Recent versions of iOS have been found to contain references to Li-Fi, an experimental high-speed wireless networking protocol that uses pulses of light to transmit data and is being marketed as a long-term replacement for Wi-Fi.
Beginning with iOS 9.1, the operating system's library cache file makes mention of "LiFiCapability" alongside other hardware and software capability declarations. The change was spotted by Twitter user Chase Fromm and independently confirmed by AppleInsider.
Li-Fi works in a way not entirely unlike a traditional infrared remote control. Data is transmitted by rapidly modulating a light source, and received with a light sensor before being reassembled into an electronic signal.
Unlike your television remote, Li-Fi uses visible light and the modulation happens in a manner imperceptible to the human eye: that means the same bulb that lights your hallway can act as a data access point. It's also much faster, with theoretical throughput capacity of up to 224 gigabits per second.
Li-Fi is still in the experimental phase, but a number of companies are working to commercialize the technology. At least one firm, India-based Velmenni, has already begun real-world testing.
In addition to the software references, Apple is known to be working on hardware implementations for light-based wireless data transfer, or optical wireless communication.
A patent application filed in 2013 and assigned to Apple describes a method of "optical modulation using an image sensor." The sensor in question could be switched between image capture and data capture modes, allowing for light capabilities without adding additional hardware.
Apple envisions this particular system being used for indoor location, but the general principle is the same as more high-bandwidth applications.
Thanks to Sebastian for the tip.