A backlight module for illuminating a display or keypad is described. The backlight module may be provided in an electronic device along with a light source. In one embodiment, the backlight module comprises: a light diffuser; a light guide located directly below the light diffuser; a prism structure located directly below the light guide, the prism structure having a plurality of prisms extending towards the light guide, wherein an air gap is defined between the prism structure and the light guide; and a reflector located directly below the prism structure.