Patent
1984-11-15
1987-04-14
Corbin, John K.
350345, G02F 113
Patent
active
046573488
DESCRIPTION:
BRIEF SUMMARY
STATE OF THE ART
The invention relates to an arrangement to remove reflection from liquid crystal displays. A liquid crystal display is already known from German Patent Disclosure Document No. DE-OS 29 34 478, which for use in motor vehicles is partially freed from reflection. In the known arrangement, a cover disk having a polarizing filter is provided to remove reflection. By means of the oblique disposition of the cover disk, the light reaching the display from the outside is partially reflected, and the reflected component of the light is deflected downward. Another component of the light is absorbed by the polarizing filter. The remaining component, about 40%, however, reaches the liquid crystal cell, where it is partially reflected from the glass surface of the cell. When the incident light is at an unfavorable angle, this reflection makes the display unreadable.
From the above-cited publication, it is also known to glue an intermediate layer to the front of the liquid crystal cell and then to apply the polarizing filter in a curved shape to this layer. The cover disk is disposed spaced apart from and parallel to the liquid crystal cell. This arrangement has the disadvantage that it is difficult to master technically and that in large-scale displays it dictates a very high weight on the part of the display unit.
It has furthermore been proposed previously that the cover disk be provided with a circular polarizer, which cooperates with a polarizer disposed on the front of the liquid crystal cell and virtually completely prevents any reflection of the interfering light. This arrangement has the disadvantage, however, that even the light required for the display is for the most part absorbed at the circular polarizer of the cover disk as well. The brightness of the display is thereby impaired.
With the present arrangement, the goal is to prevent any reflection of the interfering light striking the display from the outside, without impairing the brightness of the display.
The arrangement according to the invention has the advantage that all the light striking the display from the front, after being reflected, is practically completely absorbed upon passing again through the circular polarizer, so that the display appears as a black surface, in which only the triggered display elements stand out visually, with clear contrast. The brightness of the display is no longer impaired by the circular polarizer on the cover disk.
It is particularly advantageous if a transflector is applied to the back of the liquid crystal display, behind the linear rear polarizer. In this case, the light required for the display can be installed behind the liquid crystal cell, and it passes through the liquid crystall cell only in the areas of the triggered display elements. Since the light striking the front of the liquid crystal cell in the vicinity of the triggered display elements is further reflected at the transflector, greater contract can be attained with this arrangement, because the light arriving from the front further increases the brightness of the display.
DRAWING
Two exemplary embodiments of the invention are shown in the drawing and described in detail below. Shown are:
FIG. 1, a liquid crystal display having a .lambda./4 retarding foil;
FIGS. 2a and 2b, the polarization of the light in the path of the rays, FIG. 2(a) when the liquid crystal display of FIG. 1 is not triggered and FIG. 2(b) when the display of FIG. 1 is triggered;
FIG. 3, a further exemplary embodiment of the invention; and
FIG. 4, the corresponding polarization of the light.
DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
In FIG. 1, a liquid crystal display for a vehicle is identified as 10. It contains an LCD cell 11, in which the liquid crystal substance is enclosed in the conventional manner between two glass plates 12, 13 vapor-deposited with electrodes and with which the various parameters and data of the motor vehicle can be displayed. A linear polarizer 14 and, behind it, a transflector 15 are applied to the glass plate 13 at the rear of th
REFERENCES:
patent: 2819459 (1954-05-01), Dodd
patent: 4025161 (1977-05-01), Laroche
patent: 4196973 (1980-04-01), Hochstrate
Corbin John K.
Lewis David
Robert & Bosch GmbH
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