floating lumens! my integrating sphere project

35 posts / 0 new
Last post

Pages

djozz
djozz's picture
Offline
Last seen: 1 hour 59 min ago
Joined: 09/07/2012 - 17:04
Posts: 16708
Location: Amsterdam
floating lumens! my integrating sphere project

Considering the way I am into lights measurements, I do not need an integrating sphere. I am perfectly alright with my usual 'claim' that the light outputs of flashlights and emitters that I obtain using ceiling bounce measurements are within 5% of reality. But I was very curious about how an integrating sphere would perform and thought that it was a really neat project to build one, but it had to become an as proper IS as I could make using budget materials. So there I went, for the fun of it Smile .

I started reading, Labsphere has a very informative pdf on integrating sphere building (here), I read some recommendations from Saabluster on CPF about how he used bariumsulphate on the inner coating, and even found an article of some weird folks who extensively tested wavelength dependant reflectivity of coatings using various fractions of BaSO4 in latex wall paint (here).

First I chose a luxmeter. And at the very start of the build so much for building a truly proper integrating sphere: a calibrated luxmeter that follows the official human eye response used for the lux definition goes from 500 dollar upwards. So instead I bought a budget luxmeter that has been widely used by flashlight enthousiasts (including match, for use with his sphere), a Ceto ct1330B. I made a post on how I received the meter here Sick , there's also a few images of how the inside of the meter looks over there. And believe it or not, a good graph of how the budget meters respond to the light spectrum is impossible to find on the internet, the only graph I have is this very chinese one that was on the leaflet that came with the meter Tired (CIE=human eye response, but what are nonometers?):

Next consideration was size. The bigger an integrating sphere is, the better, because the various holes in the sphere interfere with the integrating quality of the sphere. The rough recommendation is that holes do not occupy more than 5% of the inner surface of the sphere, less is better. On the other hand, my hobby workspace is 1 meter square of the computer desk and will never extend until my son leaves home (he is 3 now Tired ), so a compromise was inevitable Wink . I decided the light input hole would be max 50mm, it would allow emitter testing, and all the flashlights but one that I own fit in it, but it is not big enough for the really big reflector lights (that I do not have anyway, and if I do in the future I will make do with good old ceiling bounce testing). I also decided to use only part of the sensor device of the luxmeter that I bought for the sphere, to save on surface use. I found a 1 euro playing ball that was 24cm diameter, the sphere would be quite small but with this size the holes still occupy less than 2% of the inner surface so that should be ok. I started with the 'match' method: paper mache, and to make the sphere a little more solid I made a 25cm wooden box for it.

 

 

   

These few pictures do not justice to the number of boring hours that went into the paper mache work (making the wooden box however was fun Smile ). So far so good, but then I started painting the inside with latex wall paint and I was really unhappy how that turned out: layers of paper bubbled up during the painting and the end result was nowhere as smooth as I wanted it to be. It would probably even work ok as an integrating sphere, but I really wanted to make a better job of it, this would not do.

Now I bought a 25cm styrofoam ball for cheap and started working on that. There were some cavities on the inside that I filled with wall repair stuff, I made a 52mm hole for the light sources and cut a bit of the outside of the sphere flat to make the hole less deep for ease of use, I thought out a neat way to mount the luxmeter's sensor at 90 degrees compared to the hole (bored out the screwholes of the black sensor-cover to allow M2 bolds go through, and made new holes at the side to screw down the white dome of the sensor), I made a baffle out of cardboard, and taped it in the middle between the hole and the sensor (to stop direct light from illuminating the sensor).

 

 

 

 

I now sanded the styrofoam to really matt with 800 grit sanding paper, made a corresponding 52mm hole in the wooden lid of the box, made a nice finish to the outside of the box with transparant floor lacker, and the sphere was ready for the first tests. First observations:

-the sensor was too sensitive: the maximum measurable output was 720 lumen. There is an aperture needed in front of the sensor.

-shining a focussed zoomie into the sphere at different angles had only little impact on the reading, so the integrating properties of the sphere were already good; it should be quite insensitive to different beam patterns Smile . Only shining directly on the baffle had considerable impact on the reading (10% lower).

-the readings were really sensitive to the size of the hole Sad , when my small K10 flashlight was surrounded by a disc of white paper, the reading was a whopping 10% higher than without the white disc. For the Convoy M2 the difference was 7%. This is partly due to the small size of my sphere (the hole is relatively large and contributes much to the total light loss in the box), but in bigger spheres it should still be quite a problem. Just adding the white disc does not solve the whole problem, the measurement error will be different for every size light, even having a reflective versus black bezel makes a measurable difference, I found. The only way to solve this would be using a fixed 'adjustment light' together with the flashlight to measure the error caused by the presence of the flashlight before switching it on.

 

 

Next phase was a coating on the inside of the sphere, it should improve the reflectivity (good for integration=beam shape insensitivity), and when using barium sulphate in the paint it should also reflect most of the visible colour-spectrum equally well (good for 'true' luxreadings, that is: if you ignore the low-quality luxmeter Sad ). The first layer of paint was plain latex wall paint. I was given 100 grams of lab-grade barium sulphate from work (worth 4 euro's), the next two layers of paint were a mixture of 40% (weight) latex paint and 60% (weight) barium sulphate, with a little bit water added to make it better brushable. When all was dry, the whole surface was carefully sanded with 1000grit sanding paper to make the surface really matt and expose the barium sulphate as well as possible. Here's a picture somewhere during the painting:

Now the sphere let less light through the wall, suggesting better reflectivity, but it still had visible light loss. I now left it that way, not wanting to apply an extra four layers of coating, I decided that it was good enough.

Now the sensitivity of the sensor was adressed: a piece of duct-tape with a small hole was sticked onto the sensor window. Low-tech but effective: the sensitivity went down, the maximum measurable light output went up to about 4200 lumen, which is fine for me. Bonus was that the angle-sensitivity of the sphere was even lower afterwards, even shining a zoomie directly onto the baffle made hardly a difference to the reading.

 

I also made a wooden ring to narrow the hole to 31 mm, that should be better for emitter measurements, but it needs a separate calibration of course.

I made an adjustment light from scratch (no, not my entry for the OL-from-scratch-contest Wink ). It had to shine into the hole on the side, occupying as little inner surface of the sphere as possible. Here's the ugly thing that I came up with, soldered together from copper, running on a 2x7135 board on a 14500 battery, the led is an Oslon Square 5000K that I had spare and is even a bit smaller than a XP-G. It was reflowed on a trimmed 10mm Sinkpad. The 'head' was simply made white using Tipp-ex correction fluid.

 

 

 

I thought it was nice to make a video of the reflow of the led on the board and the board on the copper pillar, so here's some reflow porn  Wink :

So now I am able to measure the impact of every flashlight on the reading and adjust the conversion factor accordingly Smile .

Here's the finished box once more:

The last little project was a new mount for led-testing. I found an all-copper CPU-heatsink with fan on a flee-market, and soldered a 30mm diameter copper pillar on top (lots of solder paste, large blow-torch) , with four brass holders. the top of the pillar was made really flat and two M3-holes were tapped to accomodate led-stars. This should do the job, the pillar fits nicely inside the 32mm hole of the sphere.

This is all for tonight, next thing will be a set of measurements figuring out how well the box works (not easy, hence the title of this thread!!!), with comments, this will be in the following post, but not tonight.

I hope you liked this report sofar Smile

Edited by: djozz on 05/13/2014 - 20:33
djozz
djozz's picture
Offline
Last seen: 1 hour 59 min ago
Joined: 09/07/2012 - 17:04
Posts: 16708
Location: Amsterdam

Initial measurements and alterations.

1) First thing I found is that the sphere was out of range at more than about 720 lumens. So I made an aperture in front of the sensor. I did that with duct-tape, as shown above. But during the following two weeks the readings of the same lights appeared to drop slowly. I first was afraid that it was caused by yellowing of the inner coating of the sphere, but then I thought of the piece of tape. I opened the sensor area and found indeed that the tape had slowly come a bit loose by the slight tension with which it was applied. That changed the properties of the aperture slightly and caused the measurment drop. I took the tape out and replaced it by a black piece of B&W-film I had somewhere. It could move around a bit after insertion, so i sticked small pieces of film between the sides until everything was tight:

I re-assembled the sphere and from now on I had very consistent readings.

2) Before and after the bariumsulphate/latex coating I took measurements with the unfinished sphere, expecting that the reading of the sphere would increase dramatically after applying the coating, because of improved reflectivity. Well, unfortunately that was not the case, in contrary: the readings dropped by 20%. The coating looked really white though. I still can not explain why the readings should be lower with the coating, I only hope that at least the reflectivities of all wavelengths of the colour spectrum have become more equal by the coating, so that I have had at least a reason to go through the trouble of coating Undecided.

3) The light output of the adjustment light appeared very very constant (as hoped and expected). I used it to measure the impact of the presence of different flashlights that were flush with the entrance hole of the sphere (the measurement position), the flaslights were off, just the adjustment light was on, so that the readings were a measure for the light sensitivity of the sphere, that is different for every 'hole-disturbance' :

50mm hole empty: 176

50mm hole with Sunwayman D40A: 191

50mm hole withConvoy M2: 183

placed the insert with 30mm hole: 203

insert with 30mm hole with Ultrafire K10: 203

insert with 30mm hole with copper led-mounting device+20mmSinkpad: 202

As you can see, the impact of 'what's in the hole' is quite large with a 50mm hole, and must be corrected. You can even measure a clear difference between two flashlights of the same head diameter, one with black bezel, one with silver bezel. When the insert with 30mm hole is put in, the impact of 'what's in the hole' becomes hardly measurable. So without the adjustment light to correct this, the sphere would suffer severely from the 50mm entrance hole size. A 50mm hole like I have here would without correction only be suitable for a larger sphere, like 40cm diameter instead of 20.

4) Based on the first rough measurements, the sphere as it is finished (with aperture) can measure up to 3300 lumen, and as low as 0.002 lumen. I like that range!

5) Linearity test of the light sensor: if you measure the adjustment light and another light separately, will the reading of the two lights switched on at the same time be equal to the added readings of the separate lights? Yes!

(with 30mm hole) adjustment light:152, UltrafireK10-mod:107, both:260

(with 50mm hole) adjustment light:135, ConvoyM2-mod:202, both:339

6) comparison between ceiling bounce measurements and IS-measurements of the same couple of lights. I have not done these tests well enough yet, initial results show a clear difference, perhaps caused by sensitivity of the ceiling bounce method to beam patterns.

7) influence of the 9V battery on the readings of the luxmeter. By accident I left the luxmeter switched on overnight (it has no auto-power-off) and was afraid that the readings would have altered. I measured the same lightsources with the old battery and a fresh one: no difference. this means that either the meter works fine with a low battery, or that it is uses so little battery power that you can leave it on for days without problems. Both outcomes are fine to me Smile

8) I had to find a suitable conversion factor from sphere readings to lumens. That conversion factor is different depending on 'what's in the hole', as shown above. For bare led measurements with the 30mm hole+ledmount I came up with 1.58 (reading times 1.58 gives lumen) ; for the 50mm hole with the SWM D40A it is 1.58*202/191=1.67 (I used the readings of the adjustment light for the correction here). I chose this conversion factor because with it the SWM D40A on high setting calculates exactly at 550 lumen, what is the output on high according to official specs of the light (very convenient, the D40A is also one of my reference lights Wink). Of course different units of this light will vary, but several other measurements I did with the sphere, together with old ceiling bounce results I had also point towards round about this conversion factor. Until I have an officially exact measured lightsource this conversion factor will have to do. But don't be surprised if it is 5% or a bit more off in the end Innocent.

This is it for now. There's tons more to measure and adjust if I want, but I won't, I am going to put the sphere into use with what I have Smile

Turby3Pots
Turby3Pots's picture
Offline
Last seen: 2 weeks 5 hours ago
Joined: 03/31/2013 - 20:51
Posts: 563
Location: Richmond va USA

Jeetje!

jacktheclipper
jacktheclipper's picture
Offline
Last seen: 6 hours 44 sec ago
Joined: 10/31/2010 - 21:18
Posts: 4879
Location: Florida , U.S.A.

Very impressive and ingenious , sir .

I am hoisting a beer in your honor !

Cereal_killer
Cereal_killer's picture
Offline
Last seen: 3 months 1 week ago
Joined: 07/22/2013 - 13:10
Posts: 4005
Location: Ohio

I really want to do this, it seems like an awesome project, the only thing holding me back is my meter is to expensive (especially considering the additional $120 I just paid to have it calibrated) to take it apart and mount the sensor inside a sphere like is required.

Your work looks really good. That soldering is amazing too. Congrats, I imagine your pretty proud of it, I know I would be.

 RIP  SPC Joey Riley, KIA 11/24/14. Now I am become death, the destroyer of worlds.

djozz
djozz's picture
Offline
Last seen: 1 hour 59 min ago
Joined: 09/07/2012 - 17:04
Posts: 16708
Location: Amsterdam

thanks for the replies, guys.

This was the fun part of the report, estimating the real performance (how precise it is and what calibration I should use) of this (or any other) integrating spheres I find really difficult, but I made a start with that, it will be in the second post.

I will be proud whenever I have exactly figured out the ins and outs of this thing, how precise it is, or how not precise.

Pulsar13
Pulsar13's picture
Offline
Last seen: 11 months 2 weeks ago
Joined: 02/05/2012 - 10:23
Posts: 1909
Location: Malaysia

Nice build. Any reason for using Oslon instead of regular CREE? Their binning is tighter?

Old-Lumens
Old-Lumens's picture
Offline
Last seen: 3 years 3 months ago
Joined: 11/04/2011 - 11:39
Posts: 7478
Location: Tyler, TX, USA

Wonderful!   I did a lot of research, but I never ended up doing a sphere. I liked this pdf file on the subject and I was going to use Anatase Ti02 and Varathane interior gloss diamond water based polyurethane. I decided it was just too much money, since I wanted a 24 inch sphere and the foam sphere was way out of the price range. BaSO4 is also a real good idea for a sphere.

Great to see you doing it and looking for all the results!

 

My PayPal address: oldlumens (insert the @ sign here) gmail.com

My YouTube Flashlight Video Channel

The BLF Modding Links Thread 

http://imageshack.com/a/img922/1374/jQ2wdL.jpg

 

djozz
djozz's picture
Offline
Last seen: 1 hour 59 min ago
Joined: 09/07/2012 - 17:04
Posts: 16708
Location: Amsterdam

Pulsar13 wrote:
Nice build. Any reason for using Oslon instead of regular CREE? Their binning is tighter?

No particular reason at all. It is about as efficient as a xpg2, so the output was good, and this one was not going into a flashlight anyway, it is 5700K, too cool for my taste.

djozz
djozz's picture
Offline
Last seen: 1 hour 59 min ago
Joined: 09/07/2012 - 17:04
Posts: 16708
Location: Amsterdam

Cereal_killer wrote:
I really want to do this, it seems like an awesome project, the only thing holding me back is my meter is to expensive (especially considering the additional $120 I just paid to have it calibrated) to take it apart and mount the sensor inside a sphere like is required.

It is indeed a waste to disassemble a perfectly working and even calibrated luxmeter (I'm jealous btw), but that is not at all necessary, you can clamp the intact sensor to a sphere as well (it just occupies a bit more surface). In fact that is the way all others that made an IS have done it, as far as I have seen.

djozz
djozz's picture
Offline
Last seen: 1 hour 59 min ago
Joined: 09/07/2012 - 17:04
Posts: 16708
Location: Amsterdam

wdkingery wrote:
Jeetje!

mineetje!

djozz
djozz's picture
Offline
Last seen: 1 hour 59 min ago
Joined: 09/07/2012 - 17:04
Posts: 16708
Location: Amsterdam

Old-Lumens wrote:

Wonderful!   I did a lot of research, but I never ended up doing a sphere. I liked this pdf file on the subject and I was going to use Anatase Ti02 and Varathane interior gloss diamond water based polyurethane. I decided it was just too much money, since I wanted a 24 inch sphere and the foam sphere was way out of the price range. BaSO4 is also a real good idea for a sphere.

Great to see you doing it and looking for all the results!

 

Thanks for the pdf-link, I had not seen that source. I like the abrasion set-up with the vacuumcleaner, actual science often looks like that Laughing. In the article they said that they did not use BaSO4 because it formed cracks in the paint, but the way I used it mixed with latex paint does not produce any cracking, the coating is even slightly flexible, it survives light deformations of the styrofoam.

24 inch is a nice size, and over here a 24 inch styrofoam sphere is not that expensive: 18 dollars. If you ever decide to go ahead with the sphere, please let BLF know (I'm sure you will Smile ).

Ledsmoke
Ledsmoke's picture
Offline
Last seen: 21 hours 28 min ago
Joined: 08/08/2011 - 16:05
Posts: 1995
Location: Denmark

This is such a nice project. And I am just envious of your dogged determination to make the best IS in a budget friendly style. Love it.

And thank you for the reflow porn. Would you believe me that I was feeling just as impatient when I was waiting for that final little wiggle/slide the emitter does when the solder melts in your video as I am when I do it myself. I don´t think flashlight pron is good for my heart! LOL

Such a nice project so far. Really looking forward to your findings regarding corrections and accuracy. Keep it up Smile

~ Ledsmoke ~

Dutch humor:

[quote=djozz]

 I do not think that the BLF-community ben

RaceR86
RaceR86's picture
Offline
Last seen: 4 years 1 month ago
Joined: 02/22/2012 - 08:32
Posts: 3777
Location: Norway

djozz wrote:

Thanks for the pdf-link, I had not seen that source. I like the abrasion set-up with the vacuumcleaner, actual science often looks like that Laughing. In the article they said that they did not use BaSO4 because it formed cracks in the paint, but the way I used it mixed with latex paint does not produce any cracking, the coating is even slightly flexible, it survives light deformations of the styrofoam.

(Sorry, only makes scense if you have seen "Breaking Bad TV-series".)

Nice project! Smile

BLF LED database – collaboration spreadsheet and latest news about where to buy LEDs
http://budgetlightforum.com/node/19342

MRsDNF
MRsDNF's picture
Offline
Last seen: 23 hours 8 min ago
Joined: 12/22/2011 - 21:18
Posts: 13256
Location: A light beam away from the missus in the land of Aus.

Nice work as well as read. Thanks for sharing and all the best for the rest.

 

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.

 

Illuminaria
Offline
Last seen: 5 years 5 months ago
Joined: 10/01/2013 - 11:57
Posts: 325
Location: Slidell, La.

! photo Anticipation_zpsa98fc6b0.jpg!

djozz
djozz's picture
Offline
Last seen: 1 hour 59 min ago
Joined: 09/07/2012 - 17:04
Posts: 16708
Location: Amsterdam

[quote=Illuminaria]! photo Anticipation_zpsa98fc6b0.jpg![/quote]

LOL, I was wondering already if anyone noticed that I stopped working on it. I still have to do some tests on it before I start using it but started doing other things. Thanks for trying to keep me on the job Smile

texaspyro
Offline
Last seen: 9 months 1 week ago
Joined: 04/29/2011 - 12:43
Posts: 4593

Light leaking through the wall of the sphere is not of much concern… your calibration constant for converting lux to lumens will take care of that. And the same goes for external light getting into the sphere. Just subtract the “LED off” reading from the “LED on” reading. Even less of a concern with your sphere-in-a-box that blocks external light.

In fact the Sphere-o-Many-Mysteries has a ultra-bright light testing mode where I mount the lux sensor to the outer wall of the sphere and use the styrofoam wall as a light filter. It can handle around 600,000 lumens that way. Normally the lux sensor (a Taos TCS3210 color sensor green channel) looks into the sphere through a 1/8” diameter hole in the sphere wall. The sphere wall can act as the baffle, but I do have a piece of white cardstock as a baffle. The sensor is mounted around 45 degrees from the light port.

I saw some tests that showed the just sanding the gloss off the inner surface of a styrofoam sphere performed pretty much as well as a barium coating.

leaftye
Offline
Last seen: 3 weeks 6 days ago
Joined: 07/25/2012 - 17:43
Posts: 4263
Location: San Diego, CA

Any updates?  I really like seeing these projects.  It's a kick in the butt for me to finally getting around to making one.  I really should build one since I don't have a convenient space to measure throwers with my lux meters.  I even went to the hardware store to buy the parts to build an integrating plumbing pipe, but they didn't have the parts that other folks here have been using.  It looks like I can get 30cm styrofoam hollow spheres online though, so I'll go that way.  That part is easy though.  It's calibration that I'm not looking forward to.  

The low mode should be lower.

Reviews: Efan IMR18350 700mAh 10.5A, <a href="http://

djozz
djozz's picture
Offline
Last seen: 1 hour 59 min ago
Joined: 09/07/2012 - 17:04
Posts: 16708
Location: Amsterdam

leaftye wrote:

Any updates?  I really like seeing these projects.  It's a kick in the butt for me to finally getting around to making one.  I really should build one since I don't have a convenient space to measure throwers with my lux meters.  I even went to the hardware store to buy the parts to build an integrating plumbing pipe, but they didn't have the parts that other folks here have been using.  It looks like I can get 30cm styrofoam hollow spheres online though, so I'll go that way.  That part is easy though.  It's calibration that I'm not looking forward to.  

I have precious little time for the hobby at the moment (writing posts is a bit easier than actual hobbying, I can only really work on things when the family has gone to bed and in the last couple of weeks I have been too tired to go hobbying late at night)

Concerning the integrating sphere, I'm still measuring/troubleshooting to get within the 1% accuracy that I aim for. The latest problem is that the output readings of the same flashlights and leds are slowly declining over the last couple of weeks. I already found out that it is not a battery problem of the luxmeter. Leftover is 1) declining reflectivity (yellowing?) of the coating on the inside of the sphere, which would be disastrous but I do not consider this likely, and 2) slowly peeling off of the piece of tape with the hole in it that I used to decrease the sensitivity of the sensor. So next step is to dismantle the IS and have a look at the piece of tape, I really hope that that is the problem because that makes for a relatively easy fix (not use tape but something that stays in place better).

By the way, if I would make another sphere I may not bother with a coating (just stick with careful sanding of the styrofoam inside of the sphere with fine grit paper to decrease direct reflections), the integrating properties and angle insensitivity of the sphere without coating appear to be ok already without one. Also I would perhaps start with a bigger ball, in my sphere I really need the adjustment light to compensate for the with every different flashlight varying reflectivity of the hole area of the sphere, but with a considerable bigger sphere (like: bigger than 50cm diameter), the effect of the hole may be more negligable.

Real calibration will still be a problem, also for me. The only way for me is measuring as many known lightsources as I can, and make a sort of 'average best conversion factor'. I already found that the ceiling bounce lumens that I collected for the several lights relative to each other do not exactly match with the integrating sphere readings, the reason may be that the ceiling bounce method is more or less sensitive to the detection angle of the luxmeter (in other words: the beam profile of the light source), in the IS the angle is obviously not supposed to matter.

Chloe
Chloe's picture
Offline
Last seen: 3 years 8 months ago
Joined: 01/30/2013 - 14:14
Posts: 4595
Location: 联合王国

Nice build! Can get barium sulphate on Ebay. I will try to use some if I make a sphere, though I’d like to see before and after figures.

Was the meter really overwhelmed at 200000 range without the duct tape?

djozz
djozz's picture
Offline
Last seen: 1 hour 59 min ago
Joined: 09/07/2012 - 17:04
Posts: 16708
Location: Amsterdam

Chloe wrote:
Nice build! Can get barium sulphate on Ebay. I will try to use some if I make a sphere, though I'd like to see before and after figures. Was the meter really overwhelmed at 200000 range without the duct tape?

I will post some before and after coating figures, worrying is that I actually measured a bit less after doing the coating. I like to think that is because before coating the reflection was less 'lambertian' and relatively much of the first reflected light reached the sensor (dream on, djozz), but unfortunately the easiest explanation is that the reflectivity of my coating is worse than that of the bare styrofoam Sad  (but hopefully at least more equal across the wavelength spectrum)

Before the piece of tape the maximum measurable amount of light was about 720 lumens. I was able to do some awfully precise moonlight measurements before taping the sensor Smile

Illuminaria
Offline
Last seen: 5 years 5 months ago
Joined: 10/01/2013 - 11:57
Posts: 325
Location: Slidell, La.

the various posts, the large variations on calibration methods and results is suspect. A common BLF calibration LED or source would help make the various lumen claims a more accurate.

A known common binned LED at an agreed exact voltage or using the port size method for an across the forum calibration method if you will.

djozz
djozz's picture
Offline
Last seen: 1 hour 59 min ago
Joined: 09/07/2012 - 17:04
Posts: 16708
Location: Amsterdam

Illuminaria wrote:
the various posts, the large variations on calibration methods and results is suspect. A common BLF calibration LED or source would help make the various lumen claims a more accurate. A known common binned LED at an agreed exact voltage or using the port size method for an across the forum calibration method if you will.

I like the idea: so we want a BLF version of a calibrated light source (cheaper, and a bit less accurate is no objection Wink ). I tried to make one ( http://budgetlightforum.com/node/30013 ), but for cross-BLF use an stock light would be better. During the measurents I found that the Sunwayman D40A (mine is cool white) on the high setting (not Turbo) is extremely flat regulated, as good as the reference light that I built myself. And many BLF-members own one. So if we assume that SWM uses as identical emitters as they come (not true probably), that could be a good source?

I will also have a look into a cheaper light with flat output.

texaspyro
Offline
Last seen: 9 months 1 week ago
Joined: 04/29/2011 - 12:43
Posts: 4593

You really can’t use bin ratings to get decent accuracy. LEDs from the same bin can vary over 7%.

My reference lights are an ensemble of LED light bulbs from reputable makes (Philips, Sylvania, etc). Their lumen numbers tend to be quite accurate, but I have noticed that bulbs made later than others (with the same part number) can have higher lumen outputs than the published numbers… you can get more than you paid for due to ongoing improvements in LED manufacture. The bulb makes don’t upgrade the bulb specs on older model bulbs as they improve their products. It is best to use bulbs models that have been recently released.

djozz
djozz's picture
Offline
Last seen: 1 hour 59 min ago
Joined: 09/07/2012 - 17:04
Posts: 16708
Location: Amsterdam

I updated post #2 with a report of several initial measurements and alternations that I had to do before the sphere could be put to use.

djozz
djozz's picture
Offline
Last seen: 1 hour 59 min ago
Joined: 09/07/2012 - 17:04
Posts: 16708
Location: Amsterdam

bump

Hey, I spent two and a half hours last night writing post#2 of this thread. Has anyone even read it???? Wink

(EDIT: it is officially #1 I see now, technically the first reply)

texaspyro
Offline
Last seen: 9 months 1 week ago
Joined: 04/29/2011 - 12:43
Posts: 4593
djozz wrote:
Has anyone even read it???? Wink

Yes…

BTW, I spent last night adding a 8 channel 16 bit A/D converter to the Sphere ‘o Many Mysteries. Before I was using the 10 bit A/D’s on the processor chip. Now I can measure 50 volt and 20 amp signals with around 100 micro-volt resolution (averaging readings over a second) and around 0.01% accuracy..

BTW, pasting up a board with parts that have a 0.5mm lead spacing is a royal pain.

Illuminaria
Offline
Last seen: 5 years 5 months ago
Joined: 10/01/2013 - 11:57
Posts: 325
Location: Slidell, La.

Once coated in latex the barium sulfate is now encapsulated?

I read where this was sprinkled over wet paint for 100% barium sulfate top layer if possible.

I’m about halfway on my dome until work let’s me return home in two weeks…

cheers

djozz
djozz's picture
Offline
Last seen: 1 hour 59 min ago
Joined: 09/07/2012 - 17:04
Posts: 16708
Location: Amsterdam

Thanks for reading texaspyro and Illuminaria !!

tp: I am not sure if I understand it well (I am more an analog person), but it sounds very accurate Smile

Ill: good luck finishing the dome! I read about the sprinkling technique too, I believe that was Saabluster who wrote that. I am not sure if what he did would be much better than mixing the BaSO4 with the paint and then sanding it, that would expose the BaSo4 particles just the same. And as I understand it, you need a fairly thick layer (like: more than 2 mm) of BaSO4 to get maximum reflectivity (in my sphere the layer of paint/BaSO4 is at least a mm and it still clearly lets some light through), which implies that much of the light is not directly reflected from the very surface, but the light enters the layer, bounces around, and eventually comes out again. So sprinkling a thin layer of BaSO4 on the wet paint will not make maximum use of its properties, in fact the reflectivity of his layer comes mostly from the white paint under the BaSO4 layer (the reflectivity of flat white paint is already very good so you will not easily notice the merit of the BaSO4 without accurate spectrofotometric measurements).

texaspyro
Offline
Last seen: 9 months 1 week ago
Joined: 04/29/2011 - 12:43
Posts: 4593

The barium sulphate is not meant to increase the reflectivity (it will actually decrease it for a lot of surfaces). It is meant to provide a diffuse reflective surface with a constant reflectivity coefficient over a wide range of light wavelengths and eliminate reflective “hot spots”.

For styrofoam spheres, just sanding the inner surface of the sphere with fine sandpaper (I used 220 grit) to get rid of the surface sheen works very well. I have some barium sulphate, but have seen no need to use it. You also need to be concerned with the reflectivity/aging characteristics of the paint that you use as a binder. For most people the barium is more trouble than it is worth…

Pages