Integrating sphere #4 (the fast and cheap one)

Directly for the measurement itself, the size of the sphere is unimportant, a sphere integrates the light and does that regardless of the amount of light.

But there are three other reasons for a bigger sphere at higher output:

1)A bigger sphere is needed because high output lights usually have bigger heads and thus the entrance hole must be bigger and to keep the surface percentage of the hole within the required maximum the sphere needs to be bigger.

2)the amount of heat may melt your styrofoam, going bigger spreads the heat over more material.

3)your measurement may get your luxmeter out of range, a bigger sphere increases the range. But a ND filter before the sensor does that too.

I have done BaSO4 coatings on test spheres, tried mixed with latex paint, and mixed with PVD. I did all sorts of checks but I found it difficult to find clear advantages over bare sanded styrofoam.

Yeah, I didn’t want to write all that out. I’m lazy. :stuck_out_tongue:

Was the coating thick enough to keep the light from going through?

I was thinking of smearing Elmer’s glue on the interior surface and then pouring the powder on it and shift it around. That way you have a thick, jagged surface to help integrate the light.

I cannot see images 2 & 3 in post #100.

This seems to always happen with images hosted with Google.

That suggestion was done on CPF a few years ago, I think you refer to that. But unlike some other metal salts that are used for whitening, BaSO4 cristals are fairly transmissive for light, most light will actually enter the layer instead of being reflected by the outer surface. That is why to reach the maximum reflectance for bariumsulfate, the layer must be fairly thick, several mm. A single surface coating on top of a layer of glue will hardly do much, you will deal with the reflectance of Elmer’s glue more than with that single cristal layer of BaSO4.

Sorry raccoon city, I don’t know what to do about that. Dealing with the whole image hosting fiasco, I’ve pretty much decided to just host from Google (though I’d like to hear if this really is a big problem for a lot of people not seeing the images).

Back to my sphere problem: What first tipped me off to my sphere reading too low on high lumen levels was when I measured my Sofirn SP40, Sofirn SD05 and my Astrolux HL01 (XP-L 4000k). I posted about it over in the SP40 thread, asked for other’s tested levels, and only got one (helpful) response. Basically all three of these lights (at higher levels) gave lumen numbers from my sphere that didn’t make sense. All three lights were measured on fully charged new high-drain cells (LG HG2). As seen in the SP40 thread post, my SP40 on Turbo only came out at 798 lumens. By eye I would have guessed it was putting out at least 1,000 lumens. My SD05 (on a fresh charged new Molicel P42A 21700) on high measured 2,223 lumens and on medium 792 lumens. General consensus on the SD05 (there doesn’t seem to be any authoritative measurements posted) is that it is putting out between 900 and 1,000 lumens in medium (which is a very solid stable regulated level) and +/- 2,500 lumens in high. My HL01 on turbo measured 1,030 lumens at start and 992 lumens at 30 seconds. I was expecting more like 1,200 lumens.

And now that I’ve stumbled on this issue some of my other measurements on other lights at higher lumen levels make more sense to be too low, such as my Convoy M1 XM-L2 driven @ 3.04A only coming out at 840 lumens. I also reviewed that Imalent BG10 XHP50.2 bike light which measured lower than expected at higher levels (which at the time I just thought was the manufacturer fudging #’s).

So in that SP40 thread, YogibearAl measured his 4000k SP40 in his Texas Ace Lumen Tube calibrated with Maukka lights:
Low = 7 Lumens
Med = 65 Lumens
High = 358 Lumens
Turbo = 988 Lumens start up 963 @ 30 sec on freshly charged 30Q. Continues to drop as battery drains.

So I re-ran my lumen calcs based on YogibearAl’s posted #’s above to compute a new multiplier. My previous multiplier was 0.4275, and now calibrating to Yogi’s #’s I am getting varying multipliers, with the #’s for the high outputs being significantly higher (my expectation – that my sphere is “good” at low outputs, but gets exponentially worse at higher levels). Multiplier’s I get:

Low – 0.4516
Med – 0.4422
High – 0.5000
Turbo – 0.5158

If I then run with the multiplier of 0.5000 from high mode, run that back against my SP40 measurements and also on my SD05 & Astrolux HL01 (XP-L 4000k) measurements, I get:
Low – 7.8 lumens
Med – 73.5 lumens
High – 358 lumens
Turbo – 934 lumens

Low – 324 lumens
Med- 926 lumens
High- 2600 lumens

Astrolux HL01
Stepped Ramp Levels:
Step 1 – 15.2 lumens
Step 2 – 51.3 lumens
Step 3 – 145 lumens
Step 4 – 190 lumens
Step 5 – 296 lumens
Step 6 – 472 lumens
Step 7 – 807 lumens
Turbo – 1160 lumens

So now my higher numbers seem more in line with expectations, but I suspect I’m showing lumen #’s that are too high for the lower levels. My sphere was originally calibrated with the average of (3) Fenix HL55 headlamps averaging modes Low, Medium, & High (i.e. dropping Eco & Turbo), where ANSI ratings are Low = 55 lumens, Med = 165 lumens, High = 420 lumens, however I held Selfbuilt’s tested numbers which differed slightly from ANSI: Low = 55, Med = 161, High = 402.

I’ve now finished 4 coats of matte white paint on my new foam sphere halves. I quickly held up one of these halfs to the ceiling light (a standard lightbulb, LED 60 watt equivalent) and the outside of the foam no longer glows like the original sphere, so I think this has helped immensely in keeping light inside the sphere. I’m going to try to test this with a flashlight and luxmeter tonight comparing the lux reading through each foam (unpainted vs. painted). I still don’t have a piece of glass to use, so I’m not ready to assemble the sphere yet.


Wouldn't lining the interior with aluminum tape work better?

No, it should be white and as flat as possible, ideally a photon hitting the surface from any angle has an equal chance to leave again at any angle (so-called Lambertian reflection), that is key to the integrating properties of an integrating sphere.

So, why not paint the interior with a flat white acrylic paint to mimic ceilings vs an ideal laboratory condition? I get that companies want the best possible ratings for their products.

You could do that. For a discussion on integrating spheres you could follow the links in my sigline to some posts that I wrote on my journeys towards a working sphere. A very nice read on integrating spheres in general, if you are into that, can be found here:

So I ran those checks on “light leakage” between my old unpainted sphere and the new painted half round foam. The pained foam (4 coats now) is definitely blocking light! I took my Convoy M1 XM-L2 (high at 3.04A) pressed it right against the foam on the inside and placed the luxmeter sensor right against the foam on the outside directly across from the light. Here are the results:

Unpainted foam
Low - 4,280 lux
High - 12,920 lux

Painted Foam
Low - 118 lux
High - 337 lux

Some pics (painted foam is the one where the light looks yellow):

My dilemma now is how to mount the luxmeter. This time I’m going to put the sensor hole 90º away from the light input hole. I’m going to open up the sensor hole completely to the inside (the wall is now painted, so I pretty much have to). I can either mount the sensor directly at the hole (the face of the sensor will be set back from the inner sphere wall since I can’t get it fully into the foam without some extreme cutting), use PVC pipe to “couple” the sensor to the sphere wall (inserting the PVC until it’s flush with the inner wall and painting the inside of the PVC matte white also) using either straight pipe, a 45º bend, or a 90º bend. With the bends I’m guessing I may get away without using a baffle inside the sphere. I’m concerned though about light reflecting off that PVC even with it painted matte white except maybe in the case of using a piece of really short straight piece of PVC. Any thoughts on this? Some mock up pics:

90º Bend:

45º Bend:

Straight Section:

By the way, anyone looking for glass like I have been, search for “clock glass” in order to find various size round flat glass that is readily available and doesn’t cost an arm and a leg.


Still working on my new sphere (slowly). I happened to take my company truck to get a new windshield installed and they were able to cut me glass to size, so I got (2) 4 1/2” diameter pieces for $5. Now I’m struggling with what to do about a baffle. I think I read that it’s best if the baffle is made of the same material as the sphere, or at least has the same coating. So I’ve picked up a flat piece of this same “smoothfoam” and have painted it matte white on all surfaces. This material is about 23mm wide, so it’s kinda big (thick). I was thinking to mount it using small wood dowels glued into the baffle and into the sphere (dowels painted matte white as well). My biggest problem is coming up with the proper shape/size. I think I read somewhere that light should reflect at least twice before reaching the sensor. Well if this is the case it seems you’d need quite a large baffle, because you’re not only blocking direct light from the entrance hole, but also beams from that first reflection. Also with the sphere surface being round (and hence a “sphere” - lol), you’d have to block from numerous directions.

What about this idea for a baffle?

Or is this layout preferred? This seems to be the more common approach. And is the 2nd baffle necessary?

Will it matter how close the baffle is to the sensor? Obviously I won’t put it extremely close, but is there a point where it’s too close and affects the luxmeter sensor’s readings adversely? Any help/guidance is appreciated!


I cannot see your pictures

good luck with your sphere

Aarrgghhhh! I wonder how widespread this issue is (percentage of people that can’t view my photos). I finally settled on using Google to host my pics (I wasn’t happy with alternatives I found and Google is super simple to utilize) and now run into people not seeing them. This might be better suited for a new/different thread rather than being discussed here.


I can’t see any pics in #115 and #116.

The baffle is just to prevent direct light and should be opaque.

Ok, I finally see the issue by using another browser on my phone. I’ve looked in Google Photos for sharing settings, but don’t see anything to change. And googling the issue doesn’t lead to anything helpful. Guess it’s back to the drawing board for photo hosting.


Ok, any ideas on a material to use that’s stiff enough to stay in place? And I guess styrofoam is not a good choice.


The baffle position is not critical but should be somewhere in the middle between entrance hole and sensor, and as Jason pointed out it just prevents direct light from light source to sensor so that detected photons have undergone at least one reflection (not 2). Ideally, the baffle should be as small as possible while still blocking all direct light. This is all discussed in my integrating sphere threads before, and in the sphere theory article from Labsphere.

If styrofoam is convenient, use it. Just glue a solid material over it, like posterboard, thick plastic or metal painted white. Just something to keep light from going through.

Thanks guys. It’s a lot easier to block direct light only. Poster board painted matte white sounds simple enough. I’ll definitely err on the side of making it too big (but not way too big).