Li-Fi also known as Laser-induced Fluorescence Imaging or Light Fidelity, is essentially the same as Wi-Fi except for a small difference that it uses LED light to transmit data wireless .The term Li-Fi is coined by Harald Haas , it is in the form of visible light communication and a subset of optical wireless communications (OWC) and could be a complement to RF communication (Wi-Fi or cellular networks), or even a replacement in contexts of data broadcasting.
Visible light communications (VLC) works by switching the current to the LEDs off and on at a very high rate, too quick to be noticed by the human eye. Although Li-Fi LED 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. 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 is not 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 utilizes 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 much faster than typical fast broadband in 2013. Li-Fi is expected to be ten times cheaper than Wi-Fi. Short range, low reliability and high installation costs are the potential downsides.
The idea of transmitting data through the visible light spectrum is not new. Alexander Graham Bell transmitted sound via a beam of sunlight in 1880 using a photo-phone, a sort of solar-powered wireless telephone. In the past several decades, a number of researchers have looked at using visible light to transmit data.
But what Haas seized on—the key to Li-Fi—is the use of simple LED light bulbs for data transmission. When Haas first started looking at alternative wireless systems, LED bulbs were becoming more widespread in homes, thanks to their energy savings over traditional incandescent bulbs. LED bulbs are controlled by a driver, which can rapidly dim the light or turn it on or off. Therefore, Haas figured, data could be encoded in subtle shifts of the light’s brightness, shifts imperceptible to the human eye.
It is said that in few years we will be getting Internet through light bulb.