It’s great to see more research being done on improvements. As for a standardized way to do that… perhaps the hole plug it comes with could be attached over the meter hole with some white caulk? White caulk would probably be needed instead of clear to prevent gap leaks and keep everyone standard. I wonder what the new lowest reading would be?
I actually tried using the hole plug and while it did work it only increased the reading range slightly IIRC, think the max was bumped up to around ~2000 lumens? I didn’t see anyway to increase that further easily so I started looking for other options.
Honestly something a bit thicker/denser then what I have would be ideal, should end up with a max around 10k lumens which should handle 98% of lights to be tested.
The minimum is actually still surprisingly low. I got a reading of ~9-10 lux with the S1 on moon mode.
Nice work, over my head to be sure.
Glad you got it and had the time to attack it with such vigor! 
You could also put a cheap neutral density filter directly over the sensor, sized to fit as closely as possible. Rotate the box so the sensor is at the bottom, and gravity should hold the filter in place when needed. A ND8 should increase the range to 8000 lumens, or a ND16 would let it handle 16,000 lumens. Or some people (*cough* Frankendale *cough*) might even need more than that, but the filters are available much stronger if desired.
That looks like a great idea because the effect is mathematically predictable, so there would be no unknowns in the lens calibration. One person could use the ND8 and discuss his results with someone using the ND16 and know that they are in sync.
Once we agree on the desired lens diameter, I can 3D print a lens adapter and mail them to everyone for free. Then the lenses can be removed or swapped, and still seal good.
Well, I only modded my TR-J20 to 13,500 lumens, unlike the 34,000 somebody else we know did… 
I had to make an 11 ounce heat sink for him for that one, remains to be seen how much longer it’ll run…(Ok, so I’m THINKING about it! Geesh!)
I agree, the ND filters are a great idea, never even thought of that. They are pretty cheap on ebay as well.
The ND16 would most likely work fine unless you plan on measuring a lot of moon modes and the like, although you could simply remove the filter if needed for that.
I guess most people would never build/own a light over 8k lumens, particularly with a head small enough to fit into the sphere. So maybe the ND8 is the way to go, should handle the low end down to ~5 lumens based on my testing.
The nice thing is that you can self calibrate the filter pretty simply if you have a light that is regulated and consistent.
I will leave the shopping to you, Texas_Ace. You are on a roll. I would recommend a lens with a white colored band though. Black may suck the light out of the sphere and convert it to heat, since black absorbs light. If that’s not possible, I may try to make the holder swallow the lens as much as possible, but it would be harder to remove.
That’s why the filter needs to be pretty close to the right size.
My lux meter has a black area around its white sensor cover. I figured I’d try to find something about the same diameter as the black part it already has. Just gotta make sure it gets a decent seal so all incoming light will have to pass through the filter.
What I can definitely confirm though… is that you shouldn’t put the filter right in front of a bright flashlight, like a triple XP-L with a FET. It only took about 3 seconds to get melty. 
I agree that a grey or white lens bezel would be ideal but in my searching I could not find any reasonably priced filters with anything but black. So I think we might be stuck with that. Possibly use a white pen/marker to white it out but that would be hard to standardize.
So for the filter we need to pick a size, the lux meter is about a 36mm opening, I assume the hole is about the same (don’t feel like opening it up at the moment).
So in theory anything over ~40mm should work but I figure ~50mm+ would be better to ensure the bezel is clear of the meter. Any opinion on how much oversized it should be? Say 77mm+ or just a little bit at ~55mm? Which would be easier to make a bracket for?
By cross referencing some filters from ebay to amazon it looks like even the cheap china filters get good ratings with no real complaints on lens quality that I saw. So doesn’t appear there is a need to go with anything pricey/fancy.
In which case that just leaves picking a size and seller off ebay/aliexpress.
After looking around I think that ND8 is the best option, it should allow most people to install it and forget it and use the sphere as is for just about everything. Plus they are easier to find in a wider selection of sizes.
For those that need more they can order an ND16, I will try to find a size that offers an easy ND16 option as well.
So opinions on size, slightly larger then meter or much larger?
Any opinion on Ebay vs Aliexpress?
You posted while I was typing.
This is a good point, so do we go with a small 37mm filter or a larger oversized one?
37mm seems to be the closest common size to the meter opening, aka: http://www.ebay.com/itm/Tianya-37mm-37-mm-Neutral-Density-ND-8-ND8-Lens-Filter-for-Camera-Camcorder-/250820925349?hash=item3a661797a5:g:keUAAOSwVFlT8cRE
There are a lot more sizes and options as you get into the 50mm+ range.
Thats sad but funny with the melted filter, guess they were not designed to dim flashlights!
Maybe it would be easy to remove the lens from the metal it comes with? idk. My plan for the mount was just a simple cylindrical ring that the threads could be pressed into to hold it in place. The layers of the 3D print should grab the tiny threads excellent. Then pull to remove.
I kinda doubt removing the lens from the metal ring would be feasible in most cases. Unless it is a super cheap filter they are designed specifically to not allow that to happen.
I like your mount design, simple and easy. It is possible you could extend the mount up and around the outside of the filter, thus covering all but the edge of the ring facing the middle of the sphere. Maybe have a small grove to pry it out later, although that could get risky of cracking the sphere.
Personally I think that small amount of black would be a non-issue for calibration purposes. It should absorb a fixed amount of light and thus the multiplier could be adjusted for it.
FYI, I have access to a 3D printer if that ever comes in handy, although not sure that the filament would be the same as yours and might cause a discrepancy. Not the best at CAD design either, thats still on my to learn list.
Interesting thing of note in this picture. Notice how the filter appears to be melted more around the outside edge of the LED optic?
That demonstrates why the larger head lights can’t be measured, you lose a lot of light to the foam for the reference reading and that then skews any other readings you may try to make.
If you look at the excel file you will see that the through-wall reading matched the internal diffuser reading both at around ~2500 lumens on the L6 (should be ~3500). So about 29% of the light was lost to the foam in that outside edge.
I wounder if it is possible at this stage to make the hole any larger? or was that shot down earlier in the thread?
The filament I used is this PETG It’s good stuff. That simple cylidrical ring would have a rather complex outer surface so it could make lots of contact with the foam and give better adhesion. I can send you a 3D file later in the week if you want. I just need the precise OD and height of the threads. And total height and total OD if we want to hide it.
Yeah, that is good stuff. I only have access to ABS or PLA, so it would not match for sure. Can use it for speed prototyping though if needed.
I figure it would be best to wait to print up the brackets until we actually have the filters in hand. Been there, done that with trying to design something ahead of time based on specs given in a listing.
Basically we just need to pick a size, 37mm that should fit just over the edge of the meter opening or larger ~52mm that would ensure it is out of the meter line of sight but also absorb more light?
The larger ones are cheaper and easier to get FYI, they even have them from American sellers for reasonable prices.
For the price, maybe one of each to test?
Wonderful work with all that extensive testing texas_ace! Glad we’re constantly trying to improve on this sphere. Let me get this straight, as I’m not sure I fully understand your technique.
Your saying to split open the sphere and use it as a half sphere? And place the diffuser lens over the 1 1/2 inch hole where the opening to the meter is?
Shouldnt we cut and make the opening bigger now? Because even though we get a 4inch diameter diffuser lens, and if we dont make the opening any bigger, say a 3 or 4 inch diameter head will get partially blocked by the styrophone and not all light will get passed through to the meter
Not totally sure what you were suggesting, are you talking about the meter hole or the hole for the light to shine through?
TK suggested a much better idea then the foam I used, a camera filter that is designed to reduce the light transmittance. This will be much easier to standardize and should give a better result. We are just debating on what size to get.
Far as splitting the sphere, the picture was just to show what I was doing, I put the sphere back together with the foam in place to take the measurements. With the internal diffuser in place the sphere would be used exactly like it is now, the meter readings would just be lower and thus the max lumens it could handle would be increased to approx 8000 lumens with an ND8 filter.
There is no need to change the meter mount/hole at all. Only a need to mount the filter over the meter.
Now the hole for the flashlight on the other hand could be made larger to allow for larger lights to be tested but that gets into it being hard for people to all do it the same and thus standardization would be hard.