Control of light, e.g. intensity, colour or phase (optical devices or arrangements using movable or deformable elements for controlling light independent of the light source G02B26/00; devices or arrangements, the optical operation of which is modified by changing the optical properties of the medium of the devices or arrangements for the control of light, circuit arrangements specially adapted therefor, control of light by electro-magnetic waves, electrons or other elementary particles G02F1/00)