News WiFi competitor uses visible light

Tho in hospitals sick people want to sleep, they sleep in the dark. In the daytime you don't need that much lighting. In the end you only have wifi in the evening?

 

Agree that it's probably gonna be useful only in office environments. In most offices the lights are on all day when people are working (usually a health and safety thing). So in an office/university environment this could work quite well. In a home setting it's not really very useful. Nice to see new things being tried though

 

One question, if the light bulbs are sending the data, how does your device communicate back? Do we need to have ultra bright LED's on everything?

 

Well, I'm just afraid it's a bad idea, simple as.

 

I can see so many draw-backs to this. And by the time we have LED lighting, if ever, there is no way that 10mb/s would even be remotely acceptable.

 

My router's wifi signal passes through walls. Just about every single consumer radio technology (at least in my apartment anyway) is not line of sight.

Hmm. Good question.

 

WiFi and other 2.4GHz signals (Bluetooth) also pass through your head...not to mention any RF technology that utilizes electromagnetic frequencies.

I would definitely advocate this new technology over the current RF standard. There are just one too many cancer patients out there who have faced the effects of constant electromagnetic interference. By using light waves as an alternative, this would not only reduce the effects of electromagnetic frequencies on the body, but it would also clear up the clutter of the current RF situation - all while providing better signal quality to current widespread RF technologies such as cell phones and short range wireless technologies.

 

I think you're a little confused about what "line of sight" means. Line of sight infers that there can be no scattering materials in the direct line from the transmitter to the receiver. As far as a 2.4GHz signal is concerned, there is NOTHING between the transmitter and the receiver because there's nothing in the way that's the correct size to scatter the signal, hence line of sight.

Longer wavelength signals can be bounced around obstacles (like long wavelength radio signals which can be bounced off the atmosphere and around the curvature of the Earth), hence they are not line of sight.

By your argument, visible light isn't line of sight either. Visible light propagates through a lot of material just to get to your eyes, the material just appears to be transparent.

 

You make a few good points.

Still, I just took a sheet of aluminum and placed it in the path between my router and client PC (in the next room) as close to the router as possible. After five minutes I disabled and reenabled to client's wireless card and waited some more. The signal quality was still excellent. Taking the masonry wall to be "transparent" there is now metal between the two wireless devices. I know you're not going to tell me that there is still "line of sight" communication between the two devices in this case.

 

Goty, is doing a little more than Playing a game at night with the lights off!

 

Actually, I am. Now, if you had taken some aluminum mesh with holes spaced about 5cm apart and you would have been be able to completely block the signal.

Electromagnetic radiation doesn't care about what kind material is in front of it, it only cares about its geometry. If you have a material with the proper structure to scatter a signal, then you can block it or reflect/refract it sufficiently to make it appear like you're dissipated the signal completely, otherwise the signal will continue to travel in a straight line.

 

I'm sure that this has been done before... Searching...

Here we go - back in 2004, a supermarket chain in the UK implemented a very similar system to control electronic shelf edge labels using a modulator in the starter for the florescent lights in the store... http://www.ilid.com.au/news/Retail Week UK 22 October 2004.pdf - the system is made by an australian company called ILID.

I would imagine that this new technology would be pretty much restricted to "broadcast" data - despite the pretty picture. Anyone remember "Internet over TV" - or even "Ceefax"?

Oh, and Goty... check your facts. I'm about 99% sure that a solid sheet of metal works just as well as a mesh - the trick with a Faraday cage is that you can use a mesh of the right size instead of a solid sheet. Have a look at the inside of your microwave if you don't believe me - the back and sides will be solid, and will block just as much of the radiation as the mesh on the door...
EM radiation *does* care what kind of material, it's blocked by anything that conducts and approximates an unbroken sheet... http://en.wikipedia.org/wiki/Electromagnetic_shielding

 

It only cares about what kind of material if the crystalline structure is of the correct geometry it will do the same thing as a Faraday cage. I'll check my facts if you'd like to check my degree in physics.

 

Radio waves can NOT pass through conductors.

Having a physics degree does not make one immune to mistakes and naivety. For example, I needed to brush up on radio wave scattering and interactions to confirm that you were right in what you were saying.

Do you at least agree that an electric field cannot pass through a conductor?

Try to check your degree at the door to ensure that you don't treat anyone's opinion with undue bias.

 

If you couldn't set up an electric field inside a conductor then you couldn't set up a current inside a conductor. This represents a small problem, so no, I don't agree that and electric field cannot pass through a connector.

If you'd like something better than my word, please reference "Introduction to Electrodynamics" by David J. Griffiths, specifically chapter 7. Also, you could google Ohm's Law, which is all I am referencing.

 

Since you have a copy of Griffith's, I'll refer you to chapter 2.5, regarding conductors, specifically page 97.

Now, to Ohm's Law. Sure, J = σE, and in the case where J is non-zero, there exists a non-zero E through a conductor. BUT we're talking about a metal sheet to which there is no emf applied. There is no emf and no otherwise induced currents, thus, the current density is 0. If J=0, E=0. So, in this case, the above statics principles apply, and you are wrong.

Take a radio - any radio, any frequency, and put it into a hollow metal cube. There will be zero transmission through that cube.

 

I'm NOT wrong. Make sure you read your own references. There IS an electric field set up in a conductor in that case, it's just opposite to the external electric field. Now, let's examine your J=0 claim. Yes, this is true for electroSTATICS, which is not the case here. The signal is modulated, so you will set up a small alternating current in the metal.

Let's talk about you metal cube example. How do you explain the fact that I can get a cell phone signal inside a corrugated aluminum building?

 

I will give everyone here one point, if the material has electrons in the correct energy level to absorb a 10^-5 eV photon, THEN the signal would be effectively blocked, which isn't out of the realm of possibility, but that's still not the point.