United States Patent [19]
`Ciupke et al.
`
`111111111111111111111111111111111111111111111111111111111111111111111111111
`US005461547A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,461,547
`Oct. 24, 1995
`
`[54] FLAT PANEL DISPLAY LIGHTING SYSTEM
`
`[75]
`
`Inventors: Werner W. Ciupke; William F.
`Redmond; Richard E. DuNah, all of
`Sonoma County, Calif.
`
`[73] Assignee: Precision Lamp, Inc., Cotati, Calif.
`
`[21] Appl. No.: 95,753
`Jul. 20, 1993
`
`[22] Filed:
`
`Int. Cl.6
`........................................................ F21V 8100
`[51]
`[52] U.S. CI . ............................ 362/31; 3621293; 362/327;
`362/330; 362/390; 359/49
`[58] Field of Search .................................. 359/40, 41, 48,
`359/49, 50, 64, 70; 362/26, 27, 31, 293,
`327, 330, 390
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`2,646,637
`4,011,001
`4,142,781
`4,659,183
`
`7/1953 Nierenberg et al ....................... 362/31
`3/1977 Moriya ...................................... 359/49
`3/1979 Baur et al ................................. 359/49
`411987 Suzawa ..................................... 359/48
`
`4,909,604
`5,079,675
`5,278,545
`5,339,179
`
`3/1990 Kobayashi et al. ....................... 362/31
`111992 Nakayama ................................ 362131
`111994 Streck ....................................... 359/48
`811994 Rudisill et al. ........................... 359/49
`
`FOREIGN PATENT DOCUMENTS
`
`123823
`5-107542
`664193
`
`Japan ....................................... 359/49
`7/1985
`Japan ....................................... 359/48
`4/1993
`1/1952 United Kingdom ..................... 362/31
`
`Primary Examiner-Ira S. Lazarus
`Assistant Examiner-Alan B. Cariaso
`Attorney, Agent, or Firm-Flehr, Hohbach, Test, Albritton &
`Herbert
`
`[57]
`
`ABSTRACT
`
`A fiat panel display lighting system is disclosed wherein a
`thin, fiat 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 light guide to be backlit or frontlit.
`
`17 Claims, 3 Drawing Sheets
`
`Mercedes-Benz Ex. 1005
`
`MBI_001407
`
`

`

`U.S. Patent
`
`Oct. 24, 1995
`
`Sheet 1 of 3
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`U.S. Patent
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`Oct. 24, 1995
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`U.S. Patent
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`Oct. 24, 1995
`
`Sheet 3 of 3
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`5,461,547
`
`1
`FLAT PANEL DISPLAY LIGHTING SYSTEM
`
`BRIEF SUMMARY OF THE INVENTION
`
`This invention relates generally to a lighting system for
`illuminating fiat panel displays such as liquid crystal dis(cid:173)
`plays, and more particularly, to a system employing a thin
`flat light guide with microgrooves formed on one major
`surface for extracting light introduced into the light guide.
`
`BACKGROUND OF THE INVENTION
`
`10
`
`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
`5 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,
`fiat, transparent light guide having a first planar major
`surface and a second parallel major surface which has a
`plurality of closely spaced parallel microgrooves whose
`surfaces internal! y reflect light introduced into the light
`guide in a direction substantially perpendicular to the direc-
`tion of the axis of the grooves toward the other mqjor
`surface, where it is emitted from the surface.
`
`15
`
`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(cid:173)
`tions, such as backlighting ofliquid 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 reflecting appa-
`ratus that uses a lamp, probably a fluorescent lamp,
`with light impinging on a series of exterior reflective
`surfaces which reflect 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 general! y parallel to the
`grooves.
`U.S. Pat. No. 4,257,084 discloses a display that reflects
`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(cid:173)
`erally laminar light transmissive layers, one of which 35
`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 first internally reflecting surfaces to 40
`reflect a curtain of light to a second surface which has
`internally reflecting surfaces which reflect the light to
`an opposite surface for illuminating a generally rect(cid:173)
`angular area whereby to backlight an LCD display.
`U.S. Pat. No. 5,050,946 discloses a light pipe that has a 45
`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 reflects off the facets through the
`front surface. A reflector having a planar, highly reflec(cid:173)
`tive, highly scattering surface or a sawtoothed or
`grooved reflecting surface is placed adjacent to facets.
`U.S. Pat. No. 5,126,882 discloses a light pipe in which 55
`light emitted from a surface strikes a prism member
`which causes the light to be directed in a predetermined
`direction.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`20
`
`25
`
`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
`30 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.
`
`50
`
`DESCRIPTION OF PREFERRED EMBODIMENT
`FIGS. 1 and 2 show an internally reflecting 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 2.5-10 j.ll11, and the
`spacing between v-grooves is 100-250 j.ll11. 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 reflecting 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 fiat 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
`60 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 co-axial filament 21. The filament radiates light in all
`directions as indicated by the arrows 22. AU-shaped reflec(cid:173)
`tor 23 which may comprise a thin sheet of reflective material
`encloses the lamp and reflects the energy into the light pipe
`
`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 fiat displays,
`particularly liquid crystal displays.
`It is another object of the invention to provide a thin, 65
`uniform thickness large area lighting system employing
`internal reflection of light introduced into the edge of a light
`
`MBI_001411
`
`

`

`5,461,547
`
`3
`in a plurality of directions. Preferably, the space between the
`incandescent lamp, the light pipe and the reflector is filled
`with a transparent, flexible, refractive index matching mate(cid:173)
`rial 25 which holds the lamp and cushions it from any shock
`and efficiently couples the light from the source into the light 5
`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, reflects off the
`planar surfaces and off of the facets as shown generally by
`the rays 24 and 26. A reflector 27 with reflecting surface 28
`is placed adjacent to the faceted surface and reflects 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 reflector 29 which reflects any light traveling through
`the light pipe back into the light pipe to further increase the 15
`efficiency 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 diffuser or brightness enhancing film 31 receives the
`emitted light and diffuses the light so that light of relatively 20
`uniform intensity strikes the back of the LCD. In instances
`where the LCD 12 is provided with a suitable transflective
`coating, the diffuser may be eliminated and the LCD placed
`directly on the planar surface. The efficiency can be
`improved by coating the facets 16 with a reflective material 25
`to assure that all rays striking the facets are reflected and not
`transmitted to the adjacent reflector.
`FIG. 3 shows another embodiment of the invention in
`which the reflecting surface 28 is placed adjacent to the
`planar surface 13 of the light pipe and the LCD receives light 30
`from the grooved surface 14. The light reflected by the facets
`through the planar surface 13 is reflected back into and
`through the light pipe by the back-reflecting surface 28, as
`indicated. In other respects, the construction of the embodi(cid:173)
`ment of FIG. 3 is identical to that of FIGS. 1 and 2, and like 35
`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 reflector 23 and the light source 18. 40
`The volume within the reflector is filled with a transparent,
`resilient, refractive index matching material to protect the
`light source against shock and efficiently couple the light
`into the guide. The index matching material may be tinted if
`a colored lighting system is desired. In other respects, the 45
`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 efficiency 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 reflected by
`the facets and exiting the surface strikes the LCD directly. In
`this instance the LCD, which has a totally reflective 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- 60
`nation can be improved if the LCD transflective back(cid:173)
`coating is removed to produce a transmissive LCD and a
`light diffuser is placed between the light pipe and the LCD.
`The diffuser not only diffuses the light emitted by the light
`pipe, but also acts in conjunction with the back reflector 27 65
`to enhance viewing of the LCD under ambient conditions.
`The display lighting system shown in the figures includes
`
`4
`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 reflector 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 first and
`second parallel major surfaces, said first major surface
`having a plurality of uniform, spaced v-shaped parallel
`microgrooves each extending continuously across a
`substantial portion of said first major surface and a
`plurality of planar surface portions between said micro(cid:173)
`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 first major surface which, when
`taken together with the index of refraction of the
`material of said light guide, internally reflects substan(cid:173)
`tially all the light striking said surfaces of said micro(cid:173)
`grooves toward the second major surface at a first angle
`of incidence for emission from said second major
`surface,
`said planar surface portions being configured for inter-
`nally reflecting a substantial portion of light striking
`said planar surface portions toward said second major
`surface at a second angle of incidence for internal
`reflection by said second major surface along said light
`guide.
`2. A thin, large-area lighting system as in claim 1 includ(cid:173)
`ing reflective means adjacent to said first major surface for
`50 reflecting 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 first and
`second parallel major surfaces, said first major surface
`having a plurality of uniform, spaced v-shaped parallel
`microgrooves extending continuously across a substan(cid:173)
`tial portion of said first 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 first major surface which, when
`taken together with the index of refraction of the
`
`10
`
`55
`
`MBI_001412
`
`

`

`5,461,547
`
`5
`
`20
`
`10
`
`5
`material of said light guide, internally reflects substan(cid:173)
`tial! y all the light within said light guide toward the
`second major surface at a first angle of incidence for
`emission from said second major surface,
`said planar surface portions being configured for inter-
`nally reflecting a substantial portion of light striking
`said planar surface portions toward said second major
`surface at a second angle of incidence for internal
`reflection by said second major surface along said light
`guide, and
`reflecting means adjacent to said second major surface for
`reflecting light toward said first major surface where
`the reflected light is emitted from said first major
`surface between said microgrooves.
`4. A thin large area lighting system as in claims 1, 2 or 3 15
`wherein the angle formed by said microgroove surfaces is
`between 45-55 degrees with respect to a direction perpen(cid:173)
`dicular to the first 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 2.5-1 0 J.lii1 with the 25
`spacing between microgrooves between 100-250 J.!IIl·
`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 30
`edge,
`a reflector extending from the edge of the light guide
`around said incandescent lamp to reflect light from said
`lamp into the light guide, and
`a flexible transparent material substantially filling the 35
`space between said lamp, said reflector and the edge of
`said light guide serving to cushion the lamp against
`shock and efficiently couple the light into the light
`guide.
`9. A lighting system as in claim 8 wherein the flexible 40
`transparent material is tinted to provide colored light.
`10. An illuminated LCD system including a thin, large(cid:173)
`area lighting system comprising:
`a thin, transparent, rectangular light guide having first and
`second parallel major surfaces, said first major surface 45
`having a plurality of v-shaped parallel microgrooves
`extending across said first major surface, said micro(cid:173)
`grooves having a longitudinal axis;
`means for introducing light into said light guide from at
`least one edge in a direction generally perpendicular to 50
`said longitudinal axis of said microgrooves;
`said microgrooves having surfaces which form an angle
`with respect to the first major surface which, when
`taken together with the index of refraction of the
`material of said light guide, internally reflects substan(cid:173)
`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 60
`second major surface and a reflecting back surface
`which reflects 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 first and
`
`55
`
`65
`
`6
`second parallel major surfaces, said first major surface
`having a plurality of spaced v-shaped parallel micro(cid:173)
`grooves extending continuously across a substantial
`portion of said first 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 configuration with
`each of said microgrooves having surfaces which form
`an angle with respect to said first major surface which,
`when taken together with the index of refraction of the
`material of said light guide, internally reflects substan(cid:173)
`tially all the light striking said surfaces of said micro(cid:173)
`grooves toward the second major surface at a first angle
`of incidence for emission from said second major
`surface;
`said planar surface portions being configured for inter(cid:173)
`nally reflecting a substantial portion of light striking
`said planar surface portions toward said second major
`surface at a second angle of incidence for internal
`reflection 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
`reflective means adjacent to said first major surface for
`reflecting 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 first and
`second parallel major surfaces, said first major surface
`having a plurality of v-shaped parallel microgrooves
`extending continuously across a substantial portion
`said first major surface and a plurality of planar surface
`portions between said microgrooves, said micro(cid:173)
`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 first major surface which,
`when taken together with the index of refraction of the
`material of said light guide, internally reflects substan(cid:173)
`tially all the light within said light guide toward the
`second major surface at a first angle of incidence for
`emission from said second major surface;
`said planar surface portions being configured for inter(cid:173)
`nally reflecting a substantial portion of light striking
`said planar surface portions toward said second major
`surface at a second angle of incidence for internal
`reflection by said second major surface along said light
`guide, and
`a backlit LCD placed with the back surface of said LCD
`adjacent to said first major surface; and
`reflecting means adjacent to said second major surface for
`
`MBI_001413
`
`

`

`5,461,547
`
`7
`reflecting light emitted from the second major surface
`toward said first major surface for emission from said
`first major surface between said microgrooves where
`the reflected light illuminates the LCD.
`16. An illuminated LCD system as in claim 15 wherein a 5
`diffuser is placed between said first major surface and said
`
`8
`
`LCD.
`17. An illuminated LCD system as in claim 16 wherein
`the LCD is transmissive.
`
`* * * * *
`
`MBI_001414
`
`