I. Introduction
Inside buildings, light bulbs are pervasive, have ample access to power, and are often ideally positioned for sensing applications. In this paper, we introduce a technique for transmitting data from solid-state luminaries, used for interior ambient lighting, to mobile devices like smartphones in a manner that is imperceptible to occupants. One compelling application of this approach is the ability to transform lighting sources into landmark beacons that can be used for indoor localization. If each luminaire could uniquely identify itself to nearby mobile devices, it would be possible to easily distinguish between rooms and areas within a room that are illuminated by different lights. Since visual light is completely blocked by solid obstructions like walls, this approach is well suited for semantic localization (position, rather than geographic), which remains a challenge for many existing ranging and localization systems.