You’d be surprised how much difference each tube can measure — That’s the reason for having some reference calibration lights — Like the maukka-calibrated flashlight— He has a reference type sphere — that way if you calibrate to one of his lights and others calibrate to one of his lights — we are some what close in readings
Absolutely true. It’s amazing how little a change is needed to get a different reading out of a lumen tube. That’s why T-A glues his down after calibration.
Trying for a direct readout on the lux meter takes a heck of a lot of trial and error. Many errors.
T-A said it took him months to come up with a combo that got close.
Using a tube or sphere and a correction table is simpler.
With mine, I got it to where I can get a reading that is consistent without resorting to adjustment tables. That’s the light valve allowing me to dial in the Lux to Lumen conversion.
All the Best,
Jeff
First of all, what do you want to measure?
Difference between 2 lights can be measured by testing at the same distance (that’s the method Candela can be calculated)
However if you want to measure Lumens, you need to have a reference with an exact known output.
The next step is how accurate do you want your readings to be?
The most accurate method is achieved by the sphere setup, but FYI, an accuracy of +–15% is already very high.
Calibration is key!
[quote=nottawhackjob]
[quote=Unheard]
I’ll do that. That was my original plan. To make a design that anyone could reproduce and come out with something that fairly consistent.
It’s been a while since I made my almost finished design. Might take me a while to get all the data together.
My PVC straight tubes are lined with silver metal duct tape. Also did the exterior, but eventually did the inside because I felt the plastic was sucking up some of the photons.
The tuning comes from the spacer rings and the diffusion material. The photo grade stuff I use is very consistent sheet to sheet and across the sheet. Much better than hardware grade DC film.
All the Best,
Jeff
.
I agree with djozz on this one, he is very knowledgeable on the subject of light.
.
All my lights to be tested were high lumen throwers. Flooders gave better readings.
I have 3 different shaped lumen tubes and the variables of leds, reflectors, lumens and light meters affect each one differently. The lumen tube rabbit hole is infinitely deep with no real accuracy. Some may argue with me, but I could write a book on the trials, time and experiments put into these tubes. Just when you think you got it calibrated close, in goes a new powerful thrower and a 90.2 led reads 6500 lumens. LOL…
I was unable to use the Maukka calibration lights because the higher lumen lights were reading too low, like more than 30%.
My lumen tubes are pretty much useless, just ball park numbers. Really sucks too because this is a big part of the hobby. :weary:
.
The lumen tube Texas Ace put together is without a doubt the most accurate for small to medium lights I have seen.
.
Also somewhere I read a formula to calculate a sphere for a 130mm dia reflector flashlight that required an enormous 150cm diameter integrating sphere, LOL the rabbit hole bottom. LOL. Good luck 
.
Yes, I can not measure my big lights in my 50cm integrating sphere because the maximum entrance hole is 80mm and the range goes up to just 9400 lumen. When I build it years ago, that was way sufficient, I never imagined I would own anything larger and more powerful than a Sky Ray King 
The calculation is that it is not recommended to have more than 5% of the inner surface area of a sphere used for holes, or the integrating quality of the sphere is considered too low. (this assumes a quality high reflecting surface which I do not really have but I will ignore that 
). For a 42 cm sphere (inner diameter) like mine, with two 4cm holes substracted (sensor hole and adjustment light hole), that leaves a maximum diameter for the entrance hole of 9cm. So yes indeed, if you want a 14cm entrance hole, the inner diameter of your sphere needs to be at least almost a meter 
Thanks djozz for coming back with those numbers. I once considered building an integrating sphere but the inner coating is very expensive along with obtaining good surface quality prior to the complicated application of the barium sulfate or Teflon powder evenly. A quality Light meter along with a year of college classes before starting ended that for me. LOL
.
I really wish it were not so complicated and unreachable to accurately measure thrower flashlight lumens. 
.
Guessing the smaller lights and flooders can be checked with lumen tubes. I have never given those lights any attention, maybe later.
.
I was in firehopper shoes some time ago and understand what he wants to know. A simple effective way to measure lumens accurately.
.
[quote=jeff51]
[quote=nottawhackjob]
Would appreciate it and likely so would others. Then it could also put a sock in Unheard’s nonsensical flapper-rambles for awhile. :laughing:
PS. I believe you’ve got things fine-tuned dialed in. Spacers and special diffusion film leads me to that conclusion. Even ‘fairly’ consistent results in this difficult arena is fantastic.
Btw, I have that exact same lux meter in yer pic. Other than the inherent +or- tolerance margins between each of our luxmeters that’s one heckuva good start towards building a reasonably evident consensus. Not to mention PVC ASTM.
So watt we apparently have with your current design is a widely available consistently constructed materials baseline. Huge. Irrespective of someone blathering about a dust particle 
or even two as being some insurmountable showstopper. Ridiculous blathering. :laughing: :person_facepalming:
Great applauding effort, Jeff51. I bet this took a lot of thought and work. :student:
“….you need to calibrate”.
No sh*t, Herr Sherlockengruber.
You constantly inject negative-biased trivial obfuscating egregious BS which is why yer gettin’ on my nerves. I can go on with specific examples butt watt’s the point with, Dr. No? :laughing:
Every Thread lately turns into this BS — Most of us here were trying to give advise on our own experiences with measuring lights in the Real World
Put it everywhere!
Have some fun with the new instrument. Then you will have data to compare to your perception. How intense is the center, what if you bounce them off a white ceiling, etc.
Oh man, you just exactly described my experience as well
I just added to my Lumen Tube with Light Valve thread,
Documenting the design.
CNCman and Yokiamy -
Indeed this is a rabbit hole you can fall into and not see the light of day for a long time.
I got to where I was dreaming about the design. And I swear for a while every step forward was followed by two steps back.
All the Best,
Jeff
jeff51 your lumen tube works for your lights, that is Great 
Success is difficult to achieve and if it can be copied, even better 
.
I do not wish to discourage anyone from building a lumen tube, just understand how complicated it is.
.