Light Emissive Panel Unit

1. Field of the Invention

The present invention relates to a light emissive panel unit used as a surface light source unit and a display panel unit.

2. Description of the Related Art

FIG. 1 shows a conventional surface light source unit disclosed in Japanese Laid Open Patent Application No. 2-157791. Referring to FIG. 1, a surface light source unit 10 has a plate body 11 and cold-cathode lamps 12 facing side edge surfaces of the plate body 11. The plate body 11 has a light guide plate 13 made of acrylic resin, a light diffusing plate 14 and a reflecting plate 16. The light diffusing plate 14 is provided on a surface of the light guide plate 13. The reflecting plate 16 is provided with a diffusive reflecting layer 15 formed on a surface thereof. The reflecting plate 16 is provided on another surface of the light guide plate 13 such that the diffusive reflecting layer 15 is on the surface of the light guide plate.

In the surface light source unit shown in FIG. 1, light emitted from the cold-cathode lamps 12 is shut into the light guide plate 13 and is repeatedly reflected by the diffusive reflecting layer 15 and the boundary between the surface of the light guide plate 13 and the light diffusing plate 14. While the light is being repeatedly reflected, a part of the light shut in the light guide plate 13 is emitted through the light diffusing plate 14. As a result, the surface of the diffusing plate 14 uniformly lights.

The conventional surface light source unit described above must have the light guide plate 13 which is solid. Thus, the surface light source unit is relatively heavy. In addition, it is difficult to adjust the brightness of the surface light source unit.

Accordingly, a general object of the present invention is to provide a novel and useful light emissive panel unit in which the disadvantages of the aforementioned prior art are eliminated.

A more specific object of the present invention is to provide a light emissive panel unit having a light weight.

Another object of the present invention is to provide a light emissive panel unit by which the brightness can be easily adjusted.

The above objects of the present invention are achieved by a light emissive panel unit comprising: light source means for emitting light; a prism plate to which the light emitted by the light source means is made incident, a part of the light being reflectable by the prism plate and another part of the light passing through the prism plate; and adjusting means for partially adjusting an amount of light emitted from a surface of the prism plate.

The light emissive panel unit may form a surface light source unit in which the amount of light emitted from the surface of the prism plate is partially adjusted by the adjusting means so as to be substantially uniform.

The light emissive panel unit may also form a display panel unit in which the amount of light emitted from the surface of the prism plate is partially adjusted by the adjusting means so that image patterns are formed on the surface of the prism plate.

According to the present invention, since the light emissive panel can be formed without the light guide plate, the light emissive panel can made lighter. In addition, since the amount of light emitted from the surface of the plate prism is partially adjusted by the adjusting means, the brightness of the light emissive panel can be easily adjusted.

Additional objects, features and advantages of the present invention will become apparent from the following detained description when read in conjunction with the accompanying drawings.

FIG. 1 is a diagram illustrating a conventional surface light source unit.

FIG. 2 is a diagram illustrating a surface light source unit according to a first embodiment of the present invention.

FIG. 3 is a perspective view illustrating the structure of a prism plate provided in the surface light source unit shown in FIG. 2.

FIG. 4 is a cross sectional view, taken along line IV-IV shown in FIG. 2, illustrating the prism plate.

FIG. 5 is a diagram illustrating a function of the prism plate.

FIG. 6 is a graph illustrating a relationship between a emitting rate and a prism angle (a base angle) with a parameter of a direction in which the prism plate is arranged.

FIG. 7 is a graph illustrating a brightness distribution on a lighting surface of the surface light source unit.

FIG. 8 is a perspective view illustrating a first modification of the prism plate.

FIG. 9 is a perspective view illustrating a second modification of the prism plate.

FIG. 10 is a perspective view illustrating a third modification of the prism plate.

FIG. 11 is a perspective view illustrating a fourth modification of the prism plate.

FIG. 12 is a graph illustrating variation of the prism angle in a direction in which each prism convex part extends in the prism panel show in FIG. 11.

FIG. 13 is a perspective view illustrating a fifth modification of the prism plate.

FIG. 14 is a perspective view illustrating a sixth modification of the prism plate.

FIG. 15 is a perspective view illustrating a seventh modification of the prism plate.

FIG. 16 is a diagram illustrating the surface light source unit according to a second embodiment of the present invention.

FIG. 17 is a diagram illustrating the surface light source unit according to a third embodiment of the present invention.

FIG. 18 is a diagram illustrating the surface light source unit according to a fourth embodiment of the present invention.

FIG. 19 is a diagram illustrating the surface light source unit according to a fifth embodiment of the present invention.

FIG. 20 is a graph illustrating the brightness distribution on the lighting surface of the surface light source unit shown in FIG. 19.

FIG. 21 is a diagram illustrating the surface light source unit according to a sixth embodiment of the present invention.

FIG. 22 is a diagram illustrating the surface light source unit according to a seventh embodiment of the present invention.

FIG. 23 is a diagram illustrating the surface light source unit according to an eighth embodiment of the present invention.

FIG. 24 is a diagram illustrating a display panel unit according to a first embodiment of the present invention.

FIG. 25 is a perspective view illustrating the structure of a prism panel used in the display panel unit show in FIG. 24.

FIGS. 26A and 26B are perspective views illustrating a first modification of the prism panel.

FIG. 27 is a diagram illustrating a second modification of the prism panel.

FIG. 28 is a diagram illustrating a third modification of the prism panel.

FIG. 29 is a diagram illustrating a fourth modification of the prism panel.

FIG. 30 is a diagram illustrating the display panel unit according to a second embodiment of the present invention.

FIG. 31 is a diagram illustrating the display panel unit according to a third embodiment of the present invention.

A description will now be given of a surface light source unit according to a first embodiment of the present invention.

A surface light source unit is formed, for example, as show in FIG. 2. Referring to FIG. 2, a surface light source 30 has a body 31 and a prism plate 34. The body 31 is formed of a rectangular shaped reflector 32 and holders 31a and 31b provided at both sides of the reflector 32 so that an opening facing the reflector 32 is formed between the holders 31a and 31b. The reflector 32 is provided with an aluminum sheet having a thickness of 0.5 mm on the surface thereof, a silver thin film being placed on the surface the aluminum sheet. The holders 31a and 31b respectively house cold-cathode lamps 33-1 and 33-2 so that the cold-cathode lamps 33-1 and 33-2 face each other. Each of the cold cathode tubes 33-1 and 33-2 is a cylindrical tube having, for example, a diameter of 3 .phi. and a length of 240 mm. The prism plate 34 is mounted between the holders 31a and 31b so as to cover the opening in the body 31, so that a space 37 is formed between the prism plate 34 and the reflector 32.

The prism plate 34 is a clear plate made of polycarbonate resin, and a thickness thereof is, for example, 0.36 mm. The prism plate is formed, for example, as shown in FIGS. 3 and 4. The prism plate 34 has a prism surface 34a and a flat surface 34b which are opposite to each other. On the prism surface 34a, a plurality of linear prisms 34c are formed so as to be parallel to each other at intervals of, for example, 0.35 mm (p=0.35 mm). A vertical angle .THETA. of each of the linear prisms 34c is equal to 90.degree. (.THETA.=90.degree.), and a prism angle .alpha. (the base angle) of each of the linear prisms 34c is equal to 45.degree. (.alpha.=45.degree.). A plurality of small cylindrical blocks 34d are formed at predetermined positions on the prism surface 34a so that the prism surface 34a is dotted with the small cylindrical blocks 34d. Dots made of acrylate clear resin having a ultraviolet-setting property are printed on the prism surface 34a and are then hardened, so that the small cylindrical blocks 34d are formed on the prism surface 34a.

The prism plate 34 is mounted on the body 31 of the surface light source unit 30 so that the prism surface 34a faces the reflector 32. In addition, the direction of the prism plate 34 is adjusted so that a line 35 parallel to a direction in which each of the linear prisms 34c extends is perpendicular to a line 36 parallel to a direction in which each of the cold-cathode lamps 33-1 and 33-2 extends.

A light diffusion plate 38 is formed on the flat surface 34b of the prism plate 34. The light diffusion plate 38 is formed of a clear resin film on which glass beads are scattered, the clear resin having a thickness, for example, of 0.25 mm. A surface of the light diffusion plate 38 is a lighting surface 40 of the surface light source unit 30.

In the surface light source unit 30 having the above structure, a light 39 emitted from the cold-cathode lamps 33-1 and 33-2 is incident to the prism surface 34a of the prism plate 34 as shown in FIG. 5. Referring to FIG. 5, when the light 39 is incident to each of the linear prisms 34c, a part 39a of the light 39 is reflected twice by adjacent surfaces of the linear prisms 34c producing reflected beams 39a and 39b. The twice reflected light 39b then travels in the space 37 toward the reflector 32. Another part 39c of the light 39 incident to each of the linear prisms 34 travels through the prism plate 34, this light being incident on the light diffusion plate 38. The light traveling through the light diffusion plate 38 is diffused by the light diffusion plate 38. The diffused light 39 is then emitted from the lighting surface 40.

The light 39a reflected by the surfaces of the linear prisms 34c travels in the space 37 and is reflected by the reflector 32. That is, the light 39a is repeatedly reflected by the prism surface 34a and the reflector 32 so that the light 39a is confined in the space 37. While the light 39a is being repeatedly reflected in the space 37, a parts 39c and 39e of the light 39 are made incident on the prism plate 34 and are emitted as beams 39d and 39f, respectively, through the lighting surface 40.

FIG. 6 indicates relationships between the prism angle .alpha. of each of the linear prisms 34c and the emitting rate (%), which relationships were obtained by experiments using the surface light source unit 30 as shown in FIG. 2. In these experiments, no small cylindrical blocks were formed on the prism surface 34a of the prism plate 34. Referring to FIG. 6, a first curve I indicates a relationship between the prism angle .alpha. and the emitting rate under a condition in which the prism plate 34 was mounted on the body 31 so that the line parallel to the direction in which each of the linear prisms 34c extends is parallel to the line parallel to the direction in which each of the cold-cathode lamps 33-1 and 33-2 extends. A second curve II indicates a relationship between the prism angle .alpha. and the emitting rate under a condition in which the prism plate 34 is mounted on the body 31 so that the line parallel to a direction in which each of the linear prisms 34c extends is perpendicular to the line 35 parallel to the direction in which each of the cold-cathode lamps 33-1 and 33-2 extends. In FIG. 6, a 100% emitting rate means a state in which the prism plate 34 is removed from the body 31 so that the light is not confined in the space 37, and a 0% emitting rate means a state in which an opaque is substituted for the prism plate 34 so that none of the light is emitted through the lighting surface 40. Further, an 80% emitting rate means that 20% of the light is confined in the space 37. With reference to the first curve I and the second curve II in FIG. 6, in a case where the prism plate 34 is mounted on the body 31 so that the line 35 parallel to the direction in which each of the linear prisms 34c extends is perpendicular to the line 36 parallel to the direction in which each of the cold-cathode lamps 33-1 and 33-2 extend and the prism angle .alpha. is equal to 45.degree., the lowest emission rate of 65% is obtained. That is, in this case, the light is most effectively confined in the space 37 between the prism plate 34 and the reflector 32.

The arrangement and the structure of the prism plate 34 of the surface light source unit 30 shown in FIG. 2 were decided on, based on the results of the above experiments.

On the other hand, a great part 39e of the light incident to each of the small cylindrical blocks 34d travels through the prism plate 34 and is further incident into the light diffusion plate 38. The light 39e incident into the diffusion plate 38 is diffused thereby and diffused light 39f is then emitted from the lighting surface 40 of the surface light source unit 30. That is, the small cylindrical blocks 34d lower the function, by which the light is reflected, of the prism plate 34. Thus, due to using the small cylindrical blocks 34d, the emission rate of the prism plate 34 can be partially adjusted.

On the lighting surface 40 of the surface, luminance of an area near a lamp is higher than that of an area away from the lamp. Thus, if there is no small cylindrical block lowering the function of the prism plate 34, the luminance distribution on the lighting surface 40 in a direction perpendicular to a direction in which each of the cold-cathode lamps 33-1 and 33-2 is formed as shown by a curve III in FIG. 7. In the embodiment, the small cylindrical blocks 34d are formed on the prism surface 34a so that a number of small cylindrical blocks 34d in an area away from each of the cold-cathode lamps 33-1 and 33-2 is greater than a number of those in an area near each of the cold-cathode lamps 33-1 and 33-2. Thus, the emission rate in the area away from each of cold-cathode lamps 33-1 and 33-2 is increased, and the emission rate in the area near each of cold-cathode lamps 33-1 and 33-2 is decreased. As a result, the luminance distribution on the lighting surface 40 is formed as shown by a curve V in FIG. 7 so that the lighting surface 40 uniformly lights.

A prism plate 34A shown in FIG. 8 may be substituted for the prism plate 34 shown in FIGS. 2 and 3. Referring to FIG. 8, small holes 50 are formed on the prism surface 34a instead of the small cylindrical blocks 34d. In a case where the prism plate 34A is mounted on the body 31 of the surface light source unit 30 as shown in FIG. 2, the light passes through the small holes 50. Thus, an amount of light reflected by an area on which the small holes 50 are formed is decreased, and so the emission rate of this area is increased. That is, due to using the small holes 50, the brightness of the lighting surface 40 can be partially adjusted.

A prism plate 34B shown in FIG. 9 may be also substituted for the prism plate 34 shown in FIGS. 2 and 3. Referring to FIG. 9, small notches 51 are formed on the prism surface 34a of the prism plate 34B instead of the small cylindrical blocks 34d. In a case where the prism plate 34B is mounted on the body 31 of the surface light source unit 30 as shown in FIG. 2, the light passes through the small notches 51. Thus, an amount of light reflected by an area on which the small notches 51 are formed is decreased, and so the emission rate of this area is increased. That is, due to using he small notches 51, the brightness of the lighting surface 40 can be partially adjusted.

A prism plate 34C shown in FIG. 10 may be also substituted for the prism plate 34 shown in FIGS. 2 and 3. Referring to FIG. 10, a flat surface 52 is formed on the prism surface 34a having the linear prisms 34. The flat surface is located at a center of the prism plate 34C and extends in a direction perpendicular to a direction in which each of the linear prisms 34c extends, which center is a position away from each of the cold-cathode lamps 33-1 and 33-2. The light incident to the flat surface 52 passes through the prism plate 34C. The emission rate of an area on which the flat surface 52 is formed can be increased.

A prism plate 34D shown in FIG. 11 may be also substituted for the prism plate 34 shown in FIGS. 2 and 3. Referring to FIG. 11, the prism angle .alpha. of each of the linear prisms 34Dc formed on the prism surface 34a of the prism plate 34D continuously varies as shown in FIG. 12. That is, the prism angle of each of the linear prisms 34Dc is continuously decreased from 45.degree. (=.alpha.) so that the farther from an end surface 34e which is the nearest each of the cold-cathode lamps 33-1 and 33-2, the smaller the prism angle (.alpha.l<.alpha.), as shown by a curve V in FIG. 12. According to the curve II shown in FIG. 6, the smaller the prism angle .alpha., the larger the emission rate. Thus, in the surface light source unit 30 having the prism plate 34D, the farther from each of the cold-cathode lamps 33-1 and 33-2, the larger the emission rate, so that the brightness of the lighting surface 40 can be uniform.

A prism plate 34E shown in FIG. 13 may be also substituted for the prism plate 34 shown in FIGS. 2 and 3. Referring to FIG. 13, each of the linear prisms 34c is divided into a first portion near the end surface 34e which is nearest each of the cold-cathode lamps 33-1 and 33-2 and a second portion away from the end surface 34e. The prism angle .alpha. of the first portion is greater than the prism angle .alpha.2 of the second portion. In this case, the emission rate of the first portion of each of the linear prisms 34c, which portion is near each of the cold-cathode lamps 33-1 and 33-2, is less than the emission rate of the second portion each thereof. Thus, the brightness of the lighting surface 40 can be uniform.

A prism plate 34F shown in FIG. 14 may be also substituted for the prism plate 34 shown in FIGS. 2 and 3. Referring to FIG. 14, second linear prisms 34Fc which extend in a direction parallel to the end surface 34e of the prism plate 34F are formed on the prism surface 34a so as to cross first linear prisms 34c which extend in a direction perpendicular to each of the end surfaces 34e. The second linear prisms 34Fc are located at positions at which the emission rate should be increased.

In the surface light source unit 30 having the prism plate 34F shown in FIG. 14, the first linear prisms 34c extend in a direction perpendicular to a direction in which each of the cold-cathode lamps 33-1 and 33-2 extend, and the second linear prisms 34Fc extend in a direction parallel to the direction in which each of the cold-cathode lamps 33-1 and 33-2. According to the curves I and II shown in FIG. 6, the emission rate of the linear prism extending in a direction parallel to each of the cold-cathode lamps 33-1 and 33-2 is greater than that of the linear prism extending in a direction perpendicular to each of the cold-cathode lamps 33-1 and 33-2. Thus, the emission rate of the prism plate can be partially increased by the second linear prisms 34Fc so that the brightness of the lighting surface 40 can be uniform.

A prism plate 34G shown in FIG. 15 may be also substituted for the prism plate 34 shown in FIGS. 2 and 3. Referring to FIG. 15, the prism plate 34G is formed of two prism layers 34G1 and 34G2, each of which has the same structure as the prism plate 34 shown in FIG. 3. The prism layers 34G1 and 34G2 are adhered by clear resin blocks 55 which are printed so as to be dotted on the prism layers 34G1 and 34G2. In the prism plates 34G formed of the two prism layers 34G1 and 34G2, the emission rate is decreased. As a result, a range in which the emission rate can be partially controlled by the small cylindrical blocks 34d can extend.

A surface light source unit according to a second embodiment of the present invention is formed as shown in FIG. 16. In FIG. 16, those parts which are the same as those shown in FIG. 2 are given the same reference numbers.

Referring to FIG. 16, the surface light source unit 30A has a curved prism plate 34H which is mounted on the holders 31a and 31b of the body 31 so that the distance between the prism plate 34H and the reflector 32 is decreased with going away from each of the cold-cathode lamps 33-1 and 33-2, as shown by D1, D2 and D3. That is, a space 37A formed between the curved prism plate 34H and the reflector 32 becomes narrower with going away from each of the cold-cathode lamps 33-1 and 33-2.

In the surface light source unit 30A having the above structure, since the space 37A between the curved prism plate 34H and the reflector 32 becomes continuously narrower with going away (i.e., at increased structures) from each of the cold-cathode lamps 33-1 and 33-2, the number of times by which the light emitted from each of the cold-cathode lamps 33-1 and 33-2 is reflected by the reflector 32 and the curved prism plate 34H is progressively less than the number of times in the surface light source unit 30 shown in FIG. 2. Each time a light is reflected by a surface of a medium, a part of the light is absorbed by the medium and the intensity of the reflected light is reduced. In a case, for example, where the light is reflected by the surface of the medium having a reflection coefficient of 94% eleven times, the intensity I of the reflected light becomes about half (0.94.sup.11 I=0.51 I). In the surface light source unit 30A shown in FIG. 16, since the number of times by which the light is reflected by the reflector 32 and the curved prism plate 34H is small, the quantity of light reduced in the space 37A is also small. Thus, the brightness of the lighting surface 40 is higher than that in a case of the surface light source unit 30 shown in FIG. 2.

A surface light source unit according to a third embodiment of the present invention is formed as shown in FIG. 17.

Referring to FIG. 17, a surface light source unit 30B has two prism plates 34I and 34J which are inclined on the body 31 so that spaces 37A and 37B respectively formed between the reflector 32 and the prism plates 34I and 34J becomes narrower with going away from the cold-cathode lamps 33-1 and 33-2. Thus, the number of times by which the light reflected in the spaces 34I and 34J is reduced in the same manner as that in a case of the surface light source unit 30A shown in FIG. 16. That is, the brightness of the lighting surface 40, which is a surface of the light diffusion plate 38 formed on the prism plates 34I and 34J, can be improved. In addition, since both the prism plates 34I and 34J are flat, and thus not curved, it is easy to make them.

A surface light source unit according to a fourth embodiment of the present invention is formed as shown in FIG. 18.

Referring to FIG. 18, the curved prism plate 34H and the body 31 having the holders 31a and 31b in which the cold-cathode lamps 33-1 and 33-2 are mounted are assembled in the same manner as those shown in FIG. 16. A converging prism plate 60 is formed on the surface of the curved prism plate 34H, and the light diffusion plate 38 is fixed on the surface of the converging prism plate 60. The converging prism plate 60 is formed clear polycarbonate resin. Slender prisms, in each of which the vertical angle .THETA. is 90.degree., are formed on a prism surface of the converging prism plate 60. The thickness of the converging prism plate 60 is, for example, equal to 0.36 mm.

The converging prism plate 60 refracts the light emitted through the curved prism plate 34H so that the light is perpendicularly incident to the light diffusion plate 38. As a result, the lighting surface 40 is brighter than that of the surface light source unit shown in FIG. 16.

A surface light source unit according to a fifth embodiment of the present invention is shown in FIG. 19.

Referring to FIG. 19, the prism plates 34I and 34J and the body having the holders 31a and 31b in which the cold-cathode lamps 33-1 and 33-2 are mounted are assembled in the same manner as those shown in FIG. 17. A converging prism plate 61 is formed on the surface of the prism plates 34I and 34J, and the diffusion plate 38 is fixed on the converging prism plate 61. A direction in which each of linear prisms 62 formed on the converging prism plate 61 extend is inclined by about 45.degree. with respect to the direction in which each of the cold-cathode lamps 33-1 and 33-2 extends.

The brightness distribution on the lighting surface 40 of the surface light source unit having a 8 mm thickness (this thickness corresponding to the thickness of each of holders of the cold-cathode lamps 33-1 and 33-2), the lighting surface 40 having a lighting area of 165 mm.times.225 mm, is shown in FIG. 20. The brightness of the lighting surface 40 is almost uniform and has a high level, as shown by a curve VI in FIG. 20.

A surface light source unit according to a sixth embodiment of the present invention is shown in FIG. 21.

Referring to FIG. 21, the body 31 has a holder 31Aa formed at an end of the first reflector 32, in which holder 31Aa the cold-cathode lamp 33-1 is mounted, and a second reflector 65 provided at an opposite end of the first reflector 32 so that the second reflector 65 faces the cold-cathode lamp 33-1. A curved prism plate 34K is provided between the holder 31Aa and the second reflector 65.

In this surface light source unit 30E having the single cold-cathode lamp 33-1, the light which reaches the second reflector 65 is reflected thereby so as to return into the space 37. Thus, the second reflector 65 functions as a pseudo-light-source.

A surface light source unit according to a seventh embodiment of the present invention is shown in FIG. 22.

Referring to FIG. 22, a surface light source unit 30F has a body 31B formed of a reflector 32B and a holder 31Ba provided at an end of the reflector 32B, in which holder 31Ba the cold-cathode lamp 33-1 is mounted, and the prism plate 34. Side ends of the prism plate 34 are supported by the holder 31Ba and an end of the reflector 32B opposite to the end at which the holder 31Ba is provided, so that the space between the prism plate 34 and the reflector 32B becomes continuously narrower with going away (i.e., at increased distances) from the cold-cathode lamp 33-1. The prism plate 34 is flat and the light diffusion plate 38 is formed on the prism plate 34.

The surface light source unit 30F shown in FIG. 22 can be thinned.

A surface light source unit according to a eighth embodiment of the present invention is shown in FIG. 23.

The curved prism plate 34k of the surface light source unit 30E shown in FIG. 21 is changed to two prism plate 34L and 34M, so that a surface light source unit 30G shown in FIG. 23 is formed. That is, in the surface light source unit 30G, ends of the prism plate 34L are supported by the holder 31Aa and the surface of the first reflector 32 and ends of the prism plate 34M are supported by the edge of the second reflector 65 and the surface of the first reflector 32 so that the prism plates 34L and 34M are inclined on the body 31A.

In the above embodiments (from the second embodiment to the eighth embodiment), any of the prism plates 34A, 34B, 34C, 34D, 34E, 34F, 34G shown in FIGS. 8, 9, 10, 11, 13, 14 and 15 may be used.

Each of the surface light source units described above may be used as a back light source unit of a display panel unit. In this case, a liquid crystal display panel is provided above or on the surface light source unit so that the liquid crystal display panel is lightened by the surface light source unit.

A description will now be given of a display panel unit according to an embodiment of the present invention.

A display panel unit is formed as shown in FIG. 24. Referring to FIG. 24, a display panel unit 100 has a directional lighting source 101, a prism plate 105, and a polymer dispersed liquid crystal display element 112 which element is put between the directional lighting source 101 and the prism plate 105. The directional lighting source 101 has a back light panel 102 which is a surface light source and an optical fiber array 104. The optical fiber array 104 causes light 103 emitted from the back light panel 102 to have the directivity and emits directional light 103a. The prism plate 105 is formed as shown in FIG. 25. That is, a plurality of linear prisms 106 are closely arranged on the prism plate 105. The vertical angle .THETA.l of each of the linear prisms 106 is 90.degree.. A flat surface 108 of the prism plate 105 faces the liquid crystal display element 112, and a prism surface of the prism plate 105 on which the linear prisms 106 are formed is a lighting surface 107 of this display panel unit.

When light 109 which is not scattered is perpendicularly incident to the flat surface 108 of the prism plate 105, the light 109 is totally reflected by slanting surfaces of each of the linear prisms 106. As a result, the totally reflected light indicated by reference numbers 109a and 109b returns toward the directional lighting source 101. On the other hand, scattered light 109c is incident to the flat surface 108 of the prism plate 105, the scattered light 109c passes through the prism plate 105 and light 109d is emitted from the lighting surface 107. That is, the prism plate 105 has a function by which the light 109 which is not scattered is confined in a space under the prism plate 105 and the scattered light 109 passes.

The polymer distribution type liquid crystal display element 112 has a structure in which liquid crystal material is encapsulated by polymer micro capsules. In a region (a dot) to which a voltage is supplied, the liquid crystal molecules are neatly arranged, so that the light 103 incident to the region passes through the region as shown by a reference number 113a without being scattered. On the other hand, in a region (a dot) to which no voltage is supplied, the liquid crystal molecules are arranged at random, so that the light 103 incident to the region is scattered as shown by a reference number 113b. That is, when no voltage is supplied to the liquid crystal display panel 112, the function of the prism plate 105 by which function the light is confined in the space under the prism plate 105 is canceled.

In the display panel unit 100 having the above structure, inactive areas on the lighting surface 107 is in a bright state, each of the inactive areas corresponding to the region of the liquid crystal display element 112 to which no voltage is supplied, and active areas on the lighting surface 107 is in a dark state, each of the active areas corresponding to the region of the liquid crystal display element 112 to which the voltage is supplied. Thus, a patterns having a contrast between the active areas which is in the dark state and the inactive areas which is in the bright state can be formed on the lighting surface 107. That is, due to controlling formation of the active and inactive areas, various images can be displayed on the lighting surface 107 of the display panel unit 100.

The liquid crystal display element 112 corresponds to means for partially adjusting the emission rate of the prism plate 105 (the active areas and the inactive areas).

A prism plate 105A shown in FIG. 26A may be substituted for the prism plate 105 shown in FIG. 25. Referring to FIG. 26A, the prism plate 105A has a plurality of pyramid shaped prisms 115 as shown in FIG. 26B. The pyramid shaped prisms 115 are arranged on the prism surface of the prism plate 105A in a matrix.

A prism plate assembly 105B shown in FIG. 27 may be also substituted for the prism plate 105 shown in FIG. 25. Referring to FIG. 27, the prism plate assembly 105 is formed of the prism plate shown in FIG. 25 and a light diffusion sheet 116 formed on the prism surface of the prism plate 105. The lighting surface is formed on the light diffusion sheet 116.

For example, a "Lexan film (8B36)" manufactured by GE CO., LTD. can be used as the light diffusion sheet 116.

A prism plate assembly 105C shown in FIG. 28 may be also substituted for the prism plate 105 shown in FIG. 25. Referring to FIG. 28, the prism plate assembly 105C is formed of the prism plate 105 shown in FIG. 25, a resin layer 117 formed on the prism surface of the prism plate 105 and a light diffusion plate 118. The lighting surface is formed on the diffusion plate 118. The resin layer 117 is made of resin having a low refractive index.

In a case where either the prism assembly 105B or 115C is used in the display panel unit 100, the display panel unit 100 having a wide visual angle can be obtained.

A prism plate assembly 105D shown in FIG. 29 may be also substituted for the prism plate 105 shown in FIG. 25. Referring to FIG. 29, shading walls 119 are formed in a structure of the prism plate 105 and the light diffusion sheet 116 so as to partition the prism plate assembly 105D into dots, each of the dots corresponding to one of regions of the liquid crystal display element 112 in which regions the supplying voltage can be controlled.

In a case where the prism assembly 105D shown in FIG. 29 is used in the display panel unit 100, the light from a bright dot is prevented from affecting dots close to the bright dot.

A display panel unit according to another embodiment of the present invention is formed as shown in FIG. 30.

Referring to FIG. 30, a display panel unit 100A has the directional lighting source 101 formed of the back light 102 and the optical fiber array 104, the liquid crystal display element 112 and the prism plate 105. The liquid crystal display element 112 and the prism plate 105 are integrated with each other.

A display panel unit according to another embodiment of the present invention is formed as shown in FIG. 31.

Referring to FIG. 31, a display panel unit 100B has a directional lighting source 101A, the liquid crystal display element 112 and a prism plate 105E. The directional lighting source 101A comprises a halogen lamp 120 and a reflector 121, so that light 103b having the directivity is emitted from the directional lighting source 101A. The prism plate 105E has prism elements 122-1, . . . , and 122-4. The degree of inclination of each of the prism elements 122-1, . . . and 122-4 to the outside is increased with going away from the center line 123 of the directional lighting source 101A. This structure of the prism elements 122-1, . . . , and 122-4 corresponds to slight diffusion of the light 103a emitted from the directional lighting source 101A.

The present invention is not limited to the aforementioned embodiments, and variations and modifications may be made without departing from the scope of the claimed invention.