Looking for an item in a large department store or mall can be like searching for a needle in a haystack, but that could change thanks to a hybrid location-identification system that uses radio frequency transmitters and overhead LED lights, suggested by a team of researchers from Penn State and Hallym University in South Korea.

"LED lights are becoming the norm," said Mohsen Kavehrad, W. L. Weiss Chair Professor of Electrical Engineering and director of the Center for Information and Communications Technology Research at Penn State. "The same lights that brighten a room can also provide locational information."

To locate an item in a mall, the system would not need to transfer large amounts of data. Kavehrad and his team envision large stores or malls with overhead LED light fixtures, each assigned with a location code. At the entrance, a computer that is accessible via keyboard or even telephone would contain a database of all the items available. Shortly after a query, the location or locations of the desired item would appear.

"The human eye can't see beyond 15 on and offs of a light per second," said Kavehrad. "We can get kilobytes and megabytes of information in very rapid blinking of the LEDs," he told attendees at the SPIE Photonics West 2012 conference in San Francisco.

But LED-transmitted locational information alone will not work because light does not transmit through walls. Kavehrad, working with Zhou Zhou, graduate student in electrical engineering, Penn State, designed a hybrid LiFi system using a Zigbee multihop wireless network with the LEDs.

Even when merchandise is moved from room to room, the accurate location remains available because a different LED overhead light with a different location code signals the tag.

While ideal for shopping applications, this hybrid model is also useful in other situations. LED-transmitted information is useful in places like hospitals, where radio frequency signals can interfere with equipment.