Apparatus for illuminating an object comprising a first polarising beamsplitter (2) which produces a first linearly polarised component (3) and an orthogonally polarised component (5). The two components (3, 5) are focussed onto a liquid crystal device (7) having an array of electronically controllable pixel elements each of which is bistable in that it is electronically controllable to occupy either a first state in which the plane of polarisation of the light incident on the pixel is rotated by up to 90° or a second state in which the plane of polarisation is not changed. The two light beams from the device (7) are incident on a second polarising beamsplitter (13) which recombines the incident beams into two composite beams one of which represents light rotated by the “on” pixels of the device (7), and this combined beam is refocussed onto the object.