The present disclosure concerns a lighting device (100) comprising a light source (1) and a light guide plate (2). The light guide plate (2) is disposed at a distance (D1) from the emitter surface (1a) with an air gap (3) therebetween. A side reflector (4) surrounds the emitter surface (1a) of the light source and bounds the gap (3) between the emitter surface (1a) and the light entry surface (2a). The side reflector (4) comprises a tapered reflection surface (4a) adjacent the emitter surface (1a) and facing the light entry surface (2a). The tapered reflection surface (4a) is disposed at a tapering angle (β) towards the light entry surface (2a). The tapering angle (β) is configured such that any light emitted by the emitter surface (1a) within the opening angle (Φ) of the light source (1) is not reflected by the reflection surface (4a) before being received for the first time by the light entry surface (2a).
