Li-Fi is a bidirectional, high-speed and fully networked wireless communication technology similar to Wi-Fi. The term was coined by Harald Haas^[1] and is a form of optical wireless communications (OWC) and uses the visible spectrum as well as ultraviolet and infrared radiation. Li-Fi could be a complement to RF communication (Wi-Fi or cellular networks), or even a replacement in contexts of data broadcasting. It is currently being developed by many organisations all over the world.

It is wire and UV visible-light communication or infrared and near-ultraviolet instead of radio-frequency spectrum, part of optical wireless communications technology, which carries much more information and has been proposed as a solution to the RF-bandwidth limitations.^[2]

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.^[3] 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.^[4]

Visible light communications (VLC) works by switching the current to the LEDs off and on at a very high rate,^[5] too quick to be noticed by the human eye. Although Li-Fi LEDs would have to be kept on to transmit data, they could be dimmed to below human visibility while still emitting enough light to carry data.^[6] The light waves cannot penetrate walls which makes a much shorter range, though more secure from hacking, relative to Wi-Fi.^[7][8] Direct line of sight is not necessary for Li-Fi to transmit a signal; light reflected off the walls can achieve 70 Mbit/s.^[9][10]

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.^[7][11][8] Both Wi-Fi and Li-Fi transmit data over the electromagnetic spectrum, but whereas Wi-Fi utilizes radio waves, Li-Fi uses visible light, Ultraviolet and Infrared. 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.^[12]The visible light spectrum is 10,000 times larger than the entire radio frequency spectrum.^[13] Researchers have reached data rates of over 224 Gbit/s, which is much faster than typical fast broadband in 2013.^[14][15] Li-Fi is expected to be ten times cheaper than Wi-Fi.^[6] Short range, low reliability and high installation costs are the potential downsides.^[4][5]

PureLiFi demonstrated the first commercially available Li-Fi system, the Li-1st, at the 2014 Mobile World Congress in Barcelona.^[16]

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.^[17

Bitcoin is a cryptocurrency and worldwide payment system.^[8]:3 It is the first decentralized digital currency, as the system works without a central bank or single administrator.^[8]:1[9] The network is peer-to-peer and transactions take place between users directly through the use of cryptography, without an intermediary.^[8]:4 These transactions are verified by network nodes and recorded in a public distributed ledger called a blockchain. Bitcoin was invented by an unknown person or group of people under the name Satoshi Nakamoto^[10] and released as open-source software in 2009.^[11]

Bitcoins are created as a reward for a process known as mining. They can be exchanged for other currencies,^[12] products, and services. As of February 2015, over 100,000 merchants and vendors accepted bitcoin as payment.^[13] Research produced by the University of Cambridge estimates that in 2017, there are 2.9 to 5.8 million unique users using a cryptocurrency wallet, most of them using bitcoin.^[14]