United States Patent [191
`Borchardt
`
`US005381309A
`Patent Number:
`Date of Patent:
`
`[11]
`[45]
`
`5,381,309
`Jan. 10, 1995
`
`[54] BACKLIT DISPLAY WITH ENHANCED
`VIEWING PROPERTIES
`[75] Inventor: Jerry L. Borchardt, Maple Grove,
`Minn.
`[73] Assignee: Honeywell Inc., Minneapolis, Minn.
`[21] Appl. No.: 130,084
`[22] Filed:
`Sep. 30, 1993
`
`....... .. F21V 13/00
`[51] Int. Cl.6
`[52] US. Cl. ...................................... .. 362/31; 362/26;
`362/27; 362/30; 362/331
`[58] Field of Search ................... .. 362/800, 26, 30, 27,
`362/31, 331, 332, 333; 40/546
`References Cited
`_
`U.S. PATENT DOCUMENTS
`
`[56]
`
`4,714,983 12/1987 Lang ................................... .. 362/27
`4,874,228 10/ 1989 Aho et al. .
`4,922,384 5/1990 Torrence ............................. .. 362/31
`4,984,144 l/l99l Cobb, Jr. et al. .
`4,994,941 2/ 1991 Wen .................................... .. 362/26
`5,054,885 10/1991 Melby .
`5,070,431 12/1991 Kitazawa et al. .............. .. 362/26 X
`5,190,370 3/ 1993 Miller et al. .
`5,272,601 12/ 1993 McKillip ............................. .. 362/27
`
`OTHER PUBLICATIONS
`R. McCartney, et al., “S7-7 Directional Diffuser Lens
`Array for Backlit LCD’s”, Japan Display ’92, pp.
`259-262.
`
`3M/Optical Systems, “Right Angle Backlighting Tech
`nology Design Aid”, 15 pages.
`“Brightness Enhancement Film”, 10 pages.
`3M product brochure 75-0500-0403-7, “Brightness
`Enhancement Film (BEF)”, 2 pages (1993).
`3M, “Diffusion Film”, 6 pages.
`3M product brochure 75-0500—0563-8, “Light Diffus
`ing Film”, 2 pages (1993).
`Primary Examiner—Ira S. Lazarus
`Assistant Examiner-Thomas M. Sember
`Attorney, Agent, or Firm-Charles L. Rubow
`[57]
`ABSTRACI‘
`A high aspect ratio, backlit liquid crystal display in
`which light from opposing rows of light emitting diodes
`is projected into the ends of a thin optical cavity. The
`optical cavity is bounded by one major wall of which
`the interior surface is specularly re?ective and an op
`posing major wall including a layer of transparent mate
`rial having an interior surface formed with an array of
`regularly-spaced, ?ne, triangular prisms which tend to
`collimate light received from the cavity and project it
`outwardly perpendicular to the major wall. A diffusion
`layer overlays the layer of transparent material, and a
`brightness enhancing ?lm overlays the diffusion layer
`and functions to convert diffuse illumination received
`through the diffusion layer into directed illumination
`predominantly falling within the a viewing space
`bounded by predetermined angles.
`
`10 Claims, 4 Drawing Sheets
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`LG Display Ex. 1022
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`LGD_001785
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`US. Patent
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`Jan. 10, 1995
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`Sheet 1 of 4
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`5,381,309
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`L-l
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`Fig. 2
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`LGD_001786
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`US. Patent
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`Jan. 10, 1995
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`Sheet 2 of 4
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`LGD_001787
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`U.S. Patent
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`%91091.M
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`Sheet 3 of 4
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`5,381,309
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`w a..\nP.x..W.m|NR\wl|ll§w\§§,»/////z///z///A»/4-
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`LGD_001788
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`US. Patent
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`Jan. 10, 1995
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`Sheet 4 of 4
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`5,381,309
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`37
`A
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`20
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`34 33 2
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`Fig. 5 -
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`LGD_001789
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`and have modest energization circuitry requirements.
`However, such diodes are essentially point light sources
`which, if used to backlight a relatively large area, must
`be combined with other optical elements for evenly
`distributing and directing the light output.
`A variety of multifaceted lens products are now
`available for achieving a large aperture with a thin
`element. One such family of products includes transmis
`sive and re?ective optical ?lms available through Min
`nesota Mining and Manufacturing Company, and de
`scribed in US. Pat. Nos. 4,799,137, 4,874,228, 4,984,144,
`5,054,885 and 5,190,370. These ?lms are characterized
`by a major surface formed with an array regularly
`spaced, parallel, ?ne, triangular prisms which serve to
`redirect light received from a range of angles to a rela
`tively uniform direction normal to the nominal plane of
`the ?lm. This characteristic can be utilized to imple
`ment a thin, large aperture light source by projecting
`light produced by one or more point sources onto the
`?lm at a very small angle relative to the nominal plane
`of the ?lm.
`One of the more dif?cult design problems with such
`a light source implementation is the selection and ar
`rangement of materials which will achieve illumination
`of uniform intensity and direction over the entire aper
`ture. Uniform intensity and direction of illumination is
`required to avoid “hot spots”, voids, streaks, an inade
`quate range of angles for acceptable viewing and other
`defects.
`The applicant has discovered a unique combination
`and arrangement of optical elements which provides for
`enhanced viewing of a display backlit with a thin, large
`aperture light source, thereby avoiding many of the
`disadvantages of prior known display devices.
`
`30
`
`1
`
`BACKLIT DISPLAY WITH ENHANCED VIEWING
`PROPERTIES
`
`BACKGROUND OF INVENTION
`The invention disclosed herein relates generally to
`backlighting for display panels which are at least par
`tially translucent, and to corresponding illuminated
`display devices of the type incorporating backlighting
`from a high aspect ratio illumination source. More par
`ticularly the invention relates to such a display device
`and illumination source employing light emitting diodes
`in conjunction with an optical cavity and enhancement
`?lms to provide improved viewability from a relatively
`wide range of viewing angles.
`There are various situations in which it is desired or
`necessary that information be displayed so as to be read
`able under a wide range of ambient light conditions and
`throughout a relatively wide range of viewing angles.
`In many of these situations it is also highly desirable, if
`not required, that the display apparatus be capable of
`automatic updating of the displayed information and/or
`permitting selection of the information to be displayed.
`Another characteristic which is desired and often im
`portant is that the apparatus be robust and require mini
`mum maintenance.
`A speci?c application requiring such a display device
`relates to monitoring the status and/or operation of
`environmental control equipment on mobile shipping
`containers for perishable goods. Such containers, which
`each have a refrigeration unit and/or other environ
`mental control apparatus, may, during a single trip, be
`moved by train, track and/or marine vessel, and moved
`from one mode of transportation to another by crane or
`other cargo handling equipment. During the shipping
`process, it may be necessary to periodically check on
`operation of the refrigeration or other environmental
`control equipment and the status of environmental con
`ditions within the container. A display device for pres
`enting this information is typically installed at a conve
`nient location on each container. Since it may be neces
`sary to perform a status check at any time of the day or
`night and under varying climatic conditions, the display
`must be illuminated so as to be easily readable during
`daylight as well as dark conditions. Further, since the
`45
`containers may be stacked as many as three high, and on
`platforms such as a truck or rail car bed, it may be
`necessary to read the display from a variety of viewing
`angles ranging between substantially above to some
`what below horizontal, and within a reasonable range of
`50
`horizontal viewing angles.
`The requirements for long life, robustness and mini
`mum maintenance essentially dictate solid state design
`and construction. Thinness or high aspect ratio of the
`display apparatus is also an important consideration in
`many applications, such as the previously described
`shipping container environmental control and status
`monitoring system.
`Although several ?at panel technologies are available
`for producing illumination, such technologies including
`solid state ?orescent and electroluminescent devices,
`light sources based on these technologies have various
`disadvantages, such as high initial cost, excessive degra
`dation of light output with time, limited useful life and
`/or requirements for complex driver or energization
`circuitry.
`Light emitting diodes which produce a relatively
`high light output are readily available, and inexpensive,
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`40
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`60
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`65
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`SUMMARY OF THE INVENTION
`The invention is a backlit display device and thin,
`large aperture light source for such a display device, the
`light source including an optical cavity bounded in part
`by a pair of opposing major walls, the, ?rst major wall
`having a specularly re?ective interior surface and the
`second major wall including an interior layer or ?lm of
`transparent material whose interior surface is con?g
`ured with an array of regularly spaced triangular prisms
`extending across the optical cavity substantially parallel
`with the ends thereof. The second wall also includes a
`diffuser which overlays the interior layer and a bright
`ness enhancing ?lm which overlays the diffuser, the
`brightness enhancing ?lm being adapted to convert
`diffuse illumination into directed illumination falling
`predominantly within the desired viewing space. Fi
`nally, a planar, at least partially translucent message
`carrying member overlays the brightness enhancing
`?lm.
`A light source is positioned to project light into the
`optical cavity from at least one end thereof. The light
`source may be formed of ?rst and second opposing
`rows of light emitting diodes at opposite ends of the
`optical cavity, the light emitting diodes each being
`adapted and oriented to produce a light beam whose
`center line intersects the interior surface of the ?rst
`major wall at a point substantially 40 percent of the
`length of the optical cavity from the end at which the
`diode is located.
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`LGD_001790
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`3
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a frontal view of a display device in accor
`dance with the applicant’s invention, partially broken
`away to show internal optical layers;
`FIG. 2 is an edge view of the display device of FIG.
`1, partially in section and partially broken away;
`FIG. 3 is an exploded perspective view in simpli?ed
`form of the principal optical elements in the display
`device of FIGS. 1 and 2;
`FIG. 4 is an enlarged partial cross sectional view of
`the display device of FIGS. 1 and 2, showing its internal
`geometry; and
`FIG. 5 is a much enlarged schematic representation
`in exploded form of certain optical layers in the display
`device of FIGS. 1 and 2, illustrating light processing
`within the device.
`
`5
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENT
`In FIGS. 1 and 2, reference numeral 10 generally
`identi?es a display device in accordance with the appli
`cant’s invention. The invention pertains primarily to
`optical elements which, in the embodiment shown in
`FIGS. 1 and 2, are assembled on a printed circuit board
`11. Circuit board 11 in addition to providing a structural
`base for the optical elements, carries electronic circuitry
`for selectively energizing segments of a liquid crystal
`display panel 12 and other indicator lamps, such as
`those identi?ed by reference numeral 13, in addition to
`supplying electric power to backlighting lamps 14, as
`will be further described hereinafter, in response to
`signals received through an interface connector 15.
`Display panel 12 is electrically connected to circuit
`board 11 through edge connectors, of which one is
`identi?ed by reference numeral 16 in FIG. 2.
`Liquid crystal display panel 12 is one of several pla
`nar optical elements or layers sandwiched together and
`held in place between printed circuit board 11 and a
`bezel or cover 17 having an aperture 18 through which
`40
`the display surface of liquid crystal display panel 12 can
`be viewed. Reference numeral 19 identi?es a gasket
`between display panel 12 and cover 17.
`Beneath liquid crystal display panel 12 are several
`optical layers, including a brightness enhancing ?lm 20,
`a diffuser 21 and a transmissive right angle ?lm 22,
`whose functions will be described in greater detail here
`inafter. These elements are mounted on the open face of
`a shallow. open ended trough 23 which can be better
`visualized from examination of the exploded perspec
`tive view FIG. 3. Elements 20-22 form a lens assembly
`which provides one major wall (identi?ed by reference
`numeral 24 in FIG. 2) of an optical cavity structure
`de?ning a high aspect ratio optical cavity 25 having a
`length L and a width W, as shown in FIG. 3.
`A second major wall 26 of the optical cavity struc
`ture is formed by a bottom wall of trough 23. At least
`web 26 is provided with a specularly re?ective interior
`surface 27, which may be in the form of a highly re?ec
`tive ?lm applied to the surface. A re?ective polyester
`60
`?lm product designated as Silverlux available through
`Minnesota Mining and Manufacturing Company has
`been found suitable for this application.
`Backlighting illumination is provided by two rows of
`light emitting diodes 14 at the opposite ends of the
`65
`optical cavity structure. The rows extend across the
`width of optical cavity 25. Each light emitting diode 14
`is essentially a point source of light which projects a
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`25
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`35
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`20
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`5,381,309
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`light beam along a center line identi?ed by reference
`numeral 30 in FIG. 4. The light beam predominantly
`falls within a cone having an apical angle a of nominally
`15 degrees for the diodes selected for this application. a
`represents the angle at which light output from diodes
`14 drops to one half of its intensity on center line 30.
`It has been found that best performance of display
`device 10, in terms of intensity and evenness of light
`distribution, is achieved by orienting light emitting di
`odes 14 so that their beam center lines 30 each intersect
`specular surface 27 at a point 40 percent of the length L
`of cavity 25 from the end at which the diode is located.
`This is accomplished by mounting diodes 14 on a pair of
`daughter boards 31 which are mounted on circuit board
`11 at a slight angle from perpendicular to the board.
`As is apparent from the above described geometry,
`and is most clearly illustrated in FIG. 4, light is trans
`mitted to the inner surface of transmissive right angle
`?lm 22, which is the inner element of the lens assembly
`forming major wall 24 of the optical cavity structure,
`both directly from diodes 14 and indirectly from the
`diodes by means of re?ection from specular surface 27.
`A general understanding of the light distribution char
`acteristics of the lens assembly can be obtained from
`FIG. 5 which illustrates the paths taken by representa
`tive light rays.
`It is pointed out that the features illustrated in FIG. 5
`are not to scale. In addition, the adjacent surfaces of
`?lms 20, 21 and 22 are preferably contiguous. The
`spaces in FIG. 5 between the ?lms are provided only to
`facilitate a general description of the optical character
`istics. Reference may be made to available product
`literature on brightness enhancing ?lm 20, diffusion film
`21 and transmissive right angle ?lm 22 for more detailed
`information on these products.
`As shown in FIGS. 4 and 5, the angle at which the
`predominant light rays arrive at the faceted surface of
`film 22 are within a few degrees from horizontal. The
`most horizontal rays travel directly from diode 14 to the
`end of ?lm 22 most remote from the diodes which emit
`ted the rays. The rays which arrive at the greatest angle
`from horizontal are those re?ected from the end of
`specular surface 27 nearest the emitting diodes. Refer
`ence numerals 32, 33 and 34 identify rays within this
`range at progressively greater angles from horizontal.
`As illustrated in FIG. 5, rays 32, 33 and 34 are subject
`to total internal re?ection from the facets on the inner
`surface of ?lm 22, and are redirected at approximately
`90° from the original direction. Thus, the rays emerge
`from the surface of ?lm 22 opposite the faceted surface
`thereof throughout a small range of angles from perpen
`dicular to the plane of the ?lm.
`Light transmitted through ?lm 22 is then dispersed
`over a wide range of directions by diffusion ?lm 21 to
`achieve evenly distributed illumination. The light trans
`mitted through diffusion ?lm 21 is then supplied to
`brightness enhancing film 20 which functions to redi
`rect a majority of the light to directions within angles
`bounding a desired viewing space. In particular, light
`transmitted to brightness enhancing ?lm 20 internally is
`treated in one of three ways depending on the angle at
`which light rays enter the ?lm.
`As shown at reference numeral 35, light rays ap
`proaching ?lm 20 at angles close to perpendicular to the
`?lm undergo double internal re?ection from the facets
`on an outer faceted surface of the ?lm, and returned to
`diffuser film 21 to be diffusely recycled. Light rays
`entering ?lm 20 within a small range of angles slightly
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`5,381,309
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`less than the angles which result in double internal re
`ular prisms on the inner layer at a small angle rela
`?ection undergo re?ection and refraction, and emerge
`tive to an interior surface of the second major wall.
`from the faceted surface of the ?lm in approximately
`2. The display device of claim 1 wherein said light
`horizontal directions, as shown at reference numeral 36.
`source is adapted and oriented to produce a light beam
`These rays represent a small amount of lost light. A 5
`whose center line intersects the interior surface of the
`majority of the light rays enter ?lm 20 throughout a
`second major wall at a point substantially 40 percent of
`relatively broad range of angles less than the angles of
`the length of the optical cavity from the end thereof at
`which said light source is located.
`rays at 35 and 36, and represent illumination useful for
`3. The display device of claim 2 wherein said light
`backlighting display panel 12. Such rays are shown at
`source comprises ?rst and second pluralities of light
`reference numeral 37. As illustrated, the rays entering
`emitting diodes located at ?rst and second opposing
`?lm 20 within this range of angles are refracted by the
`ends of the cavity respectively.
`faceted surface of the ?lm, and emerge from the faceted
`4. The display device of claim 3 wherein the ?rst and
`surface distributed throughout a range of angles cover
`second pluralities of light emitting diodes each comprise
`ing the desired viewing space for the display.
`a linear array of light emitting diodes substantially par
`The applicant has discovered that the particular com
`allel to the ?rst and second major walls of the optical
`bination of elements and geometry described above
`structure.
`results in a display device having signi?cantly enhanced
`5. The display device of claim 4 wherein each of the
`viewing properties. In particular, this arrangement max
`diodes in the ?rst and second pluralities of light emitting
`imizes the amount of illumination produced by the light
`diodes produce a light beam having a half peak intensity
`source which is effectively used to backlight the display
`aperture of substantially 15°.
`panel. This illumination is evenly distributed, thereby
`6. The display device claim 5 wherein said message
`avoiding voids, “hot spots”, streaking and other unde
`carrying member is a liquid crystal display panel which
`sirable characteristics. It also directs a maximum
`is translucent when unenergized, and having a plurality
`amount of the illumination to within angles bounding
`of selectively energizable display segments which be
`the desired viewing space, resulting in uniform readabil
`come substantially opaque when energized.
`ity throughout a desired extended range of angles.
`7. The display device of claim 6 wherein said optical
`Accordingly, the applicant has provided a high as
`structure is mounted on a printed circuit board with the
`pect ratio, backlit display device having superior view
`second major wall of said optical cavity structure being
`ing characteristics. A particular embodiment is shown
`adjacent printed circuit board, said optical structure
`and described for illustrative purposes. However it is
`being located between opposing rows of light emitting
`not intended that coverage be limited to that embodi
`diodes carried on said printed circuit board and forming
`ment, but only by the terms of the following claims.
`said light source, said printed circuit board also carry
`The embodiments of the invention in which an exclu~
`ing electronic circuitry for selectively energizing the
`sive property or right is claimed are de?ned as follows:
`display segments of said liquid crystal display panel.
`1. A high aspect ratio, backlit display device with
`8. A high aspect ratio illumination source for back
`enhanced viewing properties, comprising:
`lighting a planar, at least partially translucent, display
`a message carrying member having a display surface
`surface with directed illumination predominantly falling
`of predetermined length and width of which at
`within a viewing space bounded by predetermined an
`least a portion is translucent, said message carrying 40
`gles relative to the display surface, the display surface
`member having a ?rst side from which the message
`having a predetermined length and width, the light
`is to be readable within a viewing space bounded
`source comprising:
`by predetermined angles relative to the ?rst side,
`an optical cavity structure de?ning an optical cavity
`said message carrying member having a second
`having opposite ends, and having a length and
`side opposite the ?rst side;
`width at least equal to the predetermined length
`an optical structure having ?rst and second generally
`and width of the display surface, said optical cavity
`parallel major walls at least partially enclosing a
`structure having a ?rst major wall with an interior
`thin cavity having a length and width at least as
`surface adapted to provide specular re?ection and
`great as the predetermined length and width of the
`a second major wall including an interior layer of
`display surface, the cavity having a ?rst end sub
`transparent material, the interior layer of transpar
`stantially parallel with the width of the cavity and
`ent material having an interior surface con?gured
`transverse to the ?rst and second major walls
`with an array of regularly spaced triangular prisms
`thereof, the ?rst major wall of said optical struc
`extending across the optical cavity substantially
`ture including an inner layer of transparent mate
`parallel with the ends thereof;
`rial having an interior surface bounding the cavity,
`a light source adapted to project light into the optical
`an intermediate optical diffusion layer and an outer
`cavity from at least one end thereof;
`brightness enhancing film layer having an inner
`a diffusion layer overlaying the exterior surface the
`surface adjacent the diffusion layer and an outer
`interior layer of transparent material in the second
`surface adjacent the display surface, the interior
`major wall of said optical cavity structure; and
`surface of the inner layer and the outer surface of 60
`a brightness enhancing ?lm overlaying said diffusion
`the outer layer each being con?gured with an array
`layer, said brightness enhancing ?lm having a ?rst
`of regularly spaced triangular prisms parallel with
`surface adjacent said diffusion layer and a second
`the width of the cavity, the second major wall of
`opposing surface con?gured with an array of regu
`said optical structure being adapted to provide
`larly spaced triangular prisms parallel with the
`specular re?ection; and
`triangular prisms formed in the interior layer of the
`65
`a light source adapted to project light from the end of
`second major wall of said optical cavity structure,
`the cavity onto the second major wall of said opti
`the prisms on said brightness enhancing ?lm having
`cal structure in a direction transverse to the triang
`faces whose included angles and angular orienta
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`5,381,309
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`point substantially 40 percent of the length of the opti
`tions relative to the ?rst surface of said brightness
`cal cavity from said at least one end thereof.
`enhancing ?lm provide directed illumination pre
`10. The high aspect ratio illumination source of claim
`dominantly between the predetermined angles
`9 wherein the light source comprises ?rst and second
`bounding the viewing space.
`opposing rows of light emitting diodes said opposite
`9. The high aspect ratio illumination source of claim
`ends of the optical cavity, each light emitting diode
`8 wherein said light source is adapted to produce a light
`producing a light beam having a half peak intensity
`beam whose center line intersects the interior surface of
`aperture of substantially 15 °.
`the ?rst major wall of said optical cavity structure at a
`* * * * *
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`UNITED STATES PATENT AND TRADEMARK OFFICE
`CERTIFICATE OF CORRECTION
`PATENTNO. :5,381,309
`DATED
`ZJanuary 10, 1995
`INVENTUMS) I Jerry L. Borchardt
`
`It is certified that error appears in the above-identified patent and that said Letters Patent is hereby
`corrected as shown below:
`
`Column 6, line 7, cancel "optical";
`line 29, cancel "cavity";
`line 30, after "adjacent" insert --the-—.
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`Column 8, line 5, after "diodes" insert -—at—-.
`
`Signed and Sealed this
`
`Sixteenth Day of May, 1995
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`Am-
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`6144 W
`
`Atte‘sting O?icer
`
`Commissioner of Patents and Trademarks
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`BRUCE LEHMAN
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`LGD_001794