A coupling structure (110, 710, 760) for joining (i) a light guide plate (101, 701) and (ii) a lighting element comprising a mount and a light emitting diode, the coupling structure (110, 760) comprising: - a first reflective region; - a second reflective region, parallel to and spaced apart from the first reflective region; - a phosphor region (130, 730, 770)joining the first reflective region and the second reflective region, wherein the phosphor region (130, 730, 770) is positioned between the first reflective region and the second reflective region such that a section of each of first reflective region and the second reflective region extends beyond edges of the phosphor region; - a first open-ended cavity defined by an inner side of the first reflective region, an inner side of the second reflective region, and a first side of the phosphor region (130, 730, 770), and configured to be closed by the lighting element, wherein (i) the first reflective region is on a first surface of the lighting element, (ii) the second reflective region is on a second surface of the lighting element, and (iii) the light emitting diode faces the first side of the phosphor region (130, 730, 770) and is separated from it by a space; - a second open-ended cavity located on an opposite side of the phosphor region from the first open-ended cavity, and defined by the inner side of the first reflective region, the inner side of the second reflective region, and a second side of the phosphor region and configured to be closed by a light in-coupling edge (115, 705) of the light guide plate (101, 701), wherein (i) the first reflective region is on a first surface of the light guide plate and (ii) the second reflective region is on a second surface of the light guide plate; characterised in that the first reflective region, the second reflective region, and the phosphor region (130, 730, 770) are integrally formed so that the coupling structure is a single piece. - a first reflective region; - a second reflective region, parallel to and spaced apart from the first reflective region; - a phosphor region (130, 730, 770)joining the first reflective region and the second reflective region, wherein the phosphor region (130, 730, 770) is positioned between the first reflective region and the second reflective region such that a section of each of first reflective region and the second reflective region extends beyond edges of the phosphor region; - a first open-ended cavity defined by an inner side of the first reflective region, an inner side of the second reflective region, and a first side of the phosphor region (130, 730, 770), and configured to be closed by the lighting element, wherein (i) the first reflective region is on a first surface of the lighting element, (ii) the second reflective region is on a second surface of the lighting element, and (iii) the light emitting diode faces the first side of the phosphor region (130, 730, 770) and is separated from it by a space; - a second open-ended cavity located on an opposite side of the phosphor region from the first open-ended cavity, and defined by the inner side of the first reflective region, the inner side of the second reflective region, and a second side of the phosphor region and configured to be closed by a light in-coupling edge (115, 705) of the light guide plate (101, 701), wherein (i) the first reflective region is on a first surface of the light guide plate and (ii) the second reflective region is on a second surface of the light guide plate;