I want to test a few of my lights, and have the ability to do this in the future. I already own a lux meter. I was thinking about making a tube so I can achieve total darkness, and also a consistent length. I have access to cardboard tubing at my work, about 3-4”. Not sure how well this would work. Any suggestions?
It depends on what you want to measure. I assume you would like to measure total light output of a light source, then your device will favor forward directed light over sideways directed light, and thus not be very accurate. What is developed especially for measuring total light output without being dependant on beam shape is the integrating sphere. There's some good theoretical information (pdf's) on integrating spheres available on the Labsphere website, and if you click my sigline you can find links to some home-made integrating spheres that I have build, one of them is really cheap and simple to make, it may provide some inspiration.
Depending on your accuracy desires and building skills you can also consider the 4” PVC pipe design a number of us are using. It’s not as accurate as a larger well made sphere, but I’ve found mine to be close enough for my needs, and it’s cheap and portable, both excellent qualities.
It basically consists of 3 90° elbows of 4” PVC. make a 180° U shape from 2 and rotate the 3rd one 90° so it points up. Add a piece of glass about 4” in diameter on the upturned piece, and a cap on the other end that holds the sensor. I sanded the inside of mine with 180 grit sandpaper to reduce the reflectiveness of the PVC on the inside of the tubes, hopefully it made it more consistent, but I have no proof to support that.
Wow, quite a bit more involved than i realized. For the most part, i wanted to build something that would put each light in the same environment to compare. Last time I did some testing, i thought the biggest thing you wanted to control is the distance, at least a few meters? Maybe ill do a little more research into this to ensure my readings are as accurate as possible. Thanks for the input.
There is two parameters that are both interssting to know about a flashlight:
1) how much light comes out? For that you want an integrating sphere or elbow-device if that suits you better. Unit=lumen
2) how bright is the center of the beam, which is equivalent to: how far does it shine. This one is easier, just measure it with your luxmeter at a certain distance (usually >5 meter). Unit=lux.
I now begin to think that your question was about the last.
I think I misread too, it sounds like you’re trying to prevent outside light from influencing the lux reading to measure for candela. If you’re in a reasonably dark room there’s nothing to worry about, it won’t make a measurable difference in your readings.