Several reasons, that would be quite a story, but in short: in the pipe, light that goes forward has a significantly higher chance of reaching the detector than light going in an angle (in other words it is a fairly lousy integrator), which makes the pipe very sensitive for beam type. Tecas-Ace’s use of diffusers fixes some of that (on the other hand diffusers introduce extra spectral errors) but it is still not really good, nothing like the integration in a well-built integrating sphere, there is a reason why light people use those. Ceiling bounce suffers less from the errors of a pipe, especially if you keep te light source close to the ceiling and the light sensor a bit further away (if the flashlight itself does not block too much of the incoming light).
How do you compensate/calibrate for different ceiling materials and their inherently different reflective properties?
I found that when using the Ceiling Bounce method —- I had 2 correction factors —1 for throwers and 1 for the High Lumen flooders
With my PVC tube contraption as it is being mentioned and it is indeed a contraption (nothing technical for sure) I put DC fix on the glass shelf I use —that seemed to help make it a lot more consistent—- It satisfices my needs
Firehopper —the 2 lights you mentioned might be ok but I don’t recognize them as being accurate lights
As long as you’re using the measurements for yourself who cares how accurate they are —— I have 100s of lights and through trial and error I’ve come up with methods that work for me
well the one is a light from ryobi, it has 7 cree leds in a somewhat pistol grip shape. if you google ryobi p717 you will see it. and not very accurate, as the output is listed as 2500+ lumens. so greater than 2500 but no clue by how much. the other is a work/area light from walmart. hypertough not hypertools
The materials won’t change usually. If they do, because wife want’s a fresh ceiling painting, the calibration lights need to be measured again. If wife wants a violet ceiling, file for divorce. Or use a different room.
When you say light meter, we assume you mean Lux meter, not a photographic light meter.
Though a light meter can be used with a ceiling bounce comparing output to known lights.
Here is a link to what I did with PVC and a cheap lux meter.
I never got around to doing a write up on the finished version. Need to get off my butt and do that one of these days.
The ceiling bounce method is quite useful as long as you keep the conditions the same for each measurement.
Or you can re-calibrate with a known light for each test.
Or, perhaps the easiest solution, give Texas Ace a jingle and see if he has any calibrated lumen tubes left for sale.
All the Best,
Point being I can’t verify your findings becuz I can’t duplicate your unique ceiling characteristics. I then have to take your word for it. Which is ok. I understand your standard reference calibration verification approach. If it works, it works for you.
Butt at least with a pipe measuring system there are material construction standards already existing, ie., White PVC Schedule 40/ASTM standards so I can reasonably/confidently duplicate someone’s readings by a similarly constructed pipe setup as their’s. Then there’s trending consensus using such significantly similar materials. Butt I digress.
PS. If Jeff above gave me his materials list and dimensions and did my own testing then I compared my results to his and came reasonably close to it, that’s a trending consensus.
You can’t faithfully reproduce even Jeffs findings for many reasons. One being the meter used. Another the light to be measured. A third the battery he used, the amount of dust in the tube, the color variation of the material, Jeffs mood, the mood of his wife, phase of the moon and so on.
Why would you want to in the first place? If you need to measure, you need to calibrate. Admit, you’re just inventing the True Luminosity Measurement.
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,
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!
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,
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.
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.
Would appreciate it and likely so would others. Then it could also put a sock in Unheard’s nonsensical flapper-rambles for awhile.
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.
Great applauding effort, Jeff51. I bet this took a lot of thought and work.
“….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?
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