  For more than a century, artificial lighting has served mainly for
illumination. Only recently, we start to transform our lighting infrastructure
to provide new services such as indoor localization and network connectivity.
These innovative advancements rely on two key requirements: the ability to
modulate light sources (for data transmission) and the presence of
photodetectors on objects (for data reception). But not all lights can be
modulated and most objects do not have photodetectors. To overcome these
limitations, researchers are developing novel sensing and communication methods
that exploit passive light sources, such as the sun, and that leverage the
external surfaces of objects, such as fingers and car roofs, to create a new
generation of cyber-physical systems based on visible light. In this article we
propose a taxonomy to analyze these novel contributions. Our taxonomy allows us
to identify the overarching principles, challenges and opportunities of this
new rising area.
