October/November/December 2020 I 17
The most recent and ingeniously innovative use of LED
lighting is in its application for data transmission. This
new technology that is showing great promise for the
future of wireless data transmission is called light
fidelity (Li-Fi). It is committed to making an internet
connection as simple as turning on a light switch!
UNDERSTANDING THE TERMINOLOGY
Light fidelity is a visible light communication (VLC)
system and a wireless communication technology utilizing
light in high frequency to transmit data to and from
devices through light output. The VLC term dates to the
1880s. It includes any use of the visible light portion
of the electromagnetic spectrum to transmit information.
The term VLC was further defined by the IEEE
802.15.7r1 standardization committee in January 2016.
The Li-Fi concept was invented by Professor Harald
Haas from the University of Edinburgh, Scotland in 2011
when he demonstrated for the first time that by flickering
the light from a single LED, he could transmit far more
data than a cellular tower.1 The term Li-Fi was launched
at his 2011 TED Global Talk where he introduced the idea
of wireless data from every light bulb; his talk has been
watched online more than 2.4 million times.
He remains Professor of Mobile Communications
at the University of Edinburgh and the co-founder
of pureLiFi along with Dr Mostafa Afgani2 where
research and modifications toward standardization
are ongoing.
THE CONCEPT OF Li-Fi
AND HOW IT WORKS
“Light fidelity is a high-speed, bidirectional networked
technology achieving mobile communication of data
using light. Li-Fi is comprised of multiple light bulbs that
form a wireless network.”3
When an electrical current is applied to an LED light
bulb, a stream of light or photons is emitted through the
bulb. Each tiny LED lamp is a semiconductor device,
which means that the brightness of the light flowing
through it can be changed at an extremely high speed.
This allows a signal to be sent by modulating the light
at different rates. The signal can then be received by
a detector that interprets the changes in light intensity
FIGURE 1: With each light or bulb serving as an internet
connection and a means to gather data, future innovations
and applications may be limited only by the imagination.
(the signal) as data (Figure 1). This detector is incorporated
in a communications device.
The high frequency of light/data transmission
is undetectable to the human eye. The LED lights used
to transmit Li-Fi signals are modulated at such a fast rate
that the eye cannot perceive the modulation or flicker.
This is similar to the way eyes do not interpret the break
between film frames in a motion picture. Just as people
see a smooth motion on the cinema screen, they will see
an uninterrupted source of steady light streaming from
a Li-Fi-enabled luminaire. As a comparison, the lowest
frequency at which the lights are modulated is 1 MHz,
which is 10,000 times faster than the refresh rate of computer
screens. Since the intensity of modulation cannot
be seen, the data communication is the same as other
radio systems. This allows users to be connected to wireless
internet where there is Li-Fi-enabled light.
Because LED lamps are electronic devices, their
currents and, therefore, their lights can be modulated
at extremely high speeds. The modulated light is detected
by a photosensor in the electronic device that receives
it, which then converts the pulsing light into an electrical
current through a transceiver. This electrical current
forms the data signal.