Illumination – Light source or light source support and luminescent material
Reexamination Certificate
1999-03-17
2001-04-03
O'Shea, Sandra (Department: 2875)
Illumination
Light source or light source support and luminescent material
C362S027000
Reexamination Certificate
active
06210012
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a backlight system for sequential illumination in at least two wavelength ranges, comprising materials luminescing in said wavelength ranges.
The invention also relates to a display device comprising such a backlight system.
Display devices of this type are used in, for example, televisions, monitors but also in, for example, projection devices.
Such a backlight system for an LCD is described in Research Disclosure January 1991, page 74 and is based on field emission. By using such a backlight system, in which red, green and blue phosphors are activated alternately, color filters in the LCD may be dispensed with.
A drawback of the backlight system shown are the high voltages (>1000 V) which are not compatible at all with those used in LCDs (up to 10 to 20 V). The phosphor patterns are also provided in a strip-shaped pattern, which leads to a non-uniform illumination.
SUMMARY OF THE INVENTION
It is an object of the present invention, inter alia, to obviate said drawbacks completely or partly.
To this end, the backlight system comprises at least one radiation source which is suitable for emitting sufficient short-wave radiation along a path to excite the luminescent materials, a waveguide and at least one optical shutter between the radiation source and the luminescent materials or between the waveguide and the luminescent materials.
As will be shown, for example, a gas discharge tube is used for the radiation source, which can operate at a much lower voltage (up to approximately 12 V) than is necessary for field emission.
Due to the presence of the waveguide, a uniform illumination is realized.
For example, a liquid crystal switch (LC cell) is used as an optical shutter. For an efficient use of the short-wave radiation, a reflective polarizer effective in the short-wave radiation range is arranged between the radiation source and the waveguide or between the waveguide and the luminescent materials.
A first embodiment of a backlight system according to the invention is characterized in that the luminescent material comprises a layer having areas luminescing in different wavelength ranges, and in that the backlight system comprises means for causing the optical shutters to sequentially pass short-wave radiation for each wavelength range. The layer is present on, for example, the end face of a plate-shaped waveguide and comprises a layer with juxtaposed luminescent areas.
A preferred embodiment of a backlight system according to the invention is therefore characterized in that the backlight system comprises at least two layers of a material luminescing in different wavelength ranges. In this case, the (for example, red, green or blue) light is coupled into the entire surface of the end face (or more faces) of a plate-shaped waveguide. Since the areas are not juxtaposed in this case, the entire surface of the end face can be utilized for coupling in the light. In a variant, the short-wave radiation is coupled in while the luminescent material is present at the area of an exit face. In another variant, the short-wave radiation source is present on the side of the plate-shaped waveguide opposite the exit face. In a further variant, the entrance face is enlarged by providing the plate with a (part of an) edge which is bent or situated at an angle.
The efficiency of the backlight system is even further enhanced by providing a short-wave pass filter between the optical shutter and the luminescent materials, or a long-wave pass filter on the side of the luminescent materials remote from the optical shutter.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.
REFERENCES:
patent: 4678285 (1987-07-01), Ohta
patent: 5146355 (1992-09-01), Prince
patent: 5808709 (1998-09-01), Davis
patent: 5856814 (1999-01-01), Yagyu
patent: 2 096 160 (1982-10-01), None
patent: 9725650 (1997-07-01), None
Research Disclosure Jan. 1991, Cathodoluminescent Backlight for Liquid Crystal Displays, p. 74.
O'Shea Sandra
Sawhney Hargobind S.
U.S. Philips Corporation
Waxler Aaron
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