transmitting data via light...

[Steve K]

hi gang,

I came across this article about how white LEDs can be used for indoor illumination, and how this presents an opportunity for broadcasting data by modulating the light:
http://www.planetanalog.com/showArticle.jhtml?articleID=225200192&cid=NL_planet

"With preparations well under way for a societal shift to solid-state lighting based on high-output LEDs, a proverbial light bulb has appeared above the heads of some forward-looking engineers. Their proposal: Why not switch the LEDs on and off so fast the eye cannot tell, in order to use them to transmit data too?"

While I enjoy an excuse to use excessive technology as much as the next engineer, I have to wonder if this is at all practical. Mostly, I wonder why wait until there is LED lighting? Seems like you could be using a handful of LEDs right now if you just want to transmit data. Also, is white light the best choice? Why not IR, since there are a ton of existing receiver circuits in the marketplace, and it allows you to reject most of the ambient light?

I'll admit that I have some bias in this subject. For a couple of years, I had the pleasure of being paid to tinker with IR lasers intended for a communications link between satellites. Lots of fun, but the solid state laser technology just wasn't up to the task at that time.

Any thoughts on the subject?

regards,
Steve K.

p.s. to the moderator: I wasn't sure what forum this subject belonged in, so feel free to move it to it's proper home.

 

[yellow]

the "white led" might be just mentionned, because they will be lighting bulbs in some years.

for transmitting data - which is already done, btw - other (more efficient) led are better
(but noone will want to use them as light source).


... see it as it is: some "idea" on future applications

 

[Steve K]

My general assumption is that this is just an excuse to create a press release and get the company's name in print. Using LEDs for general illumination is great, but the circuits used to do this are not well suited for high speed modulation. Better to have 99% of the LEDs driven by basic switched regulators, and 1% of the LEDs devoted to transmitting data with proper high speed drivers.

a second question: what datalink applications would be best suited to the use of light instead of RF? The only thing that comes to mind is if you want a fairly secure link. i.e. the transmitting and receiving beam are relatively tight.

Well, there's also the issue of EMC compliance. Transmitting light avoids the issues associated with complying with the FCC spectrum allocations (as far as I know).

Steve K.

 

[Walterk]

Not new, see www.modulatedlight.org.

The formulas for beam-intensity of lightrays is there also explained.
And the concept of pre-collimating with aspherics/fresnel.

 

[Steve K]

Not new, see www.modulatedlight.org.

The formulas for beam-intensity of lightrays is there also explained.
And the concept of pre-collimating with aspherics/fresnel.

that's a very interesting link! I was unfamiliar with most of the historical aspects of the subject... the idea of modulating a mercury lamp is remarkable when one is more accustomed to modulating a small laser.

The challenges or rational of the short range datalink mentioned in the original article are quite a bit different than that of a long range optical communication link discussed in the Modulated Light web page, though. It seems fairly feasible that a cafe might have an optical link available so the customers can access the web with their laptops. The hard part is figuring out what sort of advantage it might have over the standard wifi link. Less non-ionizing RF that could cause cancer, perhaps?

regards,
Steve K.

(I'll have to browse the Modulated Light site and see what they have for laser modulator circuits.... I'd still like to set up a small link to shoot audio around my apartment for fun. )

 

[LukeA]

Extreme resistance to jamming?

 

[Steve K]

Extreme resistance to jamming?

that was one reason to use it for satellite communications, as well as less chance of having the sidelobes intercepted. Overall, it does allow for a secure datalink relative to RF.

I don't imagine that this is a priority in a cafe, since it would require a very tight beam on the transceivers. Besides, you could just put a network cable at each table if security was more important than convenience.

For now, I'm willing to write this off as an excuse to get publicity or get the public excited about paying for LED lighting.

regards,
Steve K.

 

[alpg88]

light has been used in data transmission, for a long time.
but it is not leds, but lasers via fiber optic, my server rooms have fiber laser links for a decade now.
also when twin towers were still up, there was laser comm line between 2 towers, no fiber, just laser, in foggy weather you could see laser line between roofs of the towers.

these binoculars are capable to transmit voice and data via optical Chanel, in ir wavelength, they are used by army and navy.