United States Patent [19]
`Akahane et al.
`
`USOO5667289A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,667,289
`*Sep. 16, 1997
`
`[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:
`
`The portion of the term of this patent
`subsequent to Jul. 14, 2009, has been
`disclaimed.
`
`[21] Appl. No.: 864,772
`[22] Filed:
`Apr. 7, 1992
`
`Related US. Application Data
`
`4,933,814
`5,124,890
`5,134,549
`5,136,483
`
`6/1990 Sanai ....................................... .. 362/26
`6/1992 Choietal.
`.... .. 362/31
`7/1992 Yokoyama ..... ..
`.. 362/31
`8/1992 Schiinigeretal. ...................... .. 362/31
`
`FOREIGN PATENT DOCUMENTS
`
`587766 8/1926 France ................................... .. 362/31
`1145934 5/1957 France
`.... .. 362/31
`327493 3/1953 France ................................... .. 362/31
`62105
`3/1988 Japan.
`175301
`7/1933 Japan.
`45002 2/1989 Japan.
`45003 2/1989 Japan.
`664193
`1/1952 United Kingdom ................... .. 362/31
`
`OTHER PUBLICATIONS
`
`Voltarc Technical Bulletin “Fluorescent Lamp”, 1987.
`Electronic Design, p. 47, Aug. 2, 1961.
`
`[63] Continuation-impart of Ser. No. 525,408, May 18, 1990,
`Pat. No. 5,130,898.
`Foreign Application Priority Data
`
`[30]
`
`Primary Examiner—James C. Yeung
`Assistant Examiner—Alan Cariaso
`
`[57]
`
`ABSTRACT
`
`
`
`May 18, 1989 Sep. 29, 1989 Feb. 27, 1990 Apr. 8, 1991 Sep. 17, 1991
`
`
`
`
`
`
`
`
`
`
`
`[JP] [JP] [JP] [JP] [JP]
`
`
`
`
`
`
`
`
`
`Japan Japan Japan Japan Japan .................................. .. 3-236347
`
`
`
`
`
`A background lighting apparatus includes a light entering
`edge surface around substantially the entire periphery of a
`highly internally re?ecting 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 diifusion system formed relative to the transparent
`plate. Uniformity of luminance provided from the back
`ground lighting apparatus is enhanced as a whole by increas
`ing 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 sub
`stantial enhancement of luminance produced from the appa
`ratus. Further, the temperature distribution on a liquid crystal
`panel positioned adjacent to the output surface of the back
`ground 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 substantially more uniform resulting in signi?cantly
`higher levels of unifonnity in luminance across the display
`as well as uniformity of displayed colors and gradations
`thereof emanating from the display panel.
`
`20 Claims, 9 Drawing Sheets
`
`[51] Int. (:1.6 ...................................................... .. F21V 8/00
`[52] US. Cl. ............................ .. 362/31; 362/27; 362/307;
`362/330; 349/70
`[58] Field of Search ................................ .. 362/31, 26, 32,
`362/227, 235, 236, 237, 307, 311, 330,
`343, 27; 359/49, 50
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`3,892,959 7/1975 Pulles ...... ..
`3,968,584 7/1976 Kingston
`4,568,179 2/1986 Durbin et a1.
`4,630,895 12/1986 Abdala, Jr. et a1.
`4,648,690
`3/1987 Ohe ................. ..
`
`362/31
`362/31
`362/343
`362/31
`362/31
`
`4,729,068
`
`3/1988 Ohe . . . . . . . . . . .
`
`. . . .. 362/31
`
`4,811,507
`4,842,378
`4,860,171
`
`. . . .. 362/31
`3/1989 Blanchet . . . . . . .
`362131
`6/1989 Flasck et al. .
`8/1989 Kojima .................................... .. 362/31
`
`LGE_000760
`
`LG Electronics Ex. 1018
`
`

`
`US. Patent
`
`Sep. 16, 1997
`
`Sheet 1 of 9
`
`5,667,289
`
`FIG._ 1
`(PRIOR A HT)
`
`lllllllll-llllllllllllll
`
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`
`FIG._2
`(PRIOR ART)
`
`LGE_000761
`
`

`
`US. Patent
`
`Sep. 16, 1997
`
`Sheet 2 of 9
`
`5,667,289
`
`FIG._3A
`
`FIG._3B
`(PRIOR ART)
`
`LGE_000762
`
`

`
`US. Patent
`
`Sep. 16, 1997
`
`Sheet 3 0f 9
`
`5,667,289
`
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`
`LGE_000763
`
`

`
`U.S. Patent
`
`Sep. 16, 1997
`
`Sheet 4 of 9
`
`5,667,289
`
`y..__._______
`
`"75133112213331.2332
`
`LGE_000764
`
`

`
`US. Patent
`
`Sep. 16, 1997
`
`Sheet 5 of 9
`
`5,667,289
`
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`LGE_000765
`
`

`
`US. Patent
`
`Sep. 16, 1997
`
`Sheet 6 of 9
`
`5,667,289
`
`A
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`AREA RATIO
`
`HQ. 108
`
`BEGINNING
`
`CENTER
`
`FIG._ 10C
`
`LGE_000766
`
`

`
`US. Patent
`
`Sep. 16, 1997
`
`Sheet 7 0f 9
`
`5,667,289
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`(PRIOR A my
`
`DISTRIBUTION
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`
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`
`DISTRIBUTION
`
`LGE_000767
`
`

`
`US. Patent
`
`Sep. 16, 1997
`
`Sheet 8 0f 9
`
`5,667,289
`
`FIG._ 13A
`
`FIG._ 13B
`(PRIOR A RT)
`
`LGE_000768
`
`

`
`U.S. Patent
`
`Sep. 16, 1997
`
`Sheet 9 of 9
`
`5,667,289
`
`4
`
`60
`
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`LGE_000769
`
`LGE_000769
`
`

`
`5,667,289
`
`1
`BACKGROUND LIGHTING APPARATUS
`FOR LIQUID CRYSTAL DISPLAY
`
`CROSS-REFERENCE TO RELATED
`APPLICATION
`This application is a continuation-in-part of patent appli
`cation Ser. No. 07/525,408 ?led May 18, 1990 now US. Pat.
`No. 5,130,898.
`
`2
`arranged in a manner to achieve uniform 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 system. 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 lumi
`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
`exothermic 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 atfected 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
`di?erent in regions of the display where the temperatures are
`di?erent in the display structure. Thus, if the applied voltage
`level for the liquid crystal elements changes and is different
`in diiferent locations of the display matrix, a significant
`problem is created in overall control of the display. This, in
`particular, has an atfect 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
`structm'e. In order to provide uniform illumination with
`evenly distributed light intensity and lurninesoence, high
`luminance is required. In order to meet the requirements of
`uniformity in illumination, it is also necessary that a uni
`formity in temperature distribution be maintained. This is
`highly important from a standpoint of operational charac
`terr'stics of the display since the transmissivity of the liquid
`crystal material is a function of temperature and can vary in
`a signi?cant manner depending upon ambient temperature
`operating conditions. Therefore, if the surface temperature at
`the back surface of the display structure diifers at different
`locations of the display, there is a serious problem in terms
`of nonuniformity in luminance and color output quality in
`operation of the display. Thus, the uniformity in temperature
`distribution across the display structure and,
`correspondingly, luminance uniformity 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 luminous efficiency and uni
`formity in luminance with a uniform temperature distribu
`tion across the display structure.
`
`10
`
`15
`
`25
`
`30
`
`35
`
`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 milky 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 113, each having a pattern of milky
`white type of light diifnsion pattern comprising a multiplic
`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,
`113 as well as brings about ditfusion 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, di?zusion
`and dispersion but it does so at the expense of providing two
`or more plates 1 in order to increase the output efficiency of
`the background lighting apparatus. Furthermore, the lumi
`nous e?iciency 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 superimposed transparent plates 1A, 1B are utilized each
`having a light diffusion pattern for diifusing the light beams.
`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, as the quantity of
`irregular re?ection is increased, the brightness level quickly
`decreases with distance from the light source so that non
`uniformity in the overall brightness of the light output from
`the lighting apparatus increases. In order to counteract this
`phenomenon, a pattern comprising an irregular re?ecting
`surface or portion and a totally re?ecting portion are
`
`45
`
`55
`
`65
`
`LGE_000770
`
`

`
`3
`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 internally re?ecting quality and
`wherein a diffusion 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
`di?iusion elements may be in the form of pixels, squares,
`dots, circles, rectangles, etc., such as, opaline color pixels,
`points, dots, squares, or linear bars. A plurality 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, di?usion and total internal re?ection until a
`portion of the light beams exits through the other of the
`maj or surfaces of the transparent plate. With the introduction ,
`of light into the transparent plate along all edge surfaces of
`the plate, the transfer of light into the plate is accomplished
`with high uniformity and e?icient dispersion. The transpar
`ent 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 significant 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 mmto 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
`appreciated by referring to the following description and
`claims taken in conjunction with the accompanying draw
`rngs.
`
`25
`
`30
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`35
`
`45
`
`50
`
`55
`
`5,667,289
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`4
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`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 dilfusion ?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 diifusion 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 the diiferent 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 appa
`ratus. of this invention.
`FIG. 13A illustrates the sectors of required light disnibu
`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.
`
`65
`
`DESCRIPTION OF THE PREFERRED
`ElVIBODIMENTS
`Reference is now made to FIG. 3 wherein there is
`disclosed one embodiment of this invention for a back
`
`LGE_000771
`
`

`
`5,667,289
`
`15
`
`5
`ground ?ghting apparatus having transparent plate 1 of
`plastic material, such as PMMA, with a uniform thiclmess 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
`I10
`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 di?iusion plate 7
`and white type, total re?ecting plate 3. A di?’usion system S
`is provided relative to the bottom surface of transparent plate
`1, i.e., between plate 1 and total re?ecting plate 33. Di?°usion
`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 7 in all embodiments of this invention has
`a frosted texture so that it is opaque in nature. A function of
`diifusion 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 di?’usion system 5 so that pattern 3A is not
`perceptible to the human eye. Another function of di?usion
`?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 di?usion ?lms that provide for a wide base di?iusion
`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, di?usion ?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 the embodiments shown in FIGS. 1 and 2. Also,
`line width of pattern 3A for di?usion 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 SE 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
`sold 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 surfaces 2 and 3.
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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 diifusion system 5 may be printed on this surface or
`added by means of an adhesive or in other convenient
`manner. The pattern of diifusion 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 surface 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 surfaces 2 and 3 of transparent plate
`1, which surfaces are substantially orthogonal 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 surface 2.
`It is preferred that transparent plate 1 be tabular in form
`and that all surfaces constituting transparent plate 1 be
`internally re?ecting surfaces so that the contribution of edge
`surfaces 4 be small relative to any involvement relative to
`the function of transmissive 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 internally re?ective natrne.
`However, because of the multitude of reoccurring internal
`light re?ections, light exit e?iciency increases signi?cantly
`with the use of diffusion 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 transparent plate 1, than the angle of total
`re?ection, 62. Angle, 61, is de?ned by:
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`where 111 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 refracted to
`interact with diffusion system 5. Thus, the re?ected light
`beams will not exit at the critical angle unless surfaces 2 and
`3 are highly internally re?ective in nature.
`Referring again to FIG. 6A, a light source 6 is position
`adjacent to each end surface 4 of transparent plate 1 so that
`light beam is associated relative to substantially the entire
`periphery of plate 1. The light beams emitted from light
`sources 6 are directed into transparent plate 1 through the
`peripheral edge surfaces 4. Because light sources 6 are
`disposed about substantially the entire periphery of edge
`surfaces 4 of plate 1, the developed luminance is 2 to 4 times
`or higher as compared to conventional background lighting
`apparatus employing one or two lamp sources.
`A?uorescent lamp may be employed relative to each light
`source 6. The size of the lamp may be smaller than in the
`case of conventional apparatus of FIGS. 1 and 2 since, in
`e?ect, the same amount of input light desired for proper
`backlighting may be spread out over an increase number of
`lamps. In fact, the diameter of sources 6 is the same as or
`smaller than the thickness of plate 1, as illustrated in FIG.
`63. The thickness‘of plate 1 may generally be, for example,
`about 4 mm. The diameter source tubes may be 3 mm or 4
`mm. As a result, the total amount of heat generated from
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`8
`sources 6 is reduced due to the employment of smaller
`intensity lamp sources. Light sources 6 may include several
`kinds of light sources, such as, incandescent lamps or
`linearly arranged light emitting diodes with light introduc
`tion to plate 1 via optical ?bers. However, the ?uorescent
`lamp is preferred in terms of light emitting efficiency,
`wavelength, emission color, and adaptability to the con?gu
`ration of the periphery of transparent plate 1.
`As best shown in FIG. 6B, diffusion ?lm 7 is provided
`relative to exit surface