Top 10 Li-Fi myths

Wired VLC imageOne only needs to read some of the daft comments posted at the foot of online visible light comms articles to understand that there are a large number of misconceptions out there.  Here is my Li-Fi myth buster top 10.

1.     The lights flicker.

We subtly modulate the current supply to the LED devices at relatively high speeds. We are not harshly switching the LEDs on and off, and we are not modulating at speeds anywhere near those perceptible to the human eye. Your TV and computer displays do flicker at just higher than perceptible rates, the same is true of some LED dimming technologies. VLC does not flicker the lights like this, it will not give you a headache!

2.     You cannot dim the lights.

There are VLC patents pending on methods to dim the LED while maintaining high data rates until the current is dimmed to about 50%. After that the data rates will begin to diminish in a very graceful manner.  So yes, you can dim the lights and maintain communications reliably.

3.     VLC is uni-directional (downlink or broadcast only).

VLC can be used for transmission in either direction. The uplink and downlink can be isolated in a number of ways – wavelength, time, code and also by spatial or optical isolation. For practical and cost reasons VLC might be implemented for downlink only since this is where bottlenecks exist with existing technologies, e.g. Wi-Fi may already provide a reliable uplink where congestion is less likely and Li-Fi provides a high capacity uncongested downlink.

4.     There will be interference from sunlight.

It is relatively simple to eliminate the vast majority of interference from natural and artificial sources using optical filters (which avoids receiver saturation).  After the photo-detector further analogue and digital filtering ensure remaining interference is negligible.

5.     Lights need to be on so this is inefficient.

To use VLC the lights do need to be on.  However in the vast majority of industrial, commercial and retail environments the lights are on when the area is occupied. Given that the lights are usually on, VLC  transmission power comes free as it is already used for illumination so this is highly efficient.

In domestic environments we do tend to switch off lights during daylight. Where the lights would have been off the power required for VLC is not free but the lights only need to be dimmed up to transmit data. The illumination need not be above ambient levels so will not be noticed. The power consumed is comparable with the watts/bit for radio transmission and so on aggregate even in domestic environments there is a significant net saving in power.

6.     You must have line-of-sight.

Line of sight is a definite advantage because the signal will be stronger. However, if you look under the table you can still see despite there being no line of sight from the sun or from artificial sources.  If a VLC receiver can collect photons, it can receive data, albeit at a lower data rate if light levels are low. Radio technology is similar in that indirect signals have a lower power and hence the data rate reduces. Visible light can be reflected but generally does not penetrate materials which can be a security advantage and perhaps a coverage disadvantage. Radio can suffer multipath interference from non-line of sight reflected signal cancelling each other by being in anti-phase – leads to signal fading. VLC signal always add and cannot cancel each other and cause fading which is a significant advantage.

7.     This is a disruptive technology.

VLC is often regarded as a disruptive technology relative to radio technology.  I do not believe this should be considered to be the case. I believe VLC is totally complementary to radio. In the same way as Wi-Fi is seen as complimentary to cellular data, VLC or Li-Fi is complementary to Wi-Fi. Cellular data is automatically off-loaded to Wi-Fi when in-doors, in the office or home. Cellular operators insist that smart phones used on their networks are Wi-Fi enabled for this reason, and for quality of service reasons we tend to turn this feature on automatically to the relief of the cellular operators. Unfortunately and consequently Wi-Fi is now becoming heavily congested. Li-Fi can provide a high speed, high density bearer onto which the congested Wi-Fi downlink traffic can be off-loaded. VLC is radio’s friend we should not be considered enemies.

8.     You need special LEDs

Specialist LEDs with ideal characteristics for VLC would be great. However, solid state LED lighting is currently being sold based on its performance for illumination purposes (colour temperature, efficacy, CRI, lifetime, etc). Communications performance is not even a secondary consideration,  so it is wholly unrealistic to expect the lighting industry to factor this into designs at this stage.

In a practical sense we can achieve excellent results with COTS LED devices, if better devices are available great, but to implement VLC we can use existing LED devices. When VLC becomes a significant part of the LED industry then we can start to influence the specification of these devices.

9.     VLC is a complex technology

VLC is a very simple technology since it uses direct modulation and direct demodulation . Infra-red remote controls are very low-cost for exactly the same reason. On the other hand radio technology is complex since it requires radio frequency circuits to modulate the data onto the radio bearer and then it requires an antenna system to transmit the signal. The radio receiver is often even more complex requiring an antenna system, radio receiver and carrier synchronisation circuits. Therefore VLC is much simpler than the equivalent radio system.

10.   It will never work!

VLC technology has been proven to work by a number of companies and research establishments.  The reliability of lighting systems has rarely been questioned but the reliability of wireless communications is increasingly in question.  To my mind the question we need to be asking is; “Could we ever make wireless communications as reliable as lighting technology?”

Surely the answer to the above question is – “If we use lighting technology to deliver wireless communications then it will become as reliable as the lighting itself”. At least that is my dream!

Posted in general | Tagged , , , , , , | 1 Comment

Flash-Matic and the Light Telephone

Last week American Eugene Polley died at the age of 96. Eugene invented “Flash-Matic” the first TV remote control in 1955. This was an early example of visible light communication (VLC) in action.

Eugene’s passing prompted me to think about some of the VLC inventions in history. I am not really thinking about the core technology, but more the early products that lay legitimate claim to being VLC applications. History will teach us how current VLC inventions might be recorded so let’s ignore these and rewind to another age.

Nintendo Light TelephoneWay back in 1971 when I was in short trousers and solid state electronics was in its infancy, the Japanese toy manufacturer Nintendo released the Light Telephone. It was developed by their #1 inventor, Gunpei Yokoi, long before their fame for Game Boys and the like. The Light Telephone was expensive, perhaps before it’s time and a bit of a novelty, but nevertheless really cool and if anyone has an original still in the box I would happily make you an offer!

The Light Telephone was capable of transmitting speech 10-30m in free space using simple incandescent torch bulbs. While the practicalities of such a device are limited, as a novelty toy there would have been a huge wow factor in 1971.

Zenith Flash-Matic

Rewinding back to 1955 and Eugene Polley’s remote control. The Zenith Flash-Matic TV was able to change channels up and down or mute and unmute the volume. These four functions were controlled by pointing the remote control’s light beam at one of the four photo-sensors located at each corner of the TV. It seems that the functions were occasionally triggered by sunlight hitting a sensor, but a TV remote control in the mid-50s was a great invention. In terms of the evolution it took a while for TV remotes to become widespread, but by the 1980’s ultrasonic devices were used. I recall our own could occasionally be triggered by opening a fizzy juice can. My brother also told me I could mute the TV by standing on the cat’s tail but I never replicated this despite repeated experiments! Remote control technology then reverted to optical technology, this time invisible light in the form of the infra-red remote controls we are all familiar with today.

Photophone transmitterTo my mind the first real VLC invention was the Photophone created by Alexander Graham Bell in 1880. Patented just 4 years after the telephone, the Photophone was used to make the very first cordless phone call. This was long before radio was used for this purpose. I posted a blog on this back in February 2011 if you want a little more detail.

It will be interesting to see how VLC will be reported in the history books of the future. I am convinced that solid state lighting will be seen as the enabler for mass market adoption of VLC which improves our lives. Bell stated that the Photophone was his greatest invention – bigger even than the telephone. History may yet prove him correct. History will hopefully prove me right too!

Posted in history, Uncategorized | Tagged , , , , , , , , | Leave a comment

WTF is… Li-Fi?

WTF is Li-Fi? asks Reg Hardware, the hardware site of The Register, in an article this week.

PureVLC Li-FiThe article features the PureVLC Li-Fire YouTube video and also mentions the Fraunhofer Institute and Casio and is a worthwhile read. I have noticed in such articles a tendency to explain how VLC works by suggesting that the lights “flicker”. While making for a simple explanation, it does raise the eyebrows of some readers who have even suggested that this will cause headaches. In practice the lights don’t flicker, but your TV does! Other comments have suggested other negative effects of VLC so I feel it is perhaps time to dispel some of the Li-Fi myths out there.

One of my next blog posts will be my top 10 Li-Fi myth buster. Watch this space!

Posted in opinion | Tagged , , , , , | Leave a comment

TED hits one million

TED Global, Ideas Worth SpreadingThe TED Global presentation on Visible Light Communication has now amassed over 1,000,000 views and generated significant worldwide interest in the technology.

Harald Haas, PureVLC CTO and Professor at the University of Edinburgh, performed the first public demonstration of visible light communications live at TED Global in July last year.  He showed an angle poise lamp fitted with an LED bulb transmitting high definition video displayed onto a massive screen. When he interrupted the light with his hand the video froze and it was then restored when he removed his hand. The official TED Global site has seen 1 million views and if you count the unofficial sources such as various YouTube versions the number is considerably more.

I think TED created a much greater awareness about this technology and has helped stimulate debate and thinking about the use cases. This can only be a good thing.

Posted in events, news | Tagged , , , , , , | Leave a comment

LightMessage by PureVLC

Today PureVLC claimed a World first. A text message sent directly from an LED lamp and received on an unmodified smart phone.

LightMessage is patented and has been under wraps for a while but was revealed at EIE’12. The demonstration video shows the LightMessage app being run on an Android device, but any smart phone could have been used. I think 2 myths have been expelled in developing this app; 1) the camera can be used as a VLC sensor and the light does not need to flicker, and 2) VLC does not need to be line of sight since LightMessage can use reflected light. The raw data rate is currently about 2.5kbps and there is considerable scope for improvements.

PureVLC developed LightMessage as a demonstration that current smart phones already posses the components required for VLC, albeit at relatively low data rates. The bill of materials does not really need to increase to implement VLC. With some adaptation or optimisation of the existing components high speed Li-Fi becomes possible. LightMessage even in its current form would be useful as an indoor positioning, or location based messaging technology.

Image: Gordon Jack,

Sir Jackie Stewart (3x F1 World Champion) was the keynote speaker at EIE’12 and he tried out LightMessage for himself.

Posted in applications | Tagged , , , , , , , , | Leave a comment

Latest VLC Market Report

Electronics CA, based in Canada, has just published what we believe to be only the second market report to cover Visible Light Communications. “Optical Wireless Systems – Visible Light Communications and Free Space Optics: Technologies and Markets” covers both VLC and FSO as the title suggests.

I have not seen the report as yet and so I cannot comment on the contents themselves but the table of contents are available and I can confirm that there are 104 pages and the headline price for a pdf single user copy is 3,900 USD.

I hope to be able to review this report in the near future. I know that the discount offered for the GBI Research report via the LinkedIn professional group, Visible Light Communications, proved very popular so I will see if we can negotiate a member’s benefit again. Watch this space!

Posted in news | Tagged , , , , , , , , | 2 Comments

LED wallpaper is here!

LED WallpaperWe have been hearing for some time about how OLED technology will be giving us walls of light.  Having seen the size (not to mention efficiency and cost) of current OLEDs I think we must accept that the OLED Light Wall from B&Q or Home Depot is some way off. However, rolls of wallpaper populated with LEDs were on display at Light + Building and I was impressed. LED wallpaperThe LED wallpapers was demonstrated on a large wall cycling through a sequence of lighting effects all around a cube motif pattern. I liked the way that the circuit board layout was used as part of the wallpaper pattern. The papers was designed by Ingo Maurer and produced by German company Architects Paper.

Another lighting display that blew me away at Light + Building was the iGuzzini stand with a massive LED floor produced by Italian company Italvideo. LED floorIt was beautifully animated with moving imagery.  The Perspex tables and chairs on the floor just added to the effect. There is no reason why this technology could not be incorporated in tomorrows click laminate floors.

So where does all this fit with VLC.  Well if walls and floors as well as ceilings, are all lit by LEDs then I think it all fits quite nicely thank you.

Posted in events | Tagged , , , | 1 Comment

Light + Building

This week I attended Light + Building in Frankfurt.

KNXThis show covers all aspects of lighting for buildings and even urban lighting.  My impression was that Light + Building was not so much about lighting technology innovation, but more about lighting design and creativity.  There was a significant area covering smart buildings and home automation with the KNX standard very much to the fore.

The previous lighting show I attended, Lux Live inLondon, was pretty much 100% LED, however this show had a mix of designs incorporating halogens, fluorescent and obviously LED. I estimate that LEDs probably accounted for 70% of all lighting on display, and OLEDs were also emerging strongly with many companies showing exciting designs.

Light + Building imageThe companies exhibiting were mainly European. Osram and Philips had a large presence but it was the smaller companies that were clearly leading the way in terms of creative design. I saw superb LED desk lamp designs, wonderful light sculptures, huge chandelier designs and much more.

A growing trend is for the LEDs to become an integral part of the light design. I saw many LED chips soldered directly into the lamp with the circuit boards an integrated part of the design.  Given the life of an LED lamp this seems a very sensible move and frees the lighting designer from the constraint of the bulb imposed form factors.  There was a section of the exhibition showcasing young lighting designers with some very refreshing designs. Many were using the halogens and even carefully sculpted fluorescent tubes but to my eye those using LEDs had the more interesting designs. This has allowed them to distribute the small point light sources wherever they desired within their designs and freed them from the constraints of older bulb designs.

One thing I took from the show is that lighting design is a vibrant industry.  I think that technology, and in particular LED technology, is creating a renaissance in lighting design never seen before.  With LEDs, architectural lighting can be achieved on any scale and a reasonable cost.  I think smart buildings are not just about efficiency, with good design we also create buildings we are comfortable to be in.

Two great design concepts grabbed my imagination at the show.  I will talk about these in my next blog.

Posted in events | Tagged , , , , , , | Leave a comment

World’s Largest Chandelier

Reflective Flow by Beau McClellanThe World’s largest chandelier “Reflective Flow” is also the largest LED light sculpture in the World with 55,000 LEDs and thousands of optical crystal elements. The LED fixture weighs in at 20 tonnes (think 2 buses or 13 cars) and scoops World records on various fronts (heaviest, biggest, longest …).

I am proud to say that this LED interactive sculpture, modelled on a river, was created by a fellow Scotsman and lighting design genius Beau McClellan.  I am less proud to admit that it was installed in an office complex in Doha,Qatar back in 2010 and I first learned of this today!

Beau McClellan, Scottish lighting designerBeau McClellan produces some stunning LED sculptures, fixtures, chandeliers (who knows the correct term) but the liberation of the LED is clear in his designs which have been widely commissioned in the Middle East.

I just love the idea of Beau’s future designs being able to provide stunning illumination combined with amazing information content via Visible Light Communications.  The Internet of Things, but big and beautiful things.

Posted in history | Tagged , , , , , , , , , | 1 Comment

The fight for more spectrum

As the spectrum crisis gets more serious, the shouts for more spectrum are getting louder.  This new infographic from Mobile Future sums this up nicely.  Fortuntunately the Li-Fi community is not suffering a spectrum crisis, quite the opposite. The question is, can we fully capitalise on the radio spectrum pain?

Mobile Data Infographic

Posted in opinion | Tagged , , , , , , | Leave a comment