Visible Light Communications (VLC) is a data communications medium using visible light between 400 THz (780 nm; 1 THz = 1000 GHz) and 800 THz (375 nm) (visible light is not injurious to vision).
It uses fluorescent lamps (ordinary lamps, not special communications devices) to transmit signals at 10 kbit/s, or LEDs for up to 500 Mbit/s. Low rate data transmissions at 1 kilometre (0.6 mi) and 2 kilometres (1.2 mi) were demonstrated. RONJA achieves full Ethernet speed (10 Mbit/s) over the same distance thanks to larger optics and more powerful LED.
Specially designed electronic devices generally containing a photodiode receive signals from such light sources although in some cases a cell phone camera or a digital camera will be sufficient. The image sensor used in these devices is in fact an array of photodiodes (pixels) and in some applications its use may be preferred over a single photodiode. Such sensor may provide either a multi-channel communication (down to 1 pixel = 1 channel) or a spatial awareness of multiple light sources.
This technology can be used as a communications medium for ubiquitous computing, because light-producing devices (such as indoor/outdoor lamps, TVs, traffic signs, commercial displays, car headlights/tail lamps etc.) are used everywhere.

fro more details, please visit http://en.wikipediawiki/Visible_Light_Communications