A Dartmouth project called ‘DarkLight’ is said to have demonstrated for the first time how visible light can be used to transmit data even when the light appears dark or off. DarkLight is claimed to provide a new communication primitive similar to infrared communication but it exploits the LED lights already installed rather than needing additional infrared emitters.

"With DarkLight, we can potentially enable light sensing so that it is always on, regardless of the light's illumination status," explained Xia Zhou, assistant professor and co-director of the Dartmouth Networking and Ubiquitous Systems Lab. "DarkLight shows new possibilities on what visible light can do. We believe there are a lot more interesting applications yet to come."

Wireless data is typically beamed through Wi-Fi or Bluetooth, yet the ‘visible light communication’ technology has emerged as a new option. There are limitations, however, due to it being easily blocked or not being able to sustain transmission when light is off.

With DarkLight, light-based communication is sustained even when LEDs emit low luminance, by encoding data into short, imperceptible light pulses, at which point the photodiodes and semiconductor devices convert the light into a current. The DarkLight prototype supports 1.6Kbit/s data rate at 1.8m distance.

According to the researchers, DarkLight could serve as a special mode that ceiling LED lights would switch to so that the light bulbs could still beam data to smart devices in the environment, or alternatively, data could be transmitted from one phone to another, by using the flashlight but without shining a light beam. The technology could potentially offer an alternative for secure communication, since visible light is directional and degrades fast over distance.