Abstract: The present invention relates to an optical arrangement (1), comprising an optical chamber (2) comprising a light exit window, wherein the chamber is defined by a bottom (21) and at least one surrounding wall (22, 23, 24, 25), and wherein a surface (4a) of the bottom (21) of the chamber (2) is reflective. At least one light source (6) is arranged at the bottom (21) of the chamber (2) and adapted to emit light towards the light exit window. The light exit window of the chamber comprises a luminescent member (10). The optical arrangement (1) further comprises a diffractive member (12) arranged between the light source (6) and the light exit window, such that light emitted from the light source towards the light exit window layer is adapted to pass through the diffractive member.