After some experiments we found that to be versatile a Lego-compatible LED must have options. Some people want to put the LED inside a construction (like a light inside a house), others want it on the outside (like a street light). Our PCB shown in Figure 2 can do both, thanks to two LED footprints. Big LEDs or small, you can even fit SMD types if you like. Respect the polarity though, otherwise the ‘+’ and ‘–‘ symbols on the PCB will be wrong. Do not fit two LEDs on the board.
  It’s up to you how to connect or wire the LED module to a supply or a controller system. We’ve a preference for a 90-degree 2-way pinheader socket, but in which direction? To get out of this pickle we put two connector footprints ‘K1’ on the PCB, allowing you to position a connector any way you like it: top mount or bottom, horizontal or vertical, North, South, East, West — whatever you like.