An LED surface lighting device (100) comprises a plurality of LED light source modules (120) assembled together side-by-side. Each of the LED light source modules comprises a light guiding plate (122) and at least one LED (124). The light guiding plate comprises a light emitting surface (1222) and a plurality of lateral sides (1225, 1227) adjacent to the light emitting surface. At least one of the lateral sides defines a groove (123) for receiving the at least one LED. The groove keeps a predetermined distance (D) from the light emitting surface.