I have to admit, I don’t get it, what are these things for? How do you use them? Is there a standard?
Isn’t the led just, well, centered? I put the board in the host, or on the pill, and center it. Isn’t it just, well, centered?
I expect this is a very simple concept but I just don’t seem to understand.
Not necessarily… It also acts as a spacer up or down as well. Can also help keep the reflector away from the solder joints…
The reflector needs to be centered over the LED or you get a light spot that’s not evenly circular.
The reflector also needs to be at the right height above the emitter, not too low or high, or you get donut rings.
Many reflectors are metal-coated and can short out the LED wiring if they touch it.
There is a certain amount of “slop” involved. So, the centering ring is necessary to hold things in place while it’s all tightened up (by the bezel, usually). Also, as hank said, the height of the reflector relative to the emitter is of crucial importance, and the centering ring also enforces that measurement when everything gets tightened up.