The system being tested in the French supermarket offers a glimpse of what light bulbs might soon be able to do. There, the light fixtures’ imperceptible blinking is transmitting a very basic stream of data, but LED light bulbs are capable of sending a lot more than just a simple pattern. They can deliver an entire internet connection.

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Five years ago, Harald Haas, a professor of electronics engineering at the University of Edinburgh, was pacing on a small stage. He was giving a TED talk as high-definition video of blooming flowers looped behind him. He approached a desk lamp he’d placed on a gray tabletop, and stuck his hand underneath the light. The video stopped. When he removed his hand, it started up again.

The light, he explained, was transmitting video data to a receiver beneath the lamp, at a speed comparable to Wi-Fi. In a lab setting, light bulbs can beam data at a speed of more than 10 gigabits per second—that’s really, really fast.

After his 2011 talk, Haas started a company called pureLiFi, which announced this year that it will install light-based internet in the Paris headquarters of the French real-estate development company Sogeprom.

“We’re basically at the stage that Wi-Fi was 15 years ago,” Haas told me. For now, connecting to a Li-Fi network requires a USB dongle—a throwback to the age of Wi-Fi cards that stick out of the side of your laptop.

Data carried over visible light doesn’t need a direct sightline between a light bulb and a device in order to work. Just like ambient light in a room still illuminates the floor beneath a table, data-laden light beams can reflect off of walls and objects on their way to a device. Haas envisions that the laptops of the future will have multiple light sensors—maybe one at every corner of the screen—so that they can continue receiving uninterrupted even if one or more of the receivers is covered. (References to LiFi have been found buried in the code of recent versions of iOS, but the technology doesn’t exist in any smartphone or computer yet.)

Unlike a Wi-Fi signal, visible light can’t, of course, travel through walls or floors—but that can actually be a useful feature, Haas says. In sensitive environments like a government building, administrators can confine a network only to the rooms where people need to access it, avoiding the threat of a hacker intruding into a wireless network that’s bled across the hall or out onto the street. Visible light can also be used to transmit data where Wi-Fi networks can interfere with delicate electronics, like in hospitals.

One of the draws of light-delivered internet is that the lighting has already been installed in just about every office and residential building. The hard part is connecting the light bulbs to the net: If each one has to be wired individually, the ease of using light bulbs is canceled out; if each fixture still has to use Wi-Fi to communicate with a central router, then LiFi will never be faster than Wi-Fi itself.