Match's Mods: Homemade Integrating Sphere

I thought real otf numbers were something like 25 to 30% less than what the cree numbers were .

It was Great!!!!!! But could you let me know making out Lumen from the Lux measured ?

Thanks!

It was great, but could you let me know making out lumen from Lux measured?

Thanks!

In the post you quoted above, the information you are looking for is right under the picture of the finished, painted sphere.

There's a quite complex formula that takes the area in sq feet inside the IS and extrapolates a lumen rating from the lux measured, while taking in the refraction and absorption of the sphere coating itself.... :Sp

Me? I cheated and just took a light with a known lumen value to determine what my sphere correction value should be.

For example.... A test light is known to give out 200lm. When you shine it in your sphere you get 2,530 lux. Dividing the lux by the lumens gives 12.65. This is the correction value (for this example).

Then, all you need to do is divide any lux readings from your sphere by this set correction value to give you the lumen output.

Hope that makes sense.

Awesome build Match!

Now I need to find me some nice round inflated rubber balls

In fact the math is quite simple:

Hit the hole in the sphere with a uniform beam of parallel light (e.g. a throwers hot spot at several (5-10) meters distance).

Measure the intensity just in front of the hole with a luxmeter.

(This number is lumens pr. square meter that hits into the sphere.)

Multiply with the hole's area in sq.meters and the result is the lumens number that enter the sphere - simple and easy.

The only difficulty I can see here is the sagging intensity from the thrower, when you remove the outer luxmeter and read the one build into the sphere the light might have dropped a little. Just repeat the procedure a couple of times and you will get corresponding values.

Thank You very much!!!!! It was really great..

Thank you!

Interesting discussion over on this thread about if a I.S. is even necessary. Linked to there to save it for posterity :)

Wow, to use cut down and use a large globe is a brilliant idea. Has anyone tried it ??????? ............ Knobby

Will work.

Sixty545 built his from two lampshades. And he used to make measurement equipment for a living.

A beach ball is cheaper...

Here’s a bump for the Xsphere.

I took an inflatable beach ball that was advertised at 24 inches across, imagine my surprise when it was actually nineteen !!!

With the vinyl being so thin, I chose to not prepare the surface for removal, as it will be a far smoother surface than I could make with paper mache.

I used Elmer’s Glue-All for the adhesive, and went to town with a bunch of newspapers from the kindling pile.

I could have made the entire thing from dollar bills, and it would STILL have been cheaper than a lab-grade sphere…

Here it is, drying after a round of paint, and a taped-up circumferential cut. I will need to carve out the light and sensor ports when the meter arrives. Barium sulfate is also en route, so we’ll see how that stuff works out.

Looking really good, ChicagoX! Did you already mount the baffle on the inside? Reason I ask is because it might be hard to line up the sensor/flashlight holes and baffle with the sphere already together.

Another thing I was thinking: If you’re interested I could make a regulated drop-in with a known output to mail to you…

In fact, that may not be a bad idea to do and use it as a pass-around with the rest of the folks who’ve done this or something similar. That way we’d all be on the same page.

Barium sulfate?

I’ve been considering building one of these as well, a known output sample is insanely necessary!
What is the sample?

Dunno…haven’t built it yet :wink:
I’m thinking something along the lines of a P-60 drop-in. An XM-L with a floody lens would be ideal, since it would really test the “integrating” of the sphere.

How do you know the exact lumen output though, this is the problem i’ve been thinking about, there are no markings on an xml saying which bin it is (we have to trust what we buy is correct), and even in the same bin there is a minimum luminous flux.

That’s a very generous offer - I would very much like that, thanks !!!

I have not mounted the baffle nor made the final cuts, as I don’t have the dedicated meter in-hand. I made an off-axis circumferential cut in relation to the valve hole to allow for 90-degree placement of the two openings, and resealed it with a single layer of masking tape prior to putting on the first coats of paint. It will take but a small pass with an exacto to rend the sphere in twain for baffling and barium sulfate coating.

It’s the same stuff that you ingest in the chalky milkshakes (or enemas) to provide contrast in G.I. tract radiology scans.

It is also used to provide a fantastic diffusion coating for integrating spheres, minimizing any favoritism of throwers over floody torches.

I think you may be a bit confused. What I intend on doing is piecing together a drop-in (spec's aren't that important), and then testing it in my I.S. and obtaining the numbers for it that way, then passing it along. It's a rather crude way to calibrate I.S.'s, but really the only practical way... It will also ensure that my future lumen numbers match ChicagoX's and anyone else who would like to use the calibration drop-in.