A spatial light modulator which may be used in 3D displays of stereoscopic type comprises substrates (19, 21) between which is disposed a liquid crystal layer (20). The layer comprises two sets of pixels (12, 13) for displaying left and right eye images. A pixellated polarisation adjustor (31, 32; 33, 34) is disposed between one of the substrates (21) and the liquid crystal layer (20) so as to minimise parallax effects. The pixels (12, 13) of the liquid crystal layer (20) are operated in the same mode i.e. all normally black or all normally white.