Vicon, a UK company that is a leading developer of motion capture systems and part of Oxford Metrics Group plc, manufactures cameras in which multiple LEDs are arranged around the camera lens.
The light emitted by the LEDs is reflected back off retro-reflective markers worn by the subject being "captured". A number of cameras are placed around the space in which the subject is moving. The reflected light is collected by the camera’s sensor, and the position of the markers can be determined if two or more cameras “see” the same marker.
There are two main frequencies used for the LEDs, one in the visible red range, the other just into the infrared range. Vicon offers the customer the choice of either, saying that the visible red has the benefit of giving excellent range, whereas the infrared gives almost as good range but is less intrusive in the capture environment.
As well as positioning the LEDs around the lens, there are several other reasons to use LEDs rather than an alternative light source. The LEDs are used as strobes, i.e. the light is not on continuously but is flashed in short bursts, and LEDs are highly suited for this purpose. Also, LEDs have a long life time and are cost-effective, and the frequency of the output light is fairly uniform (which means that the reflected light can be filtered effectively). Finally, the LEDs have a small lens that spreads the light in a uniform fashion throughout the space where the capture takes place.
Oxford Metrics’ global clients in science, medicine, sport, engineering, gaming, film and broadcast include major hospitals and research facilities such as Guy's Hospital, Nuffield Orthopaedic and Loughborough University, engineering industry leaders including Ford Motor Company, BMW, Airbus, Caterpillar, and Toyota, and in the entertainment sector, Sony, Industrial Light and Magic, The Moving Picture Company (MPC), Sega, Nintendo, UbiSoft, EA, Square Enix and many others.