A body-mountable device can include a transparent material and a substrate at least partially embedded in the transparent material. The transparent material can have a mounting surface and a surface opposite the mounting surface. A light source can be disposed on the substrate and configured to emit light through the surface opposite the mounting surface. The light source can be controlled by circuitry disposed on the substrate. The circuitry can be configured to receive modulation instructions and modulate the light emitted by the light source based on the modulation instructions.
