An optical system (10) is disclosed comprising a light mixing rod (20) having an elongate body extending between a light entry window (22) and an opposing light exit window (24), a plurality of solid state lighting elements (30, 30′, 30″) arranged to couple their respective luminous outputs into the light mixing rod (20) through said light entry window (22), said respective luminous outputs including luminous outputs having different spectral compositions, respectively, and a lenslet plate (40) having an acceptance angle (ψ,ψ′) and comprising a first surface (41) comprising a first array of lenslets (42) and a second surface (43) opposing the first surface (41) comprising a second array of lenslets (44), each lenslet of the first array (42) being aligned with a corresponding lenslet of the second array (44), wherein the light mixing rod (20) has an aspect ratio such that some light rays (35) produced by the solid state lighting elements (30, 30′, 30″) are directly incident on said first surface (41), said directly incident light rays (35) having a maximum angle of incidence (Φ) on said first surface (41) not exceeding said acceptance angle. Also disclosed is a lighting device comprising such an optical system (10).