British Develop Photoluminescent Liquid Crystal Display
Fig. 1. Structure of a photoluminescent display system. The contrast, brightness and color are essentially the same from all viewing angles, since the emission occurs at the front surface of the display module. That is, the display has essentially Lamb -- Semiconductor International, 6/1/1998
A group in the
Department of Engineering of the University of Cambridge (Cambridge, U.K.) has
pioneered work on a photoluminescent liquid crystal display technology. It
employs a narrow-band, spatially directed, near UV source of radiation that is
modulated by a liquid crystal cell. The modulated radiation excites a phosphor
on the front of the display that emits visible light by photoluminescence, as
shown in the figure. The individual pixels of this color phosphor are aligned
with the elements of the liquid crystal display. A light-emitting image, similar
to that from a cathode ray tube, is thus produced.
The contrast, brightness and color are essentially the same from all viewing angles, since the emission occurs at the front surface of the display module. That is, the display has essentially Lambertian emission characteristics. Such displays do not require the inefficient color filters that are used in conventional color liquid crystal displays, as the colored light is directly produced in the phosphor materials on the front face of the display.
This photoluminescent liquid crystal display design reduces the constraints on the liquid crystal cell, as it removes the viewing angle dependency that is a major disadvantage of conventional liquid crystal systems. The benefits include improved contrast, a reduced sensitivity to temperature change, less critical operating margins and more addressable lines that provide greater multiplexing display capability. It also makes larger displays possible.
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| Fig. 1. Structure of a photoluminescent display system. |
Screen Technology said the most important advantages offered by its photoluminescent liquid crystal display technology are the following:
- A visual performance similar to that from a cathode ray tube, but from a flat panel display.
- Existing manufacturing lines can be employed to produce photoluminescent matrix display panels at low cost.
- Color photoluminescent displays can be operated at lower power levels than conventional color liquid crystal displays.
- A much improved performance can be obtained over that from standard passive matrix liquid crystal displays.
According to Barbara Needham of Screen Technology Ltd., the power of the photoluminescent liquid crystal display design lies in it not being a fundamentally new display technology, but a basic re-engineering of back-lit LCD module architecture. The company claims it is a step function improvement in performance for passive matrix LCDs and can be implemented on standard passive matrix LCD manufacturing facilities with very low manufacturing start-up costs. She said it has the potential for changing the direction of the flat panel displays industry.
