I am getting into soldering and as an entry exercise I want to put an LED into the old Apple "puck mouse". Here he is saying that he used a 5V LED. Problem is ... How does he know how many volts to use? How would anybody know? In my usual electronics shop they are saying that 5V would be very unusual for such a thing. They told me it's usually 1.35V or 2.5V for such things. Anybody know more?