Patent ID: 8350998

Claim:
A retardation substrate comprising a substrate and a solidified liquid crystal layer facing its main surface, the solidified liquid crystal layer including first to third regions arranged parallel with the main surface, wherein a degree of depolarization calculated by the equation below is less than 5×10 −4 for each of the first to third regions and a difference between the maximum and minimum values of the degrees of depolarization obtained for the first to third regions is less than 2.0×10 −4 when supposing that: under a first illumination condition in which a pair of polarizing plates face each other such that their transmission axes are parallel with each other and one of the polarizing plates is illuminated with a white light in a normal direction, the other polarizing plate emits a transmitted light in the normal direction at a luminance L 1 ; under a second illumination condition which is the same as the first illumination condition except that said pair of polarizing plates face each other such that their transmission axes are orthogonal to each other, said other polarizing plate emits a transmitted light in the normal direction at a luminance L 2 ; a contrast ratio CR PL is a ratio L 1 /L 2 of the luminance L 1 with respect to the luminance L 2 ; under a third illumination condition which is the same as the first illumination condition except that the solidified liquid crystal layer is interposed between the pair of the polarizing plates, said other polarizing plate emits a transmitted light at a luminance L 3 in the normal direction; under a fourth illumination condition which is the same as the third illumination condition except that said pair of polarizing plates face each other such that their transmission axes are orthogonal to each other, said other polarizing plate emits a transmitted light at a luminance L 4 in the normal direction; and a contrast ratio CR RE is a maximum value of a ratio L 3 /L 4 of the luminance L 3 with respect to the luminance L 4 D = 1 - ( CR PL + 1 ) ( CR PL - 1 ) × ( CR RE - 1 ) ( CR RE + 1 ) .