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An artistic rendering of the new light-driven wireless network in action.  (Source: Boston University)
Could the networks of the future run on light

Solid-state lighting is one of the hottest topics in the tech industry, and with good reason.  The Department of Energy is sponsoring a $20M USD "L Prize" for advances in LED lighting, a type of light which uses solid-state components (diodes).  The research is a big deal as lighting currently consumes 22 percent of the electricity in the U.S.  If the DOE accomplishes its goals of reducing lighting energy use by 50 percent, it would save billions of dollars and reduce environmental impact.

New research from Boston University's College of Engineering, funded by a National Science Foundation grant, indicates that LEDs may be not only the integral lighting component of the future, but may also form the backbone of future wireless networks.

BU Engineering Professor Thomas Little describes the new research, stating, "Imagine if your computer, iPhone, TV, radio and thermostat could all communicate with you when you walked in a room just by flipping the wall light switch and without the usual cluster of wires.  This could be done with an LED-based communications network that also provides light - all over existing power lines with low power consumption, high reliability and no electromagnetic interference. Ultimately, the system is expected to be applicable from existing illumination devices, like swapping light bulbs for LEDs."

The primary goal of the research is to develop LEDs that do exactly that -- transmit information wirelessly via controlled blinking. 

Little continues, "This is a unique opportunity to create a transcendent technology that not only enables energy efficient lighting, but also creates the next generation of secure wireless communications.  As we switch from incandescent and compact florescent lighting to LEDs in the coming years, we can simultaneously build a faster and more secure communications infrastructure at a modest cost along with new and unexpected applications."

Professor Little and his colleagues imagine LED lighting in the room being hooked up to computer circuitry, which uses existing lighting to implement a wireless network which provides data to computers, personal digital assistants, television and radio reception, telephone connections and thermostat temperature control.  Prototypes of the new network design, according to Professor Little, should start at around 1 to 10 Mbps.  Better yet, bandwidth would be greater than in existing radio frequency (RF)-driven networks.

In the new network, each LED light bulb would act as an access point.  Another perk of the new design is beefed up security.  Unlike RF networks, the new signal would not pass through walls or other opaque objects.  This would help prevent snooping and connection theft.  The new system would also use much less power than RF, as solid state lighting is energetically cheaper to the strong radio signals needed for wireless internet. 

The flickering which drove the network would be performed so fast the human eye could not see it.  The network would ideally be able to operate outdoors as well as indoors.  The first test deployment may be outdoors, with a likely candidate being car interiors.  Professor Little continues, "This technology has many implications for automobile safety.  Brake lights already use LEDs, so it's not a stretch to outfit an automobile with a sensor that detects the brake lights of the car in front of it and either alerts an inattentive driver or actively slows the car."

While the technology seems very promising, one quandary is how to make the communication bidirectional.  Professor Little and his team have not elaborate on this tricky point yet in the initial press.  In order to send data requests, you would need a means of receiving light from devices such as cell phones or laptops, however, you ideally would want to avoid having to have a bright blinking transmitter on your device walls covered in sensors. 

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By elessar1 on 10/7/2008 1:39:43 PM , Rating: 1
i dont want any insect to get near to my luminous data!!!

think of those anoying mosquitoes getting in the way of your pron while downloading!!! eeek!!!

And....the fact taht we dont see it flickering doesnt mean it wont give you a headache...


RE: flys!!
By ChronoReverse on 10/7/2008 1:42:47 PM , Rating: 2
I hope you're not using an LCD then. The flickering of that backlight should be much lower than what I suspect this system would have to use to provide the kind of bandwidth they're thinking of.

And if you're using a CRT...

RE: flys!!
By Spivonious on 10/7/2008 2:19:33 PM , Rating: 1
My CRT refreshes at 120Hz. So does my work LCD's backlight. I'm good.

RE: flys!!
By ChronoReverse on 10/7/2008 2:30:22 PM , Rating: 3
That's the point, these LEDs would have to flash at rates FAR higher than 120Hz to get 1Mbps. There's simply no way to see flicker.

RE: flys!!
By tastyratz on 10/7/2008 3:57:53 PM , Rating: 2
so we speculate and assume here...

It's also possible that this uses several wavelengths to compensate for low hz. US military testing shows the human eye can detect over 200hz in some situations. If it was able to instantly flicker on and off we very well may be capable of seeing it... or it might flicker just enough to give us a headache. I can personally see a florescent light blink.

Does anyone know about what frequency we are currently up to for led light? What is the current limitation for a detectable on/off flicker via led?

Also, does it diminish as it increases in brightness/power? If it was to be used for solid state lighting of a room it will need to be measurably bright.

RE: flys!!
By mindless1 on 10/7/2008 5:00:32 PM , Rating: 2
Even a garden variety lighting LED can flicker faster than the human eye can detect, I'm not sure of the ceiling but it's well above 200Hz.

As for what frequency we are currently up to, I don't know if anyone had been trying to reach ultra-high frequency yet for room lighting (except probably those this article is about and similar researchers outside of the LED industry), generally the frequency used is one of economy in designing the power supply above Hz, in the KHz range.

Yes it diminishes as brightness/power per die increases but for practical purposes the increase in frequency could still result in the same average current, the pulse current would simply be a treshold above what the average current would've been. That is already what often happens if you drive an LED with a switching supply for efficiency instead of a resistive current limiting supply, but to achieve the lower threshold for digital communication it seems they'd need to minimize capacitance between supply output and LED.

RE: flys!!
By MrPoletski on 10/8/2008 1:19:15 PM , Rating: 2
Megahertz dude. They are the same family as transistors.

RE: flys!!
By mindless1 on 10/9/2008 1:06:14 AM , Rating: 2
Same family isn't quite the same, remember that unlike transistors, visible white light starts out blue, there is a rise and fall time involved below that of transistors. We're not just talking about attainable frequency, we're talking about attaining it within the tolerances needed for a digital threshold value of 0/1 consistently.

RE: flys!!
By MrPoletski on 10/8/2008 1:22:31 PM , Rating: 2
Does anyone know about what frequency we are currently up to for led light? What is the current limitation for a detectable on/off flicker via led?

Dude, what do you think runs gigabit fibre ethernet?

RE: flys!!
By BarkHumbug on 10/9/2008 3:24:44 AM , Rating: 2
+1! (already posted...)

RE: flys!!
By mindless1 on 10/7/2008 4:38:13 PM , Rating: 2
It is not likely your work LED's backlight refreshes at 120Hz. Perhaps the data, screen image refreshes at that but an LCD backlight's flicker rate depends on the driver board, typically operating in the KHz or higher range.

RE: flys!!
By Spivonious on 10/8/2008 9:38:27 AM , Rating: 1
Pretty sure it's a flourescent backlight, which Google told me normally "flickers" at 120Hz. It's a Dell 1708FP if someone knows the actual flicker rate of it.

The screen data refreshes at 60Hz.

RE: flys!!
By mindless1 on 10/9/2008 1:01:09 AM , Rating: 2
Google is telling you about standard flourescent area lighting running off 60Hz AC mains supplies plus ballast, not switching driver boards running off stepped-up, boost switching PSU in laptops.

Data refresh rate has nothing to do with CCFL refresh rate. Normally the CCFL driver board uses KHz range frequency because this allows for a much smaller transformer, lower cost, and as we'd mentioned already, going too low in CCFL drive rate would cause noticable flicker.

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