This is not a heavy theory article. It's just a way to let someone change the brightness of an LED to suit the use to which it is being put. It can also be used to balance the brightness of more than one LED. Different colours can look different in brightness, this will allow you to make them look closer to one another.
The 'how to' is not universal and may possibly not suit your application. If this is the case - ASK!
It's a PDF