1 January 2002
'The light told me to turn left'
Cambridge, Mass.—Pass under a revamped fluorescent light at the airport, and it will send out not only its usual cold white glow but also a message that flashes on your handheld's screen saying: "Turn left at the next corridor for Gate A. There's a cash machine just as you reach the intersection."
A professor at Massachusetts Institute of Technology (MIT) can now transform the ceiling fixtures in airports, museums, offices, and factories into inexpensive data transmitters.
To create fluorescent tubes that communicate, inventor Dr. Steven Leeb modified ordinary fluorescent fixtures so they can beam data as well as illuminate.
Dr. Leeb, who teaches circuit design and other subjects at MIT, does this by changing one component in the fixture to produce fluctuations in the light that convert to a digital signal. Light sensors easily detect these fluctuations and pass them to processors and software that produce voice, music, or text messages. The lights then form an inexpensive data network.
Passersby in subways and shopping malls may one day use messages transmitted by such lights to guide them.
Dr. Leeb formed a company, Talking Lights in Boston, to market the device.
The process of using the lights to transmit data starts with a ballast, the component of fluorescent tubes that controls the current needed to create the light. The ballast causes the vapor inside the tube to ionize many times a second, creating the imperceptible flicker. Dr. Leeb has modified the ballast to modulate the number of times per second the light flickers.
"The ballast is what makes the magic happen," Dr. Leeb said.
If, for instance, the light is flickering at 40 kilohertz, or 40,000 times per second—standard for modern fluorescent fixtures using electronic ballasts—the modified ballast might alter the frequency slightly to create a digital 1 and then alter it slightly differently to create a digital 0, thus producing a binary data stream.
"The trick is that our ballast moves the frequency around in such a way that the light doesn't flicker visibly," Dr. Leeb said.
Inexpensive photo cells on handheld computers or earphones, for instance, pick up the change in flicker and pass this signal on for conversion to graphics, music, written messages, or speech. The entire receiver packet of photo cell, circuits, and processing chips is about half the size of a pack of cigarettes, said Dr. Neil Lupton, president of Talking Lights.
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