The Lux two-minute explainer: Li-fi

Here is the Lux quick guide to Li-fi, so next time it comes up in conversation, you’ll sound like an expert…

What’s Li-fi?

Li-fi is a way of transmitting data – including the internet – to devices such as smart phones using visible light from LEDs pulsed at high frequency. Li-fi is a term coined by Professor Harold Haas of Edinburgh-based start-up company pureLiFi. It's bi-directional, unlike so-called visual light communication, or VLC, in which information is broadcast in one direction to devices. Examples of the latter are indoor-location services.

Is it completely new?

Not really. The remote control you use to send instructions to your TV uses invisible infrared light, and, at the other end of the scale, lasers send vast amounts of data down fibre optic cables to provide telecoms and broadband services, so the principle has been around for decades. The advent of LED lighting, which can be switched on and off instantaneously, has enabled this approach to be expanded and piggy-backed onto LED lighting systems.

How fast is Li-fi?

In theory li-fi can perform around 100 times faster than Wi-fi, which would mean you could download the entire set of Star Wars movies in around one second. 

Would I notice a difference in my lighting system equipped with Li-fi?

No, because the lights are pulsed at extremely high frequencies which is undetectable to the human eye. It operates at many hundreds of times faster than high-frequency lighting power supplies or ballasts which are used today.

How do devices download information using Li-fi?

One option is to use the forward-facing camera on your smart phone or laptop. In truth, the components required to deploy this technology are much simpler than Wi-fi or Bluetooth. Think about how many devices already have some sort of light-sensing capability to enable functions such as automatic screen dimming. Alternatively, a plug-in dongle with built-in photoreceptor receives the information.

How do devices upload information?

Data in most cases is a two-way street, and although you tend to receive much more data than you upload, the receiving device still needs to transmit data back. Currently, devices requires a plug-in dongle which has an integral infra-red transmitter to send information back to the luminaire. The dongle also includes a photo-receptor to download information. However, if Li-fi gets traction in the market, smart phone and laptop manufacturers may start to incorporate the necessary sensors and software, obviating the need for a separate dongle. 

How does data get in to the lighting system?

The luminaire transmitting the data still needs to connect to the internet or network. This could be with an Ethernet connection or using power-line communication, which is basically data sent over conventional mains wiring. Li-fi engineers say the best solution is to have the whole installation as a Power over Ethernet installation, where both power and data is sent along Cat 5 or Cat 6 cables.

What are the advantages over Wi-fi?

The amount of data which can be transmitted over Wifi is limited; the more users or devices which are trying to communicate, the slower it becomes. Ever tried to connect to wi-fi in a busy exhibition hall or airport departure lounge?

Is Li-fi safe?

In many situations Li-fi could be safer than Wi-fi. The radio frequencies used in Wi-fi can interfere with sensitive electronic equipment, for example in medical equipment or hazardous locations found in chemical plants.

What about security?

Light can be made very directional, and obviously can’t travel through walls, so to eavesdrop or hack a system you need to be able to see the light. 

Can lights still be dimmed when using Li-fi?

In theory, lights can be dimmed to levels undetectable by the human eye and still perform. However, range or network speed may be compromised. The minimum light level for Li-fi to work is around 60 lux.

Typical implementation - Courtesy pureLiFi

What are the applications?

These are the sectors where it gets really exciting:

Office Lighting

Power over Ethernet (PoE) – using standard network cables and infrastructure to power lights – is already starting to be used for office lighting. Adding Li-fi would seem a logical next step. This could remove the need for a separate wired data network for computers and phone systems in offices, and reduce the cost and complexity of IT systems, as well as make office layouts much more flexible.

Retail

Trials are already underway with major retailers such as Carrefour and Target using light-based location technology to interact with shoppers’ smart phones. The systems under trail at the moment still need a separate connection to the internet via Wi-fi or either 3G or 4G, but adding Li-fi would make the process simpler, quicker and more responsive.

Public areas

Large numbers of people trying to connect to the internet is a nightmare for Wi-fi systems. Equipping lights in railway stations, exhibition venues and public spaces with Li-fi would enable new experiences for visitors and commuters. 

Who’s working on this technology?

There are currently two world leaders,  PureLi-fi and Visilink

  • Li-fi and its future in the lighting industry will be one of the subjects discussed at this November's LuxLive exhibition in London on Wednesday 23 November and Thursday 24 November 2016.

Picture courtesy pureLiFi

Comments 4

Yeah, the article was easy to understand. I have some more data to share. I read about the history of LiFi. Wherever everyone thinks that Prof. Harald Haas is the real inventor of the LiFi. But an article claims that the before that many companies working on it. Based on the patent, Huawei was the first whose got the first ever patent of LiFi in 2006. So it obvious that they were working on it before that. The article contains some more facts which show the same theory. http://www.greyb.com/researching-li-fi-first-public-disclosure/ Here is the link. Get some benefits it's free.

Interested in Li Fi

Thank you for very useful information in a nutshell.

Please add a block on data going the other way - how does data get from your phone or device to the network? What is the bandwidth, battery consumption, feature set required to receive this in your lights?

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