United States Patent [19]
`Funamoto et al.
`
`lIlllllllliilllllllllllllllllllllllllllll
`USO05619 351A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,619,351
`A r. 8 1997
`P 9
`
`[54] SURFACE-TYPE ILLUMINATION DEVICE
`AND LIQUID CRYSTAL DISPLAY
`
`FOREIGN PATENT DOCUMENTS
`0317250 5/1989 European Pat. O?’. .
`
`[75] Inventors: Tatsuaki Funamoto; Toru Yagasaki;
`Fumlakl Akahane, all of Suwa, Japan
`
`[73] Assignee: Seiko Epson Corporation, Tokyo,
`Japan
`
`_
`[21] APPl- N°--
`'
`.
`[22] PCT Filed.
`[86] PCT No.:
`
`204,374
`
`Jul. 13, 1993
`PCT/JP93/00965
`
`May 10, 1994
`§ 371 Date:
`§ 102(6) Date: May 10 1994
`’
`[87] PCT Pub. No.: WO94/01795
`PCT Pub Date Jan 20 1994
`_
`_
`_
`_’
`_
`Forelgn Apphcatlon Pnonty Data
`[3O]
`4-184976
`Jul. 13, 1992
`[JP]
`Japan
`May 13, 1993
`[JP]
`Japan .................................. .. 5-111852
`
`6
`[51] Int. Cl. ................................................ ..: G021? 1/1335
`[52] U_-S- Cl- ------------ --
`349/61’ 349/5’ 349/62
`[58] Field of Search
`............. .. 359/40, 42, 48,
`359/49, 50, 70; 362/26, 31, 32, 330
`_
`References Clted
`U_S_ PATENT DOCUMENTS
`
`[56]
`
`4,729,067
`
`371938
`16/19g9
`
`‘(935809
`5’057’974 10,1991
`5:130:898
`7,1992
`5,134,549
`7/1992
`5,283,673
`2/1994
`5,363,294 11/1994
`
`Eggs“ Pat' O?' '
`5440086 3,1979 Japan '
`166585
`7/1986 Ja
`.
`6240226 5/1987 last; _
`63-45537
`311988 Japan .
`63-124217
`8/1988 Japan .
`1183626 7/1989 Japan.
`351476 5/1991 Japan .
`4102888 4,1992 Japan _
`8808149 10/1988 WIPO -
`
`OTHER PUBLICATTONS
`7
`“Advancements in Backlighting Technologies for LCDs,”
`K. Hathaway, Spie Proceedings, High-Resolution Displays
`and Projection Systems, vol. 1664, Feb. 1992, pp. 108—1l6.
`Abstract for 62-102226 May 12, 1987, Japan.
`Primary Examiner—William L. Sikes
`Assistant’ Examiner-James A. Dudek
`A?omeyi Agent, or Fiml—Eric B- Janofsky
`[57]
`ABSTRACT
`
`I
`
`A surface_type illumination device suitable for providing
`backlight in a liquid crystal display is disclosed. For
`example, an L_shaped ?uorescent light can be used as an
`illuminant and mounted next to two edges of a substantially
`rectangular light guide plate. The corner of an edge portion
`between the two edges is removed. The ?uorescent light, the
`length of whose illuminating portion is long, is positioned
`with an appropriate gap from the light gulde plate allowing
`for illumination with high brightness and low power con
`sumption. Consequently, when the illumination device is
`used in a color liquid crystal display, appropriate backlight
`with high brightness can be obtained. Moreover, because the
`in?uence of the temperature from the illumination device is
`small, a stable color display can be achieved.
`
`18 Claims, 12 Drawing Sheets
`
`23a
`
`204
`
`Mercedes-Benz Ex. 1008
`
`MBI_001449
`
`

`
`U.S. Patent
`
`Apr. 3, 1997
`
`Sheet 1 of 12
`
`5,619,351
`
`2
`
`
`1W
`
`36
`70 \'
`33
`37
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`MBI_001450
`
`

`
`US. Patent
`
`Apr. 8, 1997
`
`Sheet 2 of 12
`
`5,619,351
`
`\
`
`10b
`
`FIG._3
`
`MBI_001451
`
`

`
`US. Patent
`
`Apr. 8, 1997
`
`Sheet 3 of 12
`
`5,619,351
`
`x
`
`23a
`
`20<
`
`FIG._4
`
`j
`
`MBI_001452
`
`

`
`US. Patent
`
`Apr. 8, 1997
`
`Sheet 4 0f 12
`
`5,619,351
`
`6
`
`14
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`10b
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`
`MBI_001453
`
`

`
`US. Patent
`
`Apr. 8, 1997
`
`Sheet 5 of 12
`
`V 5,619,351
`
`'/' /'///F"////// ////- r1.
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`1
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`FIG._ 7
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`FIG._8A
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`220 1
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`22b
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`2a
`
`MBI_001454
`
`

`
`US. Patent
`
`Apr. 8, 1997
`
`Sheet 6 0f 12
`
`5,619,351
`
`,
`
`FIG._9 <
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`
`MBI_001455
`
`

`
`US. Patent
`
`Apr. 8, 1997
`
`Sheet 7 of 12
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`5,619,351
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`MBI_001456
`
`

`
`U.S. Patent
`
`Apr. 3, 1997
`
`Sheet 3 of 12
`
`5,619,351
`
`
`
`
`
` 63
`69
`
`...__-.....__....:.—__
`
`...:...._...-._.-__..-..j-..:-.._-j-j-__-j-_'_.j-__
`
`MB|_OO1457
`
`MBI_001457
`
`

`
`US. Patent
`
`Apr. 8, 1997
`
`Sheet 9 of 12
`
`5,619,351
`
`F161’. 15
`
`MBI_001458
`
`

`
`U.S. Patent
`
`Apr. 8, 1997
`
`Sheet 10 of 12
`
`5,619,351
`
`N
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`
`MBI_001459
`
`

`
`U.S. Patent
`
`Apr. 8, 1997
`
`Sheet 11 of 12
`
`5,619,351
`
`65_
`
`SURFACE TEMPERATURE
`
`(°C)
`
`55 —
`
`45 —
`
`_
`
`—
`
`—
`
`FIG. 18 25- ---------------------- —
`_
`ROOM TEMPERATURE
`
`POSITION DIRECTLY-I CENTRAL-I POSITION DIRECTLY
`OVER THE
`PORTION OF
`OVER THE
`LIGHT SOURCE
`THE IMAGE
`LIGHT SOURCE
`
`/ 72a
`
`/ 71
`
`FIG._ 19
`
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`
`FIG._22 25 -------------
`ROOM TEMPERATURE
`
`------- —
`
`END PORTION —-I CENTRAL-I POSITION DIRECTLY
`OF THE IMAGE
`PORTION OF
`OVER THE LAMP
`THE IMAGE
`LIGHT SOURCE
`
`MBI_001460
`
`

`
`U.S. Patent
`
`Apr. 8, 1997
`
`Sheet 12 of 12
`
`5,619,351
`
`40
`
`81
`
`40
`
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`
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`
`FIG._21
`
`3
`
`MBI_001461
`
`

`
`5,619,351
`
`1
`SURFACE-TYPE ILLUMINATION DEVICE
`AND LIQUID CRYSTAL DISPLAY
`
`FIELD OF THE INVENTION
`
`This invention relates in general to a thin, surface-type
`illumination device that can be used as a backlight for liquid
`crystal displays (LCD) and, in particular, to a suitable
`illumination device for use in a notebook computer display
`that provides high brightness with low power consumption
`as well as to a liquid crystal display that uses this illumi
`nation device.
`
`BACKGROUND OF THE INVENTION
`
`2
`such as microcomputers where thinness and small size are
`important.
`In accordance with the instant invention, a suitable illu
`mination device for color liquid crystal displays can be
`obtained that are small in size, lightweight, and have high
`and uniform brightness. Further, it is an object of the
`invention to provide a surface-type illumination device that
`can prevent heat generation and its resulting bad effects to
`the liquid crystal display panel.
`Another object of the invention is to provide a surface
`type illumination device that, without increasing the number
`of driver circuits for driving the ?uorescent lights, displays
`a brightness higher than conventional illumination devices
`and restricts heat radiation.
`A further object of the invention is to generate a suitable
`diifusion pattern to realize a surface-type illumination
`device, this diffusion pattern being used in the illumination
`device.
`Still another object of the invention is to provide a stable
`liquid crystal display where the driver IC for driving the
`liquid crystal display panel is positioned so that it will not be
`affected by heat.
`
`DISCLOSURE OF THE INVENTION
`
`In accordance with the instant invention, by employing an
`illuminant longer than conventional illurninants, illumina
`tion with high illumination intensity is obtained without
`increasing the number of driver circuits for driving the
`illurninants and without concentrating the heat diffusion.
`Further, by bending the illuminant, light can be introduced
`along the polygon-shaped polarizer. Also, to maintain proper
`space between the polarizer and the illuminant and to
`increase the e?iciency of the light introduced to the polar
`izer, a corner is removed from the edge of the polarizer. In
`other words, the surface-type illumination device of the
`instant invention comprises a polarizer which is polygon
`shaped and substantially transparent; a di?usion pattern
`arranged on one side of the polarizer, the diffusion pattern
`emitting substantially evenly from one side of the polarizer
`light that is introduced from the illuminant to the other side
`of the polarizer; and a cylindrically-shaped illuminant bent
`so that the illuminant faces at least two sides of the polarizer;
`wherein the edge sandwiched between the at least two sides
`is processed so that the corner does not protrude.
`Through using an illuminant bent along the polarizer, the
`length per cylindrically-shaped illuminant is long, and an
`illuminant with large illuminating area can be used. Conse
`quently, the rise in temperature of the illuminant can be kept
`down and high brightness obtained. Furthermore, an
`increase in the number of driver circuits that drive the
`illuminant can be prevented. When bending an illuminant
`such as a ?uorescent light to adjust for interference between
`the bent portion and the corner of the polarizer, the width or
`length of the entire illumination device becomes longer,
`preventing miniaturization. In the instant invention, by
`removing a comer of the polarizer, the distance between the
`polarizer and the illuminant can be kept within a ?xed range
`for high incident efficiency, and thus, a highly e?icient
`illumination device that is small in size can be realized.
`Further, by using a long illuminant as mentioned above,
`an improvement in conversion e?iciency from power to light
`is also attained. For example, in illurninants such as a
`?uorescent light, power to the illuminant is consumed by the
`cathode drop, which is due to the glow discharge, and
`consumed by positive column gradient voltage, which is due
`
`Surface-type illumination devices with a cylindrical light
`source and a ?at polarizer such as the devices described in
`Japanese Kokai No. 60-205576 and Japanese Kokai No.
`61-248079 are well-known. One such example is shown in
`FIG. 21. In the illumination device 90, cylindrical ?uores
`cent light 92 is positioned on one side of the substantially
`rectangular and ?at polarizer 91. The light introduced to
`polarizer 91 from ?uorescent light 92 is re?ected by the
`diffusion pattern printed on polarizer 91 and emitted from
`the surface of the polarizer at a ?xed density of light.
`This type of surface illumination device, in recent years,
`has been used extensively as backlights for liquid crystal
`display panels. The use of liquid crystal display panels are
`increasing as displays in such things as laptop computers,
`televisions and cameras. The use of liquid crystal display
`panels for color displays is also increasing. As the size of
`personal computers and televisions become smaller, it is
`imperative that liquid crystal display panels become thinner
`and lighter.
`Accordingly, it is necessary that the surface-type illumi
`nation device used for liquid crystal display panels as a
`backlight, in correlation with the color displays, becomes
`thinner and lighter with less power consumption. Also, to
`allow for use in color displays, a su?‘icient brightness is
`necessary to clearly show the colors displayed in the liquid
`crystal. This requires the use of a high output ?uorescent
`light in the illumination device. However, along with the
`light, heat is also radiated from the high-output ?uorescent
`light. The e?ect of this heat, as shown in FIG. 22, is great.
`The temperature may rise 30°~40° C. above a normal
`temperature of 25 ° C. Consequently, when this type of
`illumination device is used as a backlight in an MIM active
`color display panel or in a STN passive color display panel,
`a special method to reduce the heat is necessary to control,
`to a certain extent, the color and brightness irregularities.
`In stead of using one high output ?uorescent tube, it is
`also conceivable to increase the number of ?uorescent tubes.
`In this way, it is possible to control to some extent the
`temperature increase due to the light source. However, as the
`number of ?uorescent tubes is increased, many other prob
`lems appear. One of these problems is the variations in the
`illumination of the ?uorescent tubes. Because the illumina
`tion intensity of ?orescent tubes varies according to each
`tube, it is necessary to adjust such things as the resistance
`within the ?uorescent tube driver circuit to obtain a ?xed
`illumination intensity. Consequently, in the case when sev
`eral ?uorescent tubes are used in one illumination device,
`extra time is required during the manufacturing process to
`obtain a balanced and ?xed illumination intensity.
`Another problem is the increased number of driver cir
`cuits required to turn on the ?uorescent tubes. The number
`of these driver circuits can not be easily increased in devices
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`to light emission. When a plurality of illuminants are used
`and the input voltage increased, the portion consumed by the
`cathode drop voltage signi?cantly increases and an increase
`in the positive column gradient tendency for light emission
`is small. However, in the illumination device of the instant
`invention, which uses a long illuminant, power is ef?ciently
`converted into light as an increase in the positive column
`gradient voltage is smaller than the case when the number of
`illuminants is increased.
`The edge of the polarizer can be processed into many
`di?terent shapes, for example, removing the corner in the
`shape of an isosceles triangle. In the case of the isosceles
`triangle, a high incident e?iciency of light from the illumi
`nant to the polarizer can be maintained. It is desirable to
`make the length of one of the sides of the isosceles triangle
`to be removed in the approximate range of 0.6 times to 1.0
`times the smallest radius of curvature of the bent portion of
`the illuminant so as to realize a small-sized illumination
`device. Also, in order to prevent light incident from the edge,
`and to increase the uniformity of the light radiated from the
`polarizer, it is eifective to include a shield at the edge portion
`to prevent introduction of light from the illuminant.
`Also, the comer of the edge may be removed in a
`diamond-shape. In order to make the incident e?iciency high
`and keep the size of the device small, it is desirable to make
`the length of one of the sides of the comer removed in a
`diamond-shape within a range of 0.6 times to 1.0 times the
`smallest radius of curvature of the bent portion of the
`illuminant. Also, if all the comers are removed from the
`edges of the polarizer so that they do no protrude, the
`directionality of the polarizer disappears and the manufac
`turing process time required to position the polarizer
`becomes unnecessary.
`It is common to cover the illuminant with a re?ector to
`increase the incident e?iciency of the light from the illumi
`nant to the polarizer. When a bent illuminant such as the one
`described above is used, it is desirable for the re?ector to be
`comprised of a straight ?rst re?ector and a second re?ector
`positioned along two of the sides of the polarizer wherein at
`the edge, the ?rst re?ector is covered by the second re?ector.
`It is also possible for the re?ector to be comprised of a ?rst
`re?ector that covers the lower half portion of the illuminant
`on one side of the polarizer and a second re?ector that covers
`the upper half of the illuminant from the other side of the
`polarizer.
`The di?’usion pattern that diffuses light incident to the
`polarizer from the bent illuminant can be generated by the
`following method. In other words, to generate a di?iusion
`pattern that evenly radiates, from the other side of the
`polarizer, light introduced from the illuminant to the polar
`izer in an illumination device where a cylindrically-shaped
`illuminant is positioned near at least a ?rst side and a second
`side of a substantially rectangular polarizer, the density
`distribution per unit area of the diffusion pattern can be
`found by: ?nding a predicted emitted light intensity distri
`bution for the y-direction along the ?rst side based on the
`intensity of the light incident to the polarizer from the
`second side and the density distribution of a presupposed
`diffusion pattern; then ?nding a predicted emitted light
`intensity distribution for the x-direction along the second
`side based on the intensity of the light incident to the
`polarizer from the ?rst side and the density distribution of
`the presupposed di?cusion pattern; and then compensating
`the density distribution of the presupposed di?’usion pattern
`so that the sum of the predicted emitted light intensity
`distribution for the x-direction and the predicted emitted
`light intensity distribution for the y-direction on arbitrary
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`rectangular xy coordinates of the polarizer ?t within a ?xed
`range.
`When an edge re?ector is installed at at least one of the
`two sides opposite the ?rst side and the second side for
`re?ecting the light from the inner part of said polarizer to
`said polarizer, it is good to compensate the density distri
`bution by computing the re?ected light intensity incident
`from the edge re?ector to the polarizer with a ?xed attenu
`ation factor; ?nding a predicted emitted light intensity
`distribution for at least one of the xy directions of the
`re?ected light intensity; and adding this to the predicted
`emitted light intensity distribution found above.
`By printing the diifusion pattern described above on the
`polarizer or by putting on the polarizer a sheet with the
`pattern formed on it, light introduced from the bent illumi
`nant can be evenly radiated from the polarizer. Similarly,
`light can be evenly emitted by making the thickness of a
`polarizer with an even ditfusion pattern inversely proportion
`to the compensated density distribution of the diffusion
`pattern.
`E?°ects of the heat from the illuminant can be minimized
`by using as a bent illuminant an L-shaped illuminant and by
`placing in a position opposite the illuminant a driver device
`such as a driver IC for driving the liquid crystal display.
`Consequently, as the threshold value of the driver does not
`become unstable due to the heat, a color display with stable
`contrast is obtained. Further, a high quality display with high
`brightness and a small illumination device is also obtained.
`Further, a stable, high quality display can be obtained that
`reduces heat using an even longer U-shaped illuminant. The
`brightness of the display is easy to adjust when illuminants
`such as L-shaped and U-shaped illuminants are used because
`nearly the same intensity of light is incident from the
`periphery of the polarizer. Of course, an O-shaped illumi
`nant can also be arranged around the periphery of a rectan
`gular polarizer as well as an illuminant bent to ?t the shape
`of any other polygon.
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`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a sketch of a liquid crystal display using the
`surface-type illumination device in accordance with the ?rst
`embodiment of the invention.
`FIG. 2 is a cross-sectional view of FIG. 1 showing the
`structure of the liquid crystal display.
`FIG. 3 is a break-down view showing the structure of the
`liquid crystal display of FIG. 1.
`FIG. 4 is a break-down view showing the construction of
`the surface-type illumination device used in the liquid
`crystal display of FIG. 1.
`FIG. 5 is a top plan view illustrating the combination of
`the surface-type illumination device and the liquid crystal
`display panel shown in FIG. 4.
`FIG. 6 is an explanatory drawing showing the positioning
`of the polarizer and ?uorescent light of the surface-type
`illumination device of FIG. 4.
`FIG. 7 is a cross-sectional view showing the relationship
`of the polarizer, ?uorescent light, and re?ector of the sur
`face-type illumination device of FIG. 4.
`FIG. 8 is an explanatory drawing showing the assembly of
`the re?ector of FIG. 7.
`FIG. 9 is an enlarged view of the edge of the polarizer.
`FIG. 10 is an enlarged view showing several possible
`edge formations of the polarizer.
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`FIG. 11 is an explanatory drawing showing the diffusion
`pattern formed on the diffusion sheet, this diffusion sheet
`being stuck to the polarizer.
`FIG. 12(a), which differs from FIG. 11, is a plan view
`showing a polarizer where the thickness has been changed.
`FIG. 12(1)), which di?’ers from FIG. 11, is a cross
`sectional view showing a polarizer where the thickness has
`been changed.
`FIG. 13 is a top plan view showing the combination of the
`liquid crystal display panel and illumination device in accor
`dance with the second embodiment of this invention.
`FIG. 14 is a cross-sectional view showing the relationship
`of the liquid crystal display panel, illumination device, and
`illuminant as shown in FIG. 13.
`FIG. 15 is a breakdown view of the structure of the
`surface-type illumination device shown in FIG. 14.
`FIG. 16 is an explanatory drawing showing the relation
`ship of the polarizer and the ?uorescent light which is in the
`surface-type illumination device of FIG. 15.
`FIG. 17 is an explanatory drawing showing the diffusion
`pattern that is printed on the polarizer of FIG. 15.
`FIG. 18 is a graph showing the surface temperature of the
`liquid crystal display panel shown in FIG. 13.
`FIG. 19 is an explanatory drawing showing a relationship,
`di?erent from above; of theipolarizer and the ?uorescent
`light.
`FIG. 20 is an explanatory drawing showing a [still further
`different relationship] of the polarizer and the ?uorescent
`light.
`FIG. 21 is an explanatory drawing showing a conven
`tional polarizer and ?uorescent light.
`FIG. 22 is a graph showing the surface temperature of a
`liquid crystal display panel using a surface-type illumination
`device similar to the one shown in FIG. 21.
`
`BEST MODE FOR IMPLEMENTATION OF THE
`INVENTION
`
`The embodiments of the instant invention are explained
`below using the above drawings as reference.
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`EMBODIMENT 1
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`FIG. 1 is a sketch of liquid crystal display 1 in accordance
`with one embodiment of this invention. Liquid crystal
`display 1 is constructed with liquid crystal display panel 10
`and an illumination device to be described later sandwiched
`between upper case 2 and lower case 3. Upper case 2 and
`lower case 3 are ?xed in place by tooth 4. The scanning data
`that comprises the image is supplied from the host side to
`each row or column through tape electrode 5 and tape
`electrode 6. This data is latched by a driver IC which will be
`described below, is synchronized, and is supplied to liquid
`crystal display panel 10 where the image is formed. Power
`is supplied from the driver circuit of the host side to the
`?uorescent light comprising the illumination device through
`connector 7, connector 7 extending past liquid crystal dis
`play 1 and used lighting.
`The basic structure of one embodiment of liquid crystal
`display 1 will be explained using the cross-sectional view of
`liquid crystal display 1 shown in FIG. 2 and the break-down
`view of liquid crystal display 1 shown in FIG. 3. In liquid
`crystal display 1, illumination device 20 is installed in lower
`case 3. Above that, liquid crystal display panel 10 is installed
`using frame 30 and 31. Liquid crystal display panel 10 is
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`formed by enclosing the liquid crystal, transparent elec
`trodes and such between two layers of transparent glass
`substrates 11 and 12. At side 10a of liquid crystal display
`panel 10, a plurality of driver ICs 13 are installed for
`latching pixel data for the rows and sending it to the liquid
`crystal display panel. Also, at side 10b, which is adjacent to
`side 10a, a plurality of driver ICs 14 are installed for latching
`pixel data for the columns and sending it to the liquid crystal
`display panel.
`Frames 30 and 31 are used to protect illumination device
`20 and to position it within the case. At the same time, it also
`?lls the role of maintaining a ?xed distance for gap 33
`between illumination device 20 and liquid crystal display
`panel 10, for example, 0.2-1 mm. For this reason, frames 30
`and 31 are prepared so that their lower halfs 34 and 35
`support illumination device 20 and their upper halfs 36 and
`37 act as spacers between illumination device 20 and liquid
`crystal display panel 10. In this example the frame is divided
`into two pieces, however, the number of pieces is not limited
`to two. For example, three pieces, four pieces, or even more
`is possible, and even just one'piece is also conceivable.
`Furthermore, the frame need not cover the entire periphery
`of illumination device 20 or liquid crystal display panel 10.
`A plurality of pieces may be arranged in appropriate places.
`Illumination device 20 is a surface-type illumination
`device set up with a cylindrically-shaped ?uorescent light 22
`at the edge of substantially rectangular polarizer 21. Fluo
`rescent light 22 is roughly L-shaped and is covered by
`re?ectors 23a and 23b. Wires for supplying power to drive
`?uorescent light 22 extend from both ends of ?uorescent
`light 22 and are connected to the driver circuit on the host
`side through connector 7 which is for turning on the light.
`FIG. 4 is a break-down view of illumination device 20 and
`will be used to explain the structure of this embodiment of
`the illumination device. Illumination device 20 is comprised
`of polarizer 21, which is substantially rectangular in shape
`and is missing the corner of edge 40, ?uorescent light 22,
`which encompasses edge 40 in an L-shape, and re?ectors
`23a and 23b, which cover ?uorescent light 22 in the direc
`tion of polarizer 21 and e?iciently re?ect light from ?uo
`rescent light 22 to polarizer 21. On lower surface 21b of
`polarizer 21, the side opposite of the side where liquid
`crystal display panel 10 is arranged, pattern sheet 24, which
`is printed with diffusion pattern 50, and re?ecting sheet 25
`are arranged in that order. On upper surface 21a of polarizer
`21, the side where liquid crystal display panel 10 is arranged,
`dilfusion sheet 26 and prism sheet 27 are arranged. Edge
`re?ective tape 28 is installed at edge 41a and 41b, opposite
`?uorescent light 22 of polarizer 21.
`Polarizer 21 is a transparent material whose index of
`refraction is greater than that of air. An index of refraction
`equal to or greater than 1.41 is desirable using such materials
`as acrylic resin, polycarbonate resin, amorphous polyole
`?ne-type resin, and polystyrene resin. Use of these type of
`materials for polarizer 21 result in a critical angle of 45° or
`less. If upper surface 21a and lower surface 21b are smooth
`and mirror-like, the light incident from edges 41a, 41b, 41c,
`and 41d, which are formed at right angles to surface 21a and
`21b, is completely re?ected from surfaces 21a and 21b.
`Pattern sheet 24 is a transparent sheet with a ?xed number
`of diffusion patterns 50 printed on it, the printed diffusion
`patterns being adhered to the lower surface 21b of polarizer
`21. Light incident from sides 41, to some extent, reach
`di?usion pattern 50 and, without being completely re?ected
`will be diffused in the direction of upper surface 21a.
`Consequently, light incident from the ?uorescent light by
`way of edges is emitted to the liquid crystal display panel 10
`from upper surface 21a.
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`Re?ecting sheet 25 is a thin PET sheet with a thickness
`approximately 0.05—O.5 mm. Light coming from upper
`surface 21a from polarizer 21 through diffusion pattern 50
`travels through the diffusion sheet 26 or prism sheet 27,
`which are arranged on the upper portion of upper surface
`21a and light up liquid crystal display panel 10. However, a
`portion of the light is re?ected through sheet 26 and 27 in the
`lower direction. The light re?ected from the upper direction
`is returned to polarizer 21, among others, through re?ecting
`sheet 25. Re?ecting sheet 25 may also be aluminum or other
`non-PET material. Also, lower case 3 may be used in place
`of a re?ecting sheet as a re?ector. Further, the frame of a
`computer or such carrying the illumination device or liquid
`crystal display of the instant invention can also be used as a
`re?ector in place of the re?ecting sheet.
`Diffusion sheet 26 is an approximately 0.05—O.5 mm thin
`PET sheet or PC sheet. Diifusion sheet 26 diffuses the light
`that is re?ected by diffusion pattern 50 and radiated from
`upper surface 21a. Diifusion pattern 50 is often formed in a
`narrow line con?guration or net con?guration. The light that
`is re?ected by these types of patterns is diffused by diffusion
`sheet 26. The diifusion pattern cannot be recognized from
`the liquid crystal display panel 10. Diffusion sheet 26 is
`arranged with a very small layer of air between it and the
`upper surface 21a of polarizer 21. The angle mentioned
`above is maintained in regards to the angle of upper surface
`21a. Re?ection sheet 26 is not limited to a PET sheet and
`such sheets as acrylic-type sheets, among others, may be
`used.
`Prism sheet 27, which is arranged on diffusion sheet 26,
`is made up of very small linear prisms lined in a cross
`sectional array. The angle of the light radiating from diffu
`sion sheet 26 is arranged to improve the illuminating inten
`sity of the liquid crystal display panel 10. Although the
`brightness can be improved through prism sheet 27, when
`su?icient brightness is achieved through diiTusion sheet 26,
`prism sheet 27 can be omitted, thus reducing manufacturing
`cost.
`Fluorescent light 22, which is used as the light source of
`illumination device 20, is in an L-shape, and is positioned
`adjacent to edges 41c and 41d of polarizer 21. It is desirable,
`as will be explained later, to maintain a gap between edges
`41c and 41d and ?uorescent light 22 of around 0.8-1.5 mm.
`The comer of edge 40 of polarizer 21 is removed and the
`?uorescent light 22 is able to be positioned with the above
`noted gap. Also, through removing this comer, ?uorescent
`light 22 and the comer of polarizer 21 are kept from
`touching and such things as damage to the ?uorescent light
`can be prevented.
`Fluorescent light 22 is covered by re?ectors 23a and 23b
`to make the light discharged from ?uorescent light 22
`incident with good e?iciency from edge 40 of polarizer 21.
`Re?ectors 23a and 23b are PET sheets deposited with silver
`and of a thickness of approximately 0.0l—0.1 mm. In order
`to provide low cost re?ectors that cover the L-shaped
`?uorescent light and that are easy to install, two straight
`re?ectors are used. This will be explained in greater detail
`below.
`Edge re?ective tape 28 is arranged at the two edges 41a
`and 41b, which are opposite the edges 41c and 41d where
`?uorescen