Was wandering through my local Jaycar the other day and saw one of these (http://www.jaycar.com.au/productView.asp?ID=AA0274). On the way home I got to thinking (and remember I am fairly new to electronics) "How does this work?"
So As far as I can work out...
Set voltage supply from battery, say 9v
I assume the different mA values are done by providing different resistors to that led. However how can you reliably say what mA is being supplied (as per the written bits on the box) as different led's have different forward voltage drops. (I thought mA was = Excess volt/Resistance)