Thanks jhalb. I would like to make a new setup. I have been using a pretty rough light box for years. The other day I made one of those lumen tubes just for fun, but am not all that impressed with it. I was thinking for the new sphere I will probly cut the hole for the size of a maglite head since I work with them a lot. I will keep the lumen tube for measuring larger lights as it was made from 4ā pipe.
I have another question for the prosā¦ What method are you guys using to derive your multiplier?
I have always done it like this.
1. Take know source ( in my case 875 lumen maglite measured by another member).
2. Divide lumen output by lux reading.
Example 875 lumen light produces 2550 lux. So 875 divided by 2550= 0.343
So from hence forth all measurements from other lights are multiplied by .343
However just now reading posts by others I see that Match appears to be doing the opposite.
A quote from his post.
but the most accurate one I tried was to simply take a light of known value, test it to get the lux reading, and then divide that reading by itās alleged lumen rating.
Then here I looked and found yet an even more obscure method. Something about measuring the hole??
I think that match did the same as you do but he wrote it up the wrong way around.
The āobscure methodā takes a careful performance to do it accurate, but a drawback is that to get the correct number, it is essential that your luxmeter is correctly calibrated, if the luxmeter is off, the multiplier will be off. Your current method does not care about the calibration of your luxmeter, the calibration comes from the reference flashlights.
Iām interested in the coating stuff from Sphereoptics, my own DIY BaSO4 coatings did not have that high reflectivivty that this stuff claims. The website does not mention a price or retailer. If you are able to obtain it, would you mind letting me know where, how and how much?
Ya, I will report back once I hear from them. If I donāt get a response via email soon I will try to reach out to one of our German speaking members and see if they will give em a callā¦
I am thinking if that is the case I may try to make some. Here is where I found out that it was made from.
PVA is not that expensive, and Bariumsulfate is not that expensive, so I guess they just tack on an extra $450 buck for adding the word āLabsphereā
āobscureā ?? (my finger hovering over the āRUDEā button )
I would rather call my method āscientificā. It uses one fundamental formula:
LUMENS = LUX x AREA[m2] and is valid for a uniform bunch of light.
Never mind, I will issue a WARNING that this method cannot be used for a styrofoam ball because light will leak through besides the hole during the procedure and offset the calibration.
The wall has to be solid (metal in my project).
For styrofoam balls I think the best way is the āstatisticalā way (guesswork with āknownā lights).
Put your styrofoam ball in a cardboard box with a hole and off you go
Sometimes the most scientific method is not the most practical one, in this case for most people the accuracy is totally dependent on the least accurate measuring device on the planet:the dubiously calibrated chinese luxmeter. But if your luxmeter has a trusty calibration the method is really useful.
btw djozz, did you eventually get your CCT measuring device ( I guess you went after a i1Display Pro). And if so, I would like to know the price and the vendor, please. :+1:
Instead I have bougnt a very simple device, a homebrand product from Lumitronics named ColorSense. I hoped that it would work straight out of the box, but while playing with it, the reading went all over the place, could not get a grip on it. So I gave up on it for the moment. A thing to try is placing a white diffusor in front of the sensor, like luxmeters have. So I will have to make a little project of it.
Iām with ya. Iāve got nothinā but love for your project sixty I wasnāt meaning to imply that what you were doing was unscientific. I just got a little freaked out when I saw that post by match and then yours. I was like, āhave I really been doing wrong for all these years??ā
I made a video log on my build of one of the lumen tubes and on my old measuring setup last week. DIY lumen measuring device. Integrating shpere, and lumen tube.
I thought it might interest some people who want to build a cheap easy setup who are not as concerned with the level of precision discussed here. However I did want to make sure I wasnāt just spreading grotesque misinformation before posting, hence my badgering in this thread. Any misinformation in this vid will be mildly odorous at worst :student:
@vestureofblood:
No offence taken! I didānt really consider using the new button
Great video of yours btw!
(fyi footcandles and lux are related by a factor just as inches/centimeters).
Thatās what I found too, using a PublicLab spectrometer to try to measure color temperature and CRI. I could probably get it to a usable state with some effort and experimentation, but so far it hasnāt been very useful at all.
Itās at least good enough to confirm that color LEDs are the color theyāre supposed to be, but thatās easy enough just by looking. For example:
If I stick with this āHobbyā for a longer stint than last time, Iāve considered buying thisā¦Lighting Passport Smart Spectrometer. Iāve seen them listed for as little as $1295, a bargain for all they do. Measures CCT CRI CQS Illuminance Foot Candle CIE 1931 CIE 1976 Spectrum Diagram C78.377-2008 IEC-SDCM Ī»p. The bluetooth connection is pretty sweet, and I think they would work well in our DIY integrating spheres.
I think it has potential, but getting it to work well is nowhere near as simple as the site would suggest. When Iāve tried to measure flashlights with it, the readings go all over the place, making dramatic changes in response to very small changes in angle or positioning. The software for it is also pretty limited, so if you want to actually do CRI or CCT measurements youāll probably have to write the tools yourself.
So far itās kind of a neat toy, but not really a useful tool unless you put a lot of effort into it.
I hope the software has gotten better, but I havenāt looked in at least a year. They have released a new version of the hardware kit, at least, which looks like it might work a bit better, and provided better instructions on building it.
Sorry to hear that!
The instrument I made during my time at Philips also had problems with repeatability. The team that made the separate measuring head (with suction cup) started with placing the three sensors at an angle so that they pointed at the same pixels on the CRT screen to measure but they soon found out that a rotation of the head gave a different result. Eventually they ended up using a piece of milky, acrylic plastic in front of the sensors, just as you have in mind. The calibration took care of the slight miscoloring from the plastic. I hope that a piece of plastic will solve it for you.
I had been thinking of trying to attach a really white piece of paper or something at a 45 degree angle and bounce light in, but itād be physically a lot easier to just stick a translucent sheet of something on the front of the measurement device.
I have some stuff packed away somewhere that might work well. Itās a diffusion filter used in iPhone touchscreen/LCDs. Helps to equally disperse the light from the 4 or 5 LEDās mounted on the perimeter. Works really well at diffusion, will turn almost any light, even those with fairly tight beam, into more of a mule style beam pattern, all spread.
If you think that might help Iāll try to dig through my packed away stuff at storage and find you some.