United States Patent [19]
`Nakamura et al.
`
`1111 11111111111 11115115511! 1111111111111111111
`5,453,855
`Sep. 26, 1995
`
`[11] Patent Number:
`[45] Date of Patent:
`
`[54] LIQUID CRYSTAL DISPLAY DEVICE
`BACKLIT BY LED’S COUPLED TO
`PRINTED CIRCUIT BOARD
`
`[75] Inventors: Yasuo Nakamura; Etsuo Furuya, both
`of Shimizu, Japan
`
`[73] Assignee: Koito Manufacturing Co., Ltd.,
`Tokyo, Japan
`
`[21] Appl. No.: 164,373
`[22] Filed '
`Dec 9 1993
`_
`_
`’_
`_
`.
`Forelgn Apphcanon Prmmy Data
`[30]
`Dec. 15, 1992
`[JP]
`Japan ................................ .. 4-0353718
`115L221
`[g1
`iapan
`53432232
`ep. ,
`[
`]
`apan .................................. ..
`-
`[51] Int. Cl.6 ...................... .. GOZF 111335; GOZF l/ 1333
`[52] US. Cl. ........................... .. 359/49; 359/42; 359/48;
`_
`359/83
`[58] Fleld of Search """""""""
`336529/g412’2468’8409d
`’
`’
`
`’
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`5,064,276 11/1991 Endo et a1. ..... ..
`
`359/49
`
`5,184,888
`
`2/1993 Sakuma et al. ....................... .. 362/136
`
`Primary Examiner——Anita Pellman Gross
`Assistant Examiner—Fetsum Abraham
`Attorney, Agent, or Firm-Koda and Androlia
`
`ABSTRACT
`
`57
`[
`1
`Aliquid crystal display device with an illuminator installed
`in the back of a liquid crystal display panel. The illuminator
`is made of a shallow box-form holder having a re?ective
`inner surface, a plurality of LED’s installed in at least one
`side wall of the holder, at light-diifusing plate installed
`between the liquid cryst a1 display panel and the holder, and
`a printed circuit board mounted on the outer surface of the
`bottom of [he holdeij The LED’S are of diiferent light
`directional angles and inclined toward the bottom surface of
`the holder so that the light from the LED’s can be re?ected
`by the re?ective bottom surface towards the display panel.
`
`4,791,540 12/1988 Dreyer, Jr. et al. ................... .. 362/331
`
`10 Claims, 7 Drawing Sheets
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`18
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`Mercedes-Benz Ex. 1007
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`MBI_001370
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`

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`US. Patent
`
`Sep. 26, 1995
`
`Sheet 1 of 7
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`5,453,855
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`‘21....
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`
`
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`MBI_OO1371
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`MBI_001371
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`

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`US. Patent
`
`Sep. 26, 1995
`
`Sheet 2 of 7
`
`5,453,855
`
`FIG. 2
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`MBI_001372
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`

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`US. Patent
`
`Sep. 26, 1995
`
`Sheet 3 of 7
`
`5,453,855
`
`FIG. 4
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`
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`MBI_OO1373
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`MBI_001373
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`

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`US. Patent
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`Sep. 26, 1995
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`Sheet 4 of 7
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`5,453,855
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`FIG. 7
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`60a
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`6
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`PRIOR ART
`
`MBI_001374
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`US. Patent
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`Sep. 26, 1995
`
`Sheet 5 0f 7
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`5,453,855
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`m .0_..._
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`MBI_001375
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`US. Patent ‘
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`Sep. 26, 1995
`
`Sheet 6 of 7
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`5,453,855
`
`FIG. IO
`
`3
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`MBI_001376
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`

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`US. Patent
`
`Sep. 26, 1995
`
`Sheet 7 of 7
`
`5,453,855
`
`190a
`
`FIG. II
`
`MBI_001377
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`5,453,855
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`1
`LIQUID CRYSTAL DISPLAY DEVICE
`BACKLIT‘ BY LED’S COUPLED TO
`PRINTED CIRCUIT BOARD
`
`BACKGROUND OF THE INVENTION
`
`2
`transparent resin 7. With this structure, the light is easier to
`see.
`In the above light-conducting plate 1, the inclined back
`surface In forms a re?ective surface 9 which is obtained by
`the vacuum evaporation of aluminum or bonding of a
`re?ective sheet, etc..
`However, the following problem arises in the conven
`tional liquid crystal display devices that use a light-conduct
`ing plate 1 and LED 2. Brightness irregularity tends to
`occur; and as a result, the entire display of the liquid crystal
`display panel 3 is not uniformly illuminated.
`More speci?cally, the LED 2 is installed so that its optical
`axis L is roughly parallel to the surface 6 of the light
`conducting plate 1. A portion 4a of the light entering the
`light-conducting plate 1 from the LED 2 is re?ected by the
`re?ective surface 9 and is emitted to the outside from the
`surface 6 (this light is called directly re?ected light), while
`another portion 4b of the light is ?rst completely re?ected by
`the surface 6 of the light-conducting plate 1 and then
`re?ected by the re?ective surface 9 and emitted from the
`surface 6 (this light is called completely re?ected light).
`Accordingly, if the re?ective surface 9 is divided into, for
`example, three areas A, B and C along the direction of the
`optical axis (the area closest to the LED 2 is A, the next
`closest area B, and the area furthest from the LED 2 C), the
`quantities of directly re?ected light 4a and the completely
`re?ected light 4b per unit area vary depending upon the area
`involved. As a result, brightness irregularity occurs. The
`areas A and C are brighter, and the area B is darker.
`In compact liquid crystal display devices, the manufac
`turing cost, brightness, size and weight are critical, and
`devices which are low in manufacturing cost, size and
`weight and which provide a uniformly bright illumination in
`strong demand. However, in the devices which use the
`light—conducting plate as described above, the weight tends
`to be large because of the light-conducting plate. Thus, there
`are limitations to the weight reduction.
`
`SUMMARY OF THE INVENTION
`
`The present invention is to solve the problems in the
`conventional devices.
`The primary object of the present invention is to provide
`a liquid crystal display device which can achieve a reduction
`in weight and thickness, produce no irregularity in bright
`ness and provide uniform and brighter surface illumination,
`and is designed so that various areas to be illuminated can
`be illuminated with a desired color at a desired brightness.
`The liquid crystal display device according to the present
`invention is comprised of a holder with its front surface
`open, a liquid crystal display panel installed in the front
`surface opening of the holder with a light-diffusing plate
`interposed between the holder and the panel, a printed circuit
`board attached to the back of the holder, and a plurality of
`LED’s mounted on the printed circuit board so as to back
`illuminate the liquid crystal display panel from behind the
`light-diffusing plate, and in addition, the holder is provided
`with LED mounts which hold the LED’s, and the inside
`bottom surface of the holder is formed with a re?ective
`surface so that the light-di?fusing plate is back-illuminated
`by direct light emitted from the LED’s and re?ected by the
`re?ective surface.
`In the liquid crystal display device of the present inven~
`tion, two types of LED’s which differ in light directional
`angles are employed.
`
`1. Field of the Invention
`The present invention relates to a liquid crystal display
`device which is back-illuminated by means of LED’s.
`2. Prior Art
`A liquid crystal display (LCD) device is used in various
`di?ferent types of devices and instruments such as OA (o?ice
`automation) equipment, clocks, blood pressure gauges, hot
`water supply devices, etc. The display element (or display)
`is illuminated from the inside so that the visibility of the
`numbers, characters, etc. displayed thereon is improved.
`In small battery-driven liquid crystal display devices, a
`re?ective illumination method is generally employed so as
`to reduce power consumption. In this method, a light bulb
`(incandescent light bulb) is installed inside the LCD device,
`and the bulb is lit only when it required by the operator. The
`reason for this occasional use of the light bulb is that, though
`it depends on the capacity of the battery installed in the
`device, the power available is as small as 60 mW to 100 mW,
`and it is not possible to obtain a constant lighting by the light
`bulb.
`Recently, therefore, illumination of the display is accom
`plished by a back-lighting system that uses LED’s (light
`emitting diodes) because they are low in power consump
`tion.
`LED’s have a much smaller power consumption (20 mW
`per unit) than ordinary bulbs and also have a high brightness
`and a long useful life. In addition, LED’s can emit various
`different colors of light such as green, yellow, etc. in addition
`to red; and they are easy to obtain. Accordingly, LED’s are
`ideal for use as an illuminating light source in the liquid
`crystal display devices.
`However, with LED’s alone, it is di?icult to illuminate a
`broad area of the display uniformly, since the directionality
`of the emission output of the LED’s is high.
`Accordingly, as shown in FIG. 12, a ?at panel type
`light-emitting body which is obtained from a light-conduct
`ing plate 1 and LED 2 is used as an illuminating device for
`a liquid crystal panel 3.
`In this ?at panel type light-emitting body, the light
`conducting plate 1 is made of a transparent resin which is
`superior in terms of light transmissibility (e.g., an acrylic
`resin, etc.) and formed into a wedge shape when viewed
`from the side so that the back surface 1a of the light
`conducting plate 1 is inclined. Light 4 emitted from the LED
`2 enters into the interior of the light-conducting plate 1 from
`the thick end surface 5 and is then re?ected at the back
`surface 1a of the light-conducting plate 1 so that light is
`emitted out from the top surface 6. Thus, a uniform surface
`illumination is obtained, and the entire surface of the liquid
`crystal display panel 3 is uniformly illuminated.
`Compared to other ?at panel type light~emitting bodies
`that use electroluminescence, optical ?bers, etc., this ?at
`panel type light-emitting body has advantages. It is simple
`in structure and low in the manufacturing cost.
`Since the LED 2 has a small light emission area, a diode
`chip 8 is molded in a transparent resin 7 such as an acrylic
`resin, etc. so that the light emitted from the diode chip 8 is
`spread by a convex lens part 7a formed at the tip of the
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`3
`In addition, the liquid crystal display device of the present
`invention uses two types of LED’s which emit different
`colors of light.
`Furthermore, in the liquid crystal display device of the
`present invention, at least one LED mount is provided with
`a plurality of through-holes which are formed so that the
`respective axial lines of the through-holes are inclined
`toward the light-diffusing plate or toward the re?ective
`surface.
`The re?ective surface which is on the bottom of the liquid
`crystal display device of the present invention is raised at the
`center for accomplishing a higher effective back-illumina
`tion.
`In the present invention, the inside bottom surface of the
`holder forms the re?ective surface, so that a portion of the
`light emitted from the LED’ s is re?ected to the front, and the
`light-di?using plate diffuses the light from the LED’s so that
`the ?ickering of the light in a speci?ed direction is elimi
`nated. The LED’s are positioned at inclined angles in the
`through-holes of the holder so that the optical axes of the
`LED’s intersect portions of the holder. As a result, the
`proportions of the light re?ected by the re?ective surface
`and the light directed toward the light—diffusing plate are
`changed. Accordingly, the quantities of re?ected light that
`are re?ected in the respective areas of the re?ective surface
`are also can vary.
`Generally, LED’s with a narrow directional angle are
`brighter than LED’s with a broad directional angle. Thus, in
`the present invention, LED’s with a narrow directional angle
`are used for the areas where the brightness is low so that the
`brightness of the overall illumination area is adjusted so as
`to be uniform.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 shows a cross section of a ?rst embodiment of the
`liquid crystal display device according to the present inven
`tion;
`FIG. 2 is an exploded perspective view of the main
`section of the device of FIG. 1;
`FIG. 3 is a top view of the arrangement of the LED’s used
`in the device of FIG. 1;
`FIG. 4 shows an enlarged cross section of the essential
`section of the device;
`FIG. 5 is atop view illustrating the arrangement of LED’s
`in a second embodiment of the present invention;
`FIG. 6 is an perspective view of the holder of the second
`embodiment;
`FIG. 7 is a cross section of the holder of the second
`embodiment;
`FIG. 8 shows an enlarged cross section of the essential
`section of a third embodiment of the present invention;
`FIG. 9 is a partially cross-sectional perspective view of a
`fourth embodiment of the present invention;
`FIG. 10 shows an enlarged cross section of the essential
`section of the device of the fourth embodiment;
`FIG. 11 is a partially cross-sectional exploded perspective
`view of a ?fth embodiment of the present invention; and
`FIG. 12 illustrates a conventional ?at panel type light
`ernitting body that uses a light-conducting plate and an LED.
`
`4
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`The present invention will be described in detail below
`with reference to the Figures in the accompanying drawings.
`In these Figures, the same elements to those in FIG. 12 are
`indicated by the same reference numerals.
`FIG. 1 through FIG. 4 show a ?rst embodiment of the
`present invention.
`The liquid crystal display device 11 includes a case 12
`which is formed as a thin rectangular frame with an opening
`13 in the center. The case 12 is obtained form two casing
`elements: front and back (or upper and lower in the Figures)
`casing element. These casing elements are made by injection
`molding of a resin, so that the case 12 consists of a main
`casing 12A (lower casing) and a cover casing 12B (upper
`casing) which ?ts into the opening of the main casing 12A.
`The cover casing 128 is connected to the main casing 12A
`by a conventional means such as fastening screws, elastic
`engagement means, etc. (not shown in the Figures).
`Inside the case 12 is provided a liquid crystal display
`panel 3, an illuminating device 16 which includes a plurality
`of LED’s 2 so as to back-illuminate the liquid crystal display
`panel 3, and a power supply 17 for the LED’s 2 and liquid
`crystal display panel 3. A plurality of operating switches 18,
`etc. are provided on the front (or upper) surface of the cover
`casing 12B.
`The opening 13 is at the center of the front (or upper)
`cover casing 12B, and a protective plate 14 which protects
`the surface of the liquid crystal display panel 3 is ?tted in
`this opening 13.
`The liquid crystal display panel 3 is a conventional one
`and is made of a nematic liquid crystal, etc. which is
`installed between upper and lower glass plates. The liquid
`crystal display panel 3 is formed as a thin rectangular plate
`with a plurality of terminals 20 (see FIG. 2) installed on the
`two longer side surfaces that are parallel to the direction of
`the length of the display panel 3. These terminals 20 are
`connected to a conventional liquid crystal driving circuit
`(not shown) of a printed circuit board 22 by lead wires 21.
`The lead wires 21 are bent roughly at right angles toward the
`back of the liquid crystal display panel .3 along the side
`surfaces of the liquid crystal display panel 3. The rear (or
`distal) ends of the lead wires 21 are inserted into holes 23 of
`the printed circuit board 22 and electrically connected to the
`liquid crystal driving circuit by soldering.
`The illuminating device 16 includes a shallow box~form
`holder 24 which is parallel to the liquid crystal display panel
`3 on the back (lower) side of the display panel 3, a plurality
`of LED’ s 2 which are installed in the side walls 24a and 24b
`of the holder 24, the printed circuit board 22 to which the
`holder 24 is attached, and a light-diffusing plate 25 installed
`between the liquid crystal display panel 3 and the holder 24.
`The holder 24 is made of a synthetic resin. The front
`surface (or the top surface in the Figures) of the holder 24
`is open. In other words, the holder is open toward the front
`(or the top), and the entire inside surface is re?ection-treated
`which is obtained by an application of a white paint, a
`bonding of an aluminum foil, vacuum evaporation of alu
`minum, etc. A re?ective surface 26 is thus formed in the
`holder 24. If necessary, ?ne projections and indentations can
`be formed on the re?ective surface 26 so that a diffusing type
`re?ective surface is obtained.
`As seen in FIG. 2, a pair of trapezoidal projections 27a
`and 27b are installed so as to face each other on the inside
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`surfaces of the longer side walls 240 and 24d of the holder
`24. Thus, the minimum width at the central part of the holder
`24 is roughly equal to or slightly larger than the width W1
`of the display part 3a of the liquid crystal display panel 3,
`and the maximum width at both ends of the holder 24 (in the
`direction of length) is roughly equal to or slightly smaller
`than the width W of the liquid crystal display panel 3.
`Height-wise, the trapezoidal projections 27a and 27b are
`shorter than the side walls 240 and 24d by an amount of the
`combined thicknesses of the liquid crystal display panel 3
`and light-diffusing plate 25. Thus, the liquid crystal display
`panel 3 and light-diffusing plate 25 can be ?tted in the
`front-surface (or upper surface) opening of the holder 24
`with the outer edges of the light-diffusing plate 25 rested on
`the front (or upper) surfaces of the trapezoidal projects 27a
`and 27b.
`A hill-shaped raised portion 28 is formed as an integral
`part of the holder 24 at the center of the inside bottom
`surface of the holder 24. As described above, the surface of
`this raised portion 28 is a re?ective surface that is provided
`in a conventional means such as by the application of a white
`paint, bonding of an alurrrinum foil, or vacuum evaporation
`of aluminum, etc.
`In each of the shorter side walls 24a and 24b of the holder
`24, a plurality of through-holes 30 (seven through-holes 30a
`through 30g in this embodiment) for LED’s 2 are formed in
`a row at a prescribed spacing. The LED’s 2a through 2g are
`respectively installed in these through-holes 30. The
`through-holes 30 are formed at an inclined angle so that the
`axial lines of the through-holes 30 intersect the front (or
`upper) surface opening of the holder 24 at a shallow angle
`9 with respect to a horizontal line h. Thus, the through-holes
`30 are inclined toward the re?ective surface 26 of the holder
`24. In other words, the outside opening ends of the through
`holes 30 are positioned closer to the front (or upper) surface
`opening of the holder 24 than the inside opening ends of the
`through-holes 30. The angle of inclination 9 of the through
`holes 30 in this case is approximately 4.5 degrees.
`As shown in FIG. 3, out of the seven through-holes, the
`three through-holes 30c through 30e which are located in the
`center are formed so that their axial lines are parallel to the
`imaginary center line 33. The through-holes 30a and 30g
`located at both ends are inclined by an angle 71 (which is 10
`degrees) with respect to the center line 33, so that the
`imaginary extension lines of the optical axes of the through
`holes 30a and 30g intersect the center line 33 roughly at the
`center of the holder 24. The remaining two through-holes
`30b and 30f are inclined by an angle Y2 (which is 7 degrees)
`with respect to the center line 33 so that the imaginary
`extension lines of the optical axes of the through-holes 30b
`and 30f point roughly toward the center of the holder 24.
`As shown in FIG. 4, the outside surfaces of the respective
`shorter side walls 24a and 24b are inclined inwardly by an
`angle 6 which is equal to the angle of the inclination angle
`9 of the LED’s 2. In addition, as seen from FIG. 2, the center
`a of the outside surface of each side wall 24a and 24b for the
`three through-holes 300 through 30e is formed ?at so as to
`be perpendicular to the axial lines of the through-holes 30c
`through 30e. The end portions b at both ends of the side wall
`for the through-holes 30a and 30g are formed, are formed as
`inclined surfaces which are perpendicular to the axial lines
`of the through-holes 30a and 30g and inclined by an angle
`71 with respect to the center a. The middle portions 0 for the
`through-holes 30b and 30f are formed as inclined surfaces
`which are perpendicular to the axial lines of the through
`
`6
`holes 30b and 30f and inclined by the angle Y2 with respect
`to the center a.
`These angled surfaces are provided in order to insure
`stable and secure attachment of the LED’s 2 in the through
`holes 30a—30g. When the LED’s 2 are installed in the
`respective through-holes 30a through 30g, the optical axes
`L of the LED’s 2 are aligned with the center lines of the
`through-holes 30a through 30g.
`The LED’s 2a through 2g have different light directional
`angles (spread angles) [3 as seen from FIGS. 3 and 4.
`In this embodiment, the directional angle [31 (see FIG. 3)
`of the LED’s 2a, 2d and 2g positioned at both ends and in
`the center is 34 degrees, the directional angle [32 of the
`LED’s 2b and 2f which are the second LED’s from the
`respective ends is 12 degrees, and the directional angle B3
`of the LED’s 2c and 2e which are the third LED’s from the
`respective ends is 40 degrees.
`The different directional angles [3 is obtained by differ
`entiating the distance between the tip lens part of the
`transparent resin 7 (see FIG. 4) and the diode chip 8 at the
`time of molding. The directional angle B can be large when
`the diode chip 8 is positioned closer to the lens part of the
`resin 7 and small when the diode chip 8 is positioned further
`away from the lens part.
`In addition, the LED’s 2 that emit different colors of light
`are used. In this embodiment, LED’s of two different colors
`are employed. More speci?cally, the LED’s 2b, 20, 2e and
`2f which are the second and third LED’ s from the respective
`ends, emit green light; and the remaining LED’s 2a, 2d and
`2g located at both ends and in the center indicated by
`shading in FIG. 3 emit red light.
`These LED’s 2 are connected to the electrical circuitry of
`the printed circuit board 22 by lead wires 35. The electric
`circuit is constructed so that only the green LED’s 2b, 2c, 2e
`and 2f light up under normal usage via the operation of the
`operating switches 18 (see FIG. 1) so that the display part 3a
`of the liquid crystal display panel 3 is back-illuminated by
`these LED’s. The red LED’s 2a, 2d and 2g are used only as
`a warning display. Thus, variety of the illumination is
`obtained by using LED’s of different colors.
`As best shown in FIG. 4, the light-diffusing plate 25 is
`made of two diffusing ?lms 25A and 25B which are installed
`one in front (or top) of the other with an appropriate empty
`space in between and installed in the opening 13 of the
`holder 24. The empty space between the two ?lms 25A and
`25B is in fact an air layer 37 which is for increasing the
`diffusing eifect.
`The front (or top) diffusing ?lm 25A is obtained by, for
`example, applying an opaci?er to an acrylic resin. The back
`(or lower) diffusing ?lm 25B is obtained by, for example,
`subjecting the surface of a polyester ?lm to a light-diffusing
`treatment by means of sand blasting.
`Other types of diifusing ?lms 25 can be used, such as
`?lms formed by subjecting the surface of a transparent resin
`to a light~diffusing treatment based on embossing or an
`application of a transparent paint containing minute glass
`beads, metal particles, etc. Films formed from a transparent
`resin molded with minute metal particles added to the resin
`at the time of molding can be also used. The size of the space
`between the diffusing ?lms 25A and 25B is set at an optimal
`value with a consideration of the light loss caused by the air
`layer 37.
`The printed circuit board 22 has a liquid crystal driving
`circuit and a constant-current circuit. The driving circuit
`contains various electronic components 40 (see FIG. 4) such
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`as liquid crystal driving IC’s, transistors and resistors, etc.
`The constant-current circuit is used for the LED’s 2.
`The printed circuit board 22 is electrically connected to
`the power supply 17 as seen in FIG. 1 by lead wires 41. The
`constant-current circuit compensates for the temperature of
`the LED’s 2. More speci?cally, when the diode voltage
`changes as a result of change in temperature, the current
`changes because the power supply voltage is ?xed, and also
`the brightness of the LED’s 2 changes. In order to prevent
`these changes, ?eld-effect transistors (FET’s) are connected
`in series with the LED’s 2. This is especially effective in
`cases where the diode voltage is as low for example as 3 V,
`4.5 V or 6 V.
`The printed circuit board 22 is attached by screws 43 to
`a board-attachment 42 which project from the bottom of the
`main casing 12A.
`In the liquid crystal display device 11 as described above,
`the LED’s 2 2b, 20, 2e and 2f which emit green light are lit
`during ordinary operation. A portion of the light emitted
`from these LED’s 2 directly hits the inside bottom surface of
`the holder 24 or the re?ective surface 26 and is completely
`re?ected to the front (or upward), thus forming the directly
`re?ected light 4a. Another portion of the light emitted from
`the LED’s 2 is directed toward the front of the holder 24,
`thus forming the directly emitted light 4b. These two types
`of light 4a and 4b are diffused when they pass through the
`light-diffusing plate 25 and air layer 37; and as a result, the
`entire display part 3a of the liquid crystal display panel 3 is
`back-illuminated or illuminated from behind. Thus, the
`illuminating device 16 makes a plane light source.
`The light-diffusing plate 25 and the air layer 37 prevent
`?ickering of the light in a speci?ed direction by diffusing the
`light from the LED’s 2. Since the holder 24 is a shallow box
`shape, the weight is smaller compared to the devices that use
`light-conducting plates.
`The LED’s 2 are installed so that they are inclined by a
`prescribed angle 6 toward the inside of the holder 24 or
`toward the re?ective surface 26. The quantity of the light
`re?ected by the re?ective surface 26 of the holder 24,
`particularly the quantity of the re?ected light 4a re?ected
`near the foot areas of the raised portion 28 (see FIG. 1) and
`directed forward (or upward), is increased compared to a
`case where the LED’s 2 are not installed in a inclined
`fashion. Accordingly, the brightness of the central part of the
`holder 24 with respect to the direction of the length (or the
`direction of the longer sides 24c and 24d) of the holder 24
`is increased.
`Furthermore, LED’ s 2 of different directional angles [3 are
`used so that the lengthwise central area of the holder 24,
`where the brightness tends to be low, is illuminated by the
`bright light from the LED’s 2c and 22 which have a small
`directional angle [53. Thus, a more uniform surface illumi
`nation which is free of irregularity is obtained.
`The light emitted from the LED’s 2 can be precisely
`controlled by changing the installation arrangement of the
`
`
`
`LED’s 2 and using LED’s of different directional angles The brightness levels in the respective illumination areas can
`
`15
`
`25
`
`35
`
`45
`
`55
`
`be thus adjusted so as to meet the intended brightness levels.
`FIGS. 5, 6 and 7 illustrate a second embodiment of the
`present invention.
`In this embodiment, the inside dimensions of the holder
`60 are the same throughout the entire length of the holder,
`and the bottom is formed ?at. In other words, unlike the ?rst
`embodiment, the holder has no trapezoidal projections nor
`hill-shaped raised portion inside.
`
`60
`
`65
`
`8
`In the second embodiment, a plurality of through-holes 30
`which are formed in the shorter side walls 60a and 60b of the
`holder 60 are inclined toward the bottom of the holder 60 by
`an angle of 91 (which is 6 degrees) as in FIG. 7. The axial
`line of each hole 30 is parallel to the center line 33 of the
`holder 60. The bottom of the holder 60 is a re?ective surface
`26 which is obtained by the application of a white paint, the
`bonding of an aluminum foil, the vacuum evaporation of
`aluminum foil, the vacuum evaporation of aluminum, etc.
`The LED’s 2a, 2d and 2g which are provided at both ends
`and in the center of each one of the shorter side walls 60a
`and 60b of the holder 60 emit red light, and the directional
`angle [31 of these LED’s is 34 degrees. The LED’s 2b and
`2f which are second from the respective ends emit green
`light, and the directional angle [52 of these LED’s is 40
`degrees. The LED’s 2c and 2e which are third from the
`respective ends emit green light, and the directional angle [33
`of these LED’s is 40 degrees.
`Otherwise, this embodiment is generally the same as the
`?rst embodiment in structure.
`In this embodiment either, the LED’s 2 are inclined
`toward the inside of the holder 60 and are of different
`directional angles B. Accordingly, as in the ?rst embodiment,
`uniform surface illumination is obtained, and the entire
`display part of the liquid crystal display panel 3 is uniformly
`illuminated.
`FIG. 8 shows a third embodiment of the present invention.
`In this embodiment, a shade 61 which is used for glare
`prevention is provided so as to project, as an integral part,
`from the inner end of each shorter side walls 60a and 60b of
`the holder 60. Unlike the ?rst and second embodiments, the
`through-holes 30 are formed so that they are inclined toward
`the light-diffusing plate 25 or upwardly. Accordingly, the
`LED’s 2 in the through-holes 30 are inclined toward the
`front (or upward) of the holder 60 by a prescribed angle 62
`(which is 4.5 to 6 degrees).
`Otherwise, this embodiment is substantially the same as
`the previous embodiments structure-wise.
`In the structure of this third embodiment, the directly
`emitted light 417 directed toward the front (or top) of the
`holder 60 is increased, and the directly re?ected light 4a
`which is re?ected by the re?ective surface 26 can travel a
`greater distance. Accordingly, the brightness of illumination
`areas which are distant from the LED’s 2 can be increased.
`In addition, since the shades 61 are provided between the
`LED’s 2 and the light-diffusing plate 25, the LED’s 2 do not
`enter the ?eld of vision through the liquid crystal display
`panel 3. Thus, the visibility is improved. The other advan
`tages of this embodiment are the same as those of the ?rst
`embodiment.
`FIGS. 9 and 10 illustrate a fourth embodiment of the
`present invention.
`In this embodiment, a pair of holder blocks 70A (only one
`is shown) are used as the shorter sides of the rectangular
`holder 70, and a pair of conductive elements 72A and 72
`which are made of a conductive rubber, etc. are used as the
`longer sides of the holder 70. The liquid crystal display panel
`3 is provided on the thus obtained holder 70, and the holder
`70 is mounted on a printed circuit board 22 with a re?ection
`plate 74 in between. The side and peripheral portion of the
`front (or upper) surfaces of the liquid crystal display panel
`3 are covered by a casing 75.
`The liquid crystal display panel 3 is installed on the holder
`70 with a light-dilTusing plate 25 in between. A plurality of
`liquid crystal driving electrodes (not shown) are installed on
`
`MBI_001381
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`5,453,855
`
`the front (or upper) surfaces of the holder blocks 70A and the
`conductive elements 72A and 72B and also along the side
`edges of the back (or bottom) surface of the liquid crystal
`display panel 3. These driving electrode are electrically
`connected to a liquid crystal driving circuit (not shown) of
`the printed circuit board 22 via the conductive elements 72A
`and 72B.
`Each of the holder blocks 70A is formed by the injection
`molding of a resin, so that it is a squared-off “C” shape when
`viewed from the above. Each holder block 70A consists of
`a main body part 170a and a pair of board-holding parts
`170b and 170a. The main body part 170a is long in the
`perpendicular direction relative to the length of the liquid
`crystal display panel 3, and the board-holding parts 170b and
`1700 are provided at both ends of the main body part 170a,
`thus forming the “C”.
`As shown in FIG. 10, the cross-section of each main body
`part 170a in the direction parallel to the direction of the
`length of the liquid crystal display panel 3 is a C shape.
`Thus, each main body part 170a has a recessed area 76
`which opens on the inside