... only absorb infrared light thanks to their special filters and are insensitive to other light. Using the two infrared LEDs on the butterflies' bodies, they recognize their position and orientation in space and can also distinguish between visually identical flying objects. While passive reflectors must first be illuminated, the two LEDs themselves emit an infrared signal. The light only has to cover the distance between the butterfly and the camera, meaning that the active markers can cover a larger area with the same number of cameras. The markers do not light up permanently, but only flash for a millisecond. Synchronized with the flashing, the cameras record an image which they send to the master computer. So that the computer knows ...