cost, its far more then i expected but your right that its worth it for the repeatability and light colour correction!
How many hours has this project taken?

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Looks like you are doing some great work here Djozz.

About the calibration. Using a single light from a single manufacturer as the holy grail for calibration seems to be a bit of waste of all the time, energy and money and you have put making the sphere and buying a good light meter to get accurate results. Most know that different manufacturers can have quite different numbers and some like to inflate their numbers or round them up. On top of that you cant get a good average even for the type of light you use. So even that light could be a bit off the average.

I know you don't buy a lot of premium lights. But you do buy a fair amount of emitters. Cree and other manufacturers have output data that you are familiar with so why not just use that data for calibration? With the amount of emitters you test you could average out the results over time and get a good calibration that you could fine tune as you test more emitters. Maybe remove strange results if you suspect one or several emitters are off. Over time I think that could give you a much better calibration without spending any more money. Not only much better compared to using a single light as the holy grail, but also a compared to using a bunch of supposedly ANSI calibrated lights.

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Thing is that in this project I see the absolute calibration of the sphere the least interesting part to find out (my sphere project is bit a bit a case of "l'art pour l'art") because I can't really do a test on the end result, I can only pay a considerable amount of money and then get the real figure. Perhaps because I also use these spheres for emitter tests, the BLF-community deserves a better calibration than this, but taking a mean of the output of a bunch of unprecise light sources is highly unsatisfying to me, it will never get me to the 1% accuracy that is my (probably not realistic) goal for all other aspects of the light measurements . I will try to figure an affordable way to do a true calibration eventually but in the mean time my SWM D40A high output (it is my most stable output light, and I use it just for this purpose) is a very convenient 'working' calibration because I can alter any aspect of my sphere (or build entirely new ones) and the lightsource is always there to recalibrate it to the same standard. And if (at all) I arrange a true calibration in the end, all my results can be corrected with one correction number.

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