A light valve includes a light valve layer for forming an optical image as variations in its ability to scatter light, and two substrates between which the light valve layer is sandwiched and at least one of which is transparent. The light valve satisfies the following condition: ##EQU1## where t denotes a central thickness of the at least one of the substrates, n denotes a refractive index of the at least one of the substrates and d denotes a maximum diameter of an effective display area of the light valve layer. Alternatively, a transparent plate can be optically coupled to one of the substrates by a transparent body. In this case, the same condition is satisfied except that the thickness refers to a central thickness from a face of the transparent plate remote from the transparent body to the light valve layer.