I plan to build my self an integrating sphere and have read as much as possible. But I find that I can’t find any answers to the following questions.
Here is the plan: I have found a manufacturer of spheres. They come a few sizes and are made from ABS
10”(250mm) to 22”(550mm)
I plain to have 2 holes cut at right angles to each other. One for the light and one for the lux meter. I may do it my self if needs be.
I will spray paint the inside with high reflective white paint. So far I can’t find any real reason why not to use normal high gloss white paint.
The questions I can’t seem to answer is the following:
1: What size should is choose? I read the hole size area should not be more than 5% of the inside area of the sphere so assuming a hole of 4”(100mm) then the sphere should be around 15.7”(400mm) diameter. But I see DIY spheres that are under 6” which work. I hope my math is right.
2. I cant see how I will be able to get a baffle in the sphere. On this size sphere is it really needed? And if I where to insert a Baffles what size and shape should it be. Does it have to be midway between the light and the sensor? I really dont seem to find much information about the size and positions of the baffles.
3. I have a very cheap Lux meter. It seems to work but how do i know if it is LED compatible? I have been using it with LED flashlights for some time and it seems to be liner. My test is not to scientific but during a ceiling bounce test of 3 lights the readings sum to the same as the combined test.
4. Calibration of such a sphere. I would like to translate my readings to Lumen. But where can i get a calibrated light source? Take in to consideration that I am in South Africa.
Ok this is a general start. Answers are appreciated.