Li-Fi, as coined by Prof. Harald Haas during his TED Global talk, is bidirectional, high speed and fully networked wireless communications similar to Wi-Fi. Li-Fi is a subset of optical wireless communications (OWC) and can be a complement to RF communication (Wi-Fi or Cellular network), or a replacement in contexts of data broadcasting.
It is wireless and uses visible light communication or infra-red and near ultraviolet (instead of radio frequency waves) spectrum, part of Optical wireless communications technology, which carries much more information, and has been proposed as a solution to the RF-bandwidth limitations. A complete solution includes an industry led standardization process.
This OWC technology uses light from light-emitting diodes (LEDs) as a medium to deliver networked, mobile, high-speed communication in a similar manner to Wi-Fi. Li-Fi could lead to the Internet of Things, which is everything electronic being connected to the internet, with the LED lights on the electronics being used as Li-Fi internet access points. The Li-Fi market is projected to have a compound annual growth rate of 82% from 2013 to 2018 and to be worth over $6 billion per year by 2018.
Visible light communications (VLC) works by switching bulbs on and off within nanoseconds, which is too quickly to be noticed by the human eye. Although Li-Fi bulbs would have to be kept on to transmit data, the bulbs could be dimmed to the point that they were not visible to humans and yet still functional. The light waves cannot penetrate walls which makes a much shorter range, though more secure from hacking, relative to Wi-Fi. Direct line of sight isn't necessary for Li-Fi to transmit a signal; light reflected off the walls can achieve 70 Mbit/s.
Li-Fi has the advantage of being useful in electromagnetic sensitive areas such as in aircraft cabins, hospitals and nuclear power plants without causing electromagnetic interference. Both Wi-Fi and Li-Fi transmit data over the electromagnetic spectrum, but whereas Wi-Fi utilises radio waves, Li-Fi uses visible light. While the US Federal Communications Commission has warned of a potential spectrum crisis because Wi-Fi is close to full capacity, Li-Fi has almost no limitations on capacity. The visible light spectrum is 10,000 times larger than the entire radio frequency spectrum. Researchers have reached data rates of over 10 Gbit/s, which is more than 250 times faster than superfast broadband. Li-Fi is expected to be ten times cheaper than Wi-Fi. Short range, low reliability and high installation costs are the potential downsides.
Bg-Fi is a Li-Fi system consisting of an application for a mobile device, and a simple consumer product, like an IoT (Internet of Things) device, with color sensor, microcontroller, and embedded software. Light from the mobile device display communicates to the color sensor on the consumer product, which converts the light into digital information. Light emitting diodes enable the consumer product to communicate synchronously with the mobile device.   
Professor Harald Haas, from the University of Edinburgh in the UK, is widely recognised as the original founder of Li-Fi. He coined the term Li-Fi and is Chair of Mobile Communications at the University of Edinburgh and co-founder of pureLiFi.
The general term visible light communication (VLC), includes any use of the visible light portion of the electromagnetic spectrum to transmit information. The D-Light project at Edinburgh's Institute for Digital Communications was funded from January 2010 to January 2012. Haas promoted this technology in his 2011 TED Global talk and helped start a company to market it. PureLiFi, formerly pureVLC, is an original equipment manufacturer (OEM) firm set up to commercialize Li-Fi products for integration with existing LED-lighting systems.
In October 2011, companies and industry groups formed the Li-Fi Consortium, to promote high-speed optical wireless systems and to overcome the limited amount of radio-based wireless spectrum available by exploiting a completely different part of the electromagnetic spectrum. A number of companies offer uni-directional VLC products which is not the same as Li-Fi.
VLC technology was exhibited in 2012 using Li-Fi. By August 2013, data rates of over 1.6 Gbit/s were demonstrated over a single color LED. In September 2013, a press release said that Li-Fi, or VLC systems in general, do not require line-of-sight conditions. In October 2013, it was reported Chinese manufacturers were working on Li-Fi development kits.
In April 2014, the Russian company Stins Coman announced the development of a Li-Fi wireless local network called BeamCaster. Their current module transfers data at 1.25 gigabytes per second but foresee boosting speeds up to 5 GB/second in the near future.
One part of VLC is modeled after communication protocols established by the IEEE 802 workgroup. However, the IEEE 802.15.7 standard is out-of-date, it fails to consider the latest technological developments in the field of optical wireless communications, specifically with the introduction of optical orthogonal frequency-division multiplexing (O-OFDM) modulation methods which have been optimized for data rates, multiple-access and energy efficiency. The introduction of O-OFDM means that a new drive for standardization of optical wireless communications is required.
Nonetheless, the IEEE 802.15.7 standard defines the physical layer (PHY) and media access control (MAC) layer. The standard is able to deliver enough data rates to transmit audio, video and multimedia services. It takes into account optical transmission mobility, its compatibility with artificial lighting present in infrastructures, and the interference which may be generated by ambient lighting. The MAC layer permits using the link with the other layers as with the TCP/IP protocol.
The standard defines three PHY layers with different rates:
- The PHY I was established for outdoor application and works from 11.67 kbit/s to 267.6 kbit/s.
- The PHY II layer permits reaching data rates from 1.25 Mbit/s to 96 Mbit/s.
- The PHY III is used for many emissions sources with a particular modulation method called color shift keying (CSK). PHY III can deliver rates from 12 Mbit/s to 96 Mbit/s.
The modulation formats recognized for PHY I and PHY II are on-off keying (OOK) and variable pulse position modulation (VPPM). The Manchester coding used for the PHY I and PHY II layers includes the clock inside the transmitted data by representing a logic 0 with an OOK symbol "01" and a logic 1 with an OOK symbol "10", all with a DC component. The DC component avoids light extinction in case of an extended run of logic 0's.
The first VLC smartphone prototype was presented at the Consumer Electronics Show in Las Vegas from January 7–10 in 2014. The phone uses SunPartner's Wysips CONNECT, a technique that converts light waves into usable energy, making the phone capable of receiving and decoding signals without drawing on its battery. A clear thin layer of crystal glass can be added to small screens like watches and smartphones that make them solar powered. Smartphones could gain 15% more battery life during a typical day. This first smartphones using this technology should arrive in 2015. This screen can also receive VLC signals as well as the smartphone camera. The cost of these screens per smartphone is between $2 and $3, much cheaper than most new technology.
Philips lighting company has developed a VLC system for shoppers at stores. They have to download an app on their smartphone and then their smartphone works with the LEDs in the store. The LEDs can pinpoint where they are located in the store and give them corresponding coupons and information based on which aisle they are on and what they are looking at.
Cited entities and devices:
- "Light Fidelity (Li-Fi): Towards All-Optical Networking", D. Tsonev, S. Videv and H. Haas; Institute for Digital Communications, Li-Fi R&D Centre, The University of Edinburgh, EH9 3JL, Edinburgh, UK.
- Light bulbs could replace your Wi-Fi router, Digital Trends, 30 October 2013, Joshua Sherman
- Tech firm sees the light with £3m funding, The Scotsman, Peter Ranscombe, 24 December 2013
- Visible Light Communication (VLC)/Li-Fi Technology Market worth $6,138.02 Million - 2018, New International, 13 November 2013
- LiFi beats Wi-Fi with 1GB wireless speeds over pulsing LEDs, gearburn, 13 January 2013, Jacques Coetzee
- Condliffe, Jamie (28 July 2011). "Will Li-Fi be the new Wi-Fi?". New Scientist.
- Li-Fi – Internet at the Speed of Light, by Ian Lim, the gadgeteer, dated 29 August 2011.
- "Visible-light communication: Tripping the light fantastic: A fast and cheap optical version of Wi-Fi is coming". The Economist. 28 January 2012. Retrieved 22 October 2013.
- The internet on beams of LED light, The Science Show, 7 December 2013
- THE FUTURE’S BRIGHT – THE FUTURE’S LI-FI, Caledonian Mercury, 29 November 2013
- High-speed wireless networking using visible light, Spie, Harald Haas, 19 April 2013
- Li-Fi revolution: internet connections using light bulbs are 250 times faster than broadband, The Independent, James Vincent, 28 October 2013
- 'Li-fi' via LED light bulb data speed breakthrough, BBC News, Matthew Wall, 28 October 2013
- pureLiFi to demonstrate first ever Li-Fi system at Mobile World Congress, Virtual-Strategy Magazine, 19 February 2014
- Low-Complexity Visible Light Networking with LED-to-LED Communication Domenico Giustiniano, Nils Ole Tippenhauer, Stefan Mangold http://people.ee.ethz.ch/~dgiustin/images/LED-to-LED.pdf
- Very Low-Cost Sensing and Communication Using Bidirectional LEDs Paul Dietz, William Yerazunis, Darren Leigh TR2003-35 July 2003 http://www.merl.com/publications/docs/TR2003-35.pdf
- Bg-Fi datasheet http://www.publicityproviders.com/li-fi/
- Povey,, Gordon. "About Visible Light Communications". pureVLC. Archived from the original on 18 August 2013. Retrieved 22 October 2013.
- Haas, Harald (July 2011). "Wireless data from every light bulb". TED Global. Edinburgh, Scotland.
- "pureLiFi Ltd". pureLiFi. Retrieved 22 December 2013.
- "pureVLC Ltd". Enterprise showcase. University of Edinburgh. Retrieved 22 October 2013.
- Povey, Gordon (19 October 2011). "Li-Fi Consortium is Launched". D-Light Project. Archived from the original on 18 August 2013. Retrieved 22 October 2013.
- Watts, Michael (31 January 2012). "Meet Li-Fi, the LED-based alternative to household Wi-Fi". Wired Magazine.
- pureVLC (6 August 2012). "pureVLC Demonstrates Li-Fi Streaming along with Research Supporting World's Fastest Li-Fi Speeds up to 6 Gbit/s". Press release (Edinburgh). Retrieved 22 October 2013.
- pureVLC (10 September 2013). "pureVLC Demonstrates Li-Fi Using Reflected Light". Edinburgh. Retrieved 22 October 2013.
- Iain Thomson (18 October 2013). "Forget Wi-Fi, boffins get 150Mbps Li-Fi connection from lightbulbs: Many (Chinese) hands make light work". The Register. Retrieved 22 October 2013.
- Li-Fi internet solution from Russian company attracting foreign clients, Russia and India Report, Russia Beyond the Headlines, 1 July 2014
- Tsonev, D.; Sinanovic, S.; Haas, Harald (15 September 2013). "Complete Modeling of Nonlinear Distortion in OFDM-Based Optical Wireless Communication". IEEE Journal of Lightwave Technology 31 (18): 3064–3076. doi:10.1109/JLT.2013.2278675.
- An IEEE Standard for Visible Light Communications visiblelightcomm.com, dated April 2011. It is superfast modern intelnet technology.
- Breton, Johann (20 December 2013). "Li-Fi Smartphone to be Presented at CES 2014". Digital Versus. Retrieved January 16, 2014.
- Rigg, Jamie (January 11, 2014). "Smartphone concept incorporates LiFi sensor for receiving light-based data". Engadget. Retrieved January 16, 2014.
- An Internet of Light: Going Online with LEDs and the First Li-Fi Smartphone, Motherboard Beta, Brian Merchant
- Your next phone may charge and receive data through this incredible screen, Digital Trends, 19 January 2014, Jeffrey Van Camp
- Philips Creates Shopping Assistant with LEDs and Smart Phone, IEEE Spectrum, 18 February 2014, Martin LaMonica