United States Patent [19]
`Akahane et al.
`
`US005931555A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,931,555
`*Aug.3,1999
`
`[54] BACKGROUND LIGHTING APPARATUS
`FOR LIQUID CRYSTAL DISPLAY
`
`[75] Inventors: Fumiaki Akahane; Tooru Yagasaki;
`Tatsuaki Funamoto, all of SuWa, Japan
`
`[73] Assignee: Seiko Epson Corporation, Tokyo,
`Japan
`
`[*] Notice:
`
`This patent is subject to a terminal dis
`claimer.
`
`[21] Appl. No.: 08/794,652
`[22] Filed:
`Feb. 3, 1997
`
`Related US. Application Data
`
`[63] Continuation of application No. 07/864,772, Apr. 7, 1992,
`Pat. No. 5,667,289, which is a continuation-in-part of appli
`cation No. 07/525,408, May 18, 1990, Pat. No. 5,130,898.
`Foreign Application Priority Data
`
`[30]
`
`May 18, 1989
`Sep. 29, 1989
`Feb. 27, 1990
`Apr. 8, 1991
`Sep. 17, 1991
`
`[JP]
`[JP]
`[JP]
`[JP]
`[JP]
`
`Japan .................................... .. 1-57274
`Japan
`.. 1-253863
`Japan
`2-46356
`Japan
`.. 3-075093
`Japan .................................. .. 3236347
`
`Int. Cl.6 ...................................................... .. F21V 8/00
`[51]
`[52] US. Cl. ............................... .. 362/31; 362/27; 349/64;
`349/65
`[58] Field of Search ................................ .. 349/62, 64, 65;
`362/26, 27, 31, 216, 246
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`6/1967 Balchunas ............................... .. 362/31
`3,328,570
`7/1975 Pulles ......... ..
`3,892,959
`7/1976 Kingston ................................. .. 362/31
`3,968,584
`2/1986 Durbin et al. .......................... .. 355/67
`4,568,179
`4,630,895 12/1986 Abdala, Jr. et al. .................... .. 362/31
`
`FOREIGN PATENT DOCUMENTS
`
`0 317 250 5/1989 European Pat. Off. .
`0 442 529 8/1992 European Pat. Off. .
`0 561 329 9/1993 European Pat. Off. .
`587766 8/1926 France ................................... .. 362/31
`1145934 5/1957 France ................................... .. 362/31
`
`(List continued on neXt page.)
`
`OTHER PUBLICATIONS
`
`“Advancements in Backlighting Technologies for LCDs,”
`K. Hathaway, Spie Proceedings, High—Resolution Displays
`and Projection Systems, vol. 1664, Feb. 1992, pp. 108—116.
`Electronic Design, Aug. 2, 1961, p. 47.
`Voltael Technical Bulletin “Fluorescent Lamp”, 1987.
`
`Primary Examiner—Alan Cariaso
`Attorney, Agent, or Firm—Michael T. Gabrik
`[57]
`ABSTRACT
`
`A background lighting apparatus includes a light entering
`edge surface around substantially the entire periphery of a
`highly specular transparent plate Wherein light beams enter
`from peripheral light sources and travel toWard the central
`portion of the plate and are dispersed and diffused by a
`diffusion system formed relative to the transparent plate.
`Uniformity of luminance provided from the background
`lighting apparatus is enhanced as a Whole by increasing the
`incident quality of the input light beams into the transparent
`plate While easing the incident directivity of the light beams
`on the transparent plate With the overall substantial enhance
`ment of luminance produced from the apparatus. Further, the
`temperature distribution on a liquid crystal panel positioned
`adjacent to the output surface of the background lighting
`apparatus is substantially uniform across the panel so that
`the transmission quality of the liquid crystal material, Which
`is dependent upon ambient temperatures, is made substan
`tially more uniform resulting in signi?cantly higher levels of
`uniformity in luminance across the display as Well as
`uniformity of displayed colors and gradations thereof ema
`nating from the display panel.
`
`(List continued on neXt page.)
`
`10 Claims, 9 Drawing Sheets
`
`\CIEIEIEIUUU EJEIEIEIIJUBJ:
`DEIEIEIEIEIEI
`EIEIEIEIEIUEI]:
`UEIEIEIEIEIEIEIUEIEIEIEIEIEIEI
`EJUUUEIEIEIEIEIIIHIIUEIEIUU
`:JUUEIEHZIEIDDEIEIEIUUU]:
`[:JUUEHIHIIIIIIIJDIIIEIEIEIUUE]
`[:JEJEIDUUEIEIIIHIHIIUDEIEJE]
`EJEIUEIEIEIUEIEIEIEIEIEIEIEJU
`DDUUEIEIEIEIEIEIEIUDEIEIEI
`DDEIEICIEIUUEIDUEIEIEIEID
`DDDEIEIEIEICIEIEIDDDDDI:
`
`LGD_001006
`
`LG Display Ex. 1027
`
`

`
`5,931,555
`Page 2
`
`US. PATENT DOCUMENTS
`
`3/1987 Ohe ......................................... .. 362/31
`4,648,690
`3/1988 Ohe ..
`. 362/31
`4,729,067
`3/1988 Ohe .... ..
`. 362/31
`4,729,068
`3/1989 Blanchet
`.40/546
`4,811,507
`6/1989 Flasck a a1. ..
`362/31
`4,842,378
`8/1989 Kojima
`. 362/31
`4,860,171
`6/1990 Sanai
`. 362/26
`4,933,814
`4,965,950 10/1990 Yamada
`. 362/31
`4,974,122 11/1990 Shaw ' ........ ..
`. 362/31
`
`2 632 432 12/1989 France .
`834837 3/1952 Germany ............................... .. 362/31
`5440086 3/1979 Japan_
`
`5440087 3/1979 Japan "
`69205576 10/1985 Japan
`61466585 7/1986 Japan
`61-248079 11/1986 Japan .
`62-102226 5/1987 Japan .
`62105 3/1988 Japan .
`6345537 3/1988 Japan _
`
`,
`
`,
`
`2823333 13/1331 3a“? 6‘ a1‘
`5,124,890
`6/1992 C1101 a al.
`5,130,898
`7/1992 Akahane
`5,134,549
`7/1992 Yokoyama
`5’136’483
`8/1992 schoniger et al_
`5,283,673
`2/1994 Murase et a1.
`5,363,294 11/1994 Yamamoto et a1. ..
`
`1Z0 e .... ..
`
`.
`
`325131
`362/27
`.362/31
`.362/31
`362/61
`362/31
`.. 362/330
`
`"5301 “988 lap“
`“442,235; 22:32 EPZE '
`P "
`45003 2/1989 Japan
`1-183626
`7/1989 Japan ..................................... .. 349/70
`3-51476
`5/1991 Japan .
`3-201304 9/1991 Japan .
`
`5,667,289
`
`9/1997 Akahane et al- - - - - - - - - -
`
`- - - - - -- 362/31
`
`4-102888 4/1992 Japan ..................................... .. 349/70
`
`FOREIGN PATENT DOCUMENTS
`
`362/31
`327493 3/1958 Switzerland .... ..
`664193
`1/1952 United Kingdom ................... .. 362/31
`
`2 620 795 3/1989 France .
`
`WO 88/08149 10/1988 WIPO .
`
`LGD_001007
`
`

`
`U.S. Patent
`
`Aug.3, 1999
`
`Sheet 1 of9
`
`5,931,555
`
`FIG._ 1
`(PRIORART)
`
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`
`FIG._2
`(PRIOR ART)
`
`LGD_001008
`
`

`
`U.S. Patent
`
`Aug.3, 1999
`
`Sheet 2 of9
`
`5,931,555
`
`FIG._3A
`
`\
`
`FIG._3B
`(PRIOR ART)
`
`LGD_001009
`
`

`
`U.S. Patent
`
`Aug.3, 1999
`
`Sheet 3 of9
`
`5,931,555
`
`1000 -
`
`
`
`$55 wwwzEoEm
`
`B P(I)lNT
`
`I
`
`C POINT
`
`FIG._4
`
`3A
`
`35/
`
`FIG._5
`
`30
`
`LGD_001010
`
`

`
`U.S. Patent
`
`Aug.3, 1999
`
`Sheet 4 of9
`
`5,931,555
`
`
`
`1
`
`4
`
`FIG._6A 7
`
`6
`
`96 E6 :2
`
`4
`
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`
`9?
`
`35
`
`3
`
`FIG._6B 5
`
`8
`
`LGD_001011
`
`LGD_001011
`
`

`
`U.S. Patent
`
`Aug.3, 1999
`
`Sheet 5 of9
`
`5,931,555
`
`\ 6
`
`unUUUUUUUUun
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`FIG._ 9
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`
`LGD_001012
`
`

`
`U.S. Patent
`
`Aug.3, 1999
`
`Sheet 6 of9
`
`5,931,555
`
`A
`<
`
`A
`
`l
`
`D
`
`B
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`
`C /
`
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`
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`>
`
`CENTER
`
`FIG._ 10A I
`
`v
`
`
`
`AREA RATIO
`
`FIG._ 103
`
`FIG._ 10C
`
`LGD_001013
`
`

`
`U.S. Patent
`
`Aug.3, 1999
`
`Sheet 7 of9
`
`5,931,555
`
`I
`
`I
`
`l
`
`
`
`
`
`SURFACE TEMPERATURE (°C)
`
`55
`
`A 01
`
`35
`
`NORMAL TEMPERATURE
`
`I
`
`ABOVE LAMP
`LIGHT SOURCE
`
`I
`
`CENTER OF
`PICTURE
`
`I
`
`ABOVE LAMP
`LIGHT SOURCE
`
`FIG__ 11
`(PRIORART)
`
`DISTRIBUTION
`
`l
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`NORMALTEMPERATURE
`
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`3
`(D
`
`I
`
`ABOVE LAMP
`LIGHT SOURCE
`
`I
`
`CENTER OF
`P|CTURE
`
`I
`
`ABOVE LAMP
`LIGHT SOURCE
`
`FIG._
`
`DISTRIBUTION
`
`LGD_001014
`
`

`
`Aug. 3, 1999
`
`Sheet 8 of 9
`
`5,931,555
`
`FIG._ 13B
`(PRIOR ART)
`
`LGD_001015
`
`LGD_001015
`
`

`
`U.S. Patent
`
`Aug.3, 1999
`
`Sheet 9 of9
`
`5,931,555
`
`4
`
`6C
`
`6A
`
`4
`
`6
`
`4
`
`4
`
`6A
`
`6C
`
`1
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`4
`
`FIG._ 14
`
`4
`
`63
`
`6C
`
`4
`
`6A
`
`60
`
`1
`
`4
`
`FIG._ 15
`
`LGD_001016
`
`LGD_001016
`
`

`
`1
`BACKGROUND LIGHTING APPARATUS
`FOR LIQUID CRYSTAL DISPLAY
`
`CROSS-REFERENCE TO RELATED
`APPLICATION
`
`This is a Continuation of prior application Ser. No.
`07/864,772 ?led on Apr. 7,1992, now US. Pat. No. 5,667,
`289, Which, in turn, is a Continuation-In-Part of Ser. No.
`07/525,408 ?led on May 18, 1990, noW issued as US. Pat.
`No. 5,130,898.
`
`BACKGROUND OF THE INVENTION
`
`This invention relates to background lighting apparatus
`and more particularly to thin background light sources for
`liquid crystal panel displays, such as, employed in
`computers, Word processors and LCD television sets and the
`like.
`In Japanese Laid Open No. 63-62105, there is described
`a background light system in Which the irregular re?ecting
`surface is provided With a pattern of rnilky White type,
`dispersion points on a transparent plate supported in the
`housing unit of the liquid crystal display. FIG. 1 discloses
`the irregular re?ecting layer of the type disclosed in Japa
`nese Laid Open No. 63-62105 comprising two or more
`transparent plates 1A and 1B, each having a pattern of rnilky
`White type of light diffusion pattern comprising a rnultiplic
`ity of dots 50 formed on bottom re?ecting surfaces 10 of
`plates 1A, 1B. The backlighting apparatus disclosed
`includes opposed light sources 6 for providing light to enter
`opposite end surfaces of dual plates 1A, 1B. Diffusion plate
`4A permits the transmission of light beams from plates 1A,
`1B as Well as brings about diffusion of light beams that are
`not at the necessary critical angle for exiting the apparatus.
`Total re?ecting plate 5A is of the White type for the disper
`sion and re?ection of light back into plates 1A, 1B. This type
`of dispersion pattern and dispersion/re?ection plate
`approach improves the quantity of light re?ections, diffusion
`and dispersion but it does so at the expense of providing tWo
`or more plates 1 in order to increase the output e?iciency of
`the background lighting apparatus. Furthermore, the lurni
`nous efficiency of this type of re?ecting surface is loW When
`employed in the rear portion of the liquid crystal display
`housing unit. In order to increase the brightness, a plurality
`of superirnposed transparent plates 1A, 1B are utiliZed each
`halving a light diffusion pattern for diffusing the light beam.
`HoWever, the thickness of the display becomes large.
`Further, the dispersion and diffusion of light and resulting
`brightness in the re?ecting surface or multiple surfaces of
`the transparent plates is not achieved resulting in unevenness
`or nonuniforrnity in brightness in back lighting and,
`correspondingly, in the displayed image.
`In general, a background lighting apparatus for a liquid
`crystal display is required to have uniform brightness across
`its output facet or face. In this type of apparatus, Wherein
`light enters from an edge or end face of the transparent plate
`of the apparatus and is guided internally in the transparent
`plate to form a plate type lighting apparatus, such as in the
`case of this invention, the total quantity of light output can
`be increased by increasing the quantity of irregular re?ection
`occurring relative to the irregular re?ecting surface or por
`tion provided relative to the transparent plate thereby result
`ing a brighter background light. HoWever, ais the quantity of
`irregular re?ection is increased, the brightness level quickly
`decreases With distance from the light source so that non
`uniforrnity in the overall brightness of the light output from
`the lighting apparatus increases. In order to counteract this
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`5,931,555
`
`2
`phenornenon, a pattern comprising an irregular re?ecting
`surface or portion and a totally re?ecting portion are
`arranged in a manner to achieve uniforrn light output With a
`high level of brightness. As previously indicated, this has
`been accomplished in the past by a patterned surface on a
`transparent plate as described in Japanese Laid Open No.
`63-62105. HoWever, it is di?icult to increase the area ratio
`of the irregular re?ecting portion over the regular re?ecting
`portion because, in doing so, the overall light output effi
`ciency tends to decrease.
`FIG. 2 illustrates another conventional background light
`ing apparatus principally consisting of light sources and a
`light guiding systern. Light sources 6 are provided at oppo
`site ends of transparent plate 1 adjacent to its edge surfaces
`4. The design of this conventional apparatus has loW lurni
`nance and is insu?icient as a backlighting apparatus for a
`liquid crystal display structure, primarily in the case of a
`color display, because the color illumination is not uniform
`across the display. On manner of solving this problem is
`simply to increase the luminance of the light sources.
`HoWever, this accompanied by a corresponding increase in
`exotherrnic generation, i.e., heat generation, Which greatly
`effects the quality of the color image that is produced.
`Moreover, there is the situation that the temperature rise is
`greatest in the vicinity of the light sources 6 at opposite ends
`of plate 1 so that the heat generated is greatest at the vicinity
`of plate edges 4 and drops exponentially from these edges
`toWard the center of transparent plate 1. As a result, the vieW
`of an image is not uniform across the display. This is because
`the threshold voltage for operation of the plurality liquid
`crystal elements of the liquid crystal display are affected by
`the temperature distribution generated by the background
`lighting apparatus. As a result, the threshold voltage of
`operation of the liquid crystal elements will shift and be
`different in regions of the display Where the temperatures are
`different in the display structure. Thus, if the applied voltage
`level for the liquid crystal elernents changes and is different
`in different locations of the display matrix, a signi?cant
`problem is created in overall control of the display. This, in
`particular, has an affect on display of gray scale since a shift
`in light/voltage characteristics due to temperature differ
`ences Will also shift the limited range of applicable
`gradation, particularly in the case of color displays.
`The backlighting in liquid crystal displays has also been
`provided on the read surface or side of the liquid crystal
`structure. In order to provide uniforrn illumination with
`evenly distributed light intensity and luminescence, high
`lurninance is required. In order to meet the requirements of
`uniforrnity in illurnination, it is also necessary that a uni
`forrnity in temperature distribution be maintained. This is
`highly important from a standpoint of operational charac
`teristics of the display since the transrnissivity of the liquid
`crystal material is a function of temperature and can vary in
`a signi?cant rnanner depending upon ambient temperature
`operating conditions. Therefore, if the surface temperature at
`the back surface of the display structure differs at different
`locations of the display, there is a serious problem in terms
`of nonuniforrnity in lurninance and color output quality in
`operation of the display. Thus, the uniforrnity in temperature
`distribution across the display structure and,
`correspondingly, lurninance uniforrnity are critical to pro
`ducing a commercially acceptable liquid crystal display
`system.
`It is, therefore, an object of this invention to provide a
`background lighting apparatus for liquid crystal display
`panels or structures, or other such displays requiring back
`ground lighting, having high lurninous e?iciency and uni
`
`LGD_001017
`
`

`
`5,931,555
`
`3
`formity in luminance With a uniform temperature distribu
`tion across the display structure.
`
`SUMMARY OF THE INVENTION
`According to this invention, a background lighting appa
`ratus comprises a transparent plate With a peripheral edge
`surface functioning as a light input region that has tWo major
`surfaces having high specular quality and Wherein a diffu
`sion system is provided on one of the major surfaces of the
`plate and comprises a pattern of diffusion elements spatially
`formed over its surface. The pattern of diffusion elements
`may be in the form of pixels, squares, dots, circles,
`rectangles, etc., such as, opaline color piXels, points, dots,
`squares, or linear bars. Aplurality of elongated light sources
`are provided substantially along the entire periphery of the
`transparent plate With means for aiding in directing the light
`beams into the interior of the plate for dispersion, diffusion
`and total internal re?ection until a portion of the light beams
`eXits through the other of the major surfaces of the trans
`parent plate. With the introduction of light into the trans
`parent plate along all edge surfaces of the plate, the transfer
`of light into the plate is accomplished With high uniformity
`and ef?cient dispersion. The transparent plate may have a
`geometrical con?guration that is rectangular or polygonal or
`circular in nature.
`In a further aspect of this invention, the pattern of
`diffusion elements Wherein the area ratio of the siZe of the
`diffusion elements siZe relative to its surface monotonically
`increases from the peripheral edge surface to the center of
`the transparent plate at Which point the area ratio is maXi
`mum. The monotonical increase in area ratio to the center of
`the transparent plate is preferably a bell-shaped type of
`con?guration in nature.
`By providing the means for light input to the transparent
`plate along the entire outer peripheral edge surface of the
`plate, it is possible to provide a high quality illumination
`background lighting apparatus Which achieves a high level
`of brightness With uniform luminescent distribution across
`the apparatus. The effective brightness can be further
`increased by providing more light input edge surfaces, such
`as, as can be obtained from a transparent plate that has a
`polygonal or circular shape. Since additional brightness is
`being achieved through light input along the entire periph
`eral edge surface, the intensity of the lamps employed for the
`light input need not be comparatively as high as that
`employed in prior art apparatus. Further, the temperature
`generated and distributed across the surface of the apparatus
`Will be substantially more uniform in nature. Since color and
`brightness uniformity in a LCD color panel are directly
`affected by different ambient temperatures and temperature
`changes, the employment of the background lighting appa
`ratus of this invention has a signi?cant advantage of improv
`ing the quality and operating characteristics associated With
`the achievement of higher levels of uniformity both With
`respect to luminance and color of an LCD color panel.
`Because of thinness achieved in the background lighting
`apparatus of this invention, a highly thin LCD panel/
`background lighting apparatus can be achieved having a
`total thickness of only 15 mm to 20 mm. Thus, the apparatus
`of this invention lends itself to profound utility relative to
`Wall hung TV screens and displays for use in the home as
`Well as a screen display application in vehicle navigation
`system utiliZing satellite communication for display map
`information and for visually tracking distance, location and
`direction of the vehicle.
`Other objects and attainments together With a fuller
`understanding of the invention Will become apparent and
`
`4
`appreciated by referring to the folloWing description and
`claims taken in conjunction With the accompanying draW
`ings.
`
`10
`
`15
`
`25
`
`35
`
`45
`
`55
`
`BRIEF DESCRIPTION OF THE DRAWING
`FIG. 1 is a perspective vieW of a conventional background
`lighting apparatus as knoWn in the art.
`FIG. 2 is a plan vieW of another conventional background
`lighting apparatus as knoWn in the art.
`FIG. 3 is a perspective vieW of one embodiment of a
`background lighting apparatus of this invention.
`FIG. 3A is an illustration of the brightness distribution of
`the diffusion ?lm used in this invention.
`FIG. 3B is an illustration of the brightness distribution of
`the diffusion ?lm of the prior art.
`FIG. 4 is a graphic illustration of the brightness dispersion
`upon illumination of the background lighting apparatus of
`FIG. 3.
`FIG. 5 is a plan vieW of a pattern for an diffusion system
`employed in the background lighting apparatus of FIG. 3.
`FIG. 6A is a plane vieW of another embodiment of a
`background lighting apparatus of this invention.
`FIG. 6B a sectional side elevation of the embodiment
`shoWn in FIG. 6A.
`FIG. 7 is a plane vieW of a further embodiment of a
`background lighting apparatus of this invention.
`FIG. 8 is a plane vieW of a still further embodiment of a
`background lighting apparatus of this invention.
`FIG. 9 is a speci?c illustration of an eXample of an
`embodiment of the pattern for a diffusion system for the
`background lighting apparatus of this invention.
`FIG. 10A is a graphic illustration of aXis identi?cation of
`aXes A—E relative to area ratio distribution shoWn in FIG.
`10B.
`FIG. 10B is a graphic representation of the area ratio
`distribution along tile different aXes of FIG. 10A achieved
`With the pattern for the diffusion system illustrated in FIG.
`9.
`
`FIG. 10C is a contour line pattern relative to pattern
`element area density for the area distribution illustrated in
`FIG. 10B.
`FIG. 11 illustrates the temperature distribution across the
`surface of a liquid crystal panel due to heat generated and
`transmitted from an underlying conventional background
`lighting apparatus.
`FIG. 12 illustrates the temperature distribution across the
`surface of a liquid crystal panel due to heat generated and
`transmitted from an underlying background lighting
`(apparatus of this invention.
`FIG. 13A illustrates the sectors of required light distribu
`tion and penetration in the case of a four lamp background
`lighting apparatus employing a rectilinear type plate.
`FIG. 13B illustrates the sectors of required light distribu
`tion and penetration in the case of a tWo lamp background
`lighting apparatus employing a rectilinear type plate.
`FIG. 14 illustrates another embodiment of this invention
`utiliZing tWo L-shaped ?uorescent lamps each covering tWo
`edges of a rectilinear plate of a background lighting appa
`ratus.
`FIG. 15 illustrates another embodiment of this invention
`utiliZing a U-shaped ?uorescent lamp covering three edges
`of a rectilinear plate of a background lighting apparatus.
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`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`Reference is noW made to FIG. 3 Wherein there is
`disclosed one embodiment of this invention for a back
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`5,931,555
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`ground lighting apparatus having transparent plate 1 of
`plastic material, such as PMMA, With a uniform thickness in
`the range of 1 mm to 5—6 mm. If the plate thickness is
`reduced much below 1 mm, plate planar strength is reduce
`to such an extent that the plate is continually in a Warped
`condition and, therefore, not useful for the uniform disper
`sion and re?ection of light from one of its major surfaces.
`Plate 1 may also be made from polycarbonate, polystyrene
`or glass. Each of the adjacent side or end faces 4 of plate 1
`are provided With a light source 6 Which may be comprised
`of elongated ?uorescent lamps, but can also be other types
`of light sources, such as, an aligned arrangement of LEDs.
`Transparent plate 1 is positioned betWeen diffusion plate 7
`and White type, total re?ecting plate 3. A diffusion system 5
`is provided relative to the bottom surface of transparent plate
`1, i.e., betWeen plate 1 and total re?ecting plate 5. Diffusion
`system 5 may be applied to the bottom surface of plate 1 or
`may be a layer adhesively applied to the bottom surface of
`plate 1. Diffusion system 5 comprises a pattern 3A of milky
`White ?ne solid lines or dotted or dash lines of constant or
`varying Width on the bottom surface of plate 1 or on the
`surface of re?ecting plate 3. Pattern 3A may be printed by
`means, for example, of silk screen printing. Pattern 3A of
`dotted lines are rectangular in shape and the pattern is a
`concentric con?guration With decreasing concentricity in
`siZe toWard the center of transparent plate 1. The pattern has
`a high dispersion capability as Well as a re?ecting capability
`so that the re?ected light also is dispersed in a multitude of
`different directions.
`Other methods of forming these ?ne lines of diffusion
`system 5 may be utiliZed, such as, a White coating via a mask
`prepared on re?ecting plate 3 or the formation of White
`adhesive tape strips on re?ecting plate 3. Thus, the pattern
`of ?ne dash lines may be formed on the one surface of
`transparent plate 1 or may be formed on a ?lm or layer
`applied to one surface of transparent plate 1.
`Diffusion plate in all embodiments of this invention has a
`frosted texture so that it is opaque in nature. A function of
`diffusion plate 7 is to blur together, as vieW by the vieWer
`from exit surface 2, the pattern 3A of features, i.e., dots,
`pixels, etc. of diffusion system 5 so that pattern 3A is not
`perceptible to the human eye. Another function of diffusion
`?lm 7 is to cause the light exiting from surface 2 to form a
`vertically extended lobar pattern 7A, as illustrated schemati
`cally in FIG. 3A. This type of light exit from the surface of
`?lm 7 is due to the irregularity of the front surface of the
`?lm. This provides for higher output brightness compared to
`prior art diffusion ?lms that provide for a Wide base diffusion
`deployment pattern 7B that is schematically illustrated in
`FIG. 3B. Such a pattern provides for a Wide angle dispersion
`of light and, therefore, reduces the overall brightness of
`exiting light.
`Thus, diffusion ?lm 7 permits the passage of light With
`high brightness Whereas re?ector plate 3 (or re?ector plate
`8 in later embodiments) is designed to disperse as Well as
`re?ect as much light as possible. Film 7 may be a polycar
`bonate (PC), PE, PMMA or the like. Examples are PC
`diffusion ?lm available from Bayer Chemical, Lexan ?lm
`from General Electric Company, and sheet prism from 3M
`Corporation.
`Light or light beams produced from light sources 6 enter
`plate 1 via four end faces 4 and is guided internally therein
`While undergoing multiple or repeated re?ections and dif
`fusion by means of diffusion system 5, re?ecting plate 3 and
`transmissive/diffusion plate 7. These multiple re?ections of
`light are enhanced due to the presence of a slight air gap
`preferably formed betWeen diffusion plate 7 and transparent
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`plate 1 and also a slight air gap formed betWeen re?ecting
`plate 3 and transparent plate 1. As a result, the multiple
`re?ected light spreads throughout the volume of transparent
`plate 1 and ?nally a portion thereof exits through surface 2
`at the proper exit angle, i.e., at the critical angle, Which is
`discussed later, through diffusion plate 7, as indicated by
`arroW A, providing a light output of uniform distributed
`brightness.
`FIG. 4 shoWs the brightness dispersion When the back
`ground lighting apparatus of FIG. 3 is illuminated by light
`sources 6. The measured brightness Was accomplished lat
`erally across the upper face of diffusion plate 7 from edge B
`to edge C, as indicated in FIG. 3, employing a luminance
`meter Which is continually sWept across the plate surface. As
`is clearly noted from FIG. 4, the brightness of the light
`across this surface of plate 7 has substantial uniformity.
`FIG. 5 illustrates details of another diffusion system 5
`comprising a pattern of lines in the form of concentric
`rectangles. The arrangement of four light sources 6 about the
`entire periphery of transparent plate 1 and the pattern of ?ne
`lines for diffusion system 5 are formed rectilinearly relative
`to transparent plate 1 providing for greater light output so
`that total brightness is as high as possible. The total bright
`ness of the light output of these embodiments is signi?cantly
`higher than tile embodiments shoWn in FIGS. 1 and 2. Also,
`line Width of pattern 3A for diffusion system 5 monotoni
`cally increases from edge portions 3B to center region 3C
`While the pattern line pitch remains unchanged.
`Alternatively, as explained in Ser. No. 07/525,408 ?led May
`18, 1990, Which is incorporated herein by reference thereto,
`the pitch of the pattern lines for diffusion system 5 may be
`monotonically decrease from edge portions 3B to center
`region 3C While the line Width of pattern 3A remains
`unchanged.
`The pattern in FIG. 5 may alternatively be a series of
`dotted or dash lines, such as in the case of FIG. 3, rather than
`solid lines Wherein the Width of the dash lines increases from
`edge portions 3B to center region 3C. Thus, the dashed line
`Widths Would be the smallest in the four corner regions of
`plate 1. As a further alternative, the dashed line segments
`may also monotonically increase in length from edge por
`tions 3B to center portion 3C. As a still further alternative,
`the dashed line Widths may monotonically increase in Width
`from the four corner regions of transparent plate 1 in both
`orthogonal directions of plate 1, i.e., the horiZontal and
`vertical directions, so that their line thicknesses increasing
`become larger from the four corner regions of plate 1 to
`central horiZontal axis of plate 1 as Well as a vertical central
`axis of plate 1 and are the largest in central region 3C.
`Reference is noW made to another embodiment shoWn in
`FIGS. 6A and 6B. The background lighting apparatus of this
`embodiment comprises a transparent plate 1 Which is sub
`stantially rectangular in shape and of a uniform thickness.
`Plate 1 may be composed of a transparent or light transmis
`sive material Which exhibit a small amount of photo
`absorption and has a refractive index larger than air. The
`refractive index is preferably 1.41 or larger. At this level of
`index, a critical angle for exit of light from the apparatus Will
`be about 45° or less. The material of plate 1 may be, for
`example, acrylic resin, polycarbonate resin, polystyrene
`resin or glass. Plate 1 has one major surface Which is a light
`exit surface 2, Which is the light output to accompanying
`liquid crystal display panel. The other major surface of plate
`1 is termed a non-exit surface 3. Surfaces 2 and 3 are at
`substantially orthogonal to light input end surfaces 4 of plate
`1. Both of these ?at major surfaces are con?gured to smooth,
`specular surfaces. All light beams incident on end surfaces
`4 of plate 1 are internally re?ected by specular surfaces 2
`and 3.
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`5,931,555
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`Means is provided for diffusing the light beams entering
`plate 1 in the form of diffusion system 5 Which is provided
`relative to non-exit surface 3 of plate 1. The pattern com
`prising diffusion system 5 may be printed on this surface or
`added by means of an adhesive or in other convenient
`manner. The pattern of diffusion system 5 provides a plu
`rality of light diffusing elements forming reticulated points,
`dots, dashes, squares, polygons, rectangles, or ?ne lines and
`have a predetermined distribution relative to specular sur
`face 3. Such a predetermined arrangement is provided so
`that the light beams entering plate 1 via edge surfaces 4 are
`totally internally re?ected by specular surfaces 2 and 3 of
`transparent plate 1, Which surfaces are substantially orthogo
`nal to the edge surfaces 4 and, therefore, the light beams
`travel extensively into the interior or central portion of plate
`1. In contrast, some beams reach diffusion system 5 and are
`de?ected, diffused and scattered at a proper angle for exit
`from the apparatus via exit sur?ce 2.
`It is preferred that transparent plate 1 be tabular in form
`and that all surfaces constituting transparent plate 1 be
`specular surfaces so that the contribution of edge surfaces 4
`be small relative to any involvement relative to the function
`of tranmissive to light or the exiting of light, such as, in the
`case of exit surface 2 and non-exit surface 3. In any regard,
`there is a point of increased probability at Which the light
`beams are being totally internally re?ected Within the con
`?nes of plate 1 and Will remain Within the con?nes of plate
`1 due to its specular nature. HoWever, as a result, because of
`the multitude of reoccurring internal light re?ections, light
`exit ef?ciency increases signi?cantly With the use of diffu
`sion system 5. As a speci?c example, if transparent plate 1
`comprises an acrylic plate having a substantially rectangular
`shape, the critical angle for light to exit from this plate is
`approximately 42 degrees. This critical angle, 61, is an angle
`that is a larger acute angle, relative to the surface of trans
`parent plate 1, than the angle of total re?ection, 62. Angle,
`61, is de?ned by:
`
`Where n1 is the refractive index of plate 1 and n2 is the
`refractive index of air.
`It folloWs that the light beams Will not exit from plate 1
`if they travel to the opposite edge surface 4 from Whence
`they enter plate 1 Without being diverted or r