WO1993008558A1

WO1993008558A1 - Color display apparatus

Info

Publication number: WO1993008558A1
Application number: PCT/US1991/007766
Authority: WO
Inventors: Stephen Weinreich
Original assignee: Stephen Weinreich
Priority date: 1991-10-24
Filing date: 1991-10-24
Publication date: 1993-04-29

Abstract

A digitized color display provided by placing a fluorescent bulb (200) behind the cells of the digitizing screen (41) with each cell containing at least one liquid crystal element (201, 202, 203) and at least one color filter element and then selectively controlling the liquid crystals (36) to produce the digitized color display.

Description

COLOR DISPLAY APPARATUS

CROSS REFERENCE TO RELATED APPLICATIONS This application is related to my previously issued U.S. Patent No. 4,757,626, entitled DISPLAY APPARATUS, and my previously issued U.S. Patent No. 4,621,443 entitled DIGITAL SCREEN DISPLAY APPARATUS. The entire contents of each of these issued patent are hereby incorporated in total by reference into this application. This application corresponds to U.S. Application Serial No. 07/219,457, filed July 15, 1988, the disclosure of which is incorporated herein in its entirety by reference thereto.

Background of the Invention 1. Field of Invention

The invention relates to digitizing screen apparatus which may employ a mechanism for displaying color graphic images by mixing colors within cells having at least one liquid crystal element and at least one filter element. 2. Description of Related Art

In U.S. Patent No. 3,963,326, a data display panel is disclosed. Each cell of the display has a shutter type of mechanism which turns each cell on or off thus allowing each cell to either transmit light or to blank it out thereby producing an image. No provision is made for the mixing of colors within each cell nor to homogenize the color to produce a uniform color from each cell nor to effect an intermediate level of illumination. Each cell simply functions as an on or off mechanism. Other U.S. Patents of possible interest include U.S. Patents 1,832,894; 2,663,960; 2,884,883; 3,335,457; 3,237,331; 3,314,179; 3,328,475; 3,568,346; 3,686,781; 3,783,539, 3,987,558 and 4,333,707.

In addition to the foregoing, other efforts have been made to produce digital-like displays. For example, digitized screens can be found in places such as Times Square, New York

City. According to one embodiment, a field of light bulbs is

SUBSTITUTESHEET controlled by an array of photocells, each actuating a single bulb on the display screen through an amplifier circuit. Movies of shadow graphs and in some cases real shadows, are cast upon the screen from a control room behind the sign. The images projected on the photocells appear in lights on the display screen over the street.

A useful discussion of the design of light concentrators may be found in the book entitled THE OPTICS OF NONIMAGING CONCENTRATORS: Light and Solar Energy by .T. Welford and R. Winston published in 1978 by Academic Press.

SUMMARY OF THE INVENTION A color forming apparatus includes a digitizing screen providing a filtering means which includes a plurality of cells. An illuminating means is placed behind the digitizing screen. Each cell within the digitizing screen is fitted with at least one liquid crystal element and at least one color filter element wherein the liquid crystal elements are modulatable to produce a color display. In the preferred embodiment of the invention the illuminating means emits light concentrated in spectral peaks corresponding to the colors of the color filter elements. For example, a fluorescent light having its energy concentrated in narrow bands of the red, blue and green areas of the color spectrum can be used with red, green and blue filters. These and other features of the invention will be more further understood by reference to the following drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view of a liquid crystal controlled^' screen employing cone concentrator elements. Figure 2 is a detailed cross-sectional view of a liquid crystal controlled screen section from the embodiment illustrated in Figure 1.

Figure 3 is an enlarged view of a liquid crystal controlled screen section. Figure 4 is a detailed cross-sectional view of the preferred embodiment of the apparatus as illustrated in Figure 3. DETAILED DESCRIPTION OF THE INVENTION During the course of this description, like numbers will be employed to identify like elements according to the different views which illustrate the invention. A light concentrator embodiment 32 is illustrated in detail in the Figures. The application of light concentrators can be moderately broad and may include lenses. In Figure 1, a plurality of light concentrator elements 34 are located behind a sheet 38, including a plurality of liquid crystal elements 36 and associated circuitry. A digitizing screen 41, comprising a back diffuser 40, a grid 42 and a front diffuser 44 are located on the opposite sides of the liquid crystal sheet 38 from the light concentrators 34. Light presented to each concentrator 34 is concentrated at LCD element 36. LCD element 36 can be electronically modulated to control the passage of the light through the digitizing screen 41. Therefore, a digitized television-like image can be produced on front diffuser 44 by modulating the light concentrated by concentrator 34 with LCD elements 36. The use of light concentrators 34 substantially increases the efficiency of the image producing system as a whole. The concentrators 34 collect light from behind the grid and prevent light from being lost. It is possible to capture much of the light that is available on the back side of the grid through the use of concentrators. Moreover, by concentrating the light through modulatable elements such as liquid crystals, it is possible to achieve a relatively efficient image forming system wherein only a small portion of the screen area need be modulatable elements. The light concentrator 34 embodiment and the use of liquid crystals 36 described thus far is essentially the same as set forth in my U.S. Patent No. 4,757,626, the entire substance of which is incorporated herein by reference. Further details of the light concentrator and the homogenizing digital screen can be found in the aforementioned U.S. Patent No. 4,621,443, the disclosure of which is also incorporated herein by reference.

SUBSTITUTE SHEET According to the preferred embodiment of the present invention the illumination means is chosen in accordance with the colors of the color filter segments which are used in conjunction with the LCD elements 36. More specifically, the light source used as the illumination means is selected to emit light which is concentrated in spectral peaks corresponding to the colors of the color filter segments.

Figure 2 illustrates the use of fluorescent light 200 as the spectral peak selected light-source to be applied to light concentrators 34. While it is possible to use any type of spectral peak light source, fluorescent lighting such as the Thornton Jr. type that is disclosed in U.S. Patent Nos. 4,176,294 and 4,176,299 is preferable. The disclosures of these patents are incorporated herein by reference thereto. This preferred type of fluorescent lighting is characterized by having spectral peaks concentrated in narrow bands of the visible spectrum and is suited to efficiently produce a color display with improved color rendition. While fluorescent light 200 is shown as singular, the preferred embodiment would include a plurality of lights proportional in number to the size of the array of cells in embodiment 32.

Whereas the Thornton, Jr. bulb was designed to illuminate objects so that they would look the same under artificial light as they would under natural light, in the present invention, the spectral peak light source is used as a light source to synthesize colors and form an image. The spectral peak light source allows the colors of the filter segments to match with those of the light source so that unnecessary wavelengths within the^' visible spectrum will not be generated and so that pure, saturated colors can be produced when the colors of the filter segments are mixed.

The use of a spectral peak light source, such as a Thornton, Jr. type bulb, in this context, provides an elegant solution to a problem caused by attempting to meet two competing criteria unrelated to whether an illuminated object looks natural. Colors are synthesized from primary colors. In order for the synthesized colors to be pure, the primary colors from which they are synthesized must themselves be pure, that is to say, they must each lie within a narrow bandwidth. If the bandwidth is broad, the synthesized colors will appear as pastel rather than saturated colors. However, if the bandwidth of the light source is narrow, less light will be available to light up the screen and the screen will be dimmer than is desirable. If the bandwidth is broadened to supply more light, the colors lose their purity. Using a conventional (broad band) light source to attempt to solve this problem necessarily required a compromise in which neither criterion is fully satisfied. However, using a spectral peak type bulb allows both criteria to be satisfied. Pure colors can be synthesized without any loss of brightness because only light of the same wavelengths as those of the filters is emitted and the energy emitted is concentrated in those wavelengths. Thus, the present invention provides a solution for reconciling the competing criteria of the purity of the colors and the brightness of the screen.

The use of the spectral peak light source, such as the Thornton, Jr. type bulb also provides an additional unexpected benefit. Since the emitted light is concentrated in narrow bands and, therefore, does not include wavelengths which must be filtered out, it is possible to use filters having relatively broader bandwidths than would be required using a light source which produces a broad range of wavelengths which would have to be filtered out. This is likely to lead to significant cost savings over narrow bandwidth filters.

Figures 3 and 4 illustrate an exploded view of the LCD element 36 according to this invention. The preferred embodiment of LCD element 36 comprises three LCD segments, 204, 205, and 206 for each cell. Placed before LCD segments, 204, 205, and 206 are color filter segments, 201, 202, and 203. Preferably each filter segment corresponds to one of the three spectral peaks produced by fluorescent light 200. Thus, for example, filter segment 201 could be a green filter, filter segment 202 could be red filter, and filter segment 203 could be a blue filter, each filter corresponding to a peak

SUBSTITUTE SHEET wavelength produced by fluorescent light 200. Alternatively, the color filter segments 201, 202 and 203 could be placed behind LCD segments 204, 205 and 206, adjacent to back diffuser 40. The functioning of the system would be the same. Naturally, fewer, e.g. two, or more, e.g. 4 or 5, color filter segments and associated liquid crystal elements can be used.

The use of small liquid crystal elements divided into a plurality of segments, preferably three, enables each element to control a display segment many times the area of the LCD element 36. By reducing the total area of liquid crystal for a given color display, the power requirement is similarly reduced. The small size of the LCD element area also provides ample space for switching elements, or even memory elements without interfering with the display image. Further, by mixing the color within each cell by homogenizing the color through the diffusers, the image quality is enhanced by having cells composed of not only primary colors. Although a color image could be created by making each cell produce only one primary color and grouping the cells in sets of three primary colors, that embodiment would require three times as many cells for similar information and would even then appear coarser.

Still further, when the filter LCD element combination of the invention is used in conjunction with the spectral peak emitting light source as previously described the additional advantages of color purity and screen brightness are obtained.

While the invention has been described with reference to the preferred embodiments thereof it will be appreciated by those of ordinary skill in the art that modifications can be made to the various embodiments and the parts thereof without departing from the spirit and scope of the invention as a whole.

Claims

What is claimed is: 1. A color forming apparatus comprising: filter means including a plurality of cells each including at least one color filter segment and at least one liquid crystal element; and illumination means comprising at least one light source which emits light concentrated in spectral peaks corresponding to the colors of said color filter segments; wherein each cell operates to selectively transmit light from said illumination means. 2. The color forming apparatus of claim 1, wherein said filter means comprises at least three color filter segments. 3. The color forming apparatus of claim l wherein said illumination means comprises at least one fluorescent bulb which emits light concentrated in spectral peaks of the visible spectrum corresponding to the colors of said color filter segments. 4. The color forming apparatus of claim 1 further comprising: image element expansion and homogenization means for expanding and mixing light from said cells and located adjacent said filter means. 5. The color forming apparatus of claim 1 wherein said filter means includes at least two color filter segments and at least two liquid crystal elements. 6. The color forming apparatus of claim 5 further comprising: image element expansion and homogenization means for expanding and mixing light from said cells and located adjacent said filter means. 7. The color forming apparatus of claim 5 further comprising: light concentrator means located between said illumination means and said filter means, wherein said light concentrator means concentrates light from said light source onto said color filter segments and said liquid crystal elements.

SUBSTITUTE SHEET 8. The color forming apparatus of claim 5 wherein said illuminator means comprises at least one light source which emits light concentrated in spectral peaks corresponding to the colors of each of said at least two color filter segments. 9. The color forming apparatus of claim 8 wherein said light source is a fluorescent bulb. 10. The color forming apparatus of claim 8 wherein said light source is a Thornton, Jr.-type light source. 11. The color forming apparatus of claim 1 further comprising: light concentrator means located between said illumination means and said filter means, wherein said light concentrator means concentrates light from said light source onto said color filter segments and said liquid crystal elements. 12. The color forming apparatus of claim 1 wherein said light source is a fluorescent bulb. 13. The color forming apparatus of claim 1 wherein said light source is a Thornton, Jr.-type light source. 14. A color-forming apparatus for use with an illumination means, said apparatus comprising: filter means including a plurality of cells each including at least two color filter segments wherein each of said color filter segments transmits light having a specific bandwidth; at least one image element homogenization means for mixing light from said cells and located adjacent said filter means; and, image element expansion means for expanding light from said cells and located adjacent said filter means, wherein said illuminationmeans illuminates selected color filter segments thereby causing said image element expansion means and said image element homogenization means to produce a pattern of several different colors and further wherein said pattern of several different colors is formed by mixing the light transmitted by said color filters. 15. The color forming apparatus of claim 14, wherein said filter means comprises three primary color filter segments. 16. The color forming apparatus of claim 14 wherein said illumination means comprises at least one light source which emits light concentrated in spectral peaks corresponding to the colors of said color filter segments. 17. The color forming apparatus of claim 16 wherein said light source is a fluorescent bulb. 18. The color forming apparatus of claim 16 wherein said light source is a Thornton, Jr.-type light source. 19. The color forming apparatus of claim 14 wherein said image element expansion means comprises: a rear diffuser means located adjacent said color filter segments; a front diffuser means; and, a grid means separating said front diffuser means and said rear diffuser means. 20. A display apparatus comprising: image producing means including a plurality of cells wherein each cell comprises at least two liquid crystal segments and at least two color filters for producing a plurality of graphic images and presenting elements of individual images selectively; illumination means comprising at least one light source for illuminating said image producing means; and, light concentrator means located between said illumination means and said image producing means, wherein said light concentrator means concentrates light from said illumination means down onto at least two of said liquid crystal segments and color filters. 21. The display apparatus of claim 20 wherein said illumination means comprises at least one fluorescent bulb which emits light concentrated in spectral peaks of the visible spectrum corresponding to the colors of said color filter segments. 22. The display apparatus of claim 20 wherein said light source emits light concentrated in spectral peaks corresponding to the colors of said color filters.

SUBSTITUTE SHEET 23. The display apparatus of claim 22 wherein said light source is a fluorescent bulb. 24. The display apparatus of claim 22 wherein said light source is a Thornton, Jr.-type light source. 25. The display apparatus of claim 20 wherein each of said cells comprises at least three liquid crystal segments and at least three color filters. 26. A color display apparatus for forming at least one image comprising: an array of liquid crystal elements, wherein each liquid crystal element comprises at least two liquid crystal segments; an array of color filter elements, wherein each color filter element comprises at least two color filters; illuminating means for illuminating selected color filter elements thereby producing a pattern of primary colors; homogenizing means for mixing said pattern of primary colors thereby producing a multiplicity of colors and reducing the apparent coarseness of said image. 27. The color display apparatus of claim 26 further comprising: one light concentrator means corresponding to each color filter element. 28. The color display apparatus of claim 26 further comprising: one image expansion means corresponding to each color filter element. 29. The color display apparatus of claim 26 wherein said illuminating means comprises at least one light source wherein said light source emits light concentrated in spectral peaks which correspond in wavelength to the wavelength of each of said color filter elements. 30. The color display apparatus of claim 29 wherein said light source is a fluorescent bulb. 31. The color display apparatus of claim 29 wherein said light source is a Thornton, Jr.-type light source. 32. A color forming apparatus comprising: filter means including a plurality of cells each including at least two color filter segments; image element expansion and homogenization means for expanding and mixing light from said cells and located adjacent to said filter means; and, an illumination means comprising at least one light source which emits light concentrated in spectral peaks of the visible spectrum corresponding to the colors of at least two of said color filter segments, wherein said illumination means illuminates selected color filter segments thereby causing said image element expansion and homogenization means to produce a pattern of several different colors.

STITUTESHEET