Amazing effort and research. How did you work out the baffle locations and size. If I've missed this somewhere sorry.
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).
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.
Thanks Steve! :-)
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).
I think Iāll be lucky if I ever get around to making a cheap papier mache sphereā¦ and so far, Iāve 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 wonāt 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.
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.
HaHa! I just read this in your first integrating sphere build thread. 
I must re-read my threads more often, saves a lot of work and trouble ;-)
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 didnāt 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. 
Or maybe it will be coated with glass micro-beads suspended in clear epoxy, then wet-sanded. Wouldnāt that give you a better reflectivity of all wavelengths, while also diffusing the light source? Hmmm. Oh wait, epoxy yellows over time, doesnāt 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 ;-) ) will indeed be uncoated (now for real), small, and easy to make. I'll post about it when time comes :-)
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? Iām just trying to add a little silliness to your thread. :bigsmile:
I donāt 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.
In more ways than one! 
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 15ā reflector for a photography light stand.
ā¦ but those are specifically chosen for their ability to reflect light back toward its source, no matter where the source is. Itās 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 itāll do that from any angleā¦ or, just use a concave half-sphere and itāll 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.
We are planning on hooking up the sensor directly to Davidās left eye, shine the light at the right one and a readout will come out the left ear.
Thatās exactly how I tested the low end on my RRT01. That thing goes so low I canāt tell for sure if Iām seeing light or if itās just my imaginationā¦ even after adjusting to the dark for hours and holding it directly to my eye.
Getting really excited now, can I borrow your David one of these days for a performance check?
This is the sphere that I use for all my emitter tests and flashlight output numbers, and hereās a check long overdueā¦
Recently I made a tiny zoomie (host=Ultrafire AT-007) with BLF-A6 driver and dedomed XP-G2 S3 3D. which makes a bright ultra-clean hotspot (40kcd on high), and today I realised that on the lowest modes, running on the single 7135 on the driver, it must have an extremely constant output. So it could be used to measure accurately the integrating properties of the sphere.
Hereās the experiment: with the light on level 3 (a very constant ~2lumen) and lens in spot modus I shined the spot straight down into the sphere and measured the output. This is the beam of an extreme thrower. Then did that again with the light at a very steep angle, measured in several directions, like this:
This is representative of the outer part of the spill of an extreme flooder.
I corrected all measurements for the altered reflectivity of the sphere caused by holding the flashlight in different positions.
Here are the results, the first measurement is the flashlight straight down into the sphere, what is how I normally measure a flashlight/ emitter. Then with the flashlight at the steepest possible angle, in various directions.
In position 3 and position 5 the beam was pointing straight at one of the baffles, which area makes out so little in the whole of directions that these a bit lower measurements can be neglected. Still a deviation of 7% with all light pointed on a baffle I find unexpectedly good.
So what can be seen is that there is a reading variety of maximal 3% compared to the position straight down, on average I estimate 2. Considering that the most extreme flooder will still have light in all directions instead of a ring going to the side, I estimate the difference between extreme thrower and extreme flooder just 1.
I am happy with the result, it implies i.e. that Iām confident that the djozz-lumen is virtually the same both for all flashlights and for all bare emitters, something I still was a bit worried about.
Excellent work there! PM me for my shipping addressā¦
:laughing: :laughing: :laughing: :laughing: :laughing:
:person_facepalming:
What Steve? Did I beat ya to it?