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`[19]
`United States Patent
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`6,108,060
`[11] Patent Number:
`
`
`[45] Date of Patent: Aug. 22, 2000
`
`Funamoto et al.
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`U8006108060A
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`[54] SURFACE-TYPE ILLUMINATION DEVICE
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`AND LIQUID CRYSTAL DISPLAY
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`[75]
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`Inventors: Tatsuaki Funamoto; Toru Yagasaki;
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`Fumiaki Akahane, all of Suwa, Japan
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`[73] Assignee: Seiko Epson Corporation, Tokyo,
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`Japan
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`[21] Appl. No.: 09/321,687
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`[22]
`Filed:
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`May 28, 1999
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`Related U.S. Application Data
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`
`[30]
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`May 13, 1993
`
`
`
`Int. Cl?
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`
`[51]
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`
`[52] US. Cl.
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`
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`
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`[62] Division of application No. 08/689,424, Aug. 9, 1996, Pat.
`
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`
`
`
`
`
`
`No. 5,949,505, which is a division of application No.
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`
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`
`
`
`
`08/204,374, May 10, 1994, Pat. No. 5,619,351.
`
`
`
`
`
`
`
`Foreign Application Priority Data
`
`
`
`
`[JP]
`Japan .................................... 5—111852
`
`
`
`
`.......... GozF 1/1335; G01D 11/28;
`
`
`
`
`
`F21V 7/04
`
`
`349/65; 362/26; 362/27;
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`
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`362/31
`
`[58] Field of Search .......................... 349/65, 70; 362/26,
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`362/27, 31
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`
`
`[56]
`
`
`References Cited
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`
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`
`
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`
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`7/1992 Yokoyauia ..
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`
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`
`9/1999 Funamoto et a1
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`5,949,505
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`
`
`
`
`
`
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`
`
`European Pat. Off. .
`
`
`
`
`European Pat. Oif. .
`
`
`
`
`European Pat, Off. .
`
`
`
`
`(List continued on next page.)
`
`
`
`
`OTHER PUBLICATIONS
`
`
`“Advancements ln Backlighting Technologies For LCDs”,
`
`
`
`
`
`K. Hathaway, SPIE Proceedings, HighiResolution Displays
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`
`
`
`and Projection Systems, vol. 1664, Feb. 1992, pp. 108—116.
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`
`
`
`
`
`
`
`Electronic Design, Aug. 2, 1961, p. 47.
`
`
`
`
`
`
`
`Voltarc Technical Bulletin “Fluorescent Lamp”, 1987.
`
`
`
`
`
`Primary Examiner—William L. Sikes
`
`
`
`
`Assistant Examiner—Walter Malinowski
`
`
`
`Attorney, Agent, or Firm%ark P. Watson
`
`
`
`
`
`ABSTRACT
`
`[57]
`
`
`A surface—type illumination device suitable for providing
`
`
`
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`
`
`
`backlight
`in a liquid crystal display is disclosed. For
`
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`
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`example, an L-shaped fluorescent light can be used as an
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`illuminant and mounted next to two edges of a substantially
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`rectangular light guide plate. The corner of an edge portion
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`between the two edges is removed. The fluorescent light, the
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`length of whose illuminating portion is long, is positioned
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`with an appropriate gap from the light guide plate allowing
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`for illumination with high brightness and low power con-
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`sumption. Consequently, when the illumination device is
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`used in a color liquid crystal display, appropriate backlight
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`
`with high brightness can be obtained. Moreover, because the
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`influence of the temperature from the illumination device is
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`small, a stable color display can be achieved.
`
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`
`12 Claims, 12 Drawing Sheets
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`so
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`Page 1 of 137
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`TOYOTA EXHIBIT 1024
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`Page 1 of 137
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`TOYOTA EXHIBIT 1024
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`

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`6,108,060
`Page 2
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`FOREIGN PATENT DOCUMENTS
`
`
`rance.
`F
`4/1925
`0587 766
`
`
`
`
`
`0145 934 10/1957 France.
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`0327 493
`5/1958 France.
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`2620795
`3/1989 France.
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`2632 432 12/1989 France.
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`54-4008?
`Japan~
`3/1979
`
`
`
`Jap‘m'
`6020557"
`19/1985
`Japan.
`61-166585
`//1986
`
`
`
`Japan.
`61-248079
`11/1986
`
`
`
`Japan.
`62-102226
`5/1987
`
`
`
`Japan.
`63-062105
`3/1988
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`
`3/1988
`
`63-45537
`Japan.
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`,
`,
`,
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`7/1988
`Japan.
`63-175301
`
`
`
`8/1988
`Japan.
`637124217
`2/1989
`Japan-
`64-45002
`
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`
`2/1989
`Japan.
`64-45003
`
`
`
`7/1989
`Japan.
`1—183626
`
`
`
`5/1991
`Japan.
`3—15476
`
`
`
`9/1991
`Japan.
`3-201304
`
`
`
`(C,
`7,
`
`
`
`4/1))2
`Japan.
`4-102888
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`
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`1/1952 United Kingdom.
`0664193
`W088/08149 10/1988 WIPO.
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`Page 2 of 137
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`US. Patent
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`Aug. 22, 2000
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`Sheet 1 0f 12
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`6,108,060
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`36
`10X
`33
`37
`2
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`
`'lm'lnnnn'lmnn-
`I
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`V—_ L
`J—‘F—F‘
`
`11
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` —-m‘.sl
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`Page 3 of 137
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`US. Patent
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`Aug. 22, 2000
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`Sheet 2 0f 12
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`6,108,060
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`FIG._3
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`US. Patent
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`Aug. 22, 2000
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`Sheet 3 0f 12
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`FIG._4
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`Page 5 of 137
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`US. Patent
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`Aug. 22, 2000
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`Sheet 4 0f 12
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`US. Patent
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`Aug. 22, 2000
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`Sheet 5 0f 12
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`FIG._BB
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`Page 7 of 137
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`US. Patent
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`FIG._9
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`41c
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`40
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`45b
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`41d
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`FIG._ 10A
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`41d
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`HQ. 103
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`41c
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`47C 41d
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`HQ. 100
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`FIG._10D
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`41a
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`[24
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`US. Patent
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`Aug. 22, 2000
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`27
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`26.
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`61
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`25
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`L_‘_L“/_:\\\\\\\\\\\‘
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`__________________________________ J
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`US. Patent
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`Aug. 22, 2000
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`Sheet 9 0f 12
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`Aug. 22, 2000
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`Sheet 10 0f 12
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`FIG._ 16
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`4“
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`FIG._17
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`40b
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`US. Patent
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`Aug. 22, 2000
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`Sheet 11 0f 12
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`6,108,060
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`SURFACE TEMPERATURE
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`(°C)
`
`65
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`55
`
`45
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`
`35
`
`
`FIG 18
`'_
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`25 ——————————————————————
`
`ROOM TEMPERATURE
`
`
`
`POSITION DIRECTLYj
`
`
`OVER THE
`
`
`LIGHT SOURCE
`
`
`
`
`CENTRAL!T
`PORTION OF
`
`
`THE IMAGE
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`POSITION DIRECTLY
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`OVER THE
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`LIGHT SOURCE
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`65
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`55
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`( C) 45
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`35
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`SURFACE TEMPERATURE
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`POSITION DIRECTLY
`
`OVER THE LAMP
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`LIGHT SOURCE
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`72b
`ROOM TEMPERATURE
`
`FIG. -22
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`25
`
`
`END PORTION —T CENTRAL!T
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`OF THE IMAGE
`PORTION OF
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`THE IMAGE
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`US. Patent
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`Aug. 22, 2000
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`Sheet 12 0f 12
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`6,108,060
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`828
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`82b
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`FIG._20
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`[90
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`91
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`92
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`FIG._21
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`Page 14 of 137
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`Page 14 of 137
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`

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`6,108,060
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`
`1
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`SURFACE-TYPE ILLUMINATION DEVICE
`
`
`AND LIQUID CRYSTAL DISPLAY
`
`
`
`CROSS-REFERENCE TO RELATED
`
`
`APPLICATIONS
`
`
`
`
`
`
`
`
`This is a Divisional of prior application Ser. No. 08/689,
`
`
`
`
`
`
`
`
`
`
`424 filed Aug. 9, 1996, now US. Pat. No. 5,949,505, which
`
`
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`
`
`
`
`
`
`
`
`is a Division of application Ser. No. 08/204,374 filed May
`
`
`
`
`
`
`
`
`
`
`10, 1994, now U.S. Pat. No. 5,619,351. Application Ser.
`
`
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`
`
`Nos. 08/689,424 and 08/204,374 are incorporated herein by
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`reference in their entirety.
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`
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`BACKGROUND OF THE INVENTION
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`This invention relates in general to a thin, surface-type
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`illumination device for providing backlight for liquid crystal
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`displays (LCD) and, in particular, to a suitable illumination
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`device for use in a notebook computer display that provides
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`high brightness with low power consumption as well as to a
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`liquid crystal display that uses this illumination device.
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`Surface-type illumination devices with a cylindrical light
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`source and a flat
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`described in Japanese Laid—Open Patent Application No.
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`60-205576 and Japanese Laid-Open Patent Application No.
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`61-248079 are well-known. One such example is shown in
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`FIG. 21. In the illumination device 90, cylindrical fluores—
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`cent light 92 is positioned on one side of the substantially
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`rectangular and flat light guide plate 91. The light introduced
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`to light guide plate 91 from fluorescent light 92 is reflected
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`by the diffusion pattern printed on light guide plate 91 and
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`emitted from the surface of the light guide plate at a fixed
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`density of light.
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`This type of surface illumination device, in recent years,
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`has been used extensively to provide backlight for liquid
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`crystal display panels. Liquid crystal display panels are
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`increasingly used as displays in such devices as laptop
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`computers, televisions and cameras. The use of liquid crystal
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`display panels for color displays is also increasing. As the
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`size of personal computers and televisions become smaller,
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`it is imperative that liquid crystal display panels become
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`thinner and lighter.
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`Accordingly, it is necessary that the surface-type illumi-
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`nation device used for liquid crystal display panels to
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`provide backlight, along with the color displays, becomes
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`thinner and lighter with less power consumption. Also, to
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`use in color displays, a sufficient brightness is necessary to
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`clearly show the colors displayed in the liquid crystal. This
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`requires the use of a high output fluorescent light in the
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`illumination device. However, along with the light, heat is
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`also radiated from the high—output fluorescent light. The
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`effect of this heat, as shown in FIG. 22, is significant. The
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`temperature may rise 30—40° C. above a normal temperature
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`of 25° C. Consequently, when this type of illumination
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`device is used for providing backlight in an MIM active
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`color display panel or in an STN passive color display panel,
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`a special method to reduce the heat is necessary to control,
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`to a certain extent, the color and brightness irregularities.
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`Instead of using one high output fluorescent tube, one may
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`also increase the number of fluorescent tubes. In this way, it
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`is possible to control to some extent the temperature increase
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`due to the light source. However, as the number of fluores-
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`cent tubes is increased, many other problems appear. One of
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`these problems is the variations in the illumination of the
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`fluorescent
`tubes. Because the illumination intensity of
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`floresecnt tubes varies according to each tube, it is necessary
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`to adjust such things as the resistance within the fluorescent
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`tube driver circuit to obtain a fixed illumination intensity.
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`2
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`Consequently, in the case when several fluorescent tubes are
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`used in one illumination device, extra time is required during
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`the manufacturing process to obtain a balanced and fixed
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`illumination intensity.
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`Another problem is the increased number of driver cir-
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`cuits required to turn on the fluorescent tubes. The number
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`of these driver circuits can not be easily increased in devices
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`such as microcomputers where thinness and small size are
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`important.
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`SUMMARY OF THE INVENTION
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`In accordance with the instant invention, a suitable illu-
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`mination device for color liquid crystal displays can be
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`obtained that is small in size, lightweight, and has high and
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`uniform brightness. Further, it is an object of the invention
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`to provide a surface—type illumination device that can pre—
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`vent heat generation and its resulting bad effects to the liquid
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`crystal display panel.
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`Another object of the invention is to provide a surface-
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`type illumination device that, without increasing the number
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`of driver circuits for driving the fluorescent lights, displays
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`a brightness higher than that in conventional illumination
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`devices and restricts heat radiation.
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`A further object of the invention is to generate a suitable
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`diffusion pattern to realize a surface-type illumination
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`device, this dilfusion pattern being used in the illumination
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`device.
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`Still another object of the invention is to provide a stable
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`liquid crystal display where the driver IC for driving the
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`liquid crystal display panel is positioned so that it will not be
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`affected by heat.
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`In accordance with the instant invention, by employing an
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`illuminant longer than conventional illuminants, illumina-
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`tion with high illumination intensity is obtained without
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`increasing the number of driver circuits for driving the
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`illuminants and without concentrating the heat diffusion.
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`Further, by bending the illuminant, light can be introduced
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`along the polygon—shaped light guide plate. Also, to main—
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`tain proper space between the light guide plate and the
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`illuminant and to increase the efliciency of the light intro-
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`duced to the light guide plate, a corner is removed from an
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`edge of the light guide plate. According to the invention, the
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`surface-type illumination device comprises a light guide
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`plate which is polygon—shaped and substantially transparent;
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`a dilfusion pattern arranged on one surface of the light guide
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`plate for substantially evenly emitting light, the light being
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`introduced from the illuminant to the other surface of the
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`light guide plate; and a cylindrically-shaped illuminant bent
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`so that the illuminant faces at least two sides of the light
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`guide plate; wherein the edge between the two sides is
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`processed so that the corner does not protrude.
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`By using an illuminant bent along the light guide plate,
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`the length of the cylindrically-shaped illuminant is long, and
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`an illuminant with large illuminating area can be used.
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`Consequently, the rise in temperature of the illuminant can
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`be kept down and high brightness can be obtained.
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`Furthermore, the number of driver circuits for driving the
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`illuminant can be decreased. When an illuminant such as a
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`fluorescent light is bent to adjust for interference between
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`the bent portion and the corner of the light guide plate, the
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`width or length of the entire illumination device becomes
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`longer, preventing miniaturization. In the instant invention,
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`by removing a corner of the light guide plate, the distance
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`between the light guide plate and the illuminant can be kept
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`within a fixed range for high incident efficiency, and thus, a
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`highly efficient illumination device that is small in size can
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`be realized.
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`10
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`tom
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`30
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`L» .n
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`50
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`60
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`Page 15 of 137
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`Page 15 of 137
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`

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`6,108,060
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`4
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`the light incident to the light guide plate from the first side
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`and the density distribution of the presupposed diffusion
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`pattern; and then compensating the density distribution of
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`the presupposed diffusion pattern so that the sum of the
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`predicted emitted light
`intensity distribution for
`the
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`x-direction and the predicted emitted light intensity distri-
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`bution for the y—direction on arbitrary rectangular xy coor—
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`dinates of the light guide plate fit within a fixed range.
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`When an edge reflector is installed at at least one of the
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`two sides opposite to the first side and the second side,
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`respectively, for reflecting the light from the inner part of the
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`light guide plate to the light guide plate, it is desirable to
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`compensate the density distribution by computing the
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`reflected light intensity incident from the edge reflector to
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`the light guide plate with a fixed attenuation factor; finding
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`a predicted emitted light intensity distribution for at least
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`one of the x and y directions of the reflected light intensity;
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`and adding this to the predicted emitted light
`intensity
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`distribution found above.
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`By printing the diffusion pattern described above on the
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`light guide plate or by putting on the light guide plate a sheet
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`with the pattern formed on it, light introduced from the bent
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`illuminant can be evenly radiated from the light guide plate.
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`Similarly, light can be evenly emitted by making the thick-
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`ness of a light guide plate with an even diffusion pattern
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`inversely proportion to the compensated density distribution
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`of the diffusion pattern.
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`Effects of the heat from the illuminant can be minimized
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`by using as a bent illuminant an L-shaped illuminant and by
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`placing in a position opposite to the illuminant a driver
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`device such as a driver IC for driving the liquid crystal
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`display. Consequently, as the threshold value of the driver
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`does not become unstable due to the heat, a color display
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`with stable contrast
`is obtained. Further, a high quality
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`display with high brightness and a small illumination device
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`are also obtained.
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`Further, a stable, high quality display can be obtained that
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`reduces heat using an even longer U-shaped illuminant. The
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`brightness of the display is easy to adjust when illuminants
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`such as L-shaped and U-shaped illuminants are used because
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`nearly the same intensity of light
`is incident from the
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`periphery of the light guide plate. Of course, an O—shaped
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`illuminant can also be arranged around the periphery of a
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`rectangular light guide plate as well as an illuminant bent to
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`fit the shape of any other polygon.
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`fuller
`Other objects and attainments together with a
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`understanding of the invention will become apparent and
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`appreciated by referring to the following description and
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`claims taken in conjunction with the accompanying draw-
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`ings.
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`BRIEF DESCRIPTION OF THE DRAWINGS
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`FIG 1 is a sketch of a liquid crystal display using the
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`surface—type illumination device in accordance with the first
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`embodiment of the invention.
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`FIG. 2 is a cross—sectional view of FIG. 1 showing the
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`structure of the liquid crystal display.
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`FIG. 3 is a break-down View showing the structure of the
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`liquid crystal display shown in FIG. 1.
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`FIG. 4 is a break-down view showing the construction of
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`the surface-type illumination device used in the liquid
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`crystal display shown in FIG. 1.
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`FIG 5 is a top plan vier illustrating the combination of
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`the surface—type illumination device shown in FIG. 4 and the
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`liquid crystal display panel.
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`3
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`Further, by using a long illuminant as mentioned above,
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`an improvement in the conversion efliciency from power to
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`light is also attained. For example, in illuminants such as a
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`fluorescent light, the power to the illuminant is consumed by
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`the cathode drop, which is due to the glow discharge, and by
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`positive column gradient voltage, which is due to light
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`emission. When a plurality of illuminants are used and the
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`input voltage increased, the portion consumed by the cath-
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`ode drop voltage significantly increases and an increase in
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`the positive column gradient tendency for light emission is
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`small. However, in the illumination device of the instant
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`invention, which uses a long illuminant, power is efficiently
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`converted into light as the increase in the positive column
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`gradient voltage is smaller than in the case when the number
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`of illuminants is increased.
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`The edge of the light guide plate can be processed into
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`many different shapes, for example, the corner in the shape
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`of an isosceles triangle can be removed. In the case of the
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`isosceles triangle, a high incident efficiency of light from the
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`illuminant to the light guide plate can be maintained. It is
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`desirable to make the length of one of the sides of the
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`isosceles triangle in the approximate range of 0.6 times to
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`1.0 times the smallest radius of curvature of the bent portion
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`of the illuminant so as to realize a small-sized illumination
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`device. Also, in order to prevent light incident from the edge,
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`and to increase the uniformity of the light radiated from the
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`light guide plate, it is effective to include a shield at the edge
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`portion to prevent introduction of light from the illuminant.
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`Also, the corner of the edge in a diamond-shape may be
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`removed. In order to make the incident efficiency high and
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`keep the size of the device small, it is desirable to make the
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`length of one of the sides of the removed corner in a
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`diamond-shape Within a range of 0.6 times to 1.0 times the
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`smallest radius of curvature of the bent portion of the
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`illuminant. Also, if all the corners are removed from the
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`edges of the light guide plate so that they do no protrude, the
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`directionality of the light guide plate disappears and the
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`manufacturing process time for positioning the light guide
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`plate is saved.
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`It is common to cover the illuminant with a reflector to
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`increase the incident efficiency of the light from the illumi—
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`nant to the light guide plate. When a bent illuminant such as
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`the one described above is used,
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`is desirable for the
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`reflector to include a straight first reflector and a second
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`reflector positioned along two sides of the light guide plate
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`such that at the edge the first reflector is covered by the
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`second reflector. It is also possible for the reflector to include
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`a first reflector that covers the lower half portion of the
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`illuminant on one side of the light guide plate and a second
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`reflector that covers the upper half of the illuminant from the
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`other side of the light guide plate.
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`The diffusion pattern that diffuses light incident to the
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`light guide plate from the bent illuminant can be generated
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`by the following method. To generate a dilfusion pattern that
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`evenly radiates, from the other side of the light guide plate,
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`light introduced from the illuminant to the light guide plate
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`in an illumination device Where a cylindrically—shaped illu—
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`minant is positioned near at least a first side and a second
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`side of a substantially rectangular light guide plate,
`the
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`density distribution per unit area of the diffusion pattern can
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`be found by the following method:
`finding a predicted
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`emitted light intensity distribution for the y-direction along
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`the first side based on the intensity of the light incident to the
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`light guide plate from the second side and the density
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`distribution of a presupposed diffusion pattern; then finding
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`a predicted emitted light
`intensity distribution for the
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`x-direction along the second side based on the intensity of
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`10
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`tom
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`30
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`L»LA
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`40
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`50
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`60
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`Page 16 of 137
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`Page 16 of 137
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`

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`6,108,060
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`6
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`The basic structure of one embodiment of liquid crystal
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`display 1 will be explained using the cross-sectional view of
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`liquid crystal display 1 shown in FIG. 2 and the break—down
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`View of liquid crystal display 1 shown in FIG. 3. In liquid
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`crystal display 1, illumination device 20 is installed in lower
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`case 3. Above device 20, liquid crystal display panel 10 is
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`installed using frames 30 and 31. Liquid crystal display
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`panel 10 is formed by enclosing the liquid crystal, transpar-
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`ent electrodes, etc. between two layers of transparent glass
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`substrates 11 and 12. At side 10a of liquid crystal display
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`panel 10, a plurality of driver ICs 13 are installed for
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`latching pixel data for the rows and sending it to the liquid
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`crystal display panel. Also, at side 10b, which is adjacent to
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`side 10a, a plurality of driver ICs 14 are installed for latching
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`pixel data for the columns and sending it to the liquid crystal
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`display panel.
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`Frames 30 and 31 are used to protect illumination device
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`20 and to position it within the case. At the same time, it also
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`fills the role of maintaining a fixed distance for gap 33
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`between illumination device 20 and liquid crystal display
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`panel 10, for example, 0.2—1 mm. For this reason, frames 30
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`and 31 are prepared so that their lower halves 34 and 35
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`support illumination device 20 and their upper halves 36 and
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`37 act as spacers between illumination device 20 and liquid
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`crystal display panel 10. In this example the frame is divided
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`into two pieces, however, the number of pieces is not limited
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`to two. For example, three pieces, four pieces, or even more
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`is possible, and even just one piece is also possible.
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`Furthermore, the frame need not cover the entire periphery
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`of illumination device 20 or liquid crystal display panel 10.
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`Aplurality of pieces may be arranged in appropriate places.
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`Illumination device 20 is a surface-type illumination
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`device set up with a cylindrically—shaped fluorescent light 22
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`at the edge of substantially rectangular light guide plate 21.
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`Fluorescent light 22 is roughly L-shaped and is covered by
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`reflectors 23a and 23b. Wires for supplying power to drive
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`fluorescent light 22 extend from both ends of fluorescent
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`light 22 and are connected to the driver circuit on the host
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`side through connector 7 which is for turning on the light.
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`FIG. 4 is a break-down view of illumination device 20 and
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`will be used to explain the structure of the illumination
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`device of this embodiment. Illumination device 20 is com—
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`prised of light guide plate 21, which is substantially rectan-
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`gular in shape and has the corner of at edge 40 missing,
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`fluorescent
`light 22, which encompasses edge 40 in an
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`L-shape, and reflectors 23a and 23b, which cover uorescent
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`light 22 in the direction of light guide plate 21 and efficiently
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`reflect light from fluorescent light 22 to light guice plate 21.
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`On lower surface 21b of light guide plate 21, i.e., the side
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`opposite to the side where liquid crystal display aanel 10 is
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`arranged, pattern sheet 24, which is printed wit] diffusion
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`pattern 50, and reflecting sheet 25 are arranged in that order.
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`On upper surface 21a of light guide plate 21, i.e., the side
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`where liquid crystal display panel 10 is arrangec, diffusion
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`sheet 26 and prism sheet 27 are arranged. Edge reflective
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`tape 28 is put on edge 41a and 41b, opposite to ’uorescent
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`light 22 of light guide plate 21.
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`Light guide plate 21 is a transparent material whose index
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`of refraction is greater than that of air. An index 0 refraction
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`equal to or greater than 1.41 is desirable using suca materials
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`as acrylic resin, polycarbonate resin, amorphous
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`polyolefine-type resin, and polystyrene resin. Use of these
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