An arrangement (20) for coupling light into a plate-like light guide (25) having two surfaces (23, 24) on opposite sides of the light guide comprises an in-coupling diffraction grating (21) for diffracting an external light beam (26) incident on said in-coupling diffraction grating into the light guide in a direction enabling the in-coupled light beam to propagate within the light guide via total internal reflections at the light guide surfaces (23, 24). According to the present invention, the arrangement further comprises a deflection member (22) arranged to deflect the beam (27) initially diffracted by the in-coupling diffraction grating (21), before it hits the in-coupling diffraction grating again, out of the path determined by the in-coupling diffraction grating in order to reduce out-coupling of the already in-coupled light through the in-coupling diffraction grating.