An illumination apparatus is manufactured by selectively removing passive optical nanostructures from a monolithic array of light-emitting elements while preserving their relative spatial position. The nanostructures are selected such that, in at least one direction, for at least one pair of the selectively removed passive optical nanostructures, for each respective pair there is at least one nanostructure that is not selected that was positioned in the monolithic array between the pair of selectively removed passive optical nanostructures in the at least one direction, forming a non-monolithic array of passive optical nanostructures with the selectively removed passive optical nanostructures while preserving their relative spatial position, and aligning each of the passive optical nanostructures of the non-monolithic array with a respective light-emitting element of the non-monolithic array of light-emitting elements.