United States Patent [19J
`Endo et al.
`
`5,064,276
`[11) Patent Number:
`[45) Date of Patent: * Nov. 12, 1991
`
`[54)
`
`[75)
`
`LIGHT SOURCE FOR PLANAR
`ILLUMINATION IN LIQUID CRYSTAL
`DEVICE
`
`Inventors: Syuusuke Endo; Naofumi Aoyama;
`Toshihiko Yabuuchi; Teruo Seki, all
`of Mobara, Japan
`
`[73)
`
`Assignee: Hitachi, Ltd., Tokyo, Japan
`
`[ * l
`
`Notice:
`
`The portion of the tenn of this patent
`subsequent to Mar. 20, 2007 has been
`disclaimed.
`
`[21)
`
`Appl. No.: 374,148
`
`[22)
`
`Filed:
`
`Jun. 30, 1989
`
`Foreign Application Priority Data
`[30)
`Jul. 1. 1988 [JP]
`
`Japan ................................ 63-162502
`
`[51)
`[52]
`
`[58]
`
`Int. Cl. s ........................... G02F 1/13; F21 V 7/04
`U.S. Cl. ........................................ 359/49; 362/31:
`362/347
`Field of Search ....................... 350/345, 334, 360;
`362/31, 347
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`4,630,895 12/1986 Abdala et a!. ....................... 350/345
`4,909,604 3/1990 Kobayashi eta!. ................. 350/345
`
`Primary Examiner-Rolf Hille
`Assistant Examiner-S. V. Clark
`Attorney, Agent, or Firm-Antonelli, Terry, Stout &
`Kraus
`
`ABSTRACT
`[57]
`A light source device disposing light sources at both
`end faces of the transparent plate in which a surface of
`the transparent plate in the side of an observer (front
`surface) is formed as the inclined and curved surface in
`view of limiting reduction in quantity of light per unit
`area at the observing area being far from the light
`source within a certain level, the one surface of the
`transparent plate is formed as the rough surface to dif(cid:173)
`fuse the incident light, the other surface of the transpar(cid:173)
`ent plate is formed as a mirror-surface, and a reflecting
`layer having a high lightness is disposed at the lower
`side of the transparent plate in order to provide suffi(cid:173)
`cient luminance for observers.
`
`13 Claims, 8 Drawing Sheets
`
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`Page 1 of 13
`
`Mercedes-Benz USA, LLC, Petitioner - Ex. 1002
`
`

`

`U.S. Patent
`U.S.‘ Patent
`
`Nov. 12, 1991
`Nov. 12, 1991
`
`Sheet 1 of 8
`Sheet 1 0f 8
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`5,064,276
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`Page 2 of 13
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`

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`U.S. Patent
`
`Nov. 12, 1991
`
`Sheet 2 of 8
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`5,064,276
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`FIG.2
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`Page 3 of 13
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`

`

`U.S. Patent
`US. Patent
`
`Nov. 12, 1991
`
`Sheet 3 of 8
`
`5,064,276
`5,064,276 v
`
`FIG. 3
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`
`Page 4 of 13
`
`

`

`U.S. Patent
`US. Patent
`
`Nov. 12, 1991
`Nov. 12, 1991
`
`Sheet 4 of 8
`Sheet 4 of 8
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`5,064,276
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`Page 5 of 13
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`
`

`

`U.S. Patent
`
`Nov. 12, 1991
`
`Sheet 5 of 8
`
`5,064,276
`
`FIG. 5
`
`40
`
`4a
`
`FIG. 6
`
`4b
`
`4b
`
`4a
`
`48
`
`48
`
`Page 6 of 13
`
`

`

`U.S. Patent
`
`Nov. 12, 1991
`
`Sheet 6 of 8
`
`5,064,276
`
`FIG. 7
`
`d: 2. 0
`H: 7. 0
`L: 160
`h: 1. 6
`n: 2. 3
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`o: an embodiment
`x: a modification with the
`transparent pLate 4A inverted
`
`MEASURED POINTS
`
`Page 7 of 13
`
`

`

`U.S. Patent
`
`Nov. 12, 1991
`
`Sheet 7 of 8
`
`5,064,276
`
`FIG. 8
`
`d: 4. 0
`H: 7. 0
`L: 160
`h: 1. 6
`n: 2. 3
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`an embodiment
`a modification with the
`transparent pLate 4A inverted
`
`20
`
`40
`
`80
`60
`MEASURED POINTS
`
`100
`
`120
`
`140
`
`Page 8 of 13
`
`

`

`U.S. Patent
`
`Nov. 12, 1991
`
`Sheet 8 of 8
`
`5,064,276
`
`FIG. 9
`
`4A
`
`40
`
`FIG. 10 (PRIOR ART)
`
`FIG. 11 (PRIOR ART)
`
`4A
`
`40
`
`4b
`
`Page 9 of 13
`
`

`

`1
`
`5,064,276
`
`2
`transparent plate and the uniform diffusing layer on the
`inclined and curved surface thereof by disposing the
`inclined and curved surface of transparent plate on the
`side of observer, non-uniformity of luminance gener(cid:173)
`ated by mixture of incident lights from light sources at
`both sides in the center of the transparent plate is suffi(cid:173)
`ciently diffused owing to the diffusing effect of diffusing
`plate located at the area being far from the transparent
`plate and thereby uniform luminance can be obtained
`over the entire part on the diffusing plate.
`Accordingly, a liquid crystal display device employ(cid:173)
`ing a light source can provide clear liquid crystal dis(cid:173)
`play image on the liquid crystal display panel.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a cross-sectional view of an embodiment of
`the present invention;
`FIG. 2 is a disassembled perspective view explaining
`an example in which a light source of the present inven(cid:173)
`tion is applied to a liquid crystal display device;
`FIG. 3 is a perspective view of the rear side of a
`liquid crystal display device as an embodiment of the
`present invention;
`FIG. 4 is a perspective view of the essential part of a
`light source of an embodiment of the present invention;
`FIGS. 5, 6 are cross-sectional views for explaining
`the principle of a light source of the present invention;
`FIGS. 7, 8 are graphs showing luminance character(cid:173)
`istics of an embodiment of the present invention;
`FIG. 9 is a cross-sectional view of the essential part of
`a light source of another embodiment of the present
`invention; and
`FIGS. 10, 11 are cross-sectional views of a light
`source of the prior art.
`
`LIGHT SOURCE FOR PLANAR ILLUMINATION
`IN LIQUID CRYSTAL DEVICE
`
`10
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`The present invention relates to a light source and
`more particularly to an art which may be advanta(cid:173)
`geously applied to a light source of a liquid crystal
`display device which requires a planar illuminator.
`2. Description of the Prior Art
`A flat light source of the prior art is described into the
`Japanese Patent Publication No. 58-17957. As shown in
`FIG. 10, a light source 4B is disposed at an end face of
`a transparent plate 4A which is constituted using a rna- 15
`terial having a good light transmission characteristic
`and the one surface 4a on the observing side is formed
`as a smooth surface while the other surface 4b opposed
`to the surface 4a as a rough surface. This rough surface
`4b is so constituted not only as diffusing the light emit- 20
`ted from the light source 4B but also reflecting such
`light to the smooth surface 4a. The transparent plate 4A
`is constituted to provide an inclined plane, wherein it
`becomes thinner as it departs from the light source 4B.
`The prior art described utilizes, as shown in FIG. 10, 25
`a transparent plate which becomes thinner as is becomes
`far from the light source 4B (thickness is reduced with
`increase of distance x) such as a fluorescent bulb, for
`example, disposed at the end face of the transparent
`plate 4A to provide the planar illuminator in the consti- 30
`tutions, (a) a single fluorescent bulb is used as shown in
`FIG. 10 for a planar illuminator of comparatively small
`area and (b) a couple of fluorescent bulbs are used as
`shown in FIG. 11 for a planar illuminator of large area
`in order to obtain a large size and high luminance planar 35
`illuminator. However, such prior art has been accompa(cid:173)
`nied by problems, for example, in the case of (a) a thin
`and light weight planar illuminator the constitution is
`not suitable for high luminance and large size panel,
`whereas in the case of (b) a high luminance and large 40
`size planar illuminator the constitution is not suitable for
`a thin and light weight panel.
`
`SUMMARY OF THE INVENTION
`It is an object of the present invention to provide an
`art to ensure a planar illuminator which is constituted in
`large size, light weight and thin depth and insure uni(cid:173)
`form high luminance over the entire part of front sur(cid:173)
`face.
`This object may be achieved, in a light source dispos- 50
`ing light sources at both end faces of the transparent
`plate, by constituting a surface of the transparent plate
`on the side of an observer (front surface) as the inclined
`and curved surface in view of limiting reduction in
`quantity of light per unit area at the observing area 55
`being far from the light source within a certain kvd,
`forming a rough surface to diffuse the incident light at
`the one surface of the transparent plate, forming the
`other surface of transparent plate as a polished mirror(cid:173)
`surface. and arranging a reflecting layer providing a 60
`high lightness having a high L *value (lightness index in
`ULCS color system of CIE) at the lower side of the
`transparent plate in order to attain the sufficient lumi(cid:173)
`nance for an observer.
`According to the means explained heretofore. since a 65
`large size and high luminance planar illuminator can be
`obtained by disposing the light sources to both sides and
`a space can be formed between the thinnest area of the
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`A constitution of the present invention will now be
`explained with reference to an embodiment of the light
`source of a liquid crystal display device to which the
`present invention is applied.
`.
`The like reference numerals designate the like ele(cid:173)
`ments having the similar function throughout the ac-
`45 companying drawings and the same explanation will
`not be repeated hereunder.
`
`EMBODIMENT I
`A liquid crystal display device as the first embodi(cid:173)
`ment of the present invention and a light source thereof
`are respectively shown in FIG. 1 (cross-sectional view)
`and FIG. 2 (disassembled perspective view).
`As shown in FIG. 1 and FIG. 2, a liquid crystal dis(cid:173)
`play device respectively provides a liquid crystal dis(cid:173)
`play panel 3 and an illuminator 4 at the inside specified
`by a lower side frame (mold case) 1 and an upper side
`frame (cover) 2.
`The lower side frame 1 is of a square form and is
`made, for example, of a resin material. The upper side
`frame 2 is also of a square form which engages with the
`lower side frame 1. The upper side frame 2 is provided
`with an opening area 2A at the center thereof. The
`opening area 2A is so constituted as exposing the liquid
`crystal display panel 3. The upper frame 2 is made. for
`example, of a metallic material such as aluminum alloy
`or a resin material.
`The liquid crystal display panel 3 is of the dot matrix
`type, although not illustrated in detail. driven on the
`
`Page 10 of 13
`
`

`

`5,064,276
`
`Yl = H -
`
`H-h
`(L/2 - d)" x"
`
`0 ~ X ~ (L12 - d)
`
`4
`other surface provided opposite to the smooth surface
`4a of the transparent plate 4A is formed by a rough
`surface 4b which is rougher than the smooth surface 4a.
`The rough surface 4b of the transparent plate 4A is
`5 substantially equal in the roughness to the surface
`formed by the grinding process, for example, with an
`emery-paper of No. 20-200. In case the rough surface
`4b of the transparent plate 4A has directivity like the
`hair-line, it would be better from the point of view of
`10 light diffusion that the scratches are formed in the longi(cid:173)
`tudinal direction of the light source 4B than that these
`are formed in such a direction as crossing the longitudi(cid:173)
`nal direction but the equal effect can also be obtained by
`using a matte surface. In the case that the transparent
`15 plate is formed by the injected molding method, it is
`better from the viewpoint of processing-ability to form
`the matte surface because a degree of roughness of the
`surface (pitch of matte and depth of groove) can be
`controlled more easily and better molding-ability can
`20 also be attt>.ined. As shown in detail, the rough surface
`4b of the transparent plate 4A is formed as the inclined
`and curved surface so that the quantity of light per unit
`area on the surface of diffusing plate 6 disposed on the
`rough surface 4b is not reduced remarkably if such unit
`25 area becomes far from the light source 4 (if the dimen(cid:173)
`sions X increases). That is, the transparent plate 4A is
`formed to have a continuously inclined and curved
`surface and it becomes thinner as it becomes far from
`the light source 4B (its thickness changes from H to h).
`30 The inclined and curved surface of the rough platne 4b
`of the transparent plate 4A can substantially be ex(cid:173)
`pressed by the following formula.
`
`3
`time sharing basis or driven by TFT method. The liquid
`crystal display panel 3 is provided with a liquid crystal
`part 3A at the spaced defined between a lower transpar(cid:173)
`ent glass substrate 3B and an upper transparent glass
`substrate 3C. This liquid crystal part 3A seals the liquid
`crystal controlled by orientation layers formed at the
`internal surfaces (in the liquid crystal sides) of the lower
`transparent glass substrate 3B and the upper transparent
`glass substrate 3C. As the liquid crystal of this liquid
`crystal part 3A, the twisted nematic type liquid crystal
`is used. The liquid crystal of the liquid crystal part 3A
`is so constituted to control the light transmission with
`the scanning electrodes formed on the internal surface
`of the lower transparent glass substrate 3B and the dis(cid:173)
`play electrodes formed on the internal surface of the
`upper transparent glass substrate 3C. On the external
`surface of the lower transparent glass substrate 3B, a
`polarizing plate 3D is disposed, while on the external
`surface of the upper transparent glass substrate 3C, a
`polarizing plate 3E, is disposed respectively.
`As shown in FIG. 3 (perspective view observed from
`the lower side of the liquid crystal display device), the
`display electrodes are driven by segment driver circuits
`SB and SC which are removably attached (fitted) to the
`bottom of the lower frame 1. In the liquid crystal dis(cid:173)
`play panel 3 of this embodiment. the display electrodes
`are divided in the vertical direction into a couple of
`sections. Therefore, the segment driver circuits SB and
`SC are provided. The segment driver circuit SB, SC are
`respectively consituted by a printed circuit board (for
`instance, glass epoxy resin) mounting semiconductor
`devices for segment drivers.
`The scanning electrodes are driven by the common
`electrode driver circuit SA removably attached to the
`bottom of the lower frame 1. This common electrode 35
`driver circuit SA is also constituted by a wiring sub(cid:173)
`strate mounting semiconductor devices like the segment
`driver circuits SB and SC described previously
`The segment driver circuits SB and SC, and common
`electrode driver circuit SA are respectively driven by 40
`the power supply circuit for driving the liquid crystal
`display (LCD) and timing generation circuit. The liquid
`where,
`crystal drive circuit SD is constituted by a wiring sub(cid:173)
`y: distance in H or h direction
`x: distance in the L direction from the light source 4B
`strate loading semiconductor devices and passive ele(cid:173)
`When L= 160, optimum n ranges from 2 to 3. (In the
`ments such as resistors and capacitors.
`As shown in FIG. 1 to FIG. 3, the illuminator 4 de(cid:173)
`range of L/2:;§x:;§L and YI, Y2 become the curves
`symmetrical with respect to the line, x=L/2.)
`scribed above principally comprises a transparent plate
`4A, a light source 4B, a reflecting plate 4C for light
`h=0.5-3.0 mm
`source, a reflecting plate 4D for transparent plate and
`d=O.S-6.0 mm.
`an inverter power supply circuit 4E. This inverter 50
`The light source device 4 thus constituted forms re-
`flection directivity with the inclined and curved rough
`power supply circuit 4E is not comprised in some cases
`surface 4b for the quantity of light which is more attenu-
`within the liquid crystal module.
`As shown in detail in FIG. 4 (a perspective view
`ated as it becomes further from the light source 4B and
`keeps almost constant the luminance on the surface of
`observed from diagonal upper direction), the transpar-
`ent plate 4A is formed by a square transparent material 55 diffusing plate 6 on the transparent plate 4A.
`having light transmitting characteristic. The tran·)J::lr-
`Non-uniformity of luminance, which may be easily
`ent plate 4A is constituted by an acrylic resin having the
`~enerated, at the center (thinnest part) of the transpar-
`light transmission of about 90-95[%]. Moreover. the
`ent plate can be prevented because, as shown in FIG. S
`transparent plate 4A may be formed by the transparent
`and FIG. 6, the predetermined space is provided be-
`glass material. In this embodiment. the dimension of the 60 tween the thinnest part of the transparent plate and light
`width direction of the transparent plate 4A is set to 250
`diffusing plate 6 and thereby the light is diverged until
`[mm]. The dimension of the longitudinal direction of
`it is incident to diffusing plate and is diffused by the
`the transparent plate 4A is set to 160 [mm]. The dimen-
`diffusing plate 6.
`sian in the thickness direction H of the transparent plate
`The actually measured data obtained by the inventors
`4A is set to 4-15 [mm).
`65 of the present invention through researches are shown
`The one surface of transparent plate 4A on the side of
`in FIG. 7 and FIG. 8. In order to show drastic 1m prove-
`the reflecting plate 4D for transparent plate 4A is sub-
`ment in uniformity of luminance by providing the space
`stantially formed by a flat and smooth surface 4a. The
`between the thinnest part of the transparent plate and
`
`.Y:! = h
`
`L/2 - d ~ X ~ L/2
`
`45
`
`Page 11 of 13
`
`

`

`5,064,276
`
`5
`the light diffusing plate 6 thereof, distribution of lumi(cid:173)
`nance on the surface in such a case that the smooth
`surface 4a of the transparent plate is disposed on the
`side of observer, namely the space is not disposed be(cid:173)
`tween the thinnest part of the transparent plate and the
`light diffusing plate 6 thereof. and distribution of lumi(cid:173)
`nance on the surface in such a case that uniformity of
`luminance is improved by disposing the space between
`the thinnest part of the transparent plate 4A and the
`light diffusing plate 6 thereof are indicated for the com- 10
`parison purpose. FIG. 7 shows the data in case the
`dimension dis 2.0 mm and FIG. 8 shows the data in case
`the dimension d is 4.0 mm. As will be apparent from
`these figures, when the smooth surface of the transpar(cid:173)
`ent plate is located on the side of observer. reduction of 15
`luminance at the center is distinctive and, on the other
`hand, uniformity of luminance at the center is good
`according to the present invention. In addition, unifor(cid:173)
`mity of luminance at the center can be improved by
`increasing the dimension d to a certain degree (practi- 20
`cally, about 2.0-6.0 mm).
`The liquid crystal display device employing the light
`source device thus constituted is capable of making
`clear the liquid crystal display image on the liquid crys-
`tal display panel 3. In this case. any problem does not 25
`occur for practical use when luminance at the display
`surface of liquid crystal panel varies continuously
`within 30%.
`The light source 4B is arranged at the one end of the
`transparent plate 4A. As the light source 4B, a cold 30
`cathode tube, for instance, in the length of about
`270(mm] is used. This cold cathode fluorescent tube is
`driven by the inverter power supply circuit 4E disposed
`on the bottom of the lower frame 1. This inverter power
`supply circuit 4E is so designed, for example, as to 35
`convert the DC power source of 5- 30(V] into the AC
`power source of 300·400(V] of 30- 50(KHz]. The in(cid:173)
`verter power supply circuit 4E is constituted. like the
`circuits SA- SD, by the wiring substrate mounting
`semiconductor devices.
`The reflecting plate 4C for light source covers the
`light source 4B, except a part thereof, in order to effec(cid:173)
`tively reflect the light of light source 4B toward the
`transparent plate 4A and provides the ] -shaped or
`U-shaped cross-section. The reflecting plate 4C for light 45
`source is formed. for example, by an aluminum plate
`coated with white paint (acrylic resin paint on the sur(cid:173)
`face (on the side of light source 4B). Particularly, the
`white paint is required to have the value of lightness L *
`of 90 or more and the lightness value of 94 or more is 50
`more preferable. Moreover, the reflecting plate 4C for
`light source 4B may also be designed to perfectly cover
`the light source 4B for the transparent plate 4A as
`shown in FIG. 9 with the metal-evaporated sheet hav(cid:173)
`ing a high reflectivity. In this case, lead of light flux may 55
`be minimized and thereby improvement of lum1• :u.ce
`can also be expected. Meanwhile, the former design
`may be thought to be preferably in the point of view of
`assembling and easiness in replacement. The reflecting
`plate 4D is disposed on the smooth surface 4a of the 60
`transparent plate 4A so that it can effectively reflect the
`light of light source 4B to the side of liquid crystal
`display panel 3 (rough surface 4b of the transparent
`plate 4A). This reflecting plate 4D is made, for instance,
`of the material which is also used to make the reflecting 65
`plate 4C for the light source mentioned above and in
`this case, the higher the value of lightness L * of the
`reflecting plate. the more recommended it is and 94 or
`
`6
`more is preferable. The light diffusing plate 6 is ar(cid:173)
`ranged between the liquid crystal display panel 3 and
`the transparent plate 4A of the light source 4. The light
`diffusing plate 6 is formed, for example, by a semi-trans(cid:173)
`parent acrylic resin. This acrylic resin should have the
`total light transmissivity of 40-80% and diffused light
`transmissivity of 40- 80o/C and it is also preferable that
`the plate thickness is about 0.5-3.0 [mm] and moreover
`both sides are processed as rough surfaces. It is neces(cid:173)
`sary to give the function to prevent generation of New(cid:173)
`ton ring at the LCD surface or the surface with which
`the transparent plate is in intimate contact.
`The present invention can also provide the equivalent
`effect even by forming the rough surface 4b of the trans(cid:173)
`parent plate 4A of the light source 4 as the continuously
`inclined and curved surface extending from the position
`spaced from the light source by the predetermined dis(cid:173)
`tance (partially inclined and curved).
`In above embodiment, the rough surface 4b is pro(cid:173)
`vided in the side of light diffusing plate 6 on the trans(cid:173)
`parent plate 4A but it is of course possible that this
`rough surface 4b is eliminated and the effect obtained by
`the rough surface 4b is realized by the reflecting surface
`of the reflecting plate 4D or the surface 4a.
`In the present embodiment, a hot cathode fluorescent
`bulb may be used as the light source 4B of the light
`source 4. In addition, in case the dimension L is small
`(for instance, it is 50 [mm] or less), the light source 4B
`may be formed by a plurality of LEDs.
`Moreover, it is certain that the luminance may be
`raised by arranging a plurality of light sources to each
`end face of the transparent plate 4A.
`Since the light source 4 of the present invention is
`capable of providing high luminance. it may effectively
`be applied to constitute a liquid crystal display panel 3
`of the liquid crystal display device of the supertwisted
`nematic type white and black mode (having the disad(cid:173)
`vantage of lower light transmissivity).
`While the present invention has been particularly
`40 shown a.1d described with references to a preferred
`embodiment thereof, it will be understood by those
`skilled in the art that the present invention is not limited
`thereto and foregoing and other changes or modifica-
`tions in form and details may be made therein without
`departing from the spirit and scope of the invention.
`For example, the present invention can preferably be
`applied to a light source device of the liquid crystal
`display device employing the active matrix system in
`which a pixel is formed by a thin film transistor and a
`transparent pixel electrode.
`In addition, the present invention can also be applied
`to a light source device of wrist watches and meters,
`without limitation to the light source device of the
`liquid crystal display device, namely to all light source
`devices which employs a planar illuminator.
`The effect which may be attained by a typical device
`of the present invention disclosed in this patent specifi(cid:173)
`cation can be briefly summarized as that the luminance
`of planar illuminator type light source device may be
`made substantially uniform over the entire part of dis(cid:173)
`play surface.
`What is claimed is:
`1. A light source device comprising, a transparent
`plate. a reflecting plate disposed adjacent a first surface
`of said transparent plate, and at least one light source
`disposed at each of first and second end faces of said
`transparent plate, a second surface of said transparent
`plate opposite said first surface, said second surface
`
`Page 12 of 13
`
`

`

`5,064,276
`
`8
`-continued
`y = h for L/2 - d ~ x ~ L/2
`
`where
`y is a distance from said first surface to said second
`surface,
`x is a distance from said first end face,
`L is a length of said transparent plate,
`H is the value of y at said first end face,
`h is the value of y at x being (L/2 -d),
`d is a distance in said x direction of a flat portion of
`said second surface at the center area of said trans(cid:173)
`parent plate between said light sources disposed at
`said two end faces, and
`n is an arbitrary positive number larger than unity,
`and said inclined and curved second surface is sym(cid:173)
`metrical with respect to x being L/2.
`8. A light source device according to claim 4,
`wherein said light diffusing surface is a rough surface.
`9. A light source device according to claim 1.
`wherein said transparent plate is made of acrylic resin.
`10. A light source device according to claim 1,
`wherein a diffusing plate is disposed adjacent to said
`second surface.
`11. A light source device according to claim 7,
`wherein said h is in the range of 0.5 to 3.0 mm and said
`d is in the range of 0.5 to 6.0 mm.
`12. A light source device according to claim 4,
`wherein said light diffusing surface is a matted surface.
`13. A light source device according to claim 8,
`wherein said rough surface has directivity.
`* * * • *
`
`5
`
`15
`
`7
`including an inclined and curved surface portion with a
`thinnest portion of said transparent plate at the center
`area of said transparent plate between the two end
`faces.
`2. A light source device ~ccording to claim 1,
`wherein the shape of said inclined and curved surface
`portion of said second surface is expressed by an expo(cid:173)
`nential function of the distance from said light sources
`and said shape is symmetrical about the center area 10
`between said light sources.
`3. A light source device according to claim 1,
`wherein said thinnest part at the center area is almost
`flat.
`4. A light source device according to claim 1,
`wherein a light diffusing surface is provided on said
`second surface.
`5. A light source device according to one of claims 1
`to 4, wherein a liquid crystal display panel is disposed 20
`on said second surface of said transparent plate to be
`used for liquid crystal display device.
`6. A light source device according to one of claims 1
`to 5. wherein one of said end faces of said transparent 25
`plate is provided with a plurality of light sources.
`7. A light source device according to claim 2,
`wherein said exponential function is
`
`y = H -
`
`H - h
`(L/2 - d)"
`
`x" for 0 ~ x ~ (L/2 - d)
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`Page 13 of 13
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