Air travellers of the future may be able to download files to their iPads via LED lights above the seat. Colourbox

Download films through your lamp

Tuesday 02 Aug 16


Lars Dittmann
Professor, Group Leader
DTU Fotonik
+45 45 25 38 51
Li-fi Wireless communication via radio waves has its limitations, so work is now under way to expand bandwidth by using LED lights as information carriers.

Cables are history; all communication between all our various electronic devices is now to be wireless. Today, our devices communicate via radio signals in the free frequency band (2.4 GHz). The advantage of this wavelength is that everyone can transmit on it; the drawback is that it offers only a limited range, so the numerous wireless devices often disrupt one another. Simply put, more bandwidth is required—and this is precisely what is available through LED lights.

Electronic signals consists of a series of 1s and 0s, which are altered (modulated) so that they can be transmitted and decoded. Modulation can be performed in radio waves, which we know as ‘Wi-Fi’. A few years ago, however, the Scottish engineer Harald Haas demonstrated that it was also possible to transfer the signals through an ordinary household lamp by having it flash at a frequency invisible to the human eye, while still providing normal illumination.

This method for transferring information has actually proved to be many times faster than Wi-Fi, but it is subject to several physical limitations. For example, the light must of course shine directly on the receiving device, and communication is only possible in one direction: from lamp to receiver. For two-way communication to be possible, the light must be supplemented by the well-known radio waves. So the optimistic name ‘Li-Fi’ that the phenomenon has been given may be a little misleading. Nevertheless, there is huge potential in the technology known as ‘Visible Light Communication’.

"A few systems are already available on the market, but these are what are known as ‘link systems’, i.e. one-way communication."
Professor Lars Dittmann

DTU Fotonik is currently working with several aspects of the phenomenon: from optimization of the light sources themselves, their efficiency and service life, to development of detectors and control electronics for the LED lights. The researchers have received a comprehensive briefing from companies, local authorities and hospitals on the subject of potential uses for the communicative lights when major investments in LED lights are being planned.

However, there is still a long way to go before Li-Fi becomes a common form of communication, as Professor Las Dittmann emphasizes:

“A few systems are already available on the market, but these are what are known as ‘link systems’, i.e. one-way communication. Our test platform in Doll Living Lab in Albertslund features a number of lamp-posts that support Li-Fi, but we need to develop receiving equipment as well. Apple may be including some kind of Li-Fi support in its next iPhone. They have already demonstrated that you can use the camera as a receiver, but it is difficult to get the light to hit the camera aperture precisely. So it seems they are working with other solutions that are better at receiving the light.”

However, even though Li-fi is limited to one-way communication, Lars Dittmann has no difficulty identifying numerous opportunities in the technology. These are presented in the graphics on this page.

Where lights can be used to communicate

LED bulbs that flash at extremely high frequency can be used in many places to transmit data such as video, audio and information.


In aircraft
All 200 passengers on a given flight may want to watch different films, but there is not enough Wi-fi capacity to handle the demand. Back at its head office, the airline has uploaded a number of films to the aircraft server. A passenger then uses Wi-fi to call up a film, which is sent to that passenger’s seat light and then on to the passenger’s own tablet or smart phone. The entire transaction takes just a few seconds. This results in individualized entertainment for all, without having to install fixed screens with the resultant increase in weight.


Illustration: ColourboxIn hospitals
An end is in sight for the endless discussions about which programme the only TV set on the ward is to show. Each patient simply chooses what he or she wants to download via the bedside light and then watch on his/her tablet.


Illustration: ColourboxIn museums
The lights next to each exhibit are fitted with a tiny hard drive containing information about the item in question, which visitors can then download to their smartphones. The Li-fi system may replace the standard information boards, and as an added bonus, the information can be entered in several languages and supplemented with video clips.


Illustration: ColourboxIn buses
The DOLL Living Lab in Albertslund is currently running an experiment in which street lights fitted with LED bulbs are being used to transport information. The lights are located close to a technical college, and when the students set off on a long bus trip, they can use them to download entertainment for the trip to their tablets before getting on the buses.


Illustration: ColourboxIn cars
Street lights have the capacity to collect information about the traffic situation, air pollution, the state of the road surface, etc. and transmit it to private vehicles via Li-fi. Vehicles will also be able to share information with one another through the street lights, and this is sure to have a  major effect on safety in connection with the advent of self-driving cars. For example, if a car starts to brake, it can send a message to the vehicles behind it to start braking as well, or even better: cars farther back on the road can be notified to reduce speed so as to avoid the risk of a multi-vehicle collision.