DISPLAY WITH A DIELECTRIC STACK FILTER

摘要

A display has a modulator, preferably a liquid-crystal cell, adapted to modulate activating UV light (23, 25) input from the rear of the cell on to phosphor-type output elements (7) at the viewer side of the cell, and a pre-collimating device (11) such as a prismatic sheet for partially collimating the input light before it reaches the cell, in order to improve the contrast of the liquid-crystal modulator. In the invention a further collimator is included in the form of a dielectric stack filter (9) between the cell (1) and the output elements (7). This filter is tuned to block the essentially monochromatic input light (25a) emerging from the cell at angles greater than a predetermined angle to the normal to the cell, and also acts to block the passage of light at visible wavelengths. This ensures a good light throughput while eliminating the most harmful (i.e. contrast-degrading) off-axis rays.