To make it possible for the wiimotes to see the quadcopter. We added some IR-emitting diodes. To make sure the quad is visible in different angles. I searched led's with the biggest radiation angle. The maximum angle of normal IR's LED's  is 100°. But you can find SMD led's with 140°. So I ordered some SMD's . The wavelength is 940nm because the wiimote is the most sensitive to 940nm. 

They are so small it is hard to see them! :p