Floating lumens II, my second integrating sphere in the make

71 posts / 0 new
Last post
Ervin Anastasi
Ervin Anastasi's picture
Offline
Last seen: 4 years 8 months ago
Joined: 02/25/2014 - 06:29
Posts: 293
Location: Albania

attention to details and determination on this new sphere for sure hold your signature Djozz. if i ever take the courage to make my sphere your work will be my main inspiration. hope to perform inside the hi-standard you allways seems to ask from your work.
as a side note, ouch before, that nice power suply than the exotic spectrometer now the precise light meter , this hobby together with those little crees seems to have plotting to sabotage your finances Silly

some of my actual experiments and reviews:
UF-T20 review and mod —->http://budgetlightforum.com/node/30186#node-30186
My EBRZM, over 1 million cd thrower—-> http://budgetlightforum.com/node/30274#node-30274
Ervin’s try (2nd. Annual BLF Scratch Made L

led4power
led4power's picture
Offline
Last seen: 4 hours 55 min ago
Joined: 12/29/2012 - 09:48
Posts: 1284
Location: Croatia,EU

djozz wrote:

... 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 never saw <6% lumen accuracy in any of LED datasheets,so your goal sounds optimisticLaughing

Bort
Bort's picture
Offline
Last seen: 2 months 5 days ago
Joined: 06/01/2012 - 17:15
Posts: 7460
Location: Holding the proverbial flashlight

led4power wrote:

djozz wrote:

… 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 never saw <6% lumen accuracy in any of LED datasheets,so your goal sounds optimisticLaughing


Your comparing apples to oranges, datasheets are not based on accuracy of lumen measurement, they are based on tolerance in bulk manufacturing.

The Journal of Alternative Facts TM

"It is critical that there is a credible academic source for the growing and important discipline of alternative facts. This field of study will just keep winning, and we knew that all the best people would want to be on board. There is a real risk in the world today that people might be getting their information about science from actual scientists"

 

led4power
led4power's picture
Offline
Last seen: 4 hours 55 min ago
Joined: 12/29/2012 - 09:48
Posts: 1284
Location: Croatia,EU

Bort wrote:
Your comparing apples to oranges, datasheets are not based on accuracy of lumen measurement, they are based on tolerance in bulk manufacturing.

You should read datasheets more carefully,for example:

Cree: "Cree maintains a tolerance of ±7% on flux and power measurements, ±0.005 on chromaticity (CCx, CCy) measurements and ±2 on CRI measurements"

Lumileds: "Philips Lumileds maintains a tolerance of ± 6.5% on luminous flux and ± 2 on CRI measurements"

Luminus: "Luminus maintains a +/- 6% tolerance on flux measurements"

Bort
Bort's picture
Offline
Last seen: 2 months 5 days ago
Joined: 06/01/2012 - 17:15
Posts: 7460
Location: Holding the proverbial flashlight

led4power wrote:

Bort wrote:
Your comparing apples to oranges, datasheets are not based on accuracy of lumen measurement, they are based on tolerance in bulk manufacturing.

You should read datasheets more carefully,for example:

Cree: “Cree maintains a tolerance of ±7% on flux and power measurements, ±0.005 on chromaticity (CCx, CCy) measurements and ±2 on CRI measurements”

Lumileds: “Philips Lumileds maintains a tolerance of ± 6.5% on luminous flux and ± 2 on CRI measurements”

Luminus: “Luminus maintains a +/- 6% tolerance on flux measurements”


Let me explain how manufacturing works, they produce millions of chips and sort them into bins which are labelled for sale. Each LED has a slightly different output so they sort the chips into output bins, each bin has a lumen output between the stated values. If you buy two XM-L2 U2 1A chips and tested them, they would fit into the U2 bin but would not have the exact same lumen output, but would be between the 7% difference stated.

The Journal of Alternative Facts TM

"It is critical that there is a credible academic source for the growing and important discipline of alternative facts. This field of study will just keep winning, and we knew that all the best people would want to be on board. There is a real risk in the world today that people might be getting their information about science from actual scientists"

 

led4power
led4power's picture
Offline
Last seen: 4 hours 55 min ago
Joined: 12/29/2012 - 09:48
Posts: 1284
Location: Croatia,EU

Thanks,but you don't have to explain to me how manufacturing works,manufacturing tolerance and luminous flux measurement accuracy are two different things.

You said:"datasheets are not based on accuracy of lumen measurement, they are based on tolerance in bulk manufacturing";

Yes,datasheets are based on tolerance in bulk manufacturing,but how accurate you can measure those tolerances-depends only on accuracy of measuring equipment.

DB Custom
DB Custom's picture
Offline
Last seen: 4 weeks 1 day ago
Joined: 01/13/2013 - 22:28
Posts: 20623
Location: Heart of Texas

And only ToyKeeper can actually see the difference.

The rest of us mere mortals are immune to the 7% tolerances. Wink

(not said jokingly, but in utmost respect for the critical eye of a professional with talents)

djozz
djozz's picture
Online
Last seen: 14 min 20 sec ago
Joined: 09/07/2012 - 17:04
Posts: 17207
Location: Amsterdam

...a slow going thread, but this work has no urgent practical use anyway Smile  ....

A good integrating sphere integrates so well because the light is reflected multiple times with minimal loss on the inner surface of the sphere, so that the initial beam pattern of the light source 'drowns' in all subsequent reflected light. If on the inner surface the reflected percentage of the light is not the same for all wavelengths but slightly different, there is a problem that builds up, with every reflection the difference is increased, and if you realise that for the sphere's output 10+ reflections have a measurable impact, you understand that the reflection of the inner surface should be very close to the same for all (visible at least) wavelengths, or the sphere will 'favor' certain wavelengths. The crappier your sphere, the less this is a problem of course Laughing. But does a coated sphere do that any better than a bare styrofoam one? (to be honest: I can not measure 'better', I measure 'different', but that is already good information to me)

this weekend I did runtime measurements of six 'constant output' flashlights in the new sphere. I did this for two reasons, 1)to see how constant the outputs were (quite, but not really, but it is repeatable, that is even more important), 2)I will do the same measurements again when the inner surface of the sphere is coated, comparison will hopefully give a clue about what the difference is of the sphere's spectral output after integration, with the bare styrofoam, and after coating (does coating make a difference?).

To see a maximum difference of the sphere's 'response' for different parts of the spectrum I made a red, green and blue flashlight (host 602C, 1x7135-driver, XP-E2-leds), and to see how much of the (if any) differences are leftover in normal flashlight situations I made a cool white (Uniquefire S10 host, XM-L2 0D, 2x7135), neutral white (Fandyfire A10B host, XM-L2 3B, 3x7135), and warm white (Uniquefire S10 host, XM-L2 7D3, 2x7135) flashlight. All leds were on a DTP copper board and in case of a brass pill (Uniquefire and Fandyfire hosts) they were soldered to it. Batteries were freshly charged IMR batteries.

Here are the outputs of these six lights in the uncoated sphere, coating will be done later and then this will be repeated and compared:

So when made this way with good heat-paths to the shell and with only few 7135 current regulators, the flashlights have a fairly stable output but not 100%. For practical purpose, if these flashlights are used between 5 and 10 minutes, the output stays within 2%, some within 1%, for more constant output you can wait longer. BTW, I used no active cooling of the lights, they were left flat on the wooden sphere-box at room temperature (see picture below), the output may have been flatter with fan-cooling but that would make the lights very unconvenient to use. The clear winner btw is the blue flashlight, the output dropped just 2% for the entire runtime of 40 minutes, while for the red flashlight it was 10%. Differences are caused by battery voltage (even though they are supposed to deliver constant current, 7135 chips I found are slightly sensitive to input voltage) and by led temperature, while some leds are more temperature sensitive than others. . But for me the most interesting is that these runtimes are very repeateable (I showed that for the cfc-light in post #16), if I cool the lights down and recharge the batteries, these runtime graphs will be exactly reproduced.

An illustration of the problems you get when trying to measure in the 1% region is when I measured the red flashlight after 40 minutes, I noticed that during the measurement the output started rising again; it appeared that cooling of the light by touching it for the measurent was the cause: to check, I held it fully enclosed by my hand for ten seconds and that resulted in a 2% output increase, something very significant to account for when using this type of 'constant' lightsource Undecided. I have the impression though that the red XP-E2 led is more sensitive to temperature than the other leds.

2bcontinued..

led4power
led4power's picture
Offline
Last seen: 4 hours 55 min ago
Joined: 12/29/2012 - 09:48
Posts: 1284
Location: Croatia,EU

djozz wrote:

I have the impression though that the red XP-E2 led is more sensitive to temperature than the other leds.

Red,red-orange and especially amber LEDs have terrible output drop with temperature rise.As you can see,their output is much more temperature dependent than for white and other colors.

djozz
djozz's picture
Online
Last seen: 14 min 20 sec ago
Joined: 09/07/2012 - 17:04
Posts: 17207
Location: Amsterdam

Some details of the sphere, still before coating.

The sphere half with the holes and the baffles. You can see some repairs, the inner surface had notches and polystyrene bits sticking out, I cut bits away and filled holes with lightweight wall filler.

Detail of the glued in (foamboard) baffles. BTW, not all glue goes well with polystyrene.

Here is the luxmeter-sensor. While the sensor of match's sphere was easy to clamp into the sphere repeatedly in quite the same way, with this one it was not so easy. I made a mounting solution for it with a black metal ring I had leftover and that accidentally exactly would fit the sensor within a fraction of a mm, making it possible to repeatedly mount the sensor in exactly the same position.

The ring on the inside of the box. The hole in the sphere fits around it with no play.

On the outside, with the clamping mechanism.

The sensor in position.

And how it looks on the inside of the box.

djozz
djozz's picture
Online
Last seen: 14 min 20 sec ago
Joined: 09/07/2012 - 17:04
Posts: 17207
Location: Amsterdam

led4power wrote:

djozz wrote:

I have the impression though that the red XP-E2 led is more sensitive to temperature than the other leds.

Red,red-orange and especially amber LEDs have terrible output drop with temperature rise.As you can see,their output is much more temperature dependent than for white and other colors.

Ah, thanks, the specs back this up, also no surprise that the blue one is so nicely constant Smile

djozz
djozz's picture
Online
Last seen: 14 min 20 sec ago
Joined: 09/07/2012 - 17:04
Posts: 17207
Location: Amsterdam

I started on the coating. For the first layer I used plain latex wall paint, to create a stable substrate for the 60%BaSO4/40%latex paint mixture of the subsequent layers. The mixture is not very great as a paint but it does stick and does not readily crack away when the styrofoam is lightly deformed.

Only when I started painting I discovered that this paint is not really white but slightly off-white, to the yellow/rosy side, just a bit, not a real problem because there will be more layers. For the mixture with BaSo4 I will use the other pot of latex paint I have that is much whiter, actually looks as white as the BaSo4 powder itself (and the styrofoam by itself also looks surprisingly white btw).

The off-white paint of the first layer gives an opportunity to show the cumulative effect of an integrating sphere. In the first picture I shine a flashlight (Nichia 219B) through the hole of one of the sphere halves onto the other half. But because the halves are separated, multiple reflections are not possible. (the greenish tint is from my limited camera). You can see that the reflected light from the paint is (almost) the same tint as the light reflected from the bare styrofoam on the outside of the sphere.

But with the halves connected, multiple reflections are taking place, leading to a much different tint (as seen through the hole), the yellowing effect of the paint is multiplied! :

Off course I should have shown this for the bare styrofoam too, but I forgot. I will get me another styrofoam ball one of these days and do the experiment still.

MRsDNF
MRsDNF's picture
Offline
Last seen: 50 min 39 sec ago
Joined: 12/22/2011 - 21:18
Posts: 13427
Location: A light beam away from the missus in the land of Aus.

Smile  Thanks for the update.

 

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.

 

ToyKeeper
ToyKeeper's picture
Online
Last seen: 5 min 29 sec ago
Joined: 01/12/2013 - 14:40
Posts: 10612
Location: (469219) 2016 HO3

DBCstm wrote:
And only ToyKeeper can actually see the difference.

The rest of us mere mortals are immune to the 7% tolerances. Wink


… What?

I can see PWM pretty well, but I’m not very good at small differences in tint, and even worse at brightness. Especially at the red end of the spectrum, since I seem to have a bit of a blue shift in my vision.

djozz
djozz's picture
Online
Last seen: 14 min 20 sec ago
Joined: 09/07/2012 - 17:04
Posts: 17207
Location: Amsterdam

I finished the coating and tested the results. The news is bad and the news is good. First some pictures:

On the left is the wrong paint I used for the first layer on the polystyrene, on the right is the latex paint that I used for two more layers, mixed with BaSO4, it is visually the same white as the BaSO4 powder in the middle. I made the 60/40 BaSo4/latex-paint mixture much thicker than for my first sphere, so I sufficed with two layers, the combined thickness was more than what is inside my first sphere.(for a background why I use this mixture, see my first 'Floating lumens' thread)

A picture of the BaSO4 powder next to bare polystyrene, also pretty much the same white visually (part of the polystyrene can be seen painted with the off-white latex).

After finishing the coating:

The sphere was put inside the wooden box, the holes matching the holes in the wood and the sphere firmly clamped in position by some cushioning leftover from flashlight packaging.

Then the lid was screwed in place.

I let the paint dry for a day and measured the reflectivity (the output of the cfc-light and my SWMD40A on high setting), then again two weeks later. In those two weeks the reflectivity of the sphere went up 1.02%, I hope that was still the paint drying for the last bit. Now it is two days later again and the measurements are exactly the same as two days ago. I will confirm (I hope) that is still the same a month from now.

The reflectivity of the coated sphere compared to the bare sanded styrofoam had gone down significantly (like in my first sphere) , by a whopping 37%. This is not nice because that reduces the integrating properties of the sphere. Luckily all my observations suggest that the integration is still pretty good. Because the total reflectivity is a combined result of a large number of reflections taking place inside the sphere, the decrease in reflectivity of a single reflection is much less of course. To get an idea, a few months ago, to get a feeling for my first sphere, I calculated the combined reflectivity after 17 reflections (adding more reflections to the calculation does not change the number much anymore) for two efficiencies for single reflection: 88% and 90%. After 17 reflections it comes to a difference of 13.6%. I could try to calculate what the difference for single reflection would be for the combined difference of 37%, but being a bit lazy, I estimate that on 6%. Ok, a bit less lazy, I just calculated it for 90% and 84% efficiency for a single reflection, after 17 reflections the difference is 30%. So the loss in reflection efficiency is even a bit worse than 6% Frown.

So, if not for the reflectivity of the sphere, the coating must be good for something, right? At least the reflectivity for different light colours must have become more constant. A good integrating sphere must have the same reflectivity for all colours. Unfortunately I can not measure reflectivity directly, what I can do is measure the luxvalues inside the sphere of different coloured constant light sources before and after coating. If the percentual difference in luxvalue before and after coating differs for the various colours (sorry for this horrific sentence, any virtuosity in the english language really leaves me here), the coating has had an influence on the respective reflectivities over the colour spectrum (improved or gone worse I can not tell).

So I did the runtime tests again for the constant output flashlight that I measured in the uncoated spere as well. To get an idea in what analog age I am stuck:

Then I made the exact same graph that I made before coating of the sphere (see post #38), I only altered the scaling of the vertical axis, to set the runtime curves of the neutral white flashlight before and after coating on exactly the same level. So then it is easy to see if any curve has shifted (this only works if your display is wide enough to show the two sets of graphs next to each other):

Hmm, that difference is not great, let's flip the uncoated graph, so that differences are more easy to spot:

Still looks very similar, but there are changes, of course most clearly for the single colours. After the coating as compared to before coating, if the neutral white curves are defined equal (just to have an off-set), blue measures (about) 10%lower, red 10%higher, green 3%lower, coolwhite 0.7%lower, warmwhite 1.5%higher. Am I impressed by the changes in reflectivity over the colour spectrum that the coating causes? Not really. The extreme colours blue and red do have a clearly altered reflectivity, but not many will want to measure them very accurately (maybe me Wink ). What matters in the real tough flashlight world is the different whites, and going from 3000K to 6500K the difference uncoated vs coated is only 2.2% (from neutral to cool only 0.7%).

I assume here, because I did some research on what substance to use, that this coating improves the constantness of reflectivity of the integrating sphere over the colour spectrum. But I did not find anywhere how good bare styrofoam already actually is in doing that (perhaps very good, who knows?). It is not unthinkable (I do not like that thought of course) that the difference that I find here are not an improvement but a change for worse. I just measure relative changes, not absolute reflectivities.

My conclusion about coating with BaSO4/latex mix? Because the effect is not that great, and because I do not even know for sure if that not so great effect is for the better, and because it is a messy and tedious job: just don't bother! And that is bad news because coating my spheres was apparently not really worth the effort, and that is good news because this makes all those uncoated styrofoam integrating spheres out there just a bit more trustworthy Smile

texaspyro
Offline
Last seen: 1 year 3 months ago
Joined: 04/29/2011 - 12:43
Posts: 4593

The loss in reflectivity caused by the coating should not have any effect on the ability of the sphere to integrate the readings (the shape of the sphere is what mostly determines that).

As far as wavelength dependent reflectivity/absorption goes, I have seen a slight effect of the styrofoam from an ideal reflector, but it is not much. I can operate my sphere in an ultra-high lumens mode by attaching the sensor to the outside wall of the sphere, using the styrofoam wall as a light attenuator. My sphere uses a TAOS RGBW color sensor for its measurements. I get minimal changes of the color values/calculated CCT between the interior/exterior light measurements (the biggest effect seems to be on the blue channel).

I came to the same conclusion as you… the coating is not really any better than just sanding the sheen off the sphere interior.

MRsDNF
MRsDNF's picture
Offline
Last seen: 50 min 39 sec ago
Joined: 12/22/2011 - 21:18
Posts: 13427
Location: A light beam away from the missus in the land of Aus.

Amazing effort and research. How did you work out the baffle locations and size. If I've missed this somewhere sorry.

 

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.

 

djozz
djozz's picture
Online
Last seen: 14 min 20 sec ago
Joined: 09/07/2012 - 17:04
Posts: 17207
Location: Amsterdam

texaspyro wrote:
The loss in reflectivity caused by the coating should not have any effect on the ability of the sphere to integrate the readings (the shape of the sphere is what mostly determines that).

No, it does affect the integration a bit, this is why: There is an amount of light entering the sphere. Because of the baffle it can not directly illuminate the detector but light that has undergone a first reflection can. This first reflected light comes, depending on beam shape, from all sides to the detector or from a certain area in the sphere, so the angle from which it enters the detector is not random and the distance from which it comes is not average. So the reading of the first reflection is susceptible to limitations of the detector. Light that has undergone more than 1 reflection probably already is random in distance and angle from the detector. Now, the better the reflectivity, the higher the contribution of multiple reflected light to the lux-reading, and that is lowering the contribution of that first reflection of which the reading can not be fully trusted. (in case of 90% reflectivity of the combined inner surface of the sphere, which is already a challenging number for non-professional coatings and the presence of holes that fit flashlights, a quick and dirty calculation learns that light that has been reflected once contributes to about 11% of the light that reaches the detector, probably in reality this number is higher).

texaspyro wrote:
As far as wavelength dependent reflectivity/absorption goes, I have seen a slight effect of the styrofoam from an ideal reflector, but it is not much. I can operate my sphere in an ultra-high lumens mode by attaching the sensor to the outside wall of the sphere, using the styrofoam wall as a light attenuator. My sphere uses a TAOS RGBW color sensor for its measurements. I get minimal changes of the color values/calculated CCT between the interior/exterior light measurements (the biggest effect seems to be on the blue channel). I came to the same conclusion as you... the coating is not really any better than just sanding the sheen off the sphere interior.

That is of course a quite qualitative test but it does give a good indication I guess. You do not know how many reflections the light that comes through the walls of the sphere have undergone compared to light that is bounced inside the sphere, but you do know for sure that unlike the light inside the sphere there is no contribution to the reading of the first couple (10? 20? I don't know how many reflections it takes to get through 2cm of styrofoam) of reflections.

djozz
djozz's picture
Online
Last seen: 14 min 20 sec ago
Joined: 09/07/2012 - 17:04
Posts: 17207
Location: Amsterdam

MRsDNF wrote:

Amazing effort and research. How did you work out the baffle locations and size. If I've missed this somewhere sorry.

Thanks Steve! Smile

The baffle location is the middle between two holes. The size is determined by trial and error: I made test-baffles out of cardboard, and while holding them in position I looked from one hole to the other to see if it is fully covered visually. then trim the cardboard a bit and check again, until the minimum size is reached (I added an extra 2mm to be sure).

ToyKeeper
ToyKeeper's picture
Online
Last seen: 5 min 29 sec ago
Joined: 01/12/2013 - 14:40
Posts: 10612
Location: (469219) 2016 HO3

I think I’ll be lucky if I ever get around to making a cheap papier mache sphere… and so far, I’ve been using an even less accurate integrating milk carton with a bottom-of-the-line HS1010A meter.

BTW, for maximizing reflectivity and integrating properties, would it be worth attempting to cover the inside with a mirror-like material? (and perhaps aim the light in at an angle so it won’t reflect directly back at itself) The idea would be to make the light sensor the only absorbent surface. Due to increased overall brightness though, it might also be necessary to put the sensor behind a sheet of foam to attenuate the signal. I have no idea if this would actually work though.

DrJones
DrJones's picture
Offline
Last seen: 4 years 5 months ago
Joined: 01/05/2011 - 13:30
Posts: 1044
Location: Frankfurt, Germany

The integrating properties of such a sphere rely on the cosine law of diffuse reflection, a mirror-like surface would kill those properties. Great effort is made to get the surface as diffuse as possible.

DavidEF
DavidEF's picture
Offline
Last seen: 5 days 3 hours ago
Joined: 06/05/2014 - 06:00
Posts: 7699
Location: Salisbury, North Carolina, USA

djozz wrote:
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.
HaHa! I just read this in your first integrating sphere build thread. Silly

The Cycle of Goodness: “No one prospers without rendering benefit to others”
- The YKK Philosophy

djozz
djozz's picture
Online
Last seen: 14 min 20 sec ago
Joined: 09/07/2012 - 17:04
Posts: 17207
Location: Amsterdam

DavidEF wrote:
djozz wrote:
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.
HaHa! I just read this in your first integrating sphere build thread. :p

I must re-read my threads more often, saves a lot of work and trouble Wink

Ok, but now I have a sphere of which it is dubious if it is improved at all by the coating, but at least I extracted some data from the work. (I am especially fond of the quote in Bort's sig-line: "In God we trust, all others must bring data". The quote is attributed to William Edwards Deming, a thorough man, it seems)

DavidEF
DavidEF's picture
Offline
Last seen: 5 days 3 hours ago
Joined: 06/05/2014 - 06:00
Posts: 7699
Location: Salisbury, North Carolina, USA

djozz wrote:

DavidEF wrote:
djozz wrote:
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.
HaHa! I just read this in your first integrating sphere build thread. Silly

I must re-read my threads more often, saves a lot of work and trouble Wink

Ok, but now I have a sphere of which it is dubious if it is improved at all by the coating, but at least I extracted some data from the work. (I am especially fond of the quote in Bort’s sig-line: “In God we trust, all others must bring data”. The quote is attributed to William Edwards Deming, a thorough man, it seems)


Yes, the first time around you didn’t mention anything about measuring the differences in reflectivity for different wavelengths of light. This time around, you included that consideration in your testing the Styrofoam vs. the coating, so maybe when you get around to making your THIRD integrating sphere, it will be coating-free. Wink Or maybe it will be coated with glass micro-beads suspended in clear epoxy, then wet-sanded. Wouldn’t that give you a better reflectivity of all wavelengths, while also diffusing the light source? Hmmm. Oh wait, epoxy yellows over time, doesn’t it?

The Cycle of Goodness: “No one prospers without rendering benefit to others”
- The YKK Philosophy

djozz
djozz's picture
Online
Last seen: 14 min 20 sec ago
Joined: 09/07/2012 - 17:04
Posts: 17207
Location: Amsterdam

DavidEF wrote:
djozz wrote:

DavidEF wrote:
djozz wrote:
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.
HaHa! I just read this in your first integrating sphere build thread. :p

I must re-read my threads more often, saves a lot of work and trouble Wink

Ok, but now I have a sphere of which it is dubious if it is improved at all by the coating, but at least I extracted some data from the work. (I am especially fond of the quote in Bort's sig-line: "In God we trust, all others must bring data". The quote is attributed to William Edwards Deming, a thorough man, it seems)

Yes, the first time around you didn't mention anything about measuring the differences in reflectivity for different wavelengths of light. This time around, you included that consideration in your testing the Styrofoam vs. the coating, so maybe when you get around to making your THIRD integrating sphere, it will be coating-free. Wink Or maybe it will be coated with glass micro-beads suspended in clear epoxy, then wet-sanded. Wouldn't that give you a better reflectivity of all wavelengths, while also diffusing the light source? Hmmm. Oh wait, epoxy yellows over time, doesn't it?

Yes, it does, while my latex painted walls look as white as when I painted them. The glass beads must be lens-grade clear and I'm not sure if you can finish glass to such a matt that reflections are close to lambertian.

My third sphere (you hit the nail on the head here Wink ) will indeed be uncoated (now for real), small, and easy to make. I'll post about it when time comes Smile

DavidEF
DavidEF's picture
Offline
Last seen: 5 days 3 hours ago
Joined: 06/05/2014 - 06:00
Posts: 7699
Location: Salisbury, North Carolina, USA

djozz wrote:
Yes, it does, while my latex painted walls look as white as when I painted them. The glass beads must be lens-grade clear and I’m not sure if you can finish glass to such a matt that reflections are close to lambertian.

My third sphere (you hit the nail on the head here :Wink: ) will indeed be uncoated (now for real), small, and easy to make. I’ll post about it when time comes :Smile:

I was thinking about the hollow sphere glass micro-beads that are used in making reflective coatings on signs and such. The way they work is by reflecting the light off their interior concave surface. Surely, there is some clear coating that will not yellow over time. But, if a non-coated surface works, why bother anyway? I’m just trying to add a little silliness to your thread. :bigsmile:

The Cycle of Goodness: “No one prospers without rendering benefit to others”
- The YKK Philosophy

texaspyro
Offline
Last seen: 1 year 3 months ago
Joined: 04/29/2011 - 12:43
Posts: 4593
djozz wrote:
No, it does affect the integration a bit

I don’t think it makes any measurable difference. You have a zillion photon paths bouncing light around a zillion times and reaching the sensor from a zillion angles. It all averages out at the sensor to a constant value.

DB Custom
DB Custom's picture
Offline
Last seen: 4 weeks 1 day ago
Joined: 01/13/2013 - 22:28
Posts: 20623
Location: Heart of Texas

In more ways than one! Smile

I used the glass bead material for my photography lights. Not impressed. It works great on a white stripe on the road, even yellow, but questionably in a 15” reflector for a photography light stand.

ToyKeeper
ToyKeeper's picture
Online
Last seen: 5 min 29 sec ago
Joined: 01/12/2013 - 14:40
Posts: 10612
Location: (469219) 2016 HO3

DavidEF wrote:
I was thinking about the hollow sphere glass micro-beads that are used in making reflective coatings on signs and such.

… but those are specifically chosen for their ability to reflect light back toward its source, no matter where the source is. It’s like if you ever stood in front of two mirrors placed at a 90 degree angle to each other, it always reflects your image no matter where you are relative to the mirrors. Add a third mirror perpendicular to both, and it’ll do that from any angle… or, just use a concave half-sphere and it’ll reflect any light back to its source.

That seems like it would defeat the point of an integrating sphere, because the photons would be aimed to go directly back into the flashlight instead of into the light sensor.

DB Custom
DB Custom's picture
Offline
Last seen: 4 weeks 1 day ago
Joined: 01/13/2013 - 22:28
Posts: 20623
Location: Heart of Texas

We are planning on hooking up the sensor directly to David’s left eye, shine the light at the right one and a readout will come out the left ear. Wink

Pages