ORIGINAL: samarkh

To get a little technical here, they are white LED's and as such are rated at 20mA. I know that this is a fat lot of use to most users, however it works out at around 3.2v, and yes they are polarity sensitive. On HL they are wired in parallel so you need to double the current required. If you want to connect them up to the battery you can either wire them in series, and add a 39ohm resistor, wire them in parallel and put a 100ohm resistor in series with them. If you want to connect the the TK-RX13# or TK-RX14 5v then you will need to connect them in parallel and put an 81ohm in series.

I know that this is a little geeky but you did ask!

Yours Simon M.

P.S. One method to tell which way to connect an LED up is to look very closely in to the package. One connector is smaller than the other. In the vast majority of cases this is the +. In over 25years of using the things I can only think of one package where this was not the case.