An illumination apparatus comprises a first substrate; an optical structure; an array of light emitting elements disposed between the first substrate and the optical structure and an array of passive optical nanostructures disposed between the first substrate and the optical structure. Each of the passive optical nanostructures are disposed on a respective one of the light emitting elements and each passive optical nanostructure comprises an air gap. Each passive optical nanostructure is disposed between its respective light emitting element and the optical structure, wherein each passive optical nanostructure is configured to receive light emitted by its respective light emitting element, pass the received light, and output the pass light towards the optical structure.