s have been used for applications such as remote control devices since the 1980s. At around the same time, visible light emitting diodes (LEDs) found applica- tions in calculators, computer screens, and later on colour TVs, and automotive, commercial and residential lighting. With the emergence of fast switching LEDs, their application for short range telecommunications was proposed by Masao Nakagawa and members of his laboratory at Keio University in Japan in 1999-2000 [24, 25, 26, 27]. Nakagawa's vision was that white LED devices can be used simultaneously for transmission of information in addition to their usual Personal Wireless Communications Systems lighting use, thereby reducing the energy necessary Content and services layer for communications to zero. He coined the phrase visible light communications (VLC) to describe these systems (Figure 12.15). Connectivity retail layer Other sources of LED could also have a dual telecommunications utility: for example, traffic lights can be used to convey traffic information to Infrastructure layer cars, gallery lights for communicating background information on paintings, home lighting used for local area networking and SO on. Moreover, due Subscriber/end-user to the fact that telecommunications are carried out using visible light, one can naturally see if a link is active. There are many advantages to VLC systems. As noted above, transmissions are embedded in visible light and therefore telecommunication power usage is nearly zero. Light has a very wide bandwidth and therefore can support very high transmission rates. Since visible light frequency is very high, it does not interfere with devices operating in radio frequency bands. Moreover, as light is blocked by walls inter-room interference does not exist. VLC systems are also inherently secure as communications remains invisible outside a room. Furthermore, because the sources of lighting are generally fixed VLC technology can be used for locating and controlling objects such as robots with high accuracy in ind