Multicolor liquid crystal display with a dead front
First Claim
1. A multicolor liquid crystal display device having an output panel comprising:
- a liquid crystal cell including two transparent, insulating substrates arranged in parallel and each with a confronting surface bearing at least one transparent electrode, a layer of nematic liquid crystal material having liquid crystal molecules parallel to the substrates, said layer being contained between the insulating substrates with said liquid crystal molecules being gradually twisted between the substrates, the cell being capable of transmitting light therethrough in the vicinity of the electrodes upon the application of an electric field across the layer when a potential difference of appropriate magnitude is applied between the electrodes;
a light source having a relatively uniform spectral content for directing light towards one of the insulating surfaces;
means for applying a potential difference between said electrodes and producing an electric field across said cell, when an electric field exists across the cell, said liquid crystal molecules align themselves substantially parallel with the direction of the electric field;
a high extinction ratio polarizer being located on each insulating substrate surface opposite the ones with the electrodes for polarizing the light received from the light source, the polarizers having polarizing axes which are parallel or orthogonal to the direction of the liquid crystal molecules adjacent the insulating surface nearer to the light source, said polarizers having an extinction ratio which enables the attainment of a contrast ratio of greater than 100 from the liquid crystal cell during passage of the main vector component of polarized light;
a relatively small amount of dichroic dye being admixed with the liquid crystal material to form a guest-host mixture therewith, molecules of the dichroic dye being the guest molecules and being of sufficient in quantity for absorbing and thus preventing the buildup and subsequent passage of an orthogonal vector component of polarized light created by imperfect rotation of the polarized light by the orientation of the twisted nematic liquid crystal molecules when no electric field is present; and
a luminance balanced color mask located between the light source and the liquid crystal cell, the mask containing a plurality of color patches with the rest of the mask being a gray surround, each color patch being luminance balanced with each other and the gray surround in order that each different patch and the gray surround have substantially equal luminance transmission, so that the output panel appears as a uniformly dark, dead-front output panel to an observer, when a potential difference is not applied to the cell electrodes.
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Abstract
A multicolor display which comprises a high contrast liquid crystal device, light source and a luminance balanced color mask. The liquid crystal device is the transmissive, twisted nematic type having high extinction ratio polarizers on the input and output sides and functions as a light shutter for the display. The liquid crystal material has a dichroic dye admixed therein to prevent buildup of the contrast limiting orthogonal mode electric vector of polarized light. The color mask contains different colored patches with gray surround about them, and each colored patch is luminance balanced in order that each different colored data presented are of substantially equal brightness. during the off-state there is no light bleed through so that the display presents a uniformly dark state or dead front.
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Citations
19 Claims
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1. A multicolor liquid crystal display device having an output panel comprising:
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a liquid crystal cell including two transparent, insulating substrates arranged in parallel and each with a confronting surface bearing at least one transparent electrode, a layer of nematic liquid crystal material having liquid crystal molecules parallel to the substrates, said layer being contained between the insulating substrates with said liquid crystal molecules being gradually twisted between the substrates, the cell being capable of transmitting light therethrough in the vicinity of the electrodes upon the application of an electric field across the layer when a potential difference of appropriate magnitude is applied between the electrodes; a light source having a relatively uniform spectral content for directing light towards one of the insulating surfaces; means for applying a potential difference between said electrodes and producing an electric field across said cell, when an electric field exists across the cell, said liquid crystal molecules align themselves substantially parallel with the direction of the electric field; a high extinction ratio polarizer being located on each insulating substrate surface opposite the ones with the electrodes for polarizing the light received from the light source, the polarizers having polarizing axes which are parallel or orthogonal to the direction of the liquid crystal molecules adjacent the insulating surface nearer to the light source, said polarizers having an extinction ratio which enables the attainment of a contrast ratio of greater than 100 from the liquid crystal cell during passage of the main vector component of polarized light; a relatively small amount of dichroic dye being admixed with the liquid crystal material to form a guest-host mixture therewith, molecules of the dichroic dye being the guest molecules and being of sufficient in quantity for absorbing and thus preventing the buildup and subsequent passage of an orthogonal vector component of polarized light created by imperfect rotation of the polarized light by the orientation of the twisted nematic liquid crystal molecules when no electric field is present; and a luminance balanced color mask located between the light source and the liquid crystal cell, the mask containing a plurality of color patches with the rest of the mask being a gray surround, each color patch being luminance balanced with each other and the gray surround in order that each different patch and the gray surround have substantially equal luminance transmission, so that the output panel appears as a uniformly dark, dead-front output panel to an observer, when a potential difference is not applied to the cell electrodes. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 13)
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12. A method of providing a multicolor liquid crystal display device selectively capable of being in the on-state or off-state condition and having a uniformly dark, dead-front output panel when in the off-state condition, said method comprising the steps of:
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providing a liquid crystal cell having a pair of parallel, transparent glass substrates with transparent electrodes on their confronting surfaces, and a twisted nematic liquid crystal material contained between the substrates; attaching high extinction ratio polarizers on each of the substrate surfaces opposite the confronting ones, the polarizing axes of both polarizers being either parallel or orthogonal with the direction of molecules of the liquid crystal material adjacent the substrate surface selected as the input substrate which is to receive light from a light source, said polarizers having an extinction ratio which enables the attainment of a contrast ratio of greater than 100 from the liquid crystal cell during passage of the main vector component of polarized light; admixing a relatively small amount of dichroic dye with the liquid crystal material to form a guest-host mixture of liquid crystal and dye molecules, the amount of dichroic dye being sufficient to absorb an orthogonal vector component of polarized light created by the imperfect rotation of the polarized light by the orientation of the twisted nematic liquid crystal molecules when no electric field is present; directing light from a source having a relatively uniform spectral content toward said polarizer on the input substrate so that the light received by the input substrate is polarized; applying an alternating current voltage across the electrodes to change the orientation of the molecules of mixture and enable the passage of light when the passage of light is desired; and inserting a luminance balanced multicolor mask between said light source and said polarizer on the input substrate of the liquid crystal cell, so that the liquid crystal cell with the dichroic dye and two high extinction ratio polarizers in combination with the luminance balanced color mask cause said output panel to appear uniformly dark to an observer when said multicolor liquid crystal display device is in the off-state condition. - View Dependent Claims (14, 15, 16, 17, 18)
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19. The method of claim 19, wherein the opaque dots and transparent holes are photographically produced in said color patches by the use of uniform dot screens having 150 dots/inch;
- and wherein the transparent holes comprise no more than 10 to 20 percent of the total color patch area and the opaque dots comprise no more than 30 to 50 percent of the total color patch area.
Specification