An illumination module includes a longitudinal support member including a base portion and a pair of sidewalls extending from the base portion that together define a channel that extends in a longitudinal direction. A printed circuit board (PCB) on the base portion extends in the longitudinal direction within the channel. A plurality of light emitting diodes (LEDs) are on the PCB in a linear array. A reflective sheet is within and extends across the channel, and includes a plurality of holes that correspond with locations of the LEDs on the PCB, and the LEDs are positioned in the holes. An optical film extends across the channel above the reflective sheet and defines an optical cavity between the reflective sheet and the optical film. The optical film, the reflective sheet and the sidewalls of the support member recycle light in the optical cavity.