What if the light in the room could sense you waving your hand as you enter?And what if it responded by introducing minute light changes that instructed yoursmart coffee machine to switch on? Researchers at Dartmouth College havedeveloped a sensing system called LiSense that aims to make the light around us"smart." Not only does it use light to sense people’s movements, but it alsoallows them to control devices in their environment with simple gestures, using light to transmit information.

The goal is to use light to gesture and interact with objects in aroom, just like how you’d use a Wii or Kinect to interact with a TV. Xia Zhou, lead author of a paper on the research, wants to use smart light to turn every indoor spaceinto a cognitive space.

"Using purely visible light, we can not only stay connected to the internet,but also have the environment know and respond to what we do, how we behave,and how we feel," Zhou tells Gizmag. "Smart light can bring intelligence to allthe devices immersed in the light and allow them to act based on our behaviours."

To get LiSense to track a person’s movements only through light, theresearchers built a light-sensing testbed, with LED lights in the ceiling andlight sensors on the floor. The system uses the shadows cast by a personstanding on the testbed to reconstruct their 3D human skeletal posture in realtime. LiSense, the team states, essentially works on the same principle as ashadow puppet, where a hand held before a light blocks certain light rays andnot others.

"Consider a person standing under several lights," Zhou explains. "If we canrecover the shadow cast by each light in a different direction, we canaggregate the shadow information and collect the blockage information of alarge number of light rays. We then use the information to search for a 3Dskeleton posture that best matches the blockage information revealed by theseshadows."

Light sensors in the floor pick up the 2D shadow information Dartmouth College

To get their shadow-based human sensing to work, the researchers had tocrack two critical challenges. Since multiple ceiling lights lead to diminishedand complex shadow patterns on the floor, they came up with light beacons.These separate the light rays from different light sources torecover the shadow pattern cast by each light. The team also designed an algorithmcapable of taking the collected low resolution, 2D shadow maps from sensorsin the floor and reconstructing a person’s posture in 3D.

LiSense makes use of advances in visible light communication(VLC), where information is encoded as light intensity changes at highfrequency. Since most of the smart devices commonly available contain light sensors,they’re capable of receiving data by monitoring changes in light.

"The light changes are imperceptible to human eyes, yet the light sensors onour smart devices can sense the changes and decode data," Zhou tells us.

In tests, LiSense was able to reconstruct a 3D user skeleton within 16 milliseconds (ms) inreal time. It was also able to produce shadow maps of all the LEDs every 11.8 ms, which is comparable to capturing video frames(without using any cameras). The system was also found to be robust in variouslight settings with users of varying body sizes and shapes.

Going forward, the researchers plan to minimize the number of light sensors used andhave them seamlessly integrate into the environment. They also want to make thesystem sense more than low-level gestures, which could potentially open up allkinds of novel applications. For instance, smart light could monitor both ourhealth and behaviour, to catch diseases in their early stages.

"If the light around us continuously monitors how we move and gesture overtime, it might help detect early symptoms of diseases such asParkinson’s, which has movement-related symptoms," Zhou explains. "Right now patients have towear and carry bulky, cumbersome devices, or doctors have to videotape them. Lightprovides a new possibility—no on-body devices, no cameras."

A light-based sensing system also has numerous advantages over existingtechnologies, the team says. There’s no electromagnetic interference, it doesn’tpenetrate walls and it reuses existing lighting infrastructure. It’s alsosecure, has a bandwidth 10,000 times greater than the radio frequency spectrum,and isn’t limited to classifying a pre-defined set of gestures and activities.

The researchers plan to present LiSense at MobiCom,the 21st annual International Conference on Mobile Computing and Networking, inearly September. More information on the system is available in the following video.

Source: Dartmouth College