A plant growth lighting system includes a plant support and a light guide luminaire module, the plant support being configured to hold one or more plants. The light guide luminaire module includes at least one light-emitting element (LEE), a light guide arranged to receive light emitted by the at least one LEE at a first end of the light guide and guide the received light in a forward direction to a second end thereof, and an extractor arranged to receive light from the second end of the light guide and configured to output light. The light guide luminaire module is disposed relative to the plant support such that at least a portion of the light output by the extractor impinges on the plants in predetermined directions.