0:00:00.579,0:00:04.024
I would like to demonstrate[br]for the first time in public

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that it is possible to transmit a video

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from a standard off-the-shelf LED lamp

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to a solar cell with a laptop[br]acting as a receiver.

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There is no Wi-Fi involved,[br]it's just light.

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And you may wonder, what's the point?

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And the point is this:

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There will be a massive[br]extension of the Internet

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to close the digital divide,

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and also to allow for what we call[br]"The Internet of Things" --

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tens of billions of devices[br]connected to the Internet.

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In my view, such an extension[br]of the Internet can only work

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if it's almost energy-neutral.

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This means we need to use existing[br]infrastructure as much as possible.

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And this is where the solar cell[br]and the LED come in.

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I demonstrated for the first time,

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at TED in 2011,

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Li-Fi, or Light Fidelity.

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Li-Fi uses off-the-shelf LEDs[br]to transmit data incredibly fast,

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and also in a safe and secure manner.

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Data is transported by the light,

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encoded in subtle changes[br]of the brightness.

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If we look around,[br]we have many LEDs around us,

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so there's a rich infrastructure[br]of Li-Fi transmitters around us.

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But so far, we have been using[br]special devices -- small photo detectors,

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to receive the information[br]encoded in the data.

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I wanted to find a way to also use[br]existing infrastructure

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to receive data from our Li-Fi lights.

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And this is why I have been looking into[br]solar cells and solar panels.

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A solar cell absorbs light[br]and converts it into electrical energy.

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This is why we can use a solar cell[br]to charge our mobile phone.

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But now we need to remember

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that the data is encoded in subtle changes[br]of the brightness of the LED,

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so if the incoming light fluctuates,

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so does the energy harvested[br]from the solar cell.

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This means we have[br]a principal mechanism in place

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to receive information from the light[br]and by the solar cell,

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because the fluctuations[br]of the energy harvested

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correspond to the data transmitted.

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Of course the question is:

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can we receive very fast and subtle[br]changes of the brightness,

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such as the ones transmitted[br]by our LED lights?

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And the answer to that is yes, we can.

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We have shown in the lab

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that we can receive up to 50[br]megabytes per second

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from a standard, off-the-shelf solar cell.

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And this is faster than most[br]broadband connections these days.

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Now let me show you in practice.

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In this box is a standard,[br]off-the-shelf LED lamp.

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This is a standard,[br]off-the-shelf solar cell;

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it is connected to the laptop.

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And also we have an instrument here

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to visualize the energy[br]we harvest from the solar cell.

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And this instrument shows[br]something at the moment.

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This is because the solar cell already[br]harvests light from the ambient light.

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Now what I would like to do first[br]is switch on the light,

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and I'll simply, only switch on the light,

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for a moment,

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and what you'll notice is that[br]the instrument jumps to the right.

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So the solar cell, for a moment,

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is harvesting energy[br]from this artificial light source.

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If I turn it off, we see it drops.

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I turn it on ...

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So we harvest energy with the solar cell.

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But next I would like to activate[br]the streaming of the video.

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And I've done this[br]by pressing this button.

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So now this LED lamp here[br]is streaming a video

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by changing the brightness of the LED[br]in a very subtle way,

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and in a way that you can't[br]recognize with your eye,

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because the changes[br]are too fast to recognize.

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But in order to prove the point,

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I can block the light of the solar cell.

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So first you notice[br]the energy harvesting drops

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and the video stops as well.

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If I remove the blockage,[br]the video will restart.

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(Applause)

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And I can repeat that.

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So we stop the transmission of the video[br]and energy harvesting stops as well.

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So that is to show that the solar cell[br]acts as a receiver.

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But now imagine that this LED lamp[br]is a street light, and there's fog.

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And so I want to simulate fog,

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and that's why I brought[br]a handkerchief with me.

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(Laughter)

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And let me put the handkerchief[br]over the solar cell.

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First you notice

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the energy harvested drops, as expected,

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but now the video still continues.

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This means, despite the blockage,

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there's sufficient light coming through[br]the handkerchief to the solar cell,

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so that the solar cell is able to decode[br]and stream that information,

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in this case, a high-definition video.

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What's really important here is that[br]a solar cell has become a receiver

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for high-speed wireless signals[br]encoded in light,

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while it maintains its primary function[br]as an energy-harvesting device.

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That's why it is possible

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to use existing solar cells[br]on the roof of a hut

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to act as a broadband receiver

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from a laser station on a close by hill,[br]or indeed, lamp post.

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And It really doesn't matter[br]where the beam hits the solar cell.

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And the same is true

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for translucent solar cells[br]integrated into windows,

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solar cells integrated[br]into street furniture,

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or indeed, solar cells integrated[br]into these billions of devices

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that will form the Internet of Things.

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Because simply,

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we don't want to charge[br]these devices regularly,

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or worse, replace the batteries[br]every few months.

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As I said to you,

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this is the first time[br]I've shown this in public.

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It's very much a lab demonstration,

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a prototype.

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But my team and I are confident[br]that we can take this to market

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within the next two to three years.

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And we hope we will be able to contribute[br]to closing the digital divide,

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and also contribute

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to connecting all these billions[br]of devices to the Internet.

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And all of this without causing

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a massive explosion[br]of energy consumption --

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because of the solar cells,[br]quite the opposite.

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Thank you.

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(Applause)