Electronic devices may be provided with light sensors. Light sensors may be proximity sensors or ambient light sensors. Proximity sensors may include a light-emitting component and a light-sensitive component. The electronic device may include an enclosure formed from housing structures and some or all of a display for the device. The enclosure may include openings such as openings formed from clusters of smaller openings. Each light sensor may receive light through one of the clusters of openings. The light sensor may receive the light directly through the openings or may receive light that passes through the openings and is guided to the light sensor by light guiding structures. The light guiding structures may include fiber optic structures or light-reflecting structures. Fiber optic structures may fill or partially fill the openings. Light reflecting structures may be machined cavities in an internal support structure.