An eye-mountable device can include a transparent material and a substrate at least partially embedded in the transparent material. The transparent material can have a concave surface and a convex surface, with the concave surface configured to removably mount the eye-mountable device on a corneal surface overlaying a pupil. A light source can be disposed on the substrate and configured to emit light through the concave surface and towards the corneal surface such that the emitted light is viewable through the pupil. The light source can be controlled by circuitry disposed on the substrate. The circuitry can be configured to modulate the light emitted by the light source to provide modulated light.