Patent ID: 7110054

Claim:
A liquid crystal switchable color filter for switching between a first, a second and a third color band, with a light path having a light input side and a light output side, the color filter comprising: a first switchable liquid crystal cell ( 81 ; 121 ) capable of at least two switching states; a first retarder layer ( 101 ; 135 ) which acts for the first color band as a quarter-wave plate; a first cholesteric filter ( 89 ; 127 ) having a selective reflection band for the first color band; a second cholesteric filter ( 91 ; 129 ) having a selective reflection band for the second color band; a second retarder layer ( 103 ; 137 ) which acts for the second color band as a quarter-wave plate; a second switchable liquid crystal cell ( 83 ; 123 ) capable of at least two switching states; a third retarder layer ( 105 ; 139 ) which acts for the second color band as a quarter-wave plate; a third cholesteric filter ( 93 ; 131 ) having a selective reflection band for the second color band; a fourth cholesteric filter ( 95 ; 133 ) having a selective reflection band for the third color band; a fourth retarder layer ( 107 ; 141 ) which acts for the third color band as a quarter-wave plate; a third switchable liquid crystal cell ( 85 ; 125 ) capable of at least two switching states; and a polarization blocking element ( 149 ; 109 , 97 ); characterized in that all cholesteric filters have the same handedness; a fifth retarder layer ( 111 ; 143 ) which acts as a half-wave plate is provided between the first cholesteric filter ( 89 ; 127 ) and the second cholesteric filter ( 91 ; 129 ) and a sixth retarder layer ( 113 ; 145 ) which acts as a half-wave plate is provided between the third cholesteric filter ( 93 ; 131 ) and the fourth cholesteric filter ( 95 ; 133 ); and for the blocking state of the respective color band the optic axis of the corresponding switchable liquid crystal cell is either substantially parallel or substantially perpendicular to the light polarization direction.