Abstract: A plant illumination device positioned above a plant tray to illuminate plants in the plant tray is disclosed. The device comprises a reflector and a light source, wherein the light source is arranged to emit light directed towards the reflector and the light is reflected by the reflector towards the plant tray. The reflector has a shape in a cross-sectional plane perpendicular to a length direction wherein the shape comprises a central portion and two peripheral portions adjacent to the central portion and the shape is symmetrical with respect to an axis of symmetry extending through the central portion along a height direction perpendicular to the length direction, The central portion comprises a protrusion at the axis of symmetry that protrudes downward along the height direction towards the light source. The peripheral portions of the reflector reflect the light received from the central portion towards the plant tray.