Patent Grant
6888301
1. Field of the Invention
The present invention relates to a gas-discharge display apparatus that can display color images.
A plasma display panel (PDP) that is a typical display device having a screen emitting light by gas discharge is becoming widely available as a wide screen display for a television set after the color display thereof has been succeeded in commercialization. One of the challenges to improve the image quality of PDPs is to enhance the reproducible color range.
2. Description of the prior art
As a color display device, an AC type PDP having three-electrode surface discharging structure is commercialized. This type has a pair of main electrodes for sustaining, which are arranged in parallel for each line (row) of the matrix display, and an address electrode for each column. Division walls for preventing interruption of discharge between cells are provided in stripes. A surface discharging structure includes a substrate on which the pairs of main electrodes are arranged and an opposing substrate on which a fluorescent layer for color display is arranged, so that deterioration of a fluorescent layer due to an ion impact upon discharge can be reduced to obtain a longer life. The “reflection type” that has the fluorescent layer on the back substrate is superior to the “transparent type” that has the fluorescent layer on the front substrate concerning light emission efficiency.
In general, Penning gas containing neon (Ne) and a trace of xenon (Xe) (4-5%) is used as a discharging gas. When the discharge between main electrodes occurs, the discharging gas radiates ultraviolet rays, which excite the fluorescent material to emit light. Each pixel includes three cells for red (R), green (G) and blue (B) light colors, and the display color is decided by controlling the light intensity of the fluorescent material of each color. Conventionally, the composition of the fluorescent materials and the ratio of light intensities of three colors are selected so that the display color becomes white when each of the red, green and blue color light intensities is set to the maximum within the variable range.
Concerning the composition of the discharge gas, many studies have been done, a three-component gas (Ne, Xe and He) that is a mixture of the above-mentioned Penning gas and helium, a two-component gas containing helium and xenon (He and Xe), and another three-component gas containing helium, argon and xenon (He, Ar and Xe) are known well.
As explained above, since the fluorescent material emits light by gas discharge in a PDP, the mixing of the light color of the discharge gas into the light color of the fluorescent material cannot be avoided. This causes a problem of deterioration of the color reproducibility.
As shown in
Since the display capacity of blue color is degraded by the gas light emission, the display color of white pixels has a low color temperature compared with the color reproduced by the fluorescent materials of three colors. It is difficult to optimize the relative light intensities of red, green and blue colors in consideration of relative luminosity factor by combining materials because there are few kinds of fluorescent materials that satisfy the use condition at present. Therefore, the color temperature of the white color is low compared with a CRT even if the color of the gas light emission is not added. Furthermore, if the color of the gas light emission is added, the color temperature drops further. More specifically, the color temperature of the white color display is 5,000-6,000 K under the condition of the same amplitude signal applied for red, green and blue colors, while the color temperature of a CRT for a TV set in Japan is above 10,000 K. Therefore, it is necessary to raise the color temperature of the white color. However, since the color temperature has different optimal values depending on the use of the display, the region (the country) where the display is used or other factor, it is preferable that the color temperature can be selected easily within the range of about 6,000-12,000 K.
The color temperature can be raised by weakening the relative light intensities of green and red colors to blue color. The conventional method for adjusting the color temperature and disadvantages thereof are explained below.
(1) Adjustment by Fluorescent Material:
There is a method for adjusting the relative light intensities of red, green and blue colors by selecting the fluorescent materials, a forming shape thereof (i.e., the shape in which the fluorescent material is found) or the forming area thereof (i.e., the area on which the fluorescent material is formed). This method substantially reduces the brightness of the panel since the light intensities of green and red fluorescent materials are weakened compared with that of the blue fluorescent material that is usually lacking in intensity. Furthermore, there is a limited selection of materials as mentioned above. The adjustment by the forming shape has low reproducibility. If the cell size of blue color is increased to enlarge the forming area thereof, the margin of the voltage to be applied is narrowed and the display becomes unstable since the display characteristics depend on the cell size. In addition, manufacture of panels having different light intensities of the fluorescent material in accordance with the use and the region (country) of use may deteriorate the productivity.
(2) Adjustment by Signal:
The intensity balance between the video signals of red, green and blue colors is adjusted. In an example where the level of the video signal is represented by eight bits, i.e. 0-255, the maximum intensities of blue, green and red are represented by 255, 200 and 180, respectively so as to display white color of the maximum intensity. Thus, the color temperature of white color is raised by reducing the amplitude of the input signal of green and red colors compared with that of blue color. This method reduces the brightness of the panel in the same manner as the method (1) mentioned above, and degrades the capacity of gradation display of green and red colors compared with that of blue color that can be displayed in 256 steps of gradation.
Another problem about the color temperature is that contrast in a well-lighted room is low. The contrast in a well-lighted room (hereinafter, referred to as the bright-room contrast) means a ratio of intensity of light emitted by the fluorescent material and intensity of external light reflected by the PDP. In general, PDPs have a large reflection ratio of external light and a small value of the bright-room contrast. It is clear that the bright-room contrast will be improved by raising the light intensity of the panel and reducing the reflection ratio of external light, but it is not easy to satisfy the compatibility between them. For example, improvement of the filter for EMI measure is considered. Usually, the front surface of the PDP is provided with a filter having transmittance of 40-70% over the entire region of visible light wavelength for protecting interference of electromagnetic field. Though the light emitted inside the panel passes through the filter only once, the external light passes through the filter twice, once each in both directions. Therefore, the filter improves the bright-room contrast. If the filter having less transmittance is used, the bright-room contrast is further improved. However, since the improvement of the color temperature by the above-mentioned method will reduce the light intensity of the panel, the filter having low transmittance cannot be used for improving the bright-room contrast.
The object of the present invention is to reduce the influence of the light emission of the discharge gas for enlarging the color reproducible range, and to cause the color purity of red color to approach the ideal value. Another object of the present invention is to prevent reduction of the color temperature of white color. Still another object of the present invention is to raise the contrast without reducing the display brightness.
In the present invention, an optical filter having a size uniformly covering the entire screen is arranged in an appropriate position. The optical filter has characteristics of selectively absorbing visible light having a wavelength within the overlapped range of the light emission wavelength range of neon or helium and the light emission wavelength range of red fluorescent material.
Light within the wavelength range that can deteriorate the color reproducibility in the light emitted inside is selectively absorbed. Since the optical filter makes the proper color reproducibility, each of the fluorescent materials having different light colors can emit light with the maximum intensity in white color, for example. The placement of the optical filter covering the entire screen is much easier than providing a color filter for each light color of the fluorescent material.
According to a first aspect of the present invention, a gas-discharge display apparatus is provided which utilizes at least one of neon and helium gases to generate gas discharge for exciting three kinds of fluorescent materials having different light colors to emit light for displaying a color image. The apparatus includes an optical filter that is an element overlapping the entire screen, being disposed in front of gas discharge space for selectively absorbing light having wavelength equal to that of light emission of the gas. The optical filter has characteristics in which the transmittance T585 at the wavelength of 585 nanometers is smaller than the transmittance T450 at the wavelength of 450 nanometers and the transmittance T620 at the wavelength of 620 nanometers.
In a second aspect of the present invention, the optical filter has characteristics in which the wavelength of peak absorbency in the visible light wavelength range has a value within the range of 550 to 620 nanometers.
According to a third aspect of the present invention, the apparatus includes an optical filter that is an element overlapping the entire screen, being disposed in front of gas discharge space for selectively absorbing light having wavelength equal to that of light emission of the gas. The optical filter has characteristics in which first and second peak absorbencies exist in the visible light wavelength range. The wavelength of the first peak absorbency has a value within the range of 550 to 620 nanometers, and the wavelength of the second peak absorbency has a value within the range of 500 to 550 nanometers.
In a fourth aspect of the present invention, the optical filter has characteristics in which first and second peak absorbencies exist in the visible light wavelength range, the transmittance T585 at the wavelength of 585 nanometers is smaller than the transmittance T450 at the wavelength of 450 nanometers and the transmittance T620 at the wavelength of 620 nanometers, and the transmittance T528 at the wavelength of 525 nanometers is smaller than the transmittance T450.
In a fifth aspect of the present invention, the transmittance T585 is smaller than 0.7 times the transmittance T450.
In a sixth aspect of the present invention, the transmittance T585 is smaller than 0.7 times the transmittance T450 and is smaller than the transmittance T525.
According to a seventh aspect of the present invention, the apparatus includes an optical filter that is an element overlapping the entire screen, being disposed in front of gas discharge space for selectively absorbing light having wavelength equal to that of light emission of the gas. The optical filter has characteristics in which first and second peak absorbencies exist in the visible light wavelength range. The wavelength of the first peak absorbency has a value within the range of 580 to 600 nanometers. The wavelength of the second peak absorbency has a value within the range of 500 to 550 nanometers. The transmittance of the optical filter at the first peak absorbency is smaller cog than 0.5 times the average transmittance in the blue wavelength range. The average transmittance in the green wavelength range is larger than the transmittance at the first peak absorbency and is smaller than the average transmittance in the blue wavelength range.
In an eighth aspect of the present invention, the optical filter is made as a component separate from a display device having the gas discharge space, and is disposed in front of the display device.
In a ninth aspect of the present invention, the optical filter is made of a film having said characteristics.
In a tenth aspect of the present invention, the optical filter is in contact with the front surface of a transparent substrate making up the screen.
In an eleventh aspect of the present invention, the optical filter is made of an organic resin in which a substance absorbing light of a specific wavelength is dispersed.
In a twelfth aspect of the present invention, a non-glare layer is disposed in front of the optical filter.
Hereinafter, the present invention will be explained more in detail with reference to embodiments and drawings.
The plasma display apparatus 100 includes a PDP 1 that is a color display device, a driving unit 80 for lighting cells of the PDP 1 in accordance with display contents, an optical filter 60 having a spectrum transparent characteristic unique to the present invention, a front plate 92 for protecting the PDP 1, and an armor cover 90. The front plate 92 is made up by providing an electromagnetic field shield film and an infrared cutting filter onto a substrate that is optically transparent, and applying a surface treatment for non-glare finish. Glass, acrylic resin, polycarbonate, or other materials can be used for making the substrate.
The optical filter 60 has a dimension covering the entire screen that is a set of cells in the PDP 1, and is in intimate contact with the front surface of the PDP 1. The optical filter 60 can be formed by a process such as sticking (i.e., adhering) a laminated filter film, sticking a film in which a pigment or a colorant is dispersed, or laminating a multicoated interference film utilizing thin film technology on the front surface of the PDP 1 directly, or on the front plate 92 so as to overlay the surface of the PDP 1. Characteristics of the optical filter 60 and the front plate 92 are uniform over the entire screen.
In the plasma display apparatus 100b shown in
In the plasma display apparatus 100c shown in
In the above-explained three examples, the optical filter 60 is disposed between the PDP 1 and the front plate 92. However, the optical filter 60 can be disposed in front of the front plate 92. If the optical filter 60 is disposed in front of the light emitting portion of the PDP 1, the optical filter 60 can be formed inside the PDP 1.
The PDP 1 has first and second main electrodes X and Y making a pair arranged in parallel for generating a sustaining discharge. In each cell (display element), the main electrodes X, Y and an address electrode A as a third electrode cross to make a three-electrode surface discharge structure. The main electrodes X and Y extend in the row direction of the screen (the horizontal direction), and the second main electrode Y is used as a scan electrode for selecting-cells in a row upon addressing. The address electrode A extends in the column direction (the vertical direction), and is used as a data electrode for selecting cells in a column. The area of the substrate where the main electrodes and the address electrodes cross is the display screen.
In the PDP 1, a pair of main electrodes×and Y is arranged in each row on the inner surface of a glass substrate 11 that is a substrate of a front substrate structure 10. The row is a line of cells in the horizontal direction of the screen. Each of the main electrodes X and Y includes a transparent conductive film 41 and a metal film (a bus conductor) 42, and is covered with an insulating layer 17 having a thickness of approximately 30 microns made of low-melting glass. The surface of the insulating layer 17 is coated with a protection film 18 made of magnesia (MgO) having a thickness of several thousands angstroms. The address electrodes A are arranged on the inner surface of a glass substrate 21 that is a substrate of a rear substrate structure 20, and is covered with an insulating layer 24 having a thickness of approximately 10 microns. On the insulating layer 24, a division wall 29 having a shape like a band of height 150 microns viewed from the top is disposed at each space between the neighboring address electrodes. These division walls 29 divide the discharging space 30 in the row direction into plural subpixels (plural unit lighting regions), and define the gap size of the discharging space 30. In addition, red fluorescent material 28R, green fluorescent material 28G and blue fluorescent material 28B for color display are arranged coating the inner surface of the rear side including the upper portion of the address electrode A and the side surface of the division wall 29, so that the three colors are arranged in a periodic pattern. The fluorescent materials 28R, 28G and 28B are selected so that white color is reproduced when each of them emits light in the maximum intensity, and the forming shapes of them are the same. A preferred example of the fluorescent materials is shown in TABLE 1.
The discharging space 30 is filled with a discharging gas containing neon as a base and xenon (4-5%), and each color of the fluorescent materials 28R, 28G and 28B is partially exited by ultraviolet rays emitted by xenon upon discharging so as to emit light. In the plasma display EA apparatus 100 according to the present invention, a color balance of red, green and blue colors can be adjusted by designing the characteristics of the optical filter 60. Therefore, it is not required to select the fluorescent materials severely or to adjust the forming shape of the fluorescent material of each color for optimizing the color balance.
One element of display (a pixel) includes three subpixels having different light colors arranged in the row direction. The structure of each subpixel is the cell. Since the division walls 29 are arranged in a stripe pattern, the portion of the discharging space 30 corresponding to each column is continuous over all rows. An electrode gap between neighboring rows is set to a value substantially larger than the surface discharge gap (e.g., 80-140 microns), which can prevent discharge connection in the column direction, e.g. a value within a range of 400-500 microns. The address discharge is generated between the main electrode Y and the address electrode A of a cell to be lightened (in the case of write address format) or a cell to be not lightened (in the case of erase address format), so that a charged state is formed in each row where only the cells to be lightened have an appropriate quantity of wall discharge. Then, a sustaining voltage VS is applied between the main electrodes X and Y, so that the cells to be lightened can generate surface discharge.
Hereinafter, characteristics of the optical filter 60 will be explained. In the following explanation, Ne-Xe (4%) Penning gas is used as the discharging gas, which emits light having the spectrum shown in FIG. 13. However, any gas containing helium (He) or krypton (Kr) can be used as the discharging gas regardless of whether neon is contained or not. Helium and krypton emit light having a wavelength in the range of 580˜600 nanometers in the same way as neon, so the optical filter 60 of the present invention having wavelength selecting property is effective.
As shown in
The inventors have studied about the wavelength range to be eliminated, and obtained the following result. Namely, if the wavelength spectrum of the light emission spectrum in which the product of the light intensity and the relative luminosity factor becomes the maximum, i.e., 585 nanometers and the surrounding wavelength spectrum are eliminated, the purities of blue and green colors can be improved along with suppressing the deterioration of red color intensity, the latter result being achieved, at a minimum. In addition, the spectrum of red light emission approaches the monochrome light emission of 620 nanometers that Is the ideal in the NTSC standard.
As shown in
The improvement of the color temperature will be explained next. As explained above, if a filter that absorbs light having a wavelength around 590 nanometers is provided, the light intensity of red color decreases and the coordinate of the white color on the chromaticity diagram moves in the direction in which the x value decreases. In other words, the color temperature increases as the arrow in
When L0 is light intensity ratio at the front surface of the PDP 1, T is transmittance of the optical filter 60, S is illumination of external light at the front surface of the optical filter 60, and R is diffuse reflection ratio at the front surface of the PDP 1, a contrast ratio can be derived from the following equation.
CONTRAST RATIO=(LIGHT INTENSITY AFTER PASSING THE FILTER)/(REFLECTION INTENSITY OF EXTERNAL LIGHT)
=(L0×T+S/π×R×T2)/(S/π×R×T2)
=(L0+S/π×R×T)/(S/π×R×T)
=L0/(S/π×R×T+1
Supposing that R and S are constants, the larger L0 is or the smaller T is, the larger the contrast ratio becomes. The improvement of the color purity and the adjustment of the color temperature according to the present Invention do not reduce the light intensity L0, since the adjustment of fluorescent material, the cell structure, and the signal amplitude. In addition, the improvement of the color purity and the adjustment of the color temperature are achieved by reducing the transmittance T, so that the bright-room contrast is Improved.
As shown in
Such characteristics are obtained by forming a pigment layer that can absorb light of the wavelength 585 nanometers on a polyethylene film having thickness of 200 microns. As the pigment, 1-Ethyl-4-[(1-ethyl-4(1H)-quinolinylidene)methyl]quinolinium iodide whose peak absorbency (Absorption Maximum) is 590 nanometers (KABUSIKIGAISHA NIPPON KANKOUSHIKISO KENKYUUSHO Product Number NK-6), and 3-Ethyl-2-[3-(1-ethyl-4(1H)-quinolinylidene)-1-propenyl]benzoxazolium iodide whose peak absorbency is 594 nanometers (KABUSIKIGAISBA NIPPON KANKOUSHIKISO KENKYUUSHO Product Number NK-741) can be used. By adjusting the quantity of additives of these and other pigments, desired characteristics can be achieved. Though it is ideal for selectively absorbing light emitted by the discharging gas that the peak absorbency wavelength of the filter is identical to the gas light emission wavelength, some beneficial result can be obtained if the peak absorbency is in the range of approximately 550-620 nanometers. However, if the difference between the peak absorbency wavelength and the gas light emission wavelength is large, the absorbency wavelength range should be widened, resulting in increase of filter color. Therefore, the appropriate value of the peak absorbency wavelength is in the range of 580˜600 nanometers.
It is understood that the color reproducible range is enlarged in all ranges of red, green and blue colors, and the chromaticity coordinate of the white color is reduced both in X and Y (i.e., the color temperature is raised). The color temperature is raised from 5,000 K to 7,000 K. However, the chromaticity coordinate of white color is a little shifted upward from the blackbody radiation curve shown in the solid line to be greeny white color.
In the characteristics of
It is understood that the color reproducible range is enlarged in all ranges of red, green and blue colors, and the chromaticity coordinate of the white color is reduced both in X and Y (i.e., the color temperature is raised). The color temperature is raised from 5,000 K to 7,000 K. In addition, the chromaticity coordinate of white color is on the blackbody radiation curve, to be ideal coordinate. Furthermore, the bright-room contrast when the illumination of the PDP 1 at the front surface is 3001x is further improved from 20:1 to 40:1 by the arrangement of the optical filter 60 having the characteristics shown in FIG. 11.
The color temperature can be adjusted to any value within the range of 5,000-13,000 K by controlling the spectrum transparent characteristic of the optical filter 60. More specifically, if the absorption quantity around 590 nanometers in
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