Using Light to Send Data Across the Room
Researchers around the world are fine-tuning technologies that use standard lighting equipment to cheaply transmit high-speed data streams wirelessly, even while the equipment appears to be producing nothing more than normal illumination. Generally, the technologies rapidly and subtly fluctuate the intensity of light-emitting diodes, or LEDs, in a way that is imperceptible to the human eye.
The idea of using light to send information, a field now known as visible light communications, has been around for well over a century. In fact, Alexander Graham Bell sent a wireless phone message in 1880 using his invention known as the Photophone.
But academic and commercial interest in visible light communication has accelerated in recent years. The increasing popularity of LED lights, which can be more finely controlled than traditional incandescent bulbs, makes light-based technology more practical and economical. Also, the exponentially growing demand of wireless communication devices has taxed radio spectrum, resulting in a need to find alternatives.
Harald Haas, a professor at the University of Edinburgh who began his research in the field in 2004, gave a debut demonstration of what he called a Li-Fi prototype at the TEDGlobal conference in Edinburgh last week. He used a table lamp with an LED bulb to transmit a video of blooming flowers that was then projected onto a screen behind him. The prototype can be built economically in part because it uses cheap off-the-shelf parts that cost just a few dollars, he said. “There is no antenna,” he said in an interview.
Dr. Haas jokingly suggested that people might think it was all “academic tricks,” so he stuck his hand under the light to block it from the receiver, and the video immediately paused. After resuming the video, he also turned the lamp away from the receiver, which also paused the video.
The speed of data transmission was about 10 megabits per second, though Dr. Haas is aiming to have it reach 100 megabits per second by the end of the year. Siemens, which is also working on visible light communication, last year announced that it was able to transmit at speeds of 500 megabits per second within a five-meter distance.
Light-based data transmission technology is attractive because it allows wireless communication without the use of radio gear, which can be dangerous in places like oil platforms (where it can cause sparks) and underwater (where the salt conducts electricity), or on planes (where it can interfere with other radio equipment). In addition, transmissions can be stopped simply by blocking the light, and thus can be stopped by walls, so there is less risk of data leaking out of a house or office. And researchers say they believe that signals can piggyback on lights that are already in use — street lamps, car headlights or room lighting. Indeed, Klipsch, a speaker manufacturer, last year introduced speakers which could receive music data from normal LED lightbulbs in the home.
