Visible Light Communication – Transmit data wirelessly using beams of light

Visible light communication (VLC) is a data communications variant which uses visible light between 400 and 800 THz (780–375 nm). VLC is a subset of optical wireless communications technologies.
The technology uses fluorescent lamps (ordinary lamps, not special communications devices) to transmit signals at 10 kbit/s, or LEDs for up to 500 Mbit/s. Low rate[vague] data transmissions at 1 and 2 kilometres (0.6 and 1.2 mi) were demonstrated. RONJA achieves full Ethernet speed (10 Mbit/s) over the same distance thanks to larger optics and more powerful LEDs.

RONJA (Reasonable Optical Near Joint Access) is a free-space optical communication system originating in the Czech Republic, developed by Karel Kulhavý of Twibright Labs. It transmits data wirelessly using beams of light. Ronja can be used to create a 10 Mbit/s full duplex Ethernet point-to-point link. It has been estimated that 1000 to 2000 links have been built worldwide

Visible Light Communication

Imagine a flash light which you might use to send a morse code signal. When operated manually this is sending data using the light signal, but because it is flashing off and on it cannot be considered to be a useful illumination source, so it is not really VLC by our definition. Now imagine that the flash light is switched on and off extremely quickly via a computer, then we cannot see the data and the flash light appears to emitting a constant light, so now we have illumination and communication and this does fits our definition of VLC. Of course we would need a receiver capable of receiving the information but that is not too difficult to achieve.

Visible Light Communication

In literal terms any form of information that can be sent using a light signal that is visible to humans could be considered to be VLC, but by our definition we should be able to see the light, but cannot “see” the data. So although there seems to be no universally agreed definition of VLC is, we can at least agree what we mean by VLC.

The opportunity to send data usefully in this manner has largely arisen because of the widespread use of LED light bulbs. LEDs are semiconductor devices similar to silicon chips. Consequently we can switch these bulbs at very high speeds that were not possible with older light bulb technologies such as fluorescent and incandescent lamps. The rapid adoption of LED light bulbs has created a massive opportunity for VLC. The problem of congestion of the radio spectrum utilised by Wi-Fi and cellular radio systems is also helping to create the market for VLC.

In literal terms any form of information that can be sent using a light signal that is visible to humans could be considered to be VLC, but by our definition we should be able to see the light, but cannot “see” the data. So although there seems to be no universally agreed definition of VLC is, we can at least agree what we mean by VLC.

The opportunity to send data usefully in this manner has largely arisen because of the widespread use of LED light bulbs. LEDs are semiconductor devices similar to silicon chips. Consequently we can switch these bulbs at very high speeds that were not possible with older light bulb technologies such as fluorescent and incandescent lamps. The rapid adoption of LED light bulbs has created a massive opportunity for VLC. The problem of congestion of the radio spectrum utilised by Wi-Fi and cellular radio systems is also helping to create the market for VLC.
Specially designed electronic devices generally containing a photodiode receive signals from light sources,[1] although in some cases a cell phone camera or a digital camera will be sufficient.[3] The image sensor used in these devices is in fact an array of photodiodes (pixels) and in some applications its use may be preferred over a single photodiode. Such a sensor may provide either multi-channel communication (down to 1 pixel = 1 channel) or a spatial awareness of multiple light sources.[1]

Now, researchers at Dartmouth have found a way for light-based messages to travel in poorly illuminated environments. A study entitled “The DarkLight Rises: Visible Light Communication in the Dark” demonstrates how light can transmit data by utilizing low luminance LEDs. This works by encoding the information on very short, practically undetectable light pulses through the use of low-cost LEDs and photodiodes, which can convert light into a current.

The DarkLight technology disproves the hypothesis that visible light communication needs, well, visible light beams in order to function. One previously impossible application of DarkLight is to send data over phones. In this situation, one could transmit information to another mobile device in the area by using their phone’s flashlight. No light beam would actually be shone, however. Since visible light quickly deteriorates over distances, information sent over in this manor would receive an extra level of security.

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