Light Conversation

Posted on 31.07.11

Harald Haas and his team from the University of Edinburgh have invented what he calls “speaking light”. In a TED talk on 15 July Haas demonstrated the wireless transmission of HD video via a rapidly blinking desk lamp. The trick involves quickly modulating the intensity of “high-brightness” LEDs, allowing binary-encoded data to be sent to any receiving device connected by line of sight. Haas can currently send at 10MB/s – already rivalling most home Wi-Fi – but is confident that he can roll out a consumer transmitter capable of 100MB/s by next year. Theoretically, at least, speeds of up to 1TB/s may be possible.

Because the lights blink on and off at such high frequencies the flicker is imperceptible to the naked eye. Haas therefore claims that by swapping existing lights with LEDs capable of data transmission we’ll be able to harness much of the lighting infrastructure already in place. Domestic and office lighting are obvious candidates but street lights, traffic lights, and even car headlights could all be co-opted for our many wireless needs. The key importance of Haas’s alternative to Wi-Fi is that it offers a way around the potential bottleneck created by those many millions of laptops, phones and smart-pads all currently clogging up the radio airwaves. BT is apparently trying hard in its recent TV ads to give the impression it’s yoked the aurora borealis for its wireless broadband, but Haas’s light work is the real thing.

All of which puts me in mind of Alexander Graham Bell.

Bell was an unconventional communicator. As a child he discovered the trick of putting his hand into a dog’s mouth and pulling on its lips and vocal cords until the animal’s growls could be heard to enunciate “How are you Grandma?” Inspired at first by a deaf mother and later a deaf wife, Bell dedicated his life to researching novel ways to communicate. The telephone was just one of his many inventions.

The device of which Bell was most proud was developed four years after the one for which he is best known. The photophone was an apparatus for transmitting sound via modulated patterns of light. Bell first demonstrated this wonder on a cloudless day in 1880, successfully sending his voice by reflected sunbeam to his waving assistant over 200m away. The photophone used a concave receiver coated in selenium, which varied its electrical resistance with the intensity of light that fell on it. By hooking this up to a telephone Bell was able to speak to somebody over a wireless connection a good few years before the invention of radio. Indeed, Bell was so taken by the photophone that he tried to bestow the name on his second daughter, to Mrs Bell’s obvious consternation.

But the photophone was publicly mocked. As an uncharitable New York Times editorial of 30 August 1880 put it, “until (the public) sees a man going through the streets with a coil of No. 12 sunbeams on his shoulder, and suspending them from pole to pole, there will be a general feeling that there is something about Professor Bell’s photophone which places a tremendous strain on human credulity”.

A large part of the problem is that communicating by light only works when there is no obstruction between transmitter and receiver and sadly for Bell, who initially envisaged his photophone working between ships at sea, even fog was a deal-breaker.

In the end, Bell had to be content with the thrill of personal discovery: “I have been able to hear a shadow and I have even perceived by ear the passage of a cloud across the sun’s disk”, he once wrote to his father. But Haas has what Bell couldn’t have imagined – billions of potential transmitters everywhere we look and each rarely more than a few metres away. Over short distances and with the robustness that multiple transmitters will bring, Bell’s original dream looks like it might at last see the light.



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