Backlight illuminated colour display device

Abstract: To achieve a backlighting device having excellent light utilization, there is provided an edge lighting-type backlight having a light guiding member (3), a high-refractive-index layer (4) formed thereon and having a higher refractive index than the light guiding member (3), and a scattering layer (5) formed on the high-refractive-index layer (4). Light from a light source (1) disposed facing the edge of the light guiding member (3) enters the high-refractive-index layer (4) through the light guiding member (3), and effectively scatters to produce high brightness, and furthermore, to achieve a color display device that eliminates color mixing in a transparent display device for decorative or various display uses, a construction is provided in which on one surface of a light guiding plate (3) there are formed a high-refractive-index layer (4) having a higher refractive index than the light guiding plate (3), a light scattering layer (5), and a low-refractive-index layer having a lower refractive index than the light guiding plate (3), one on top of another in this order, and on top of that structure another light guiding plate is provided, on top of which a high-refractive-index layer and a light scattering layer are likewise formed, while a color filter is disposed on one edge face of each light guiding plate and a light source is disposed near each color filter.

Description: BACKGROUND OF THE INVENTION 1.Field of the Invention The present invention relates to a backlighting device used as a surface-area light source for various kinds of display devices, and also relates to a display device, and particularly a color display device, that is used, for example, in transport means such as an automobile , vessel , train car, and that allows the driver or operator of the transport means to view images or characters displayed on the display in superimposed fashion on an outside view ahead. 2.Description of the Related Art In recent years, an edge lighting method has become a predominant method for flat display backlighting. This method uses a substrate made of an acrylic resin or the like, and a light source (such as a fluorescent lamp or cold-cathode lamp) disposed in close proximity to an edge of the substrate, and light from the light source is introduced into the transparent resin substrate and is made to emerge from the display surface. If a picture or other visual means is used instead of a display, this edge lighting method can be used for a decorative panel or a signboard. In such applications, in order to utilize efficiently light it is usual to place a reflecting plate on the reverse side of the substrate and a diffusing plate on the front side. The refractive index of the acrylic resin (polymethyl methacrylate) is n = 1.49. Therefore the critical angle of reflection at the interface with air is about 42°, and most of the light from the light source propagates through the substrate without emerging from the substrate. A variety of methods have been proposed to avoid this limitation and to extract the light in the desired direction (Japanese Patent Unexamined Publication Nos. 61-55684 or GB 2 165 631 and 1-245220, Japanese Patent Examined Publication No. 58-17957 or US 4 059 916, Japanese Patent Unexamined Publication No. 59-194302, etc.). In a method that involves applying a white paint or the like on the front side to diffuse light, light absorption by the paint cannot be ignored. Another method involves roughening the front surface from which the light emerges, but with this method also, sufficient light utilization cannot be obtained. In most of the currently practiced methods, direct emergent light from the front surface is not actively utilized, but a reflective film is placed on the reverse side of a light guiding plate and reflected light from the reflective film is made to emerge from the front surface. A white-colored film (including a white color painted plate, white color printed film, etc.) or a metallized film is used as the reflective film. The diffusing plate on the front side is used presumably for the purpose of evening out the reflected light, and furthermore, to enhance the directionality of the emergent light and increase its brightness, a method that uses a prism film or the like is employed. However, with the shift from the traditional monochrome display to the more advanced full-color display, it is becoming increasingly important to increase the screen brightness, and a further improvement in the efficiency of backlighting is needed. To achieve this, various improvements have been proposed, such as reducing the cold-cathode lamp diameter, improving the reflective film, and improving the geometrical shape of the light guiding plate. While these improvements have been successful in increasing the brightness, they have had other problems such as increased cost and increased complexity of the system. Furthermore, utilizing reflected light is reaching its technological limit. The only way left to further improve the efficiency is to utilize the directly emerging light from the front surface of the light guiding plate. Utilizing the direct light from the front surface involves the problem of using the surface-area light source as a transparent body. In applications where a picture or other visual means is used instead of a display to create a display apparatus (static) such as a light-guiding type decorative panel or signboard, as earlier described, in the case of displaying a color picture the color picture can be used as is, and in other cases, usually a light-scattering image or sign pattern is drawn and cut and is overlaid on a background color plate, while using a color filter to accomplish a color display. On the other hand, if a dynamic display is to be achieved with this display, one possible way will be to use a light-scattering image using, for example, a macromolecular dispersion-type liquid crystal (polymer dispersed liquid crystal). In connection with this method, constructions similar to the above display apparatus are disclosed, for example, in Japanese Patent Unexamined Publication Nos. 3-73926 and 3-23423 or EP 0 399 506. The former proposes arranging different-colored light sources on two edge sides of a liquid crystal panel and switching the color between the two light sources thereby changing the color of a single image in time sequence. The latter states that a color display can be realized using color filters though no specific examples are shown. In the (static) display apparatus of the above prior art, since color filters are used for the image portion, the number of colors that can be produced is fixed. Furthermore, with the exception of special examples, since a reflecting plate or a colored screen or the like is used for the background, they generally lack the concept that the whole construction should be made transparent. On the other hand, in the dynamic display apparatus using a macromolecular dispersion-type liquid crystal, the image can be displayed in mono-color but cannot be displayed in multi-colors at any arbitrary time and in any arbitrary region. Japanese Patent Unexamined Publication Nos. 3-73926 and 3-23423, cited above, both use a reflecting plate or a colored absorbing plate in their embodiments and lack the concept that the whole construction should be made transparent. The freedom of color selection can be increased and multi-color capability achieved by making the construction transparent and by stacking one on top of another a plurality of display devices each used to introduce a different color. In this case, however, the problem of how to separate the respective colors-has to be addressed. There is also the problem of how to increase the variety of colors. A further problem is how these requirements can be accomplished in a compact and efficient construction. There are two main types of display device: the self-luminous type such as the CRT, PDP, LED, and EL, and the external light type, such as the liquid crystal and electrochromic display, that produces the display by receiving light from a separate light source. In some applications, such display devices are positioned for use near a window glass or a show window. In other and more recent applications, such display devices are used as instrument and other display devices in automobiles, vessels, train cars, etc., a typical example being a direct-view head-up display (HUD). Since the display area of any of these display devices displays information thereon by emitting some form of display light, if the display device is positioned within such a distance that the display light reaches a window glass or a show window, the displayed image is reflected more or less onto the window glass or show window and comes into the viewer's visual field. The phenomenon of such reflection also occurs on a window glass or a show window near which a signboard or the like is put up. In such cases, when light from the background of the window glass or illumination inside the show window is sufficiently strong, the reflection hardly disrupts the viewer's view, but when the light from the background of the window glass or the illumination inside the show window is weak, or when the display light from the display device is very strong, the reflection on the window glass or the show window becomes pronounced and annoys the viewer, and in the case of vehicular applications, adversely affects the driving operation of the driver. Traditional methods to prevent such reflection have been to position the display device so that the display area does not face the window glass or the show window, to block the display light using a shade so that the display light does not fall on the window glass, to reduce the ambient light as well as the brightness of the display to reduce the intensity of the display light, and so on. For example, in a train or a bus running in the nighttime, in order that the panel faces such as instrument panels in the cab may not be reflected onto the windshield by the illumination from the passenger compartment and be brought into the visual field of the operator or driver, a shade is provided around the cab to block the illumination from the passenger compartment from entering the cab, or the lighting in and around the cab is dimmed so that the panel faces such as instrument panels in the cab are not reflected by the lighting onto the windshield and brought into the visual field of the operator or driver. However, the methods employed to prevent the reflection on the window glass or the show window involve the following problems. In the method that positions the display device so that the display area does not face the window glass or the show window, the position where the display device can be placed is very limited, and particularly, if the display device is positioned against the window glass, the display become very difficult to view when the outside light is bright, though it is easy to view when the outside light is weak. In the method that provides a shade on the display device, a very wide shade may become necessary depending on the positional relationship between the display device and the window glass or the show window, and often the use of such a shade is not permitted by space limitations or design considerations. In the method to reduce the ambient light and reduce the intensity of the display light, it becomes necessary to protect the area around the display device from light as the display would become difficult to view if the light through the window glass or the show window is incident on the display device. The display becomes very difficult to view particularly when the outside light from the window glass or the show window is bright. Instrument panels in passenger cars are a typical example where reflections cause a serious problem. The instrument panel of a passenger car is mounted in a recess in the dashboard, and the surrounding areas are painted black or dark color, to prevent the panel illumination from being reflected onto the windshield during night driving and to prevent outside light from falling directly on the instrument panel during day driving. In such applications where the intensity of the ambient light varies greatly, the method of installing the display device is demanding and very limited in freedom. Furthermore, the display can be viewed from a specified position but cannot be viewed when the viewer's head is moved, if slightly, from the specified position. Liquid-crystal displays constructed with twisted nematic (TN) liquid crystals sandwiched between two substrates having transparent electrodes have been widely used. When the liquid crystal molecules on the surface of a substrate are forced to align in one direction with their long axes arranged at 90° with respect to the liquid crystal molecules on the surface of a substrate on the opposite side, the liquid crystal molecules are arranged gradually changing their orientation and twisting through 90° between the substrates. A polarizing plate with its direction of polarization indicated by arrow "a" and a polarizing plate with its direction of polarization indicated by arrow "b" are attached to the outer surfaces of the substrates, respectively. When light is incident on this structure, only light vibrating in the same direction as the direction of polarization of the polarizing plate is passed through it, and follows the twisted structure of the liquid crystal molecules, the polarization of the light thus being rotated through 90° until reaching the polarizing plate on the opposite side. Since the direction of polarization of the light now coincides with that of the polarizing plate, the light is passed through it. On the other hand, when a voltage is applied between the electrodes on the substrates, the liquid crystal molecules align themselves with their long axis direction parallel to the direction of the resulting electric field, so that the light entering the liquid crystal layer is passed through it with the direction of polarization of the light remaining unchanged and reaches the polarizing plate on the opposite side where the light is blocked, creating a dark spot. An image or character is thus displayed by applying a voltage at a portion where the image or character is to be displayed. Figure 40 shows another type of liquid crystal display which uses a macromolecular dispersion-type liquid crystal. In the macromolecular dispersion-type liquid crystal, the orientation of the liquid crystal molecules dispersed in the form of fine droplets in a macromolecular matrix is changed by applying an electric field, and the resulting change of refractive index is utilized to produce a display. In the OFF state in which no voltage is applied, the optical axes of the liquid crystal molecules are random, and the difference in refractive index between macromolecule and liquid crystal causes the entering light to scatter in many directions. On the other hand, when the voltage is applied, that is, in the ON state, the liquid crystal molecules are aligned in the direction of the applied electric field, because refractive indices of macromolecular and liquid crystal are substantially same so that the entering light is passed through without being scattered. That is, in the OFF state, the display is like frosted glass because of scattering light, and in the ON state, the display is like transparent glass. In this way, by placing image or character portions in the OFF state and other portions in the ON state, an image or character is displayed on a transparent screen. However, the conventional twisted nematic liquid crystal display requires the use of two polarizing plates, as earlier described, and therefore, the light transmittance is 40 to 50% at most. This low transmittance is not suitable for forming an image on a transparent display screen, and it is difficult to display an image or character in superimposed fashion on the background view. On the other hand, in the case of the macromolecular dispersion-type liquid crystal display which does not require the use of polarizing plates, the transmittance in the ON state is nearly 80 to 90%, which provides good transparency. However, when displaying patterns portions corresponding to the patterns to be displayed are placed in the OFF state to form scattered light images, while the other portions are placed in the ON state and thus made transparent, but since the wiring patterns for the display patterns placed in the OFF state also cause scattering of light, making the wiring patterns visible on the screen, visibility and transparency are impaired when the displayed images or characters are superimposed on the background view; this presents a problem particularly when displaying a plurality of patterns requiring an increased number of wiring patterns. Furthermore, when an AC voltage is applied between the electrodes, a slight amount of current flows as this system is a kind of capacitor. When displaying patterns such as shown in Figure 42, larger current flows through the wiring for the larger display pattern, and hence ia > ib. Voltage drops Va and Vb through the respective wiring patterns are expressed by Va = r*ia and Vb = r*ib. Assuming the wiring patterns have the same resistance r, since ia > ib, it follows that Va > Vb, which indicates that the voltage drop is larger for the larger display pattern. As described above, if the same voltage is applied to the respective display patterns from the drive circuit, the voltages actually applied to the respective liquid crystal portions are different. This gives rise to the problem that variations are caused in the transparency of the screen and the transparent appearance is impaired. Furthermore, if the area sizes of the display patterns are the same, the resistance r is larger for the longer wiring pattern, which means a larger voltage drop. This also presents the problem that variations are caused in the transparency of the screen and the transparent appearance is impaired. In view of the problems that have made it difficult to use the above-described prior art liquid crystal displays as transparent displays, it is an object of the present invention to provide a transparent liquid crystal display that can display only images and characters that are to be displayed, on a transparent screen in superimposed fashion on the background view, thereby providing good visibility. For an automotive head-up display (HUD), a projection method is generally used wherein a CRT or a transmission-type liquid crystal display, for example, is used as the image source, and using optics consisting of a lens, mirror, and hologram, a display image or character produced on the image source is projected onto a combiner positioned in front of the driver's seat (or on the windshield) and displayed in superimposed fashion on a forward view. In this projection method, the image source is separately mounted, and a prescribed light path is necessary for projecting the image. The resulting problem is that the system becomes large in size and requires large space for installation, for example, in the dashboard. Furthermore, in recent automotive instrumentation, a combination instrumentation system is used that displays warning indications, etc. as necessary in superimposed fashion on the ordinary speedometer and tachometer displays. Since this system uses the so-called virtual image display method, the system is complex, occupies large space for installation, and is expensive, which has been a major problem with this system. US-A-4949489 discloses an edge-lit multiple image display device which utilizes a plurality of stacked intemal-reflecting-light sheets. Images are formed on the surfaces of the sheets with a coating of a material that changes the density on the internal reflecting surface of its respective sheet. A light source illuminates the edges of the stacked sheets. A light shield allows to selectively direct the light to one edge at a time of the edges of the sheets in the stack. When a selected edge is illuminated, the image displayed on that edge-lit plate becomes illuminated and visible. This mentioned prior art represents the basis from which the subject matter of the invention starts. SUMMARY OF THE INVENTION In view of the above-outlined problems with the prior art, it is the object of the present invention to provide a backlighting device for various kinds of display devices, that achieves excellent light utilization. The invention provides a color display device that eliminates the problem of color mixing and that is compact and efficient. The invention provides a color display device that does not cause reflections when positioned near a window or windshield where the ambient light intensity varies greatly, and that can constantly provide good visibility over a wide viewing angle. The invention provides a head-up display, instrument, and rearview mirror that are compact in construction and require much smaller space for installation compared with the prior art construction. This object is achieved by the features of the independent claims. Advantageous embodiments are set forth in the dependent claims. The invention also provides a color display device comprising: a light guiding member constructed with a pair of wedge-shaped light guiding plates bonded together, the bonded surfaces each serving as a reflecting surface; light sources of different colors, each disposed facing one edge of each of the light guiding plates; substantially transparent layers, each formed on a light emergence surface of each of the light guiding plates and having a higher refractive index than the light guiding member; and scattering layers each formed on top of each of the transparent layers. Using the light guiding member having the above-described structure, the backlighting device of the present invention can achieve improved surface brightness compared with the prior art edge lighting-type backlighting device. The higher-refractive-index layer preferably has a refractive index 0.05 to 1.50 higher than the refractive index of the light guiding member itself, and may be formed from LaF 3 , NdF 3 , Al 2 O 3 , CeF 3 , PbF 2 , MgO, ThO 2 , SnO 2 , La 2 O 3 , In 2 O 3 , Nd 2 O 3 , Sb 2 O 3 , ZrO 2 , CeO 2 , TiO 2 , or ZnS, or from a complex with a prescribed composition. This layer can be easily formed using a conventional thin film deposition process. If the refractive index of the higher-refractive-index layer is higher by 1.5 or more than that of the light guiding member, coloring at a certain wavelength and a decrease in transparency may occur depending on the material used. For the scatterer, an ordinary paint or fluorescent paint may be used, but specifically the present invention uses a mixture of two or more kinds of polymers having different refractive indices, a mixture of a polymer and a high-refractive-index compound, etc. The scatterer may be formed uniformly throughout or may be cut in a prescribed pattern (e.g., a character, symbol, sign, etc.). For the light guiding material, any optically transparent material, such as a glass plate, an acrylic plate, a polycarbonate plate, etc., can be used. A suitable material should be selected according to the film deposition conditions. Further, the light guiding plate shape, such as parallel plates or wedge-shaped plates, can be used as desired according to the purpose. The present invention is primarily concerned with the utilization of the direct light emerging from the front surface, but it is apparent that the effectiveness can be further enhanced by using it in combination with the conventional edge light system having a reflective layer on the back surface. When no reflective layer is used, the structure is a transparent surface-area light source corresponding to the pattern of the scatterer. If the method of the invention is used on both sides of a light guiding plate, a double image can be presented, and a multi-color display is also possible by using multiple light sources and switching the light source color. The effects of the invention having the above-described construction will be described below. When light is introduced from an edge of a single light guiding plate, such as an acrylic plate, the light undergoes total internal reflection at the critical angle of about 42°, as previously described. In an optical fiber, the core material is surrounded with a lower-refractive-index material to ensure total internal reflection and eliminate losses during propagation. On the other hand, when a higher-refractive-index material is applied on the surface, as in the present invention, the total reflection condition is eased and the light inside the light guiding plate penetrates into the high-refractive-index layer. However, in theory, the light entering this layer propagates while undergoing total internal reflection at a smaller critical angle at the interface with air and does not leak outside. In actuality, however, when a scatterer is placed on the surface of this layer, surface brightness increases compared with a structure where a scatterer is placed directly on the light guiding plate itself. Though the following explanation does not impose any restrictions on the present invention, generally light is not perfectly reflected at total reflection surfaces but leakage occurs due to a phenomenon called evanescent wave coupling, etc. To prevent this, in an optical fiber, a low-refractive-index layer is provided to confine the light deeply inside. By contrast, in the present invention, it is presumed that the brightness improves not only because the light reaches the outermost layer but because the leakage is promoted by thin film irregularities, etc. In this way, the present invention achieves efficient utilization of the direct light emerging from the front surface, and by using it in combination with the conventional backlighting method that uses a reflective layer, an excellent backlighting device with further improved brightness can be realized. Furthermore, by patterning the scattering layer, the structure of the invention can also be used as a transparent display medium. The present invention also provides a color display device as defined in claim 2 comprising: light guiding plates, disposed parallel to each other, for guiding a plurality of lights therethrough; a light scattering layer formed on a display side of each of the light guiding plates; a low-refractive-index layer formed between the light guiding plates and on the display side of the light scattering layer; a color filter disposed on one edge face of each of the light guiding plates; and a light source disposed near the color filter. In addition to the above structure, a layer having a higher refractive index than the light guiding plates is formed on top of and/or beneath the light scattering layer. The high-refractive-index layer is a transparent conductive layer, and the light scattering layer is constructed with a macromolecular dispersion-type liquid crystal. Also preferably, the low-refractive-index layer is also formed on one side of the light guiding plate located at the farthest end from the display side, the one side being opposite from the display side. Further preferably, the color filters are of three kinds, R, G, and B, respectively. Also preferably, the color filters are each constructed to be movable with respect to each light guiding plate, allowing selection of a different color. The present invention also provides a vehicular onboard color display apparatus comprising a color display device as defined in claim 2, a drive circuit for driving the color display device, and a signal generator for supplying the drive circuit with a signal concerning display contents, the color display device being positioned near a glass surface in such a manner as to allow an image displayed on the color display device to be viewed superimposed on an outside view seen through the glass surface. The invention also provides a vehicular onboard combination color display as defined in the independent claim 2 apparatus comprising a color display device in combination with an instrument panel for displaying various conditions of a vehicle, and comprising a control section for controlling the color display device and the instrument panel, and an operation section for allowing a manual operation of displayed conditions on the color display device and the instrument panel. The invention also provides a color display operation panel comprising the above-described color display device in combination with a transparent touch panel switch, and comprising a control section for controlling the transparent touch panel switch and the color display device; and a drive circuit for driving the control section. In this way, according to the present invention, display devices for decorative and various display uses can be adapted to produce images in desired colors with a wide variety of colors. The color display device of the invention is compact in construction and provides improved display efficiency. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic diagram showing a side view of a backlight display device comprising two wedge-shaped light guiding plates according to a first embodiment of the present invention; Figure 2 is a diagram showing the structure of a (static) color display device according to a second embodiment of the present invention; Figure 3 is a diagram showing the structure of a (dynamic) color display device according to an third embodiment of the present invention; Figure 4 is a diagram showing the structure of a (static) color display device according to a forth embodiment of the present invention; Figure 5 is a diagram illustrating a color filter moving method according to the fifth embodiment; Figure 6 is a diagram showing the structure of a vehicular onboard display apparatus according to a sixth embodiment of the present invention; Figure 7 is a diagram showing examples of light guide module displays of the vehicular onboard display apparatus according to the sixth embodiment; Figure 8 is a diagram showing a display example of an instrument panel according to an seventh embodiment of the present invention; Figure 9 is a diagram showing the configuration of a combination color display apparatus according to the seventh embodiment; Figure 10 is a diagram showing examples of light guide module displays of the combination color display apparatus according to the seventh embodiment; Figure 11 is a diagram showing the construction of a color display device adapted to a decorative transparent medium according to a eighth embodiment of the present invention; Figure 12 is a diagram showing the structure of an operation panel according to a ninth embodiment of the present invention; Figure 13 is a diagram for explaining the operation of the operation panel according to the ninth embodiment; Figure 14 is a diagram showing the structure of a (static) color display device for comparison; Figure 15 is a diagram showing the structure of a (dynamic) color display device for comparison; DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. In the embodiments hereinafter given, a glass plate with a refractive index of 1.52 is used as a representative example of a light guiding plate. In the structure of the first embodiment of Fig. 1, if the scatterer is formed in a desired pattern, the scatterer itself can be used as a display medium. Figure 1 shows one such example, wherein reference numerals 8 and 17 are light sources, 8 being red and 17 blue, for example. Wedge-shaped light guiding plates 10 and 11 are bonded together in the center with a transparent adhesive 12. Reference numerals 13 and 15 are high-refractive-index layers, and 14 and 16 are patterned scattering layers. When the light sources 8 and 17 are turned on, light entering the respective light guiding plates 10 and 11 is reflected at their interface where the refractive index is slightly different between the material of the light guiding plates 10, 11 and the adhesive layer 12; the reflected light enters the respective surface layers together with the direct light and is scattered in the respective scattering layers 14 and 16. By suitably selecting the incident direction of light, the wedge angle, and the material of the adhesive layer 12, the red and blue colors do not mix together and can be scattered only through the respective scatterers; when the display is viewed from one direction toward the display surface, the patterns are seen displayed in two colors, while portions where the patterns overlap appear purple, thus producing a three-color display. Figure 14 shows a structure in which a light guide module is constructed by forming a light scattering layer on a light guiding plate with a high-refractive-index layer sandwiched between them in accordance with the foregoing embodiments and by bonding two such light guide modules together, to achieve color display capability. In Figure 14, reference numeral 1 is a light source, 2 is a reflecting plate, 1703 and 1704 are color filters, 1705 and 1708 are light scattering layers, and 1706 and 1709 are high-refractive-index layers formed to improve the introduction of light into the respective light scattering layers. Further, 1707 and 1710 are light guiding plates. However, since color mixing occurs, as will be described later, further improvements are made to the above structure in the present embodiment. Figure 2 shows a structure with two light guide modules bonded together in accordance with the present invention. In Figure 2, reference numeral 511 shows a low-refractive-index layer. In this structure, since 510 is in contact with an air layer at its endmost surface, the low-refractive-index layer to be formed on its outside surface is omitted. A fluorescent lamp, cold-cathode lamp, halogen lamp, LED, or the like is used as the light source 1. The light scattering layers 505 and 508 are each formed using an ordinary paint, fluorescent ink, or from a material such as a system consisting of two or more kinds of dispersing substances having different refractive indices. The high-refractive-index layers 506 and 509 are formed from LaF 3 , NdF 3 , Al 2 O 3 , CeF 3 , PbF 2 , MgO, ThO 2 , SnO 2 , La 2 O 3 , In 2 O 3 , Nd 2 O 3 , Sb 2 O 3 , ZrO 2 , CeO 2 , TiO 2 , or ZnS, or from a complex of substances selected from these substances; that is, any material may be used as long as the refractive index is higher by 0.05 to 1.50 than the refractive index of the light guiding plate itself. The low-refractive-index layer can be formed from any material, such as CaF 2 , NaF, KiF, MgF 2 , etc., that has a refractive index lower than that of the light guiding plate itself. The light guiding plate is usually constructed from a glass plate or a transparent plastic plate, such as a plate made of an acrylic resin, that has a refractive index of around 1.5. Light from the light source 1 entering the light guiding plates 507 and 510 through the color filters 503 and 504, propagates through the light guiding plates and is scattered in the respective light scattering layers 505 and 508. Since the light scattering layers 505 and 508 are formed in prescribed patterns, scattered light images colored through the respective color filters are obtained. On the other hand, in the case of the structure shown in Figure 14, the light introduced through the color filter 503 is scattered not only in the light scattering layer 505 but also in the light scattering layer 508. The light scattering layer 508 thus scatters both lights passed through the color filters 503 and 504, resulting in color mixing. By contrast, in the case of the present embodiment shown in Figure 1, the light introduced through the color filter 503 is passed through the high-refractive-index layer 506 and enters the light scattering layer 505 where the light is scattered to form an image. Because of the presence of the low-refractive-index layer 511 between the light scattering layer 508 and the light guiding plate 507, the light entering the light guiding plate 507 undergoes total reflection at the interface with the low-refractive-index layer and does not emerge into the light scattering layer 508. Here, the light passed through the transparent portions of the light scattering layer 505 is totally reflected back at the boundary to the outside since the outside is an air layer of low refractive index, and therefore, the light does not emerge directly into the outside. Accordingly, the light introduced into the light guiding plate 507 through the color filter 503 is used only for scattering in the light scattering layer 505. On the other hand, the light entering the light guiding plate 510 through the color filter 504 is passed through the high-refractive-index layer 509 and enters the light scattering layer 508 to form an image by the preformed pattern. The light scattered in scattering portions 508a of the light scattering layer 508 is not reflected by the low-refractive-index layer 511 but is passed through the light guiding plate 507, this high-refractive-index layer 506, and the light scattering layer 505, and emerges outside. At this time, if there is light leakage through transparent portions 508b of the patterned light scattering layer 508, such light is reflected back by the low-refractive-index layer 511 and does not emerge into the light guiding plate 507. In this way, in the color display device of the present embodiment, light emitted from the light source 1 is color-separated by the differently colored color filters 503 and 504, and the colored lights enter the respective light guiding plates 507 and 510 and are scattered only in the respective light scattering layers 505 and 508 without interfering with each other, to form respective color images. Each of these scattered light images, when seen from the viewer, is viewed as a so-called self-light-emitting image; therefore, those portions of the images which are independent of each other are displayed in the colors corresponding to the respective color filters 503 and 504, and portions where the images overlap are displayed in a color produced by mixing the two colors. When three such light guide modules are used in conjunction with R, G, and B color filters, an image of any desired color can be obtained by suitably overlapping the scattered light images of the respective colors. The light guiding plate 510 located at the farthest end from the display side may also be provided with a low-refractive-index layer 511 on the side thereof opposite from the display side. Next, an embodiment will be described in which the color display device of the invention is adapted to a dynamic display. Figure 15 is a diagram showing two liquid crystal panels bonded together, each panel being identical in construction to the prior art macromolecular dispersion-type liquid crystal panel except that the reflecting plate or absorbing plate on the rear side is removed. In the figure, reference numerals 1812 and 1817 are transparent substrates of glass or the like, and 1813, 1815, 1818, and 1820 are transparent electrodes made, for example, of ITO, which also serve as high-refractive-index layers because their refractive index is higher than that of the substrates. Further, 1814 and 1819 are macromolecular dispersion-type liquid crystal layers, and 1816 and 1821 are transparent substrates of glass or the like, which also serve as light guiding plates. The liquid crystals are electrically driven (drive circuitry is not shown here). When a voltage is applied between the transparent electrodes, for example, the macromolecular dispersion-type liquid crystals become transparent, and when the voltage is off, they scatter light. Images and symbols can thus be displayed. Figure 3 shows a dynamic color display device according to the present invention. In the figure, reference numeral 622 is a low-refractive-index layer according to the present invention. In the present invention, the glass substrate 1817 is not needed. In Figure 15, light from the light source 1 is color-separated by the color filters 1803 and 1804, and the colored lights enter the respective light guiding plates 1816 and 1821 and are propagated through them. The propagated lights are passed through the ITO layers 1815 and 1820 and enter the liquid crystal layers 1814 and 1819 where scattered, portions are displayed as colored images. However, the light entering the light guiding plate 1816 is passed through 1817 and 1818 and scattered also in the liquid crystal layer 1819. Accordingly, scattering portions in the liquid crystal layer 1819 scatter the two lights colored through the respective color filters 1803 and 1804, thus causing color mixing. By contrast, in the display device of the present invention shown in Figure 3, light introduced through a color filter 603 is passed through an ITO layer 615 of high refractive index and enters a liquid crystal scattering layer 614 where the light is scattered in a pattern corresponding to an electrical signal, thus forming an image. Because of the presence of the low-refractive-index layer 622 between a liquid crystal scattering layer 619 and a light guiding plate 616, the light entering the light guiding plate 616 undergoes total reflection at the interface with the low-refractive-index layer and does not emerge into the liquid crystal scattering layer 619. Accordingly, the light introduced into the light guiding plate 616 through the color filter 603 is scattered only in the liquid crystal scattering layer 614. On the other hand, light entering a light guiding plate 621 through a color filter 604 is passed through an ITO layer 620 of high refractive index and enters the liquid crystal scattering layer 619 to form an image of the pattern corresponding to the applied electrical signal. At this time, if there is light leakage through transparent portions of the patterned liquid crystal scattering layer 619, such light is reflected back by the low-refractive-index layer 622 and does not emerge into the light guiding plate 616. In this way, in the color display device of the present embodiment, light emitted from the light source 1 is color-separated by the differently colored color filters 603 and 604, and the colored lights enter the respective light guiding plates and are scattered only in the respective liquid crystal scattering layers without interfering with each other, to form respective color images. Each of these scattered light images, when seen from the viewer, is viewed as a so-called self-light-emitting image; therefore, those portions of the images which are independent of each other are displayed in the colors corresponding to the respective color filters 603 and 604, and portions where the images overlap are displayed in a color produced by mixing the two colors. When three such light guide modules are used in conjunction with R, G, and B color filters, an image of any desired color can be obtained by suitably overlapping the scattered light images of the respective colors. Next, an embodiment will be described in which the color display device of the invention is adapted for use as a signpost. Three light guide modules are prepared, each constructed with an acrylic plate that has a scattering pattern written with white ink as shown in Figure 4. Module (a) has a green color filter, module (b) a blue color filter, and module (c) a red color filter. These modules are integrated into one unit. The result is the color display device (d) embodying the present invention. In Figure 4(d), reference numeral 723 is the color display device constructed from the light guide modules, and 724 is a background plate which, in this case, is colored black. The light source 1 is a white-light fluorescent lamp. When the fluorescent lamp is turned on, the road pattern written in white on the signpost appears floating in space against the black background, with directional arrow displayed in green, direction pointing arrow in blue, and N direction in red. Each color filter can be constructed to be detachable and movable. This can be accomplished by constructing each filter 825 with a guide 826 that holds it in place, as shown in Figure 5(a). Desired color filters can thus be selected and replaced so that the same image pattern can be displayed in various combinations of colors. Further, if an RGB three-color filter tape 825' is used that is movable by rollers 827 to 830, as shown in Figure 5(b), filter color selection is made easier. By adopting this filter tape system for each light guide module 723, a colored image can be displayed easily with a very wide range of color combinations. The method of moving the color filter tape is not limited to the illustrated one; rather, it is apparent that various types of moving means can be used. Next, an embodiment will be described in which the color display device of the invention is adapted for use in a vehicular onboard display apparatus. Figure 6 shows an example in which the color display device of the invention is installed on a automobile dashboard 933. The display device itself is the same as that described in the eighth embodiment, and uses three color filters of R, G, and B. In the figure, reference numeral 931 is the color display device of the invention, and 934 indicates a place where liquid crystal driving circuitry is accommodated. This display device is connected to a navigation system via a harness (not shown), and is driven by signals from the navigation system. since this color display device uses macromolecular dispersion-type liquid crystal, an image is displayed in the form of a scattered light image on a transparent screen. Since portions other than the displayed image port'ions are transparent, this allows viewing of the displayed image superimposed on the outside view seen through the windshield 932, so that the driver need not look away from the road ahead when viewing the image. Figure 7 shows display examples. Part (a) is a display of automobile speed which is displayed, for example, in green. In this light guide module, three-digit numbers are produced by transparent electrodes patterned in the form of segments, and "km/h" i's displayed from different patterns "k /h" and "m". Part (b) shows an intersection guide mode, in which distance is displayed in green using the same patterns that are used in (a). In this second light guide module, "AHEAD" and an arrow are formed as patterns. Therefore, "AHEAD" and the arrow are displayed, for example, in blue. Part (c) shows a display when an warning indication is produced using, in this case, the third light guide module. A warning "DISABLED VEHICLE AHEAD" is displayed, for example, in red alongside the green speed display. These displays can be accomplished either by segment display or by dot display. The vehicular onboard color display apparatus of the invention is compact, thin, and transparent, and can be installed in a convenient position in an automobile. The display device can be attached to the windshield or built into the windshield glass. The vehicular onboard color display apparatus of the present invention is not limited to the example shown in this embodiment, but the vehicular onboard color display apparatus can be constructed in any suitable configuration as long as it comprises the color display device of the present invention, drive circuitry, and a signal generator such as a navigation system, and is capable of allowing viewing of displayed images superimposed on the outside view. Next, an embodiment will be described in which the present invention is combined with an automotive instrument panel. Figure 8 shows an example of a conventional analog display instrument panel. Various kinds of meters and indicators are arranged, of which those that the driver are constantly looking at are the speedometer and tachometer. The other meters and indicators need only be displayed when necessary. Further, if some kind of information in the event of an emergency or information, for example, on traffic congestion can be displayed superimposed on the instrument panel only when necessary, this will be preferable since this can alleviate the burden imposed on the driver when looking at the displays. Therefore, of the instrument panel displays shown in Figure 11, the speedometer, tachometer, directional arrows for turn signal indications, and A/T shift position indicator are left as the basic displays, and all other displays and indicators are omitted. The present embodiment uses the same kind of color display device as that used in the invention shown in the 10th embodiment, and mounts it in overlaying fashion on the instrument panel, as shown in Figure 9. The light guide modules used are shown in Figure 10: for example, as shown in Figure 10(a), a fuel gauge and a water temperature gauge are patterned in the green panel; a fuel indicating needle and a water temperature indicating needle are patterned in the blue panel, as shown in part (b); and a fuel empty indicator E, an overheat indicator H, and various warning indicators can be displayed in red, as shown in part (c), along with an information display (dot or character display) in the center. This combination color display apparatus constituting the combination instrument panel is constructed by overlaying the color display device 236 of the present invention on the conventional instrument panel 235, and information from various sensors 237, external information 238 or internal information, and navigational information 239 are supplied directly or through a suitable controller 240, as shown in Figure 9. Usually, these operations are controlled automatically, but can also be controlled manually via an operation panel 241. During driving, when the display is not necessary, the entire display area is in a transparent mode, and only the speedometer, tachometer, etc. are visible. When the engine is started, water temperature is displayed with the blue needle on the green water temperature display panel, and when the temperature reaches a predetermined value, the display is blacked out. Similarly, the fuel gauge is displayed on the green display panel with its blue needle indicating the amount of remaining fuel, and the display is blacked out after a predetermined time. If the driver wants to check the indication, he can operate the operation panel 241 (for example, switch ON) to turn on the display. In the event of an engine overheat, the water temperature gauge is again displayed, with the red overheat indicator H superimposed on it; similarly, when the fuel becomes low, the fuel gauge is displayed along with the red indicator E. The various other warning indicators are illuminated in red when necessary. Some kind of information, such as traffic information or emergency information, is displayed in red on the large display area in the center, in superimposed fashion on the underlying instrument panel displays. In this way, the present invention can provide an excellent on-demand type combination color display apparatus that is capable of displaying necessary information only when necessary in superimposed fashion on the instrument panel information. Next, an embodiment will be described in which the present invention is applied for use in a decorative transparent display medium. An example is shown below in which the color display device of the present invention is adapted for use in a store's show window or the like, for example, as shown in Figure 11. In the figure, reference numeral 1 is a light source, 2 is a reflecting plate, 442 is a color filter attached to each light guide module, and 443 is a panel constructed by combining three light guide modules made of glass. The color display device used here is of the same type as that used in the embodiment of Fig. 6, except that the size and display contents are different. When the size is substantially large, it is preferable that the light source, reflecting plate, and color filters be arranged on each side of the light guide module panel. Further, in applications where the display is not produced over the entire panel surface, transparent electrodes and macromolecular dispersion-type liquid crystals may be arranged only in necessary areas, leaving other areas as glass only. As in the embodiment of Fig. 6, the color display device of the present embodiment is constructed together with drive circuitry for driving the display device and a signal generator for supplying drive signals (not shown). When patterns, dots, etc. corresponding to R, G, and B colors are formed using transparent electrodes on the light guide modules to which the color filters of R, G, and B are respectively attached, various images and characters are displayed, floating on the seemingly transparent glass, when the display device is driven. Since merchandize displayed inside the show window can be seen through the transparent portions, an excellent display effect can be obtained. The effect can be further enhanced by using in combination the movable filters described in the ninth embodiment in accordance with the display contents. The application of the present embodiment is not limited to the store show window described above; rather, the present embodiment can be used in a wide variety of decorative transparent display applications, such as a stage setting, advertisement media on train windows, etc. Next, an embodiment will be described in which the color display device is adapted to an operation panel. Figure 12 is a diagram showing a cross-sectional structure of the operation panel according to this embodiment. In the figure, reference numeral 1 is a light source, 2 is a reflecting plate, 153 and 154 are color filters, and 144 and 145 are light guide modules of the same kind as those used in the 10th embodiment. Further, 146 is a transparent touch panel which is constructed, for example, from a pair of films, each having a transparent conductive layer, bonded together facing each other with a prescribed spacing provided between them; 147 is a background plate which is installed when necessary and which is, for example, a colored light-absorbing plate; and 148 is a control circuit which outputs signals to a drive circuit 149 for driving the color display device, to an operation system, and to other operation panels in response to the operation made on the touch panel 146. The touch panel 146 is connected to the drive circuit 149 via the control circuit 148. As the touch panel 146 is pressed, the prescribed display contents change sequentially. Next, an operational example of a construction using a plurality of such operation panels will be described with reference to Figure 13. Figure 13 is a diagram showing a cluster of operation panels as viewed from the front. An operation panel 350 is, for example, a mode setting operation panel. As the panel is pressed, the display changes sequentially, for example, from A to B to C, and so on (these may be numeric or alphabetic), each being produced in the form of a scattered light image colored through a color filter and displayed superimposed on the background plate. An operation panel 351 is set in the mode specified by a signal from the operation panel 350, and displays, for example, temperature setting. When the operation panel 351 is pressed, up and down arrows are displayed on operation panels 352 and 353. When the operation panel 352 is pressed, the display on the operation panel 351 changes to a temperature indicator, and the temperature set value changes upward as this panel is pressed (in the figure, both the temperature indicator and the letters "TEMPERATURE SETTING" are shown, but actually the letters "TEMPERATURE SETTING" go off when the temperature indicator comes on). The operation panel 353 is used to lower the temperature setting. When the operation panel 350 is pressed again, the mode changes, for example, to time setting mode, and "TIMING SETTING" is displayed on the operation panel 351. When the operation panel 351 is pressed, the operation panel 352 displays "HOURS" and the operation panel 353 displays "MINUTES". When the operation panel 352 is pressed, the operation panel 351 displays "**HOURS **MINUTES", and the HOURS setting changes as this panel is pressed (at this time, the display "TIME SETTING" goes out). Likewise, when the operation panel 353 is pressed, the MINUTES setting changes. Needless to say, various methods may be employed to implement these display modes by those who carry out the present invention, and it will be easily recognized that various improvements are also possible. As described above, the operation panel of the present embodiment can present a display simultaneously with a switch operation, while permitting the display to be changed with a certain degree of freedom. This achieves the operation panel that is easy to understand and easy to operate with a reduced number of switches. In the present embodiment, two light guide modules are shown in Figure 15, but it will be appreciated that a suitable number of modules can be used according to the purpose.

Claims: A color display device comprising: a light guiding member constructed with a pair of wedge-shaped light guiding plates (10,11) bonded together; light sources of different colors (8,17), each disposed facing one edge of each of said wedge-shaped light guiding plates (10,11); substantially transparent layers (13,15), each formed on a light emergence surface of each of said wedge-shaped light guiding plates (10,11) and having a higher refractive index than said light guiding member; and a light scattering layer (14,16) formed in a desired pattern on each of said transparent layers (13, 15). A color display device comprising: a plurality of light guiding plates (507,510;621,614;1707,1710), disposed parallel to each other, for guiding a light therethrough; a light scattering layer (505,508;614,619;1705,1708) formed in a desired pattern on a display side of each of said light guiding plates and a color filter (503,504;603,604;1703,1704;1803,1804) disposed on one edge face of each of said light guiding plates; and a light source (1) disposed near said color filter; characterized by a light transparent layer (506,509;615,620;1706,1709) having a higher refractive index than said light guiding plates (510;621,614;1707,1710) being formed on top of each of said light guiding plates (510;621,614;1707,1710), the light scattering layers are disposed on top of said light transparent layers. The color display device according to claim 2, wherein said high-refractive-index layer is a transparent conductive layer (15,20), and said light scattering layer (1814,1819) is constructed with a macromolecular dispersion-type liquid crystal. The color display device according to claim 2, wherein a low-refractive-index layer (511,622) is formed between said light guiding plates (507,510;616,621) and on the display side of said light scattering layer (508;619). The color display device according to claim 4, wherein said low-refractive-index layer is also formed on one side of the light guiding plate located at the farthest end from the display side, said one side being opposite from the display side. The color display device according to claim 2, wherein said color filters (503,504;603,604;1703,1704;1803,1804) are of three kinds, R, G, and B, respectively. The color display device according to claim 2 or 5, wherein said color filters (503,504;603,604;1703,1704;1803,1804) are each constructed to be movable with respect to each of said light guiding plates (507,510;621,614;1707, 1710; 1816,1821), allowing selection of a different color. A vehicular onboard color display apparatus comprising: said color display device of claim 3; a drive circuit (149) for driving said color display device; and a signal generator (148) for supplying said drive circuit (149) with a signal concerning display contents, said color display device (931) being positioned near a glass surface (932) in such a manner as to allow an image displayed on said color display device to be viewed superimposed on an outside view seen through said glass surface. A vehicular onboard combination color display apparatus comprising: said color display device of claim 3; an instrument panel, installed in combination with said color device, for displaying various conditions of a vehicle; a control section form controlling said color display device and said instrument panel; and an operation section for allowing a manual operation of displayed conditions on said color display device and said instrument panel through said control section. A color display operation panel comprising: a transparent touch panel switch; said color display device of claim 3 overlaid on said transparent touch panel switch; a control section for controlling said transparent touch panel switch and said color display device; and a drive circuit for driving said control section.

Inventors: ASAKAWA SHIRO, OKAUCHI TOHRU, OKUDA EIICHIRO, ASAKAWA, SHIRO, OKAUCHI, TOHRU, OKUDA, EIICHIRO
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1996
Main classification: F21V8
IPC codes: G02B5, G02B27, G01C21, G02F1, F21V8, G02B6