Which of the following does Li-Fi most probably stand for?

W: Welcome to Technology Weekly. We keep you informed about the latest technology. Today, we’re going to talk about Li-Fi. Yes, you heard it right. It’s Li-Fi, not Wi-Fi. With us is Dr Gordon Povey from the University of Edinburgh. Good evening, Dr Povey, what’s the Li-Fi thing we’re talking about today?
M: Good evening. (1) Before explaining what Li-Fi is, let’s first start with Wi-Fi. Many of us are familiar with the term. It stands for wireless fidelity, which is a mechanism that allows an electronic device to exchange data wirelessly over a computer network. A device enabled with Wi-Fi, such as a personal computer, video game console, smartphone, tablet, or digital audio player, can connect to a network resource such as the Internet via a wireless network access point.
W: Access point?
M: Or hotspot, as we generally call it. Li-Fi is doing the same thing through light.
W: Are we just coming up with the idea or is Li-Fi something that already exists?
M: Well, among the many new gadgets unveiled at the recent Consumer Electronics Show in Las Vegas was a pair of smartphones able to exchange data using light. These phones, as yet only prototypes from Casio, a Japanese firm, transmit digital signals by varying the intensity of the light given off from their screens. The flickering is so slight that it is imperceptible to the human eye, but the camera on another phone can detect it at a distance of up to ten metres.
W: That sounds like going back to sending messages with an Aldis lamp.
M: In fact, it may well be the beginning of a fast and cheap wireless-communication system, Li-Fi. Yet that is still only a flicker of what is possible. Last October a number of companies and industry groups formed the Li-Fi Consortium, to promote high-speed optical wireless systems. (2) The idea is that light can help with a looming capacity problem.
W: We’re having a capacity problem?
M: Yes. As radio-based wireless becomes ubiquitous, more and more devices transmitting more and more data are able to connect to the internet, either through the mobile-phone network or through Wi-Fi. But there is only a limited amount of radio spectrum available. Using light offers the possibility of breaking out of this conundrum by exploiting a completely different part of the electromagnetic spectrum, one that is already because it is ubiquitously used for illumination.
W: That sounds incredible, how can we achieve that?
M: To turn a light into a Li-Fi router involves modulating its output, to carry a message, and linking it with a network cable to a modem that is connected to a telephone or cable-broadband service, just like a Wi-Fi router.
W: You mean, we can turn a incandescent light bulb into a router.
M: Incandescent light bulbs and fluorescent tubes are not really suitable for modulation, but they are yesterday’s lighting technology. Tomorrow’s is the light-emitting diode. (3) LEDs are rapidly replacing bulbs and tubes because they are more efficient. And because they are semiconductor devices, tinkering with their electronics to produce the flickering signals required for data transmission is pretty straightforward. I’m now working on light communication with my colleagues. The rate of data transfer is also good. My group is already up to 130 megabits a second which is faster than some older Wi-Fi routers, over a distance of about two metres, using standard LEDs.
W: That sounds interesting. And the speed can surely be improved.
M: You can say that again. We think such devices should be able to reach 1 gigabit per second, and do so over greater range. Specially constructed LEDs would be even faster. The Li-Fi consortium reckons more than 10 Gbps is possible. In theory, that would allow a high-definition film to be downloaded in 30 seconds. Adapting existing LEDs to work with the sensors and light sources—cameras, ambient-light detectors, screens, flashbulbs, torches and so on—already found in smartphones and similar devices will be the fastest way to bring Li-Fi to market. VCL, which is my company, already produced a smartphone app which allows low-speed data transmission between a pair of iPhones. It has also made an experimental optical transceiver that plugs into a laptop to receive and send light signals.
W: Is there any downside of the new technology though?
M: There are limitations to using light, of course. Unlike radio, light waves will not penetrate walls.
W: Which means the connection may be confined to a small room.
M: (4) Which for secure applications could also be a bonus. Light bulbs are almost everywhere and often on. As they are gradually replaced by LEDs, every home, office, public building and even streetlight could become a Li-Fi hotspot. Moreover, spotting a nearby light in order to sit next to it is certainly easier than finding the location of a Wi-Fi router.
W: No need to carry my smartphone all around to find a hotspot.
M: But communication is a two-way street. That means the LEDs involved in Li-Fi would need photo detectors to receive data. Some LED systems have such sensors already like the ones that know when to turn on at night. But even if LEDs are not modified hybrid systems are possible: data could be downloaded using light but uploaded using radio. In an office, for example, an LED-powered desk lamp could work as a Li-Fi router, able to link up with any networked device placed on the desk. (5) Another big advantage of light is that it can be used in areas which contain sensitive equipment that radio signals might interfere with, such as aircraft and operating theatres. LEDs in the ceiling of an airliner would not only allow internet access but could also transmit films on demand to individual seats, removing the need for heavy cabling, thus saving airlines fuel.
W: Then it really makes this idea fly. Thank you for joining us.
M: You’re welcome.