Light valve apparatus and display system using the same

Abstract: A light valve apparatus comprising: a light valve layer (33) for forming an optical image as changes of light scattering state; and two substrates (31, 32) between which said light valve layer (33) is gripped and at least one of which is transparent such that the following condition is satisfied: t ≧ d 4 √ n² - 1 where t denotes a central thickness of said at least one of said substrates (31, 32), n denotes a refractive index of said at least one of said substrates (31, 32) and d denotes a maximum diameter of an effective display area of said light valve layer (33).

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light valve apparatus for forming an optical image as changes of light scattering state and a display system using the light valve apparatus. 2. Description of the Prior Art In order to obtain an image on a large screen, a method has been well known in which an optical image corresponding to an image signal is formed on a light valve and light is irradiated to the optical image so as to project the optical image onto the screen at an enlarged scale by a projection lens. Recently, a projection display system employing a liquid crystal panel as the light valve attracts much attention. Various kinds of liquid crystal panels are known in which phenomena of electrical changes of optical characteristics include changes of optical rotation, changes of birefringence, changes of light scattering state and changes of light absorption. A projection display system based on a phenomenon in which optical rotation of twist nematic (TN) liquid crystal changes according to electric field is already commercially available. A liquid crystal panel employing TN liquid crystal should be provided, at its input and output sides, a pair of polarizers for modulating light, respectively, thereby resulting in low efficiency of utilization of light. Meanwhile, TN liquid crystal are required to be oriented in a predetermined state. Thus, an alignment film should be provided and is required to be subjected to rubbing. Liquid crystal panels for forming an optical image by changes of light scattering state employ, for example, a thermal writing mode, a dynamic scattering mode, polymer dispersion liquid crystal and ferroelectric liquid crystal. Furthermore, it is known that an optical image can be formed as changes of light scattering state also in translucent ceramics "PLZT" which is obtained by adding lanthanum oxide to solid solution of zircon lead titanate. Liquid crystal panels employing changes of light scattering state can be expected to have large optical output due to the needlessness to provide the polarizer in contrast with TN liquid crystal in order to modulate light and can be produced relatively easily owing to elimination of the need of rubbing of the alignment film. Figs. 17(a) and 17(b) show basic structure and operational model of a known polymer dispersion liquid crystal panel. A polymer dispersion liquid crystal layer 3 is gripped between glass substrates 1 and 2 each having a thickness of about 1 mm. Transparent electrodes 4 and 5 are provided on inner faces of the glass substrates 1 and 2, respectively. In the polymer dispersion liquid crystal layer 3, liquid crystals 7 in the form of water drops are dispersed in polymer resin 8. Refractive index for ordinary ray in the liquid crystals 7 is substantially identical with that in the polymer resin 8. When no voltage is applied to the liquid crystal layer 3, liquid crystal molecules 9 of the liquid crystals 7 are oriented at random as shown in Fig. 17(a). When a light ray 10 is perpendicularly incident upon the liquid crystal layer 3 at this time, the light ray 10 has different refractive indexes at a boundary face between the liquid crystal 7 and the polymer resin 8. Therefore, the light ray 10 repeats refraction at the boundary face and then, is outputted as scattered light. On the contrary, when a sufficiently high voltage is applied to the liquid crystal layer 3, the liquid crystal molecules 9 of the liquid crystals 7 are oriented in a direction perpendicular to the glass substrates 1 and 2 as shown in Fig. 17(b). As a result, refractive index for the light ray 10 in the liquid crystals 7 becomes identical with that in the polymer resin 8 and thus, the light ray 10 proceeds linearly without being scattered so as to be outputted. Fig. 18 shows one example of a prior art projection display system employing a polymer dispersion liquid crystal panel. Light emitted from a lamp 11 is converged by a concave mirror 12 so as to be incident upon a liquid crystal panel 13. The liquid crystal panel 13 is formed by a polymer dispersion liquid crystal panel and includes a polymer dispersion liquid crystal layer 17 gripped between glass substrates 15 and 16. Pixel electrodes are provided in a pattern of a matrix on one face of each of the glass substrates 15 and 16 adjacent to the liquid crystal layer 17. Hence, an optical image corresponding to an image signal can be formed, as changes of light scattering state, on the liquid crystal panel 13. Since all light rays emitted from the pixels subjected to a sufficiently high voltage are incident upon a projection lens 14 and reach a screen 21, bright pixels are displayed at corresponding positions on the screen 21. On the other hand, since scattered light rays are emitted from pixels not subjected to the voltage and only a portion of the scattered light rays is incident upon the projection lens 14, dark pixels are displayed at corresponding positions on the screen 21. Thus, the optical image formed, as changes of light scattering state, on the liquid crystal panel 13 is projected onto the screen 21 at an enlarged scale by the projection lens 14. In order to convert the optical image formed, as changes of light scattering state, on the light valve into changes of luminance, such a phenomenon is utilized in which when only light rays having a predetermined solid angle are taken from output light rays of the light valve, quantity of light falling in the solid angle changes according to degree of light scattering. To this end, a central shielding method and an aperture method can be used. In the central shielding method, light is shielded in a transparent state of the light valve so as to be prevented from reaching the screen. In case the light valve is in light scattering state, light rays which are not shielded by a shielding plate reach the screen. In the aperture method, light proceeding in a central direction of directivity characteristics is utilized and quantity of light incident upon the projection lens from the pixels of the liquid crystal panel drops as scattering degree of the light is increased. The central shielding method provides a projected image having excellent contrast but has such drawbacks that structure is complicated and the projected image is dark. In the aperture method, structure is simple and a bright projected image can be obtained. However, the aperture method poses a problem that contrast of the projected image is poor in comparison with those of the central shielding method and a method employing TN liquid crystal. This problem arises also in the light valve for forming the optical image as changes of light scattering state. In order to solve this problem, a measure may be considered in which the solid angle for converging light by the projection lens is reduced. However, since this measure leads to drop of brightness of a projected image, such a feature of the aperture method that the projected image is bright deteriorates. Meanwhile, video cameras are required to be made compact and light in weight as a whole for improvement of their portability. Thus, in order to make the video cameras compact as a whole, it is considered that a liquid crystal panel is employed in a viewfinder system. In case TN liquid crystal is used for the liquid crystal panel, two polarizers are employed. As a result, since efficiency of utilization of light is low, power consumption of a light source should be increased and thus, such an inconvenience is encountered that period enabling continuous use of the light source after charging of rechargeable batteries for the light source is shortened. Thus, a polymer dispersion liquid crystal panel having high efficiency of utilization of light may be employed in the viewfinder system. However, in this case, such a problem arises that the polymer dispersion liquid crystal panel provides an image having poor contrast. The article in Research Disclosure 304 describes a composite PDLC device for controlling light transmittance through a substrate or panel having a complex curvature, examples of which are architectural windows, windows for automobiles or other vehicles, and sunroofs. The outer substrates need not have a planar surface because they are bonded with Polyvinyl butyryl (PVB) to the inner substrates which enclose the light valve layer. The Japanese Patent Abstract JP-55 108 622 discloses a plano-concave lens positioned on a liquid crystal. The lens serves for removing unwanted reflections when the observer faces the concave surface of the lens and the image is watched in the backward direction. The EP-A-122 737 describes a liquid crystal apparatus comprising liquid crystal material in a support medium for selectively primarily scattering light or transmitting light in response to a prescribed input and reflecting means for effecting reflection of light scattered by said liquid crystal material. Furthermore, means are disclosed for displaying relatively bright characters or other information on a relatively dark background. In all these documents, however, no information about a favourable correlation between the dimensions of the substrates and their refractive indices for improving the contrast of the displayed image is disclosed. SUMMARY OF THE INVENTION Accordingly, an essential object of the present invention is to provide a display system, a projection display system and a viewfinder system employing a light valve for forming an optical image as changes of light scattering state, which are capable of displaying an image having excellent contrast. A light valve apparatus of the present invention comprises a light valve layer for forming an optical image as changes of light scattering state and two substrates between which the light valve layer is gripped and at least one of which is transparent such that the following condition is satisfied: t ≥ d 4 n 2 - 1 where t denotes a central thickness of the one of the substrates, n denotes a refractive index of the one of the substrates and d denotes a maximum diameter of an effective display area of the light valve layer. A face of the one of the substrates, which is held in contact with air, may have a concave surface. Meanwhile, in the above described arrangements, if a light reflecting means is provided on a face of each of the one of the substrates a reflection type light valve apparatus can be obtained. In the above arrangements, it is desirable that a light absorbing means is provided on an ineffective face of each of the one of the substrates while an anti-reflection means is provided on an effective area of each of a face of the one of the substrates in contact with air. If a positive lens is provided in close vicinity to the concave surface, uniformity of image quality is improved. Meanwhile, a projection display system of the present invention comprises a light source, a light valve apparatus which receives light emitted from the light source so as to form an optical image as changes of light scattering state and a projection lens for projecting the optical image onto a screen. The above mentioned light valve apparatus is used as the light valve apparatus of the projection display system. Furthermore, a viewfinder system of the present invention comprises a light source, a light valve apparatus which receives light emitted from the light source so as to form an optical image as changes of light scattering state and a magnifying lens for forming a virtual image of the optical image. The light valve apparatus referred to above is used as the light valve apparatus of the viewfinder system. In addition, a display system of the present invention comprises a light source and a light valve apparatus which receives light emitted from the light source so as to form an optical image as changes of light scattering state. The above described light valve apparatus is used as the light valve apparatus of the display system. BRIEF DESCRIPTION OF THE DRAWINGS This object and features of the present invention will become apparent from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings, in which: Fig. 1 is a schematic view explanatory of operation of a model of a light valve apparatus of the present invention; Fig. 2 is a graph showing a characteristic curve of the model of the light valve apparatus of Fig. 1; Fig. 3 is a schematic diagram explanatory of luminance distribution of the model of the light valve apparatus of Fig. 1; Fig. 4 is a schematic view explanatory of operation of another model of the light valve apparatus of Fig. 1; Figs. 5(a) and 5(b) are schematic views showing arrangements of the light valve apparatus of Fig. 1; Fig. 6 is a schematic view of a projection display system according to a first embodiment of the present invention; Fig. 7 is an enlarged fragmentary sectional view of a liquid crystal panel employed in the projection display system of Fig. 6; Fig. 8 is a schematic view of a projection display system according to a second embodiment of the present invention; Fig. 9 is a schematic view of a projection display system according to a third embodiment of the present invention; Fig. 10 is a schematic view of a projection display system according to a fourth embodiment of the present invention; Figs. 11(a) to 11(k) are schematic views showing various modifications of the light valve apparatus of Fig. 1, respectively; Fig. 12 is a schematic view of a projection display system according to a fifth embodiment of the present invention; Fig. 13 is a schematic view of a projection display system according to a sixth embodiment of the present invention; Fig. 14 is an enlarged fragmentary sectional view of a liquid crystal panel employed in the projection display system of Fig. 13; Fig. 15 is a schematic sectional view of a viewfinder system of the present invention; Fig. 16 is a schematic sectional view of a display system of the present invention; Figs. 17(a) and 17(b) are schematic views explanatory of operation of a prior art polymer dispersion liquid crystal panel (already referred to); and Fig. 18 is a schematic view of a prior art projection display system (already referred to). Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout several views of the accompanying drawings. DETAILED DESCRIPTION OF THE INVENTION Before the description of the present invention proceeds, operation of the present invention is described. Initially, contrast of a displayed image is described by adopting a polymer dispersion liquid crystal panel as one example. Fig. 1 shows a model of the polymer dispersion liquid crystal panel. In the liquid crystal panel, a polymer dispersion liquid crystal layer 33 is interposed between two transparent substrates 31 and 32 disposed at input and output sides of the liquid crystal panel, respectively. Thickness of the substrate 31 disposed at the input side of the liquid crystal panel is so set as to be sufficiently large relative to area of a display region. A case is here considered in which thin collimated rays 35 are irradiated from the input side to only a minute region 34 having a point A as its center in the display region without applying a voltage to the liquid crystal layer 33. Assuming that E o denotes illuminance of the collimated rays on an input face of the liquid crystal layer 33,  o denotes an output angle of the collimated rays, i.e. an angle formed between the collimated rays and a normal direction of the liquid crystal layer 33 and B o ( o ) denotes luminance of front scattered light in the direction of the angle  o , the luminance B o ( o ) is expressed by the following equation (1). B o ( o ) = 1 π G f ( o ) E o In the equation (1), the quantity G f ( o ) is referred to as "front scattering gain in the direction of the angle  o ". When the minute region 34 has an area S, luminous intensity I o ( o ) of a light emitting portion in the direction of the angle  o is given as follows. I o ( o ) = B o ( o ) S cos o At a point B on an output face 36 of the substrate 32 disposed at the output side of the liquid crystal panel, a light ray 37 outputted from the point A in the direction of the angle  o is divided into a transmitted light ray 38 and a reflected light ray 39. When the substrate 32 has a refractive index n and the transmitted light ray 38 has an output angle  1 , the following relation is obtained from Snell's law. sin 1 = n sin o Supposing that the front scattered light from the liquid crystal layer 33 is natural light and  oτ denotes a critical angle of total reflection, reflectance R( o ) of the front scattered light on the output face 36 is expressed as follows. The critical angle  oτ of total reflection is given by the following equation.  oτ = sin -1 1 n Light subjected to total reflection returns wholly to the liquid crystal layer 33. The light ray 39 reflected at the point B on the output face 36 is incident upon the liquid layer 33 at a point C. Supposing that E( o ) represents normal illuminance at the point C and t denotes a thickness of the substrate 32 disposed at the output side of the liquid crystal panel, an incident angle of the reflected light ray 39 at the point C is  o and an optical path length from the point A to the point C is 2t / cos o . Thus, the illuminance E( o ) obtained at the point C by the reflected light ray 39 is given as follows. E( o ) = I R( o ) cos  o (2t / cos  o ) 2 When the reflected light ray 39 is incident upon the liquid crystal layer 33, a scattered light ray 40 is forwardly outputted again by rear scattering from the liquid crystal layer 33 at an angle  2 . This corresponds to formation of a secondary light source in the liquid crystal layer 33. Luminance B( 2 ) of the scattered light ray 40 from the point C in the direction of the angle  2 is expressed as follows. B( 2 ) = G r ( 2 ,  o ) E π In the above equation (7), the quantity G r ( 2 ,  o ) is referred to as "rear scattering gain of the light ray incident in the direction of the angle  o and outputted in the direction of the angle  2 ". By combining the equations (1), (2), (6) and (7), the following relation is obtained. B( 2 ) = G f ( o ) G r ( 2 ,  o ) R( o ) E o S cos 4  o 4π 2 t 2 A distance r from the point A to the point C is expressed as follows. r = 2t tan o From the equations (8) and (9), it is possible to obtain distribution of luminance of the scattered light ray 40. Subsequently, by simplifying the equation (8), meaning of the equation (8) is considered. In order to improve contrast of an image displayed by the polymer dispersion liquid crystal panel, diffusion at the time of application of no voltage is approximate to perfect diffusion. Assuming that the light ray is subjected to perfect diffusion forwardly and rearwardly from the the liquid crystal layer 33, G f ( o ) = 1/2 and G r ( 2 ,  o ) = 1/2 are obtained and thus, the equation (8) is changed as follows. B( 2 ) = R( o ) E o S cos 4  o 16π 2 t 2 Since it is apparent from the equation (10) that the luminance B( 2 ) is a function of  o , distribution of luminance of the scattered light ray 40 from the liquid crystal layer 33 becomes symmetric with respect to thin input collimated rays. Since relation between the luminance B( 2 ) and the distance r is obtained from the equations (9) and (10), the results are shown in Fig. 2. It is seen from Fig. 2 that luminance of the scattered light ray 40 assumes a maximum value at a location spaced a predetermined distance from the output point A. The angle  o leading to the maximum value of distribution of luminance is approximately equal to the angle  oτ . Therefore, distribution of luminance of the scattered light ray 40 is formed into a ring having a radius r R given as follows. r R = 2t tan oτ By using the equation (5), the equation (11) is changed as follows. r R = 2t n 2 - 1 Actual luminance of a pixel is equal to a total of luminance of front scattered light and luminance of light outputted again by influence of scattered light emitted from the remaining pixels. When the pixel is used for white display, luminance of the front scattered light is far larger than luminance of the light outputted again, so that actual luminance of the pixel may be regarded as being substantially identical with luminance of the front scattered light. However, in case the pixel is used for black display, actual luminance of the pixel becomes high through addition of luminance of the light outputted again, even if luminance of the front scattered light is quite low. It should be noted that actual luminance of the pixel is likely to be most influenced by the scattered light emitted from pixels spaced the radius r R of the equation (12) from the pixel. From the above, it will be understood that poor contrast of a projected image of a projection display system employing a polymer dispersion liquid crystal panel is partly due to the fact that gain at the time when no voltage is applied to the liquid crystal panel is not low but also partly due to the above mentioned mechanism. Hereinbelow, function of the present invention is described. It is seen from the equation (10) that as the thickness t of the substrate 32 disposed at the output side of the liquid crystal panel becomes larger, the luminance B( 2 ) of the scattered light ray 40 becomes smaller. Therefore, if the thickness t of the substrate 32 disposed at the output side of the liquid crystal panel is increased, contrast of the displayed image is improved. This is the first function of the present invention for improving contrast. As shown in Fig. 3, a case is considered in which points P and Q give a maximum diameter of an effective display region 41 of the liquid crystal layer 33 and collimated rays are irradiated to only a minute region 42 having the point P as its center. A light ray outputted from the point P and reflected by the output face 36 is again outputted from the liquid crystal layer 33 so as to form a ring 43 on the liquid crystal layer 33. At this time, in order to restrict luminance of the light ray outputted again from the liquid crystal layer 33, the point Q should be disposed inside the ring 43. Namely, supposing that d denotes a length from the point P to the point Q, the following relation should be satisfied. r R ≥ d When the radius r is eliminated from the equations (12) and (13), the following relation is obtained. t ≥ d 2 n 2 - 1 When the condition of the equation (14) is satisfied, rise of luminance due to unnecessary light is restricted in the effective display region 41 as a whole, thereby resulting in improvement of contrast. Increase of the diameter of the ring 43 is the second function of the present invention for improving contrast. Meanwhile, through various experiments, the present inventors have found that contrast can be effectively improved sufficiently for practical use if a maximum diameter of the effective display region 41 is smaller than the diameter of the ring 43, namely the following relation is satisfied. 2r R ≥ d When the radius r is eliminated from the equations (12) and (15), the following relation is obtained. t ≥ d 4 n 2 - 1 The thickness t of the substrate 32 disposed at the output side of the liquid crystal panel may be selected so as to satisfy the equation (16). Then, a case is described in which the output face 36 of the substrate 32 is concave as shown in Fig. 4. Material and central thickness of the substrate 32 of Fig. 4 are identical with those of the substrate 32 of Fig. 1 and thus, the substrate 32 of Fig. 4 is different from that of Fig. 1 in that the substrate 32 of Fig. 4 has the concave output face 36. As shown in Fig. 4, without applying a voltage to the liquid crystal layer 33, the thin collimated rays 35 are irradiated from the input side to only the minute region 34 having the point A as its center in the display region. When a light ray is outputted from the point A on the liquid crystal layer 33 and reflected at the point B on a concave surface 44 so as to be incident upon the point C on the liquid crystal layer 33, a distance between a virtual image of the minute region 34 seen at the point C and the point C becomes longer as compared with that of Fig. 1 because the output face 36 of Fig. 4 has the concave surface 44, while the output face 36 of Fig. 1 has a flat surface. Meanwhile, in Fig. 4, since the incident angle of the light ray incident upon the point C after having been reflected at the point B becomes larger as compared with that of Fig. 1, luminance of the light ray outputted again from the liquid crystal layer 33 at the point C drops in view of the equation (10). Meanwhile, since the distance from the point A to the point C is increased, the diameter of the ring increases. Thus, by changing the output face 36 from the flat surface of Fig. 1 to the concave surface 44 of Fig. 4, the luminance of the light ray outputted again from the liquid crystal layer 33 can be reduced and thus, contrast of the displayed image can be improved. This indicates that in comparison with the substrate 32 having the flat surface as shown in Fig. 1, the substrate 32 having the concave surface 44 as shown in Fig. 4 shows greater effects for improving contrast even if the central thickness of the substrate 32 of Fig. 4 is smaller than that of Fig. 1. Subsequently, when a light ray is reflected on an ineffective face of the substrate 32, the light ray returns to the liquid crystal layer 33, thereby resulting in rise of luminance of a black display portion. As shown in Figs. 5(a) and 5(b), this problem can be solved by a technique in which a light absorbing means 46 is provided on the ineffective face of the substrate 32 so as to absorb unnecessary light. Furthermore, if an anti-reflection coating 47 is provided on an effective area of the output face 36 of the substrate 32, reflectance of the light ray on the output face 36 after having been outputted from the liquid crystal layer 33 at the small angle is reduced and thus, rise of luminance of the black display portion can be lessened. Thus, rise of luminance of the black display portion on the liquid crystal layer 33 can be reduced, so that it is possible to provide a light valve apparatus for displaying a bright image having high contrast. Meanwhile, if this light valve apparatus is used for a projection display system, a viewfinder system or a display system, a bright image having excellent contrast can be obtained. Hereinbelow, embodiments of the present invention are described with reference to the attached drawings. Fig. 6 shows a projection display system according to a first embodiment of the present invention. In Fig. 6, a light valve apparatus 51 includes a liquid crystal panel 52, a transparent plate 53 and a transparent body 54. A sealed vessel is constituted by the liquid crystal panel 52, two glass substrates 55 and 56 and sealing compound 57 such that polymer dispersion liquid crystal is filled, as a liquid crystal layer 58, into the sealed vessel. The liquid crystal layer 58 is interposed between the glass substrates 55 and 56 disposed at input and output sides of the liquid crystal panel 52, respectively. As shown in Fig. 7, a common electrode 59 formed by a transparent and electrically conductive film is provided on one of opposite faces of the substrate 55 adjacent to the liquid crystal layer 58. Meanwhile, a number of pixel electrodes 60 are provided in a shape of a matrix on one of opposite faces of the substrate 56 adjacent to the liquid crystal layer 58. A thin film transistor (TFT) 61 acting as a switching element is provided in the vicinity of each of the pixel electrodes 60. In the TFT 61, a source electrode 62 is connected to a signal line, a gate electrode 63 is connected to a scanning line and a drain electrode 64 is connected to each of the pixel electrodes 60. The signal line is connected to a signal supply line, while the scanning line is connected to a scanning circuit. A signal voltage is supplied to each pixel by the signal supply circuit and the scanning circuit. When subjected to a sufficient electric field, the liquid crystal layer 58 causes incident light to proceed straightforwardly. On the contrary, when subjected to no electric field, the liquid crystal layer 58 scatters incident light. As a result, the liquid crystal layer 58 at each pixel is capable of controlling light scattering state by applied voltage. Thus, an optical image can be formed, as changes of light scattering state, on on the liquid crystal panel 52 in accordance with an image signal. The transparent plate 53 is coupled, through the transparent body 54, with the output side of the liquid crystal panel 52. A spacer 65 is peripherally provided between the substrate 56 and the transparent plate 53 so as to regulate thickness of the transparent body 54. Black paint 67 is coated on a side face 66 of the transparent plate 53, while an anti-reflection coating 69 is provided in an effective region of an output face 68 of the transparent plate 53. The glass substrate 56 is formed by a glass sheet having a thickness of 1 mm, while the transparent plate 53 is formed by a glass plate having a thickness of 10 mm. The glass substrate 56 and the transparent plate 53 each have a refractive index of 1.52. The transparent body 54 is formed by transparent silicone resin "KE1051" (brand name of Shin-Etsu Chemical Co., Ltd. of Japan) and has a thickness of 2 mm and a refractive index of 1.40. This resin is formed by two kinds of liquids. When the two kinds of the liquids are mixed with each other and are either allowed to stand at room temperature or heated, the two kinds of the liquids are set into gel through addition polymerization. Alternatively, the transparent plate 53 may be made of transparent resin such as acrylic resin. Since transparency is the only prerequisite for the transparent body 54, the transparent body 54 may be made of liquid such as ethylene glycol, epoxy type transparent adhesive, transparent silicone resin which is set into gel through irradiation of ultraviolet rays thereto, etc. In the case of each of the above mentioned alternative materials of the transparent body 54, an air gap should not be formed between the substrate 56 and the transparent plate 53 because abnormal image quality is produced if the air gap exists between the substrate 56 and the transparent plate 53. A light source 70 is constituted by a lamp 71 and a concave mirror 72. Light emitted from the lamp 71 is concentrated by the concave mirror 72 such that light having relatively narrow directivity is outputted from the light source 70. The output light from the light source 70 is sequentially transmitted through a field lens 73, the liquid crystal panel 52, the transparent body 54 and the transparent plate 53 so as to be incident upon a projection lens 74. A pupil of the projection lens 74 is sized such that when a pixel disposed at a center of an image plane of the liquid crystal panel 52 is in transparent state, about 90 % of quantity of light outputted from the pixel diffusely is incident upon the pupil. The field lens 73 is provided for the following purpose. Namely, light transmitted through a periphery of the display region of the liquid crystal panel 52 is refracted inwardly by the field lens 73 so as to be incident upon the pupil of the projection lens 74 such that a peripheral portion of a projected image is not made dark. The projection lens 74 is used in combination with the transparent body 53 such that excellent image forming property is obtained. Focusing adjustments of the projected image are made by displacing the projection lens 74 along an optical axis 75. The optical image is formed, as changes of light scattering state, on the liquid crystal panel 52 in accordance with the image signal. Among light rays outputted from the pixels, the projection lens 74 receives a portion of the light rays, which is contained in a certain solid angle. If scattering state of the light rays outputted from the pixels changes, quantity of the light rays contained in the solid angle also changes. Thus, the optical image formed, as changes of light scattering state, on the liquid crystal panel 52 is converted into changes of illuminance on a screen 76. Thus, the optical image formed on the liquid crystal panel 52 is projected onto the screen on an enlarged scale by the projection lens 74. In the arrangement of Fig. 6, thickness from the liquid crystal layer 58 to the boundary surface 68 of the transparent plate 53 in contact with air is large. Hence, when front scattered light outputted from the liquid crystal layer 58 is reflected by the output face 68 of the transparent plate 53 so as to return to the liquid crystal layer 58 and then, is again outputted from the liquid crystal layer 58 through rear scattering in case no voltage is applied to the liquid crystal layer 58, luminance of the light outputted again from the liquid crystal layer 58 becomes smaller in comparison with a case in which the transparent plate 53 is not provided. Meanwhile, since light incident upon the side face 66 of the transparent plate 53 is absorbed by the black paint 67 coated on the side face 66, unnecessary light which will return to the liquid crystal layer 58 is reduced and thus, contrast of the displayed image on the liquid crystal layer 58 is improved. Furthermore, since the anti-reflection coating 69 is provided on the output face 68 of the transparent plate 53, reflection on the output face 68 of light which has been outputted from the liquid crystal layer 58 at a small output angle is lessened, which also contribute to improvement of contrast of the displayed image on the liquid crystal layer 58. Fig. 8 shows a projection display system according to a second embodiment of the present invention. In Fig. 8, the liquid crystal panel 52 and the light source 70 are the same as those of Fig. 7. A light valve apparatus 78 includes the liquid crystal panel 52, a plano-concave lens 79 and a transparent adhesive layer 80. An output face of the glass substrate 56 is bonded to the plano-concave lens 79 by the transparent adhesive layer 80 such that a concave surface 81 of the plano-concave lens 79 is oriented towards an output side. Black paint 83 is coated on a side face 82 of the plano-concave lens 79, while an anti-reflection coating 84 is deposited on the concave surface 81 of the plano-concave lens 79. The plano-concave lens 79 is made of acrylic resin by molding. Since dies of molding enable production of identical lenses, molding is suitable for mass production. A projection lens 85 is used in combination with the plano-concave lens 79 such that an optical image on the liquid crystal layer 58 is formed on the screen 76. Since light outputted from the concave surface 81 is required to be incident upon the projection lens 85, light incident upon the liquid crystal panel 52 should be converged light. Focusing adjustments of the projected image are made by displacing the projection lens 85 along an optical axis 87. Light from the light source 70 is transmitted through a field lens 88 so as to be incident upon the liquid crystal panel 52. Since the output face of the light valve apparatus 78 has the concave surface 81, rise of luminance due to light outputted again from the liquid crystal layer 58 can be restricted as described above. Therefore, contrast of the displayed image on the liquid crystal layer 58 is excellent and thus, contrast of the projected image is also improved. Meanwhile, the black paint 83 coated on the side face 82 of the plano-concave lens 79 and the anti-reflection coating 84 deposited on the concave surface 81 of the plano-concave lens 79 perform functions identical with those of the first embodiment so as to improve contrast of the projected image. Fig. 9 shows a projection display system according to a third embodiment of the present invention. In Fig. 9, the liquid crystal panel 52 and the light source 70 are the same as those of Fig. 6. A light valve apparatus 91 includes the liquid crystal panel 52, a plano-concave lens 92, a transparent adhesive layer 93 and a positive lens 94. The plano-concave lens 92 is bonded to an output face of the glass substrate 56 by the transparent adhesive layer 93 such that a concave surface 95 of the plano-concave lens 92 is oriented towards an output side. At an output side of the plano-concave lens 92, the positive lens 94 is provided in close vicinity to the plano-concave lens 92. A radius of curvature of a convex surface 96 of the positive lens 94 is identical with that of the concave surface 95 of the plano-concave lens 92. A small air gap is provided between the concave surface 95 and the convex surface 96. Black paint 98 is coated on a side face of the plano-concave lens 92, while an anti-reflection coating (not shown) is deposited on the concave surface 95 of the plano-concave lens 92. Although not specifically shown, anti-reflection coatings are deposited also on opposite faces 96 and 99. A projection lens 100 is used in combination with the plano-concave lens 92 and the positive lens 94 such that an optical image on the liquid crystal layer 58 is formed on the screen 76. Focusing adjustments of the projected image are made by displacing the projection lens 100 along an optical axis 101. Also in the arrangement of Fig. 9, since the plano-concave lens 92 is bonded to the output face of the liquid crystal panel 52 and the black paint 98 is coated on the side face 97 of the plano-concave lens 92 in the same manner as in the arrangement of Fig. 8, the projected image has excellent contrast. The polymer dispersion liquid crystal panel is not so dependent upon incident angle of optical characteristics as a TN liquid crystal panel. However, also in the polymer dispersion liquid crystal panel, when incident angle of light is extremely large, scattering characteristics change due to increase of optical path length at the time when the light passes through the liquid crystal panel 58. Namely, if incident angle of a light ray incident upon the liquid crystal panel 52 varies according to its location, image quality of the projected image becomes nonuniform. On the other hand, in the arrangement of Fig. 8, if radius of curvature of the concave surface 81 is to be reduced, either converged light having a large convergence angle should be incident upon the liquid crystal panel 52 or effective diameter of the projection lens 85 should be increased. However, in the former case, since image quality is not uniform at locations on the liquid crystal panel 52, image quality of the projected image becomes nonuniform. Meanwhile, in the latter case, such a problem arises that the projection lens 85 becomes larger in size, thereby resulting in rise of production cost of the display system. In the case where the liquid crystal panel 52 is heavily dependent upon incident angle of scattering characteristics, the plano-concave lens 92 may be combined with the positive lens 94 as shown in Fig. 9, so that light approximate to collimated rays can be incident upon the liquid crystal panel 52 without the need for making the projection lens 100 larger in size and thus, uniform image quality of the projected image can be readily secured. One of opposite faces of the positive lens 94 adjacent to the liquid crystal panel 52 may have a radius of curvature identical with or smaller than that of the concave surface 95 of the plano-concave lens 92. Thus, since the positive lens 94 is fitted into the concave surface 95, distance from the liquid crystal layer 58 to one of opposite vertexes of the positive lens 94 adjacent to the projection lens 100 can be shortened. Fig. 10 shows a projection display system according to a fourth embodiment of the present invention. In Fig. 10, other elements than a light valve apparatus 103 are the same as those of Fig. 6. The light valve apparatus includes the liquid crystal panel 52, a transparent plate 104 and a transparent body 105. The transparent plate 104 is coupled with an input side of the liquid crystal panel 52 through the transparent body 105. Black paint 107 is coated on a side face 106 of the transparent plate 104, while an anti-reflection coating is deposited on an input face of the transparent plate 104. When no voltage is applied to the polymer dispersion liquid crystal panel, rear scattering occurs in addition to front scattering. Thus, in the arrangement of Fig. 6, rear scattered light is reflected on the input face 102 of the glass substrate 55 disposed at the input side of the liquid crystal panel 52 so as to be again incident upon the liquid crystal layer 58. Since the light incident again upon the liquid crystal layer 58 raises luminance of the black display portion, contrast of the projected image is lowered. However, in the arrangement of Fig. 10, even if rear scattered light is reflected on the input face 108 of the transparent plate 104 so as to be again incident upon the liquid crystal layer 58, illuminance on the liquid crystal layer 58 based on the light incident again upon the liquid crystal layer 58 becomes low due to increase of its optical path length. Therefore, in the arrangement of Fig. 10, the projected image has excellent contrast in comparison with a case in which the transparent plate 104 is not provided. When the first embodiment of Fig. 6 and the fourth embodiment of Fig. 10 are combined with each other, namely, the transparent plates are, respectively, provided at both the input side and the output side of the polymer dispersion liquid crystal panel 52, contrast of the projected image is further improved. Thus, many modifications of the light valve apparatus of the present invention can be considered as shown in Figs. 11(a) to 11(k). In Figs. 11(a) to 11(k), the righthand portion corresponds to the input side, while a transparent plate 111 and a plano-concave lens 112 are connected to the liquid crystal panel 52 by transparent adhesive. Meanwhile, black paint is coated on ineffective faces of the transparent plate 111 and the plano-concave lens 112. When the plano-concave lens 112 is employed, a positive lens 114 may be combined with the plano-concave lens 112. Meanwhile, in order to brighten a peripheral portion of the projected image, it is desirable that a field lens be provided at the input side of the light valve apparatus. However, in case the plano-concave lens 112 is provided at the input side of the liquid crystal panel 52 and the positive lens 114 is provided at the input side of and in close vicinity to the plano-concave lens 112, the positive lens 114 functions as a field lens. In any one of the arrangements of Figs. 11(a) to 11(k), the projected image has excellent contrast as compared with the conventional arrangements in the same manner as the foregoing embodiments. Meanwhile, in the light valve apparatus, a section from the liquid crystal layer to a surface in contact with air may be made of a single material or may also be made of a plurality of materials. Fig. 12 shows a projection display system according to a fifth embodiment of the present invention. In Fig. 12, light valve apparatuses 121, 122 and 123 have an identical arrangement. Namely, the light valve apparatus 121 includes a liquid crystal panel 124, plano-concave lenses 127 and 130 and positive lenses 133 and 136. Similarly, the light valve apparatus 122 includes a liquid crystal panel 125, plano-concave lenses 128 and 131 and positive lenses 134 and 137, while the light valve apparatus 123 includes a liquid crystal panel 126, plano-concave lenses 129 and 132 and positive lenses 135 and 138. Each of the liquid crystal panels 124 to 126 is formed by a polymer dispersion liquid crystal panel and is identical with that of Fig. 7. The plano-concave lenses 127, 128 and 129 are, respectively, coupled with the input sides of the liquid crystal panels 124, 125 and 126 by transparent adhesive, while the plano-concave lenses 130, 131 and 132 are, respectively, coupled with the output sides of the liquid crystal panels 124, 125 and 126 by transparent adhesive. The positive lenses 133, 134 and 135 are, respectively, disposed at the input sides of the plano-concave lenses 127, 128 and 129 through a narrow air gap. On the other hand, the positive lenses 136, 137 and 138 are, respectively disposed at the output sides of the plano-concave lenses 130, 131 and 132 through a narrow air gap. Black paints 139, 140, 141, 142, 143 and 144 are coated on side faces of the plano-concave lenses 127, 128, 129, 130, 131 and 132, respectively. A light source 145 is constituted by a lamp 146, a concave mirror 147 and a filter 148. The lamp 146 is formed by a metal halide lamp and emits light including color components of primary colors of red, green and blue. The concave mirror 147 is made of glass. A multilayer film for reflecting visible light but transmitting infrared rays is deposited on a reflecting surface 149 of the concave mirror 147. The filter 148 is formed by depositing on a glass substrate a multilayer film for transmitting visible light but reflecting infrared light and ultraviolet light. Visible light contained in radiated light from the lamp 146 is reflected on the reflecting surface 149 of the concave mirror 147 and the reflected light approximates to collimated rays. The filter 148 eliminates infrared light and ultraviolet light from reflected light outputted from the concave mirror 147 such that the reflected light outputted from the concave mirror 147 is visible light. Subsequently, the light from the light source 145 is incident upon a color separation optical system formed by a combination of dichroic mirrors 150 and 151 and a flat mirror 152 so as to be separated into three light rays of the primary colors. The light rays of the respective primary colors are, respectively, incident upon the light valve apparatuses 121, 122 and 123 so as be transmitted through the positive lenses 133, 134 and 135 functioning as field lenses, respectively. The light rays outputted from the light valve apparatuses 121, 122 and 123 are composed into a single light ray by a color composition optical system formed by a combination of dichroic mirrors 153 and 154 and a flat mirror 155 so as to be incident upon a projection lens 156. Optical images corresponding to image signals are formed, as changes of scattering state, on the liquid crystal panels 124, 125 and 126, respectively and are projected onto a screen on an enlarged scale. Since the plano-concave lenses 127 and 130, the plano-concave lenses 128 and 131 and the plano-concave lenses 129 and 132 are, respectively, provided at the input and output sides of the liquid crystal panels 124, 125 and 126 in order to restrict stray light, drop of contrast due to stray light is lessened. Meanwhile, since the three liquid crystal panels 124, 125 and 126 are used for red, green and blue, respectively, the projected image has excellent brightness and resolution. In the arrangement of Fig. 12, each of the light valve apparatuses corresponds to that shown in Fig. 11(k) but may also be replaced by the light valve apparatuses shown in Figs. 6 to 10 and 11(a) to 11(j). An optimum construction for the light valve apparatuses should be selected in view of applications and restrictive conditions of the projection display system. Fig. 13 shows a projection display system according to a sixth embodiment of the present invention. The display system includes the light source 70, a light valve apparatus 171 and a projection lens 184. The light source 70 is the same as that shown in Fig. 6. The light valve apparatus 171 is constituted by a reflection type liquid crystal panel 172, a plano-concave lens 173 and a positive lens 174. In the liquid crystal panel 172, sealed space is defined by first and second glass substrates 175 and 176 and sealing compound 177 and polymer dispersion liquid crystal is filled, as a liquid crystal layer 178, into the sealed space. As shown in Fig. 14, TFTs 179 are formed in a pattern of a matrix on the first glass substrate 175 and a pixel electrode 181 made of aluminum is provided, through an insulating layer 180, on each of the TFTs 179. The pixel electrode 181 is connected to a drain electrode 182 of each of the TFTs 179. A common electrode 183 is formed on the second glass substrate 176 and is a transparent and electrically conductive film. The projection lens 184 is constituted by a first lens group 185 disposed adjacent to the liquid crystal panel 172 and a second lens group 186 disposed adjacent to the screen. A flat mirror 187 is provided between the first and second lens groups 185 and 186. After scattered light emitted from a pixel disposed at a center of an image plane of the liquid crystal panel 172 has been transmitted through the first lens group 185, about a half of the scattered light is incident upon the flat mirror 187 and the remainder is incident upon the second lens group 186 without being incident upon the flat mirror 187. A normal for a reflecting surface of the flat mirror 187 extends at an angle of 45° relative to an optical axis 188 of the projection lens 184. Light from the light source 70 is reflected by the flat mirror 187 so as to be transmitted through the first lens group 185 and then, is sequentially transmitted through the positive lens 174 and the plano-concave lens 173 so as to be incident upon the liquid crystal panel 172. Reflected light from the liquid crystal panel 172 is sequentially transmitted through the plano-concave lens 173, the positive lens 174, the first lens group 185 and the second lens group 186 so as to reach the screen. Through combination of the plano-concave lens 173 and the positive lens 174, the projection lens 184 is adapted such that an optical image on the liquid crystal layer 178 is formed on the screen. Meanwhile, a telecentric system is employed such that a light ray proceeding from a center of a stop of the projection lens 184 towards the liquid crystal panel 172 is substantially perpendicularly incident upon the liquid crystal layer 178. In the projection display system employing the polymer dispersion liquid crystal panel, scattering gain should be reduced so as to obtain excellent contrast of the projected image. In order to reduce the scattering gain, the liquid crystal layer may be made larger in thickness. However, if the liquid crystal layer is made thicker, voltage for setting the liquid crystal layer to transparent state becomes higher, so that output voltage of a drive IC is required to be increased and thus, quantity of heat produced by the drive IC becomes extremely large. As a result, such a problem arises that since uniformity of temperature of the liquid crystal layer cannot be secured, uniformity of image quality deteriorates. When the liquid crystal panel is of reflection type, light passes through the liquid crystal layer twice. Thus, in the reflection type liquid crystal panel, scattering gain can be reduced as compared with a transmission type liquid crystal panel including a liquid crystal layer having a thickness identical with that the liquid crystal layer of the reflection type liquid crystal panel. Therefore, regarding contrast of the projected image, the reflection type liquid crystal panel is advantageous over the transmission type liquid crystal panel. Namely, in the reflection type liquid crystal panel, the projected image has excellent contrast by lowering output voltage of the drive IC. Furthermore, in the arrangement of Fig. 13, since effects for improving contrast can be achieved by the plano-concave lens 173 at both the input side and the output side of the liquid crystal panel 172, contrast of the projected image is made remarkably excellent. By modifying the projection lens 184 in the arrangement of Fig. 13, the positive lens 174 may be eliminated or the plano-concave lens 173 may be replaced by a thick transparent plate. Fig. 15 shows a viewfinder system to which a light valve apparatus 201 of the present invention is applied. The light valve apparatus 201 includes a liquid crystal panel 202, a transparent plate 203, a plano-concave lens 204 and a positive lens 205. The liquid crystal panel 202 is formed by a polymer dispersion liquid crystal panel having a display image plane of 0.7 inch in diagonal. In the liquid crystal panel 202, sealed space is defined by two glass substrates 211 and 212 and sealing compound 213 and polymer dispersion liquid crystal is filled, as a liquid crystal layer 214, into the sealed space. The glass substrates 211 and 212 each have a thickness of 1.1 mm. The transparent plate 203 is coupled with an input side of the liquid crystal panel 202 by using transparent adhesive, while the piano-concave lens 204 is coupled with an output side of the liquid crystal panel 204 by using transparent adhesive. The positive lens 205 is disposed at an output side of and in close vicinity to the plano-concave lens 204. In addition, an ocular 206 is provided at an output side of the positive lens 205. Black paint is coated on ineffective faces of the transparent plate 203 and the plano-concave lens 204, while anti-reflection coatings are deposited on effective areas of faces of the transparent plate 203 and the plano-concave lens 204, which faces are held in contact with air. By using the plano-concave lens 204, the positive lens 205 and the ocular 206 in combination, a virtual image corresponding to an optical image on the liquid crystal panel 202 is arranged to be formed at a location disposed at a least distance of distinct vision when an observer watches the virtual image through the ocular 206 by shifting an eye of the observer close to the ocular 206. A lamp 207 is formed by a DC fluorescent lamp having a diameter of 7 mm and a length of 20 mm. Light diffused from the lamp 207 is converted by a pin hole 208 and a condenser lens 209 into light having narrow directivity and is transmitted through the transparent plate 203 so as to be incident upon the liquid crystal layer 214. At this time, since distance from an input face 215 of the transparent plate 203 to the liquid crystal layer 214 is long, drop of contrast due to rear scattering is restrained by the above described function of the pin hole 208 and the condenser lens 209. Meanwhile, the plano-concave lens 204 disposed at the output side of the liquid crystal panel 202 restrains drop of contrast caused by front scattered light. As a result, an image having excellent contrast can be obtained through the ocular 206. All the above mentioned constituent elements are accommodated in a housing 210. A light source having a small light radiator and high luminance, for example, an LED, a halogen lamp, a cathoderay tube, etc. may be desirably used as the lamp 207. Meanwhile, the light valve apparatus may be modified variously as shown in Figs. 11(a) to 11(k) and an image having excellent contrast can be obtained by any one of the arrangements of Figs. 11(a) to 11(k). Since the viewfinder system of the present invention does not employ a polarizer in the liquid crystal panel, its optical utilization efficiency is high. Therefore, in case the viewfinder system is mounted on a video camera, period for allowing continuous operation of the viewfinder system after charging of its batteries increases in comparison with a viewfinder system employing a TN liquid crystal panel. Fig. 16 shows a display system to which a light valve apparatus 221 of the present invention is applied. The light valve apparatus 221 is constituted by a liquid crystal panel 222 and two transparent plates 223 and 224. An effective display area of the liquid crystal panel 222 has a diagonal length of 10 inches. The liquid crystal panel 222 includes two transparent substrates 225 and 226 between which polymer dispersion liquid crystal is gripped as a liquid crystal layer (not shown). Although not specifically shown, transparent electrodes are provided in a pattern of a matrix on one of opposite faces of each of the transparent substrates 225 and 226 adjacent to the liquid crystal layer. When voltage corresponding to an image signal is applied to the transparent electrodes, an optical image is formed, as changes of light scattering state, on the liquid crystal layer. Transparent plates 223 and 224 are, respectively, bonded to input and output sides of the liquid crystal panel 222 by transparent adhesive. Each of the transparent plates 223 and 224 has a thickness of 40 mm and is made of acrylic resin. Black paint is coated on ineffective faces of the transparent plates 223 and 224, while anti-reflection coatings are deposited on effective areas of faces of the transparent plates 223 and 224, which faces are held in contact with air. A lamp 228 is formed by a DC fluorescent lamp having a diameter of 20 mm and a length of 40 mm. Light emitted from the lamp 228 is reflected by a flat mirror 229 and then, is converted by a Fresnel lens 230 into light having narrow directivity so as to be incident upon the light valve apparatus 221. Since luminance of light outputted again from the liquid crystal layer can be restrained by the two thick transparent plates 225 and 226, an image having excellent contrast is displayed on the liquid crystal panel 222. In the display system, although range of visual field angle is limited, a bright image having excellent contrast can be observed when viewed from a predetermined direction. Thus, the display system can be used for display at stores. In the foregoing embodiments of the present invention, the polymer dispersion liquid crystal panel is used as the light valve apparatus. In addition, any member which is capable of forming an optical image as changes of light scattering state, for example, a thermal writing mode liquid crystal panel employing phase change liquid crystal, a liquid crystal panel employing ferroelectric liquid crystal based on changes of scattering state, PLZT, etc. can also be used as the light valve apparatus of the present invention. As is clear from the foregoing description of the light valve apparatus of the present invention in which the optical image is formed as changes of scattering state, a bright image having excellent contrast can be obtained by making the transparent substrate thicker or combining the transparent plate or the plano-concave lens with the transparent substrate. Meanwhile, such a remarkable effect is gained that by using this light valve apparatus, display systems such as a projection display system and a viewfinder system, which are capable of displaying a bright image having excellent contrast, can be obtained.

Claims: A light valve apparatus comprising: a light valve layer (33) for forming an optical image as changes of light scattering state; and two substrates (31, 32) between which said light valve layer (33) is gripped and at least one of which is transparent; characterized in that the following condition is satisfied: t ≥ d 4 n 2 - 1 where t denotes a central thickness of said at least one of said substrates (31, 32), n denotes a refractive index of said at least one of said substrates (31, 32) and d denotes a maximum diameter of an effective display area of said light valve layer (33). A light valve apparatus as claimed in claim 1, further comprising: a light absorbing means (46) which is provided at a portion of said at least one of said substrates (31, 32), through which portion light effective to image does not pass. A light valve apparatus as claimed in claim 1 or 2, further comprising: an anti-reflection means (47) which is provided at a portion of a face of said at least one of said substrates (31, 32), through which portion light effective to image passes; said face of said at least one of said substrate (31, 32) being held in contact with air. A light valve apparatus as claimed in one of the claims 1 to 3, wherein one (36) of opposite faces of said at least one of said substrates (31, 32) remote from said light valve layer (33) has a concave surface. A light valve apparatus as claimed in claim 4, further comprising: a positive lens (94) which is provided in close vicinity to said concave surface (95). A light valve apparatus as claimed in one of the claims 1 to 5, further comprising: a reflection means (181) which is provided between said at least one of said substrates (175) and said light valve layer (178). A projection display system comprising: a light source (70; 145); a light valve apparatus (51; 78; 91; 103; 121, 122, 123; 171) which receives light emitted from said light source (70; 145) so as to form an optical image as changes of light scattering state; and a projection lens (74; 85; 100; 156; 184) for projecting the optical image onto a screen (76); said light valve apparatus (51; 78; 91; 103; 121, 122, 123; 171) including a light valve layer (58; 178) for forming the optical image as changes of light scattering state and two substrates (55, 56) between which said light valve layer (58; 178) is gripped and at least one of which is transparent; characterized in that the following condition is satisfied: t ≥ d 4 n 2 - 1 where t denotes a central thickness of said at least one of said substrates, n denotes a refractive index of said at least one of said substrates (55, 56) and d denotes a maximum diameter of an effective display area of said light valve layer (58; 178). A projection display system as claimed in claim 7, further comprising: a light absorbing means (67; 83; 98; 107; 113; 139-144) which is provided at a portion of said at least one of said substrates (55, 56), through which portion light effective to image does not pass. A projection display system as claimed in claim 7 or 8, further comprising: an anti-reflection means which is provided at a portion of a face of said at least one of said substrates (55, 56), through which portion light effective to image passes; said face of said at least one of said substrates (55, 56) being held in contact with air. A projection display system as claimed in one of the claims 7 to 9, wherein one (81) of opposite faces of said at least one of said substrates (55, 56) remote from said light valve layer (58) has a concave surface . A projection display system as claimed in claim 10, further comprising: a positive lens (94) which is provided in close vicinity to said concave surface (95). A projection display system as claimed in claim 11, further comprising: a reflection means (181) which is provided between said at least one of said substrates (175) and said light valve layer (178). A viewfinder system comprising: a light source (207); a light valve apparatus (201) which receives light emitted from said light source (207) so as to form an optical image as changes of light scattering state; and a magnifying lens (206) for forming a virtual image of the optical image; said light valve apparatus (201) including a light valve layer (214) for forming the optical image as changes of light scattering state and two substrates (211,212) between which said light valve layer (214) is gripped and at least one of which is transparent; characterized in that the following condition is satisfied: t ≥ d 4 n 2 - 1 where t denotes a central thickness of said at least one of said substrates (211, 212), n denotes a refractive index of said at least one of said substrates (211, 212) and d denotes a maximum diameter of an effective display area of said light valve layer (214). A viewfinder system as claimed in claim 13, further comprising: a light absorbing means which is provided at a portion of said at least one of said substrates (203, 204), through which portion light effective to image does not pass. A viewfinder system as claimed in claim 13 or 14, further comprising: an anti-reflection means which is provided at a portion of a face of said at least one of said substrates (203, 204), through which portion light effective to image passes; said face of said at least one of said substrates (203, 204) being held in contact with air. A viewfinder system as claimed in claims 13 to 15, wherein one of opposite faces of said at least one of said substrates (211, 212) remote from said light valve layer (214) has a concave surface. A viewfinder system as claimed in claim 16, further comprising: a positive lens (205) which is provided in close vicinity to said concave surface. A display system comprising: a light source (228); and a light valve apparatus (221) which receives light emitted from said light source (228) so as to form an optical image as changes of light scattering state; said light valve apparatus (221) including a light valve layer for forming the optical image as changes of light scattering state and two substrates (225, 226) between which said light valve layer is gripped and at least one of which is transparent; characterized in that the following condition is satisfied: t ≥ d 4 n 2 - 1 where t denotes a central thickness of said at least one of said substrates (225, 226), n denotes a refractive index of said at least one of said substrates (225, 226) and d denotes a maximum diameter of an effective display area of said light valve layer. A display system as claimed in claim 18, further comprising: a light absorbing means which is provided at a portion of said at least one of said substrates (225, 226), through which portion light effective to image does not pass. A display system as claimed in claim 18 or 19, further comprising: an anti-reflection means which is provided at a portion of a face of said at least one of said substrates (225, 226), through which portion light effective to image passes; said face of said at least one of said substrates (225, 226) being held in contact with air. A display system as claimed in one of the claims 18 to 20, wherein one of opposite faces of said at least one of said substrates (225, 226) remote from said light valve layer has a concave surface. A display system as claimed in claim 21, further comprising: a positive lens (230) which is provided in close vicinity to said concave surface.

Inventors: MIYATAKE YOSHITO, OHMAE HIDEKI, TAKAHARA HIROSHI, MIYATAKE, YOSHITO, OHMAE, HIDEKI, TAKAHARA, HIROSHI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1993
Main classification: G02F1
IPC codes: G02F1, G03B21, G02B1, H04N5