By Maggie Romuld

While many of us still dither about exchanging our incandescent light bulbs for compact fluorescents, improvements in the performance and applications of light-emitting diodes (LEDs) have taken a quantum leap forward, and researchers around the globe are making significant advances in both lighting and the next generation of wireless network technology, visible light-based communication. Although few people have heard of visible light communication (and even fewer understand it) the LED-based technology is fast approaching the practical application stage and, in the not-too-distant future, the physics of our hyper-connected world may change dramatically.

An LED is a "device that produces light when an electrical current flows through it." LEDs produce light very efficiently and although costs are still a little high, recent developments in diode technology are quickly making them a viable alternative to conventional light sources. They have been described as "energy-sipping" for their low power requirements, as well as reliable, durable and bright (and, as if to prove this last point, on the evening of September 19 engineering students at the University of Calgary used LED panels to choreograph a Morse code message to astronaut alumni Robert Thirsk as he passed overhead in the International Space Station).

Communication engineers are interested in LEDs because of their quick response to "ON" and "OFF" signals, unlike normal light bulbs, which have longer warm-up and response times. Visible light communication takes advantage of this property - by rapidly turning LEDs on and off, data can be sent by light flashing at speeds undetectable to the human eye. Flickering the light in specific configurations enables data transmission without any perceptible change in room lighting, and a wireless device within sight of an enabled LED could send or receive information though the air with each LED serving as an access point to the network.

One of the major advantages of visible light communication is the potential to transmit data by adding optical communication devices to the sockets of existing light fixtures. By piggybacking lighting and communication, existing lights throughout our homes and work spaces could do double duty, reducing energy use and infrastructure costs. LED technology could also alleviate a number of problems associated with the radio frequency (RF) communication systems that we currently use. Light sources used for communication are extremely secure because they are focused in a narrow beam, which requires placing equipment within the beam itself for interception. Also, since the light does not breach opaque surfaces such as walls, electronic "eavesdropping" is not possible. In contrast, RF communications can be easily intercepted because RF signals radiate in all directions. Other benefits of an LED versus RF system include less susceptibility to interference from other equipment, and less production of noise that could interfere with other devices. An LED-based system would also consume far less energy than the current system, allowing the expansion of communication networks without added energy requirements and potentially reducing carbon emissions over the long term.

Several large visible light communication research projects are currently underway throughout the world. In North America, the Centre of Ubiquitous Communication by Light (UC-Light) at the University of California, Riverside, is a five year, $3.5 million project funded by the MultiCampus Research Program and Initiatives (MRPI) competition within the University of California system. "The visible light spectrum is several orders of magnitude larger than the crowded radio frequency (RF) spectrum, and thus has huge potential for low cost and high data rate communication" said Zhengyuan Xu, the principal investigator and director of the new research center, "PDAs, HDTV, information kiosks, computers and laptops all can be interconnected wirelessly through visible light."

Boston University's College of Engineering is also launching a major program to develop optical communication technology. The Smart Lighting Engineering Research Center is part of an $18.5 million, multi-year National Science Foundation grant awarded to Boston University and several partners. "This is a unique opportunity to create a transcendent technology that not only enables energy efficient lighting, but also creates the next generation of secure wireless communications," notes BU Engineering Professor Thomas Little, "As we switch from incandescent and compact florescent lighting to LEDs in the coming years, we can simultaneously build a faster and more secure communications infrastructure at a modest cost along with new and unexpected applications."

Although it may still sound a little futuristic, many researchers expect visible light to be the communication method of the coming generation, replacing or at least supplementing current wireless networks. Confident that remaining technological hurdles can be overcome, researchers believe an LED system will reshape the way we communicate and navigate. While the technology would be of particular use in places where RF communication is prohibited, such as hospitals or airplanes, researchers also foresee retrieving various types of information via cell phone from electronic billboards on our daily commute. Some of the more practical scientists also envision more consumer-based uses for the space age technology - just think, it's possible that one day your fridge light will be able to tell you what you need to pick up the next time you go to the grocery store.

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