Using these two pieces and some other stuff, I made a mousemat, that would work best with a non-optical mouse.
Step 1: Ingredients:
1x USB cable, old camera cable etc, with the end cut off..
1 or 2x Blue/ green LED (ones that work on 5volts.)
1x White insulating tape
1x Soldering iron (OPTIONAL)
1x multimeter, optional, but really useful..
Step 2: Secure the backing
Along with the plastic/ glass backing, there should be a flexible plastic white sheet, using the white insulating tape to stick this to the back of the plastic, this stops light escaping the back, and lets light only through the top.
Step 3: Wire up the LED/s
so you should be left with a cable with four wires on one end, and a USB end on the other.
find the red and black wires, they should be positive and negative wires, use the multimeter to double check.
Attach your LED/s either by soldering or wrapping the wires around each other. Remember to check polarity! If you have more than one, wire them up in parallel (for more information about parallel circuits, read this instructable)
Attach the LED/s to the corner/s of your board, making them face in, if there are more than one, put them on different corners, facing into the center on the side opposite to it.