Integrating sphere #4 (the fast and cheap one)

135 posts / 0 new
Last post
twinclouds
Offline
Last seen: 5 years 8 months ago
Joined: 07/25/2015 - 17:33
Posts: 274
Location: San Diego, CA, USA

I found the problem is the direct path. After put a baffle between the flashlight and the lux meter sensor, the reading reduced a lot. Right now, my maximum reading (XM-L2 U2 at battery current of 1.5A) is about 10000.
By definition, if total light is 1 lumen over an area of 1 square meter, the lux reading should be 1 lux. I think the relationship of lumen and lux reading can be derived in theory. Of course due to various factors, the result will vary greatly.

Twinclouds

djozz
djozz's picture
Offline
Last seen: 7 hours 36 min ago
Joined: 09/07/2012 - 17:04
Posts: 17971
Location: Amsterdam

Now I'm getting curious how it looks like Smile

I'm glad that with some troubleshooting you are getting it to work. What is the lumenrange you are getting now?

twinclouds
Offline
Last seen: 5 years 8 months ago
Joined: 07/25/2015 - 17:33
Posts: 274
Location: San Diego, CA, USA

When I use a big baffle made by carton board, there reading is about 10000 for 1.6A battery current and XM-L2 U2). However, when I use a thin carton photo paper as the baffle, the reading increase to 35000 again. Maybe some light leaks through. I need to test some more before post photos.

Twinclouds

twinclouds
Offline
Last seen: 5 years 8 months ago
Joined: 07/25/2015 - 17:33
Posts: 274
Location: San Diego, CA, USA

I cut the baffle to be smaller. Now the reading is about 15000lux. The key is I need to find the correction, or dividing, factor.
I took a few photos of the sphere but don’t knw how to attach them.

Twinclouds

djozz
djozz's picture
Offline
Last seen: 7 hours 36 min ago
Joined: 09/07/2012 - 17:04
Posts: 17971
Location: Amsterdam

twinclouds wrote:
I cut the baffle to be smaller. Now the reading is about 15000lux. The key is I need to find the correction, or dividing, factor. I took a few photos of the sphere but don't knw how to attach them.

There's a thread about how to post pictures. You can not upload pictures directly to BLF,you have to upload them to an image hosting site and paste the URL of the picture into the insert picture menu:

http://budgetlightforum.com/node/18059

twinclouds
Offline
Last seen: 5 years 8 months ago
Joined: 07/25/2015 - 17:33
Posts: 274
Location: San Diego, CA, USA

Thanks!
The photos are attached. To have correct lumen values, it looks like I need to have a large dividing factor (>20). I don’t know if it is normal.

Twinclouds

djozz
djozz's picture
Offline
Last seen: 7 hours 36 min ago
Joined: 09/07/2012 - 17:04
Posts: 17971
Location: Amsterdam

Ah, now I understand how you have build it. I'm not sure if it is done intentially, but your build is essentially different from the sphere in the OP in that you made a hole for the luxmeter. The sphere of the OP does not have that, the luxmeter sees the light through the sphere's wall, and that was for reason of simplicity:1) no baffle was needed this way, 2) some extra integration takes place, and 3) and the light reaching the luxmeter is decreased, getting the range useful without extra grey filters and such.

Now that you made it the way you did I think the best is to make the baffle as small as possible (and white coloured) , just big enough to stop the two holes 'seeing each other', and lower the luxreading in another way: a grey filter before the sensor, or making a longer black coloured tube with the luxmeter at the end of it. Using a dark coloured baffle to reduce the reading, like you do, also reduces the integration of the sphere, making it more sensitive to beam profile of the light source (the whole point of using an integrating sphere is to measure the amount of light of a source independant of what shape the beam is).

twinclouds
Offline
Last seen: 5 years 8 months ago
Joined: 07/25/2015 - 17:33
Posts: 274
Location: San Diego, CA, USA

Thanks. What you said make sense. Now I am not sure my baffle is really needed. It does reduce the luxmeter’s reading but may or may not because the directly light was blocked. In any case, the reading was very high previously and I like it to be a little lower so what I measured will not exceed my luxmeter’s reading. I just want to compare different flashlights anyway so accuracy is less a concern.
Now, what I need to do is find a way to calibrate it.
BTW, just curious, what is your correction factor, i.e., the ratio of lux readings divided by estimated lumen?

Twinclouds

djozz
djozz's picture
Offline
Last seen: 7 hours 36 min ago
Joined: 09/07/2012 - 17:04
Posts: 17971
Location: Amsterdam

You still need a baffle between entrance hole and detection hole so that no direct light from the source can get into the exit hole. It helps integration to great extend. A small roundish blockage in between can do the job.

The conversion factor (strictly spoken it is a conversion instead of a correction) differs a bit between different spheres that I made. As you can read there, the sphere of the OP has a conversion factor (I use lumen/klux for ease of use)  of about 83, so 83lumen/klux measured. The max of the used luxmeter is 200klux, so the maximum output the sphere can measure is 16600 lumen.

twinclouds
Offline
Last seen: 5 years 8 months ago
Joined: 07/25/2015 - 17:33
Posts: 274
Location: San Diego, CA, USA

Thanks for your clarification.
I read from one posting somewhere about a calibration method. I think it would be a good one. He suggested to measure the lux value of direct sunlight. Then pointing the IS’s inlet port directly face the same sunlight and measure the lux value at the sensing port. The lux value (directly from sunlight) times the port opening area gives value of lumen. The conversion factor can be computed from the computed lumen and the lux value measured form the IS’s sensing port. One may need to adjust the lux meter and the inlet port such that they are both at the highest values so they are measure the same thing.
I will need to paint the outside of the IS to be black so no light will come from the ball directly before I try it.
What do you think about this approach?

Twinclouds

djozz
djozz's picture
Offline
Last seen: 7 hours 36 min ago
Joined: 09/07/2012 - 17:04
Posts: 17971
Location: Amsterdam

twinclouds wrote:
Thanks for your clarification. I read from one posting somewhere about a calibration method. I think it would be a good one. He suggested to measure the lux value of direct sunlight. Then pointing the IS's inlet port directly face the same sunlight and measure the lux value at the sensing port. The lux value (directly from sunlight) times the port opening area gives value of lumen. The conversion factor can be computed from the computed lumen and the lux value measured form the IS's sensing port. One may need to adjust the lux meter and the inlet port such that they are both at the highest values so they are measure the same thing. I will need to paint the outside of the IS to be black so no light will come from the ball directly before I try it. What do you think about this approach?

Calibration with the sun like this will work, but your calibration will not be independant from your luxmeter's calibration, if your lux is off, your lumen will be off. And luxmeters cheaper than several hundred dollars have big tolerances, even if they are correctly calibrated (which the cheap ones will not be).

Perhaps the best 'budget' calibration is using a household reflector led bulb of a trusted brand (Philips, Osram come to mind, they usually come with a (multiple) TIR), switch it on and let it settle for half a hour before using it for calibration. Your entrance hole must be big enough for it (50mm)

Do not paint your sphere black, with its thin walls it is even advised to paint it white for improved reflectivity. For a sun calibration event, put it in a cardboard box with a hole or something like that.

twinclouds
Offline
Last seen: 5 years 8 months ago
Joined: 07/25/2015 - 17:33
Posts: 274
Location: San Diego, CA, USA

Thanks for your comments and suggestions. I don’t know how large is the error of my luxmeter. I will keep this in mind.
As for using household lamps for calibration, the problem is that my inlet light port is not large enough. In any case, I just want to have an idea about the flashlights that I have anyway.
I will let you know once I have more test results.

Twinclouds

Rufusbduck
Rufusbduck's picture
Offline
Last seen: 5 months 1 week ago
Joined: 04/04/2012 - 15:34
Posts: 10389
Location: Golden state

Found This 300 mm one on amazon for $11.35

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

twinclouds
Offline
Last seen: 5 years 8 months ago
Joined: 07/25/2015 - 17:33
Posts: 274
Location: San Diego, CA, USA

Shipping costs more than the price Sad .

Rufusbduck wrote:
Found This 300 mm one on amazon for $11.35

Twinclouds

garrybunk
garrybunk's picture
Offline
Last seen: 1 week 2 days ago
Joined: 10/31/2011 - 09:25
Posts: 6098
Location: Johnstown, PA

Glad I stumbled on this thread.  Great work Djozz!  Looks like I can locally pickup (2) 12 inch half balls @ $8each.  Question, with a 12 inch ball (30.5cm), what's the largest size hole I could use and be within reason for decent results?  Can I go up to 75mm?  (i.e. for a Courui?)  My use would be for bike lights which could also involve shapes that are not round (more oval).

Thanks,
Garry

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

, MTBR’s Lights & Night Riding Forum
NOTE: Now hosting my photos from my Google account. Post up if you can’t see them. Older photos hosted on Photobucket or Flickr may disappear (PM me if you want access to them).
djozz
djozz's picture
Offline
Last seen: 7 hours 36 min ago
Joined: 09/07/2012 - 17:04
Posts: 17971
Location: Amsterdam

garrybunk wrote:

Glad I stumbled on this thread.  Great work Djozz!  Looks like I can locally pickup (2) 12 inch half balls @ $8each.  Question, with a 12 inch ball (30.5cm), what's the largest size hole I could use and be within reason for decent results?  Can I go up to 75mm?  (i.e. for a Courui?)  My use would be for bike lights which could also involve shapes that are not round (more oval).

Thanks,
Garry

Hi Gary, a 30.5cm outer diameter is about 26cm inner diameter. You're fine with a 75mm hole in that, it will affect the amount of integration quite a lot, but even up to 116mm is within 5% of the inner surface area (5% of the inner surface taken up by holes is a rule-of-thumb-maximum for proper integration, according to the Labsphere theory, but that is with a very high reflective inner surface, and sanded polystyrene is pretty white but not that white). But you could also make an insert in the 75mm hole for a smaller hole, say 42mm (a C8 would fit in that) by re-using the cut-out of the 75mm hole, if the cut is neatly made with a scalpel or exacto-knife. You need to use a separate multiplier for the two holes (so calibrate the sphere for each hole separately).

(for real accuracy the multiplier should be adjusted for each measured flashlight, but then you need to make use of an multiplier measurement light and that was not the focus of the 'cheap and easy one' Smile ).

 

I repeat this because someone above made a hole for the luxmeter also: do not make a hole for the luxmeter, the light is measured through the styrofoam in this design. The design of the OP assumes a wall thickness of around 2cm, this reduces the amount of light reaching the luxmeter enough to get the lumen-measurements into a workable range.

garrybunk
garrybunk's picture
Offline
Last seen: 1 week 2 days ago
Joined: 10/31/2011 - 09:25
Posts: 6098
Location: Johnstown, PA

Thanks for the detailed response djozz! 

-Garry

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

, MTBR’s Lights & Night Riding Forum
NOTE: Now hosting my photos from my Google account. Post up if you can’t see them. Older photos hosted on Photobucket or Flickr may disappear (PM me if you want access to them).
zipelgas
zipelgas's picture
Offline
Last seen: 38 min 53 sec ago
Joined: 08/25/2014 - 09:22
Posts: 325
Location: Estonia

Thanks to this thread I now have my own little sphere..
is1.jpg is2.jpg is3.jpg is4.jpg
Thank you djozz!

Overkill is just about enough!

garrybunk
garrybunk's picture
Offline
Last seen: 1 week 2 days ago
Joined: 10/31/2011 - 09:25
Posts: 6098
Location: Johnstown, PA

Cool! What did you use for the base and the “rings” for the light entrance and light meter? Looks like the base is thin cardboard? And the rings thin PVC?

My new lux meter should be coming tomorrow! (Curious to check it against my HS1010 to see if my HS1010 is off as badly as I suspect.)

-Garry

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

, MTBR’s Lights & Night Riding Forum
NOTE: Now hosting my photos from my Google account. Post up if you can’t see them. Older photos hosted on Photobucket or Flickr may disappear (PM me if you want access to them).
djozz
djozz's picture
Offline
Last seen: 7 hours 36 min ago
Joined: 09/07/2012 - 17:04
Posts: 17971
Location: Amsterdam
zipelgas wrote:
Thanks to this thread I now have my own little sphere.. is1.jpg is2.jpg is3.jpg is4.jpg Thank you djozz!

Looking immaculate! Smile
I see that your entrance hole is quite long, so could you do a little experiment for me that I’m curious of?: could you check how (in percentage) the luxmeter reading differs while you move the flashlight up and down the hole. The reflecting mirror surface should make that the difference is not much (all light should be directed into the sphere, and the reflectivity should not differ too much either), I would like to know how much.

ToyKeeper
ToyKeeper's picture
Online
Last seen: 9 min 3 sec ago
Joined: 01/12/2013 - 14:40
Posts: 10743
Location: (469219) 2016 HO3

I think I must make one of these. It appears to hit a sweet spot between effort and accuracy.

BTW I’ve been using white paperboard stencils around the head of each light on my old light box. I assume the same could be used here to minimize light leakage, with no significant ill effects?

My old light box is also wrapped in aluminum foil to prevent contamination from outside light. Would that be pointless here, or might it still be relevant?

MRsDNF
MRsDNF's picture
Offline
Last seen: 1 month 2 weeks ago
Joined: 12/22/2011 - 21:18
Posts: 13473
Location: A light beam away from the missus in the land of Aus.

So djozz has made someone else here do something. Nice work djozz and zipelgas can I please put an order in? smiley

 

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.

 

zipelgas
zipelgas's picture
Offline
Last seen: 38 min 53 sec ago
Joined: 08/25/2014 - 09:22
Posts: 325
Location: Estonia

garrybunk wrote:
Cool! What did you use for the base and the “rings” for the light entrance and light meter? Looks like the base is thin cardboard? And the rings thin PVC?

Yep – all the assumptions are correct. Base is just a ring of cardboard and the rings are made out of plastic pill containers. I managed to find the exact right fit for the light meter, so I don’t have to fix it with tape:)
djozz wrote:
I see that your entrance hole is quite long, so could you do a little experiment for me that I’m curious of?

The difference was indeed not much, but I will get back to you with some exact numbers.

Overkill is just about enough!

djozz
djozz's picture
Offline
Last seen: 7 hours 36 min ago
Joined: 09/07/2012 - 17:04
Posts: 17971
Location: Amsterdam

MRsDNF wrote:

So djozz has made someone else here do something.


ToyKeeper wrote:
I think I must make one of these. It appears to hit a sweet spot between effort and accuracy.

BTW I’ve been using white paperboard stencils around the head of each light on my old light box. I assume the same could be used here to minimize light leakage, with no significant ill effects?

My old light box is also wrapped in aluminum foil t Smile o prevent contamination from outside light. Would that be pointless here, or might it still be relevant?


]

The intention of a good working light box is not keeping as much light in as possible (although you need to keep the light loss under a certain minimum to obtain enough integration) , but to keep the light loss as constant as possible (in other words: make the combined internal reflectivity of the sphere constant), which is a different thing. Then the multiplier is constant and the box is accurate. The flashlight that is held in the entrance hole provides the light for measuring, but also influences the combined reflectivity of the sphere. Wether you need white stencils around the light, or grey or even black, is not known, what you want is creating the same reflectivity as when the reference light was measured.

Outside light probably is usually so much less than your flashlight (unless moonlight is measured), that alu-foil is not really necessary, but it does no harm either, I think it would make me feel better too Smile

Muto
Offline
Last seen: 1 hour 19 min ago
Joined: 09/04/2012 - 16:42
Posts: 2660
Location: Southeast, PA

50% off coupon good today at JoAnn Fabrics
http://www.joann.com/coupon/?icn=WEEKLYDEALS&ici=Coupons_drawer1

here is the ball
http://www.joann.com/smoothfoam-12-inch-half-ball/12384335.html

Going with Wifepoo today armed with 2 50% off coupons, $10 for a sphere is BLF kinda deal!

Later,
Keith

The difference between Hoarding and Collecting is the illusion of Organization
.

“History doesn’t repeat itself, but it sometimes rhymes,” Mark Twain

After the Apocalypse there will be only 2 things left alive, Cockroaches and Keith Richards

djozz
djozz's picture
Offline
Last seen: 7 hours 36 min ago
Joined: 09/07/2012 - 17:04
Posts: 17971
Location: Amsterdam

It just occurred to me:
-the measuring range of the 15cm sphere of the OP is 0-17,000 lumen (which is a useful range)
-with the same build, a 30cm sphere (with the same 2cm wall thickness) would have a range of 0-68,000 lumen, which is less useful because you will never measure this high output, and the resolution at the lowest light levels gets too low.
-to solve that, you could slice the wall of the sphere thinner at the position of the detector (actually like I sliced a bit off the sphere where I made the entrance hole), before attaching the ring, this will get more light to the detector and therefore bring the range down. So you can adjust the range by slicing more or less styrofoam off at the detector spot, and I can not think of a reason why this would affect integration in a grossly negative way.

zipelgas
zipelgas's picture
Offline
Last seen: 38 min 53 sec ago
Joined: 08/25/2014 - 09:22
Posts: 325
Location: Estonia

First of all a little explanation why I left entrance port longer. I wanted to keep the inner surface vs ports ratio very small (about 3%) and still get a usable reading form some lights that are just a bit too large for the opening. So I tried to be a bit sneaky. I hope the pictures explain my plan a bit better..
11_IMG_20160211_195048.jpg 12_IMG_20160211_195134.jpg 13_IMG_20160211_205050.jpg 14_IMG_20160211_221715.jpg 16_IMG_20160211_195611.jpg
The port is covered with aluminum tape, depth is about 32mm and the diameter is almost perfect for X6 and D80. So these will be the test lights.

X6 triple test1
21_IMG_20160211_210727.jpg 22_IMG_20160211_210730.jpg 23_IMG_20160211_210732.jpg 24_IMG_20160211_210735.jpg

X6 triple test2 – different output mode
31_IMG_20160211_210255.jpg 32_IMG_20160211_210258.jpg 33_IMG_20160211_210303.jpg 34_IMG_20160211_210307.jpg 35_IMG_20160211_210313.jpg
So basically very little difference in lux reading when traveling almost 3cm up or down. When the head is pushed too far down inside the sphere, there is off course a sudden drop in numbers.

D80 test1
41_IMG_20160211_204237.jpg 42_IMG_20160211_204241.jpg 43_IMG_20160211_204244.jpg 44_IMG_20160211_204247.jpg 45_IMG_20160211_204251.jpg

D80 test2
51_IMG_20160211_200734.jpg 52_IMG_20160211_200739.jpg 53_IMG_20160211_200741.jpg 54_IMG_20160211_200747.jpg 55_IMG_20160211_200752.jpg
The last picture shows a drop, because the head is already too deep inside.
But as you can see, the numbers are not so stable anymore. Almost 10% difference. My best guess is that the culprit is reflective bezel?

Overkill is just about enough!

djozz
djozz's picture
Offline
Last seen: 7 hours 36 min ago
Joined: 09/07/2012 - 17:04
Posts: 17971
Location: Amsterdam

Thanks a lot for the measurements Smile

So the position in the entrance hole does make quite a difference, even with its reflective walls. Pity, that implies that you will have to define a fixed depth for your measurements (not that much of a problem though). Yes, it is the reflector that is increasing the overall reflectivity of the sphere, and when it is too deep in, the side of the head is eating light, and with so many reflections going on, it is soon adding up to a considerable loss of reflectivity. With a bigger sphere the things going on in the entrance hole will have less influence on the reflectivity (multiplier).

If you like this DIY tinkering, you could build a reflectivity measuring light into your sphere, to compensate for entrance hole effects, but it will definitively not be a fast build anymore. See for an example my integrating sphere #3.

fatboy
Offline
Last seen: 1 year 7 months ago
Joined: 11/17/2012 - 08:18
Posts: 224
Location: MN

sub

zipelgas
zipelgas's picture
Offline
Last seen: 38 min 53 sec ago
Joined: 08/25/2014 - 09:22
Posts: 325
Location: Estonia

The first two tests done with X6 triple had very stable results. Surprisingly stable!? But this was a triple with tir optics = no reflecting surfaces whatsoever.
From 444 -> 455 and from 217 -> 222. That is only 2,5% increase if you consider that the travel distance inside the entrance was over one inch.

With lights giving more unstable results (like the D80 in this example) it’s very intuitive to find the sweet spot. You start lowering the light inside (lux numbers climbing) and the moment the numbers start to decrease you pull the light back just a little bit.
I found that this basically means that the flashlight is almost flush with the inner surface or just a bit higher.

But these were just a few quick tests. I have not had a lot of time to play with my ball Big Smile

Overkill is just about enough!

Pages