United States Patent [191
`Ciupke et a1.
`
`llllllllllllllllllllllIIIIIHMHIQLWIIIlllllllllllllllllllllll
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`[11] Patent Number:
`[45] Date of Patent:
`
`5,461,547
`Oct. 24, 1995
`
`[54] FLAT PANEL DISPLAY LIGHTING SYSTEM
`
`4,909,604
`
`3/1990 Kobayashi et a1. ..................... .. 362/31
`
`5,079,675
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`1/ 1992 Nakayama . . . . . . . . .
`
`. . . . .. 362/31
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`
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`Inventors: Werner W_ Redmond; Richard E. DuNah, all of F.
`
`
`
`
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`5,278,545 5,339,179
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`
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`Streck . . . . . . . . . . . . 8/1994 Rudisill et a1. ........................ .. 359/49 . . . . ..
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`
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`50mm County’ Calif-
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`FOREIGN PATENT DOCUMENTS
`
`[73] Assignee: Precision Lamp, Inc., Cotati, Calif.
`
`[21] AppL NOJ 95,753
`
`[22] Filed:
`
`JUL 20, 1993
`
`[51] Int. Cl.6 ...................................................... .. F21V 8/00
`[52] US. Cl. .......................... .. 362/31; 362/293; 362/327;
`362/330; 362/390; 359/49
`[58] Field of Search ................................ .. 359/40, 41, 4s,
`359/49’ 50’ 64, 70; 362/26’ 27’ 31’ 293’
`327’ 330’ 390
`
`[56]
`
`4,011,001
`4,142,781
`4,659,183
`
`_
`References cum
`U_S_ PATENT DOCUMENTS
`_
`.................... ..
`Nierenberg Ct
`359/49
`3/1977 Moriya ........................ ..
`359/49
`3/1979 Baur et a1.
`4/1987 Suzawa ................................... .. 359/48
`
`123823 7/1985 Japan ..................................... .. 359/49
`5-107542 4/1993 Japan .................. ..
`.. 359/48
`664193
`1/1952 Umted Kmgdom ................... .. 362/31
`
`Primary Examiner—1ra S. Lazarus
`Assistant Examiner—Alan B. Cariaso
`Angmey, A gem, or Firm—Flehr, Hohbach, Test, Albn'tton &
`Herbert
`
`ABSTRACT
`[57]
`A ?at panel display lighting system is disclosed wherein a
`thin, ?at light guide has two spaced major surfaces with light
`introduced into one edge of the guide. Light is extracted
`from the light guide by the facets in a plurality of parallel
`microgrooves disposed to intersect the light introduced into
`the light guide. A liquid crystal display is placed adjacent to
`the
`guide to be
`or frontlit~
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`17 Claims, 3 Drawing Sheets
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`26
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`29
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`LG Display Ex. 1005
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`LGD_001221
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`

`

`US. Patent
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`0a. 24, 1995
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`Sheet 1 of 3
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`5,461,547
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`:2.
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`mm
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`mm
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`LGD_001222
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`

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`US. Patent
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`Oct. 24, 1995
`
`Sheet 2 of 3
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`5,461,547
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`SE:
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`2 o. - 3
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`2108.00. l
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`I \
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`LGD_001223
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`

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`US. Patent
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`Oct. 24, 1995
`
`Sheet 3 of 3
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`5,461,547
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`29
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`LGD_001224
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`5,461,547
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`1
`FLAT PANEL DISPLAY LIGHTING SYSTEM
`
`BRIEF SUMMARY OF THE INVENTION
`
`This invention relates generally to a lighting system for
`illuminating ?at panel displays such as liquid crystal dis~
`plays, and more particularly, to a system employing a thin
`?at light guide with microgrooves formed on one major
`surface for extracting light introduced into the light guide.
`
`2
`guide to provide substantially uniform emission of light
`from a major surface.
`It is a further object to provide a thin, uniform thickness
`large area lighting system for front-lighting liquid crystal
`displays.
`It is a further object to provide a lighting system having
`an injection-modable, low cost light guide.
`The foregoing and other objects are achieved by a thin,
`?at, transparent light guide having a ?rst planar major
`surface and a second parallel major surface which has a
`plurality of closely spaced parallel microgrooves whose
`surfaces internally re?ect light introduced into the light
`guide in a direction substantially perpendicular to the direc
`tion of the axis of the grooves toward the other major
`surface, where it is emitted from the surface.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The foregoing and other object of the invention will be
`more fully understood from the following description, read
`in connection with the accompanying drawings, where:
`FIG. 1 is a plan view of a back light LCD illuminated by
`a light pipe in accordance with one embodiment of the
`invention.
`FIG. 2 is a greatly enlarged cross-sectional view of the
`embodiment of FIG. 1.
`FIG. 3 is a greatly enlarged cross-sectional view of a large
`area lighting system in accordance with another embodiment
`of the invention.
`FIG. 4 is an enlarged cross-sectional view of another
`embodiment of a backlighting system incorporating two
`light sources.
`FIG. 5 is an enlarged cross-sectional view of a large area
`lighting system in accordance with the invention, which is
`front-lighting an LCD.
`FIG. 6 shows a backlit transmissive LCD assembly in
`accordance with another embodiment of the invention.
`
`DESCRIPTION OF PREFERRED EMBODIMENT
`
`FIGS. 1 and 2 show an internally re?ecting light pipe or
`guide 11 used for backlighting a liquid crystal display (LCD)
`12. The light pipe includes one planar surface 13 and an
`opposite light extracting surface 14 created by facets 16
`created by grooves 17. The v-shaped grooves 17 extending
`across the surface 14 having a longitudinal axis 15. FIG. 3
`shows that typical v-groove depths are 2.5—l0 um, and the
`spacing between v-grooves is 100—250 pm. As will become
`apparent, the spacing between grooves may be varied along
`the length of the light pipe to provide improved uniformity
`of the light emitted from the light along the length of the
`light guide. The internally re?ecting light pipe has v-grooves
`whose facets make an angle with respect to a direction
`perpendicular to the light pipe which is typically 45-55
`degrees. In one ?at panel display lighting system, the
`thickness of the light pipe was one millimeter, which
`matched the dimensions of the miniature incandescent light
`sources which edgelit the light guide. In general, we have
`found that the light guide or pipe provides the best lighting
`efficiency when it has a thickness which is the same or
`greater than the dimension of the light source. A typical light
`source 18 includes a cylindrical envelope 19 which houses
`a coaxial ?lament 21. The ?lament radiates light in all
`directions as indicated by the arrows 22. A U-shaped re?ec
`tor 23 which may comprise a thin sheet of re?ective material
`encloses the lamp and re?ects the energy into the light pipe
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`BACKGROUND OF THE INVENTION
`Lighting systems for illuminating liquid crystal displays
`employing light guides with edge lit end surfaces are known.
`These large area lighting systems generally do not have a
`uniform thickness, which is undesirable in many applica
`tions, such as backlighting of liquid crystal displays (LCDs)
`for pagers, hand-held computers, organizers and the like.
`Examples of prior art light sources are described in the
`following patents:
`U.S. Pat. No. 4,706,173 discloses a light re?ecting appa
`ratus that uses a lamp, probably a ?uorescent lamp,
`with light impinging on a series of exterior re?ective
`surfaces which re?ect the light into an associated
`display.
`U.S. Pat. No. 4,277,817 discloses two embodiments of a
`wedge—shaped body with a microgroove surface for
`emitting light from the grooved surface. The light is
`introduced in a direction that is generally parallel to the
`grooves.
`U.S. Pat. No. 4,257,084 discloses a display that re?ects
`light off an angled surface to strike a diffusing surface
`which has prismatic serration to extract the light.
`U.S. Pat. No. 4,323,951 discloses a display having gen
`erally laminar light transmissive layers, one of which
`has a roughened back surface whereby light will be
`transmitted through a front surface of the laminar unit.
`U.S. Pat. No. 4,528,617 discloses a light distribution
`apparatus that uses a transparent double wedge-shaped
`member having ?rst internally re?ecting surfaces to
`re?ect a curtain of light to a second surface which has
`internally re?ecting surfaces which re?ect the light to
`an opposite surface for illuminating a generally rect
`angular area whereby to backlight an LCD display.
`U.S. Pat. No. 5,050,946 discloses a light pipe that has a
`planar front surface for back-lighting LCDs. Light is
`injected into the light pipe from the ends. The back
`surface has a series of planar portions parallel to the
`front surface connected by facets, which are angled so
`that the injected light re?ects off the facets through the
`front surface. Are?ector having a planar, highly re?ec
`tive, highly scattering surface or a sawtoothed or
`grooved re?ecting surface is placed adjacent to facets.
`U.S. Pat. No. 5,126,882 discloses a light pipe in which
`light emitted from a surface strikes a prism member
`which causes the light to be directed in a predetermined
`direction.
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`OBJECTS AND SUMMARY OF THE
`INVENTION
`
`It is an object of this invention to provide a thin, uniform
`thickness large area lighting system for lighting ?at displays,
`particularly liquid crystal displays.
`It is another object of the invention to provide a thin,
`uniform thickness large area lighting system employing
`internal re?ection of light introduced into the edge of a light
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`LGD_001225
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`5,461,547
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`3
`in a plurality of directions. Preferably, the space between the
`incandescent lamp, the light pipe and the re?ector is ?lled
`with a transparent, ?exible, refractive index matching mate
`rial 25 which holds the lamp and cushions it from any shock
`and e?iciently couples the light from the source into the light
`pipe. The index matching material may be tinted to provide
`a colored lighting system. The light, which is directed in a
`direction generally perpendicular to the longitudinal axis 15
`of the v-grooves into the end of the light pipe, re?ects off the
`planar surfaces and off of the facets as shown generally by
`the rays 24 and 26. A re?ector 27 with re?ecting surface 28
`is placed adjacent to the faceted surface and re?ects any light
`which escapes from this surface back into the light pipe and
`toward the surface 13. The end of the light pipe is provided
`with a re?ector 29 which re?ects any light traveling through
`the light pipe back into the light pipe to further increase the
`ef?ciency of conversion of light from the incandescent
`source for backlighting the LCD. As is apparent, light rays
`eventually strike the facets and are extracted at the surface
`13. A di?fuser or brightness enhancing ?lm 31 receives the
`emitted light and di?cuses the light so that light of relatively
`uniform intensity strikes the back of the LCD. In instances
`where the LCD 12 is provided with a suitable trans?ective
`coating, the diffuser may be eliminated and the LCD placed
`directly on the planar surface. The ei?ciency can be
`improved by coating the facets 16 with a re?ective material
`to assure that all rays striking the facets are re?ected and not
`transmitted to the adjacent re?ector.
`FIG. 3 shows another embodiment of the invention in
`which the re?ecting surface 28 is placed adjacent to the
`planar surface 13 of the light pipe and the LCD receives light
`from the grooved surface 14. The light re?ected by the facets
`through the planar surface 13 is re?ected back into and
`through the light pipe by the back-re?ecting surface 28, as
`indicated. In other respects, the construction of the embodi
`ment of FIG. 3 is identical to that of FIGS. 1 and 2, and like
`reference numbers have been applied to like parts.
`In instances where more light is required, light sources
`may be placed at each end of the light pipe, as illustrated in
`FIG. 4. In FIG. 4, the light pipe is provided with an opening
`41 which receives the re?ector 23 and the light source 18.
`The volume within the re?ector is ?lled with a transparent,
`resilient, refractive index matching material to protect the
`light source against shock and e?iciently couple the light
`into the guide. The index matching material may be tinted if
`a colored lighting system is desired. In other respects, the
`lighting system shown in FIG. 4 operates similar to that
`shown in FIG. 3, and like reference numbers have been
`applied to like parts.
`We have found that e?iciency of the lighting of certain
`LCDs can be improved if the LCD is illuminated from the
`front. This is illustrated in FIG. 5, where the LCD is placed
`adjacent to the planar surface 13, and the light re?ected by
`the facets and exiting the surface strikes the LCD directly. In
`this instance the LCD, which has a totally re?ective back
`surface 32, is viewed through the thin transparent light pipe.
`Operation of the light pipe to extract light is as described
`above and like reference numerals have been applied to like
`parts.
`We have also found that for backlit displays, the illumi
`nation can be improved if the LCD trans?ective back
`coating is removed to produce a transmissive LCD and a
`light diifuser is placed between the light pipe and the LCD.
`The diffuser not only diiTuses the light emitted by the light
`pipe, but also acts in conjunction with the back re?ector 27
`to enhance viewing of the LCD under ambient conditions.
`The display lighting system shown in the ?gures includes
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`a long, narrow light pipe or light guide with a light source
`at one or both ends. It is, of course, apparent that the light
`guide may have different shapes and that the source of light
`may be located along an edge of the guide rather than the
`end, with the longitudinal axis of the v~grooves extending
`generally perpendicular to the light source. The light source
`may include a plurality of incandescent light sources, glow
`discharge sources, or other types of light sources which
`direct light into the light guide or pipe in a direction
`generally perpendicular to the longitudinal axis of the
`v-grooves. An assembly of this type is shown in FIG. 6.
`The assembly of FIG. 6 includes a light guide 43 of the
`type described above, which is lit by a plurality of spaced
`light sources 44 including incandescent lamps 46. The light
`guide includes a back surface re?ector 47. A transmissive
`LCD 48 is placed adjacent to the front surface of the light
`guide with a diffuser 49 placed between the light guide 43
`and the LCD 48. The assembly operates as described above.
`The LCD is therefore backlit and viewed from the front as
`indicated at 51.
`What is claimed:
`1. A thin, large-area lighting system comprising:
`a thin, transparent, rectangular light guide having ?rst and
`second parallel major surfaces, said ?rst major surface
`having a plurality of uniform, spaced v-shaped parallel
`microgrooves each extending continuously across a
`substantial portion of said ?rst major surface and a
`plurality of planar surface portions between said micro
`grooves, said light guide having a uniform thickness,
`said microgrooves having a longitudinal axis;
`means for introducing light into said light guide from at
`least one edge in a direction generally perpendicular to
`said longitudinal axis of said microgrooves,
`said microgrooves having surfaces which form an angle
`with respect to the ?rst major surface which, when
`taken together with the index of refraction of the
`material of said light guide, internally re?ects substan
`tially all the light striking said surfaces of said micro
`grooves toward the second major surface at a ?rst angle
`of incidence for emission from said second major
`surface,
`said planar surface portions being con?gured for inter
`nally re?ecting a substantial portion of light striking
`said planar surface portions toward said second major
`surface at a second angle of incidence for internal
`re?ection by said second major surface along said light
`guide.
`2. A thin, large-area lighting system as in claim 1 includ
`ing re?ective means adjacent to said ?rst major surface for
`re?ecting light which leaves the light guide back into the
`light guide and toward said second major surface to enhance
`the emitted light intensity.
`3. A thin, large-area lighting system comprising:
`a thin, transparent, rectangular light guide having ?rst and
`second parallel major surfaces, said ?rst major surface
`having a plurality of uniform, spaced v-shaped parallel
`microgrooves extending continuously across a substan
`tial portion of said ?rst major surface and a plurality of
`planar surface portions between said microgrooves,
`said microgrooves having a longitudinal axis;
`means for introducing light into said light guide from at
`least one edge in a direction generally perpendicular to
`said longitudinal axis of said microgrooves,
`said microgrooves having surfaces which form an angle
`with respect to the ?rst major surface which, when
`taken together with the index of refraction of the
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`LGD_001226
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`5,461,547
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`5
`material of said light guide, internally re?ects substan
`tially all the light within said light guide toward the
`second major surface at a ?rst angle of incidence for
`emission from said second major surface,
`said planar surface portions being con?gured for inter—
`nally re?ecting a substantial portion of light striking
`said planar surface portions toward said second major
`surface at a second angle of incidence for internal
`re?ection by said second major surface along said light
`guide, and
`re?ecting means adjacent to said second major surface for
`re?ecting light toward said ?rst major surface where
`the re?ected light is emitted from said ?rst major
`surface between said microgrooves.
`4. A thin large area lighting system as in claims 1, 2 or 3
`wherein the angle formed by said rnicrogroove surfaces is
`between 45-55 degrees with respect to a direction perpen
`dicular to the ?rst major surface.
`5. A lighting system as in claim 4 wherein the grooves
`microgrooves are equally spaced.
`6. A thin, large-area lighting system as in claim 1 in which
`the light guide material is tinted for the desired light color.
`7. A lighting system as in claims 1, 2 or 3 wherein the
`thickness of the light guide is approximately 1 mm and the
`depth of the microgrooves is between 2.5—l0 pm with the
`spacing between microgrooves between 100-250 pm.
`8. A lighting system as in claims 1, 2 or 3 wherein said
`means for introducing light into said light guide comprises:
`an elongated, incandescent lamp adjacent to said one
`edge,
`a re?ector extending from the edge of the light guide
`around said incandescent lamp to re?ect light from said
`lamp into the light guide, and
`a ?exible transparent material substantially ?lling the
`space between said lamp, said re?ector and the edge of
`said light guide serving to cushion the lamp against
`shock and e?iciently couple the light into the light
`guide.
`9. A lighting system as in claim 8 wherein the ?exible
`transparent material is tinted to provide colored light.
`10. An illuminated LCD system including a thin, large
`area lighting system comprising:
`a thin, transparent, rectangular light guide having ?rst and
`second parallel major surfaces, said ?rst major surface
`having a plurality of v-shaped parallel microgrooves
`extending across said ?rst major surface, said micro
`grooves having a longitudinal axis;
`means for introducing light into said light guide from at
`least one edge in a direction generally perpendicular to
`said longitudinal axis of said microgrooves;
`said microgrooves having surfaces which form an angle
`with respect to the ?rst major surface which, when
`taken together with the index of refraction of the
`material of said light guide, internally re?ects substan
`tially all the light within said light guide toward the
`second major surface for emission from said second
`major surface; and
`a front-lit LCD having a front surface in contact with said
`second major surface and a re?ecting back surface
`which re?ects light introduced into the front surface to
`display information in the display, whereby the display
`is illuminated from the front and the display informa
`tion is viewed through the light guide.
`11. An illuminated LCD system comprising:
`a thin, transparent, rectangular light guide having ?rst and
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`second parallel major surfaces, said ?rst major surface
`having a plurality of spaced v-shaped parallel micro
`grooves extending continuously across a substantial
`portion of said ?rst major surface and a plurality of
`planar surface portions between said microgrooves,
`said light guide being of a uniform thickness, said
`microgrooves having a longitudinal axis;
`means for introducing light into said light guide from at
`least one edge in a direction generally perpendicular to
`said longitudinal axis of said microgrooves;
`said microgrooves having a uniform con?guration with
`each of said microgrooves having surfaces which form
`an angle with respect to said ?rst major surface which,
`when taken together with the index of refraction of the
`material of said light guide, internally re?ects substan~
`tially all the light striking said surfaces of said micro
`grooves toward the second major surface at a ?rst angle
`of incidence for emission from said second major
`surface;
`said planar surface portions being con?gured for inter
`nally re?ecting a substantial portion of light striking
`said planar surface portions toward said second major
`surface at a second angle of incidence for internal
`re?ection by said second major surface along said light
`pipe; and
`a backlit LCD placed with the back surface of said LCD
`adjacent to said second major surface.
`12. An illuminated LCD system as in claim 11 wherein a
`diffuser is placed between said second major surface and
`said LCD.
`13. An illuminated LCD system as in claim 11 wherein the
`LCD is transmissive.
`14. An illuminated LCD system as in claim 11 including
`re?ective means adjacent to said ?rst major surface for
`re?ecting light which leaves the light guide back into the
`light guide and toward said second major surface to enhance
`the emitted light intensity.
`15. An illuminated LCD system comprising:
`a thin, transparent, rectangular light guide having ?rst and
`second parallel major surfaces, said ?rst major surface
`having a plurality of v-shaped parallel microgrooves
`extending continuously across a substantial portion
`said ?rst major surface and a plurality of planar surface
`portions between said microgrooves, said micro
`grooves having a longitudinal axis;
`means for introducing light into said light guide from at
`least one edge in a direction generally perpendicular to
`said longitudinal axis of said microgrooves;
`said microgrooves having a uniform shape and size with
`each of said microgrooves having surfaces which form
`an angle with respect to said ?rst major surface which,
`when taken together with the index of refraction of the
`material of said light guide, internally re?ects substan
`tially all the light within said light guide toward the
`second major surface at a ?rst angle of incidence for
`emission from said second major surface;
`said planar surface portions being configured for inter
`nally re?ecting a substantial portion of light striking
`said planar surface portions toward said second major
`surface at a second angle of incidence for internal
`re?ection by said second major surface along said light
`guide, and
`a backlit LCD placed with the back surface of said LCD
`adjacent to said ?rst major surface; and
`re?ecting means adjacent to said second major surface for
`
`LGD_001227
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`

`5,461,547
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`7
`re?ecting light emitted from the second major surface
`toward Said ?rst major surface f°r emission from Said
`?rst major surface between said microgrooves where
`the re?ected light illuminates the LCD.
`16. An illuminated LCD system as in claim 15 wherein a 5
`di?’user is placed between said ?rst major surface and said
`
`8
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`LCD.
`17. An illuminated LCD system as in claim 16 wherein
`th LCD _
`,
`,
`6
`1S transmlsslve'
`
`* * * * *
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`LGD_001228
`
`