.
`
`Unlted States Patent [19]
`Tai et al.
`
`USOO5359691A
`
`[11] Patent Number:
`[45] Date of Patent:
`
`5,359,691
`Oct. 25, 1994
`
`[54] BACKLIGHTING SYSTEM WITH A
`MULTI-REFLECI‘ION LIGHT INJECTION
`SYSTEM AND USING MICROPRISMS
`
`_ [75] lnvemom Chen-Y“ Ta}; Ha" Z“, both of
`
`Toledo, 0h1o
`
`[73] Assignee: Bri'teview Technologies, Toledo,
`Ohlo
`
`[21] Appl. N0.: 49,509
`.
`_
`[22] F?ed'
`
`Apr’ 19’ 1993
`
`Related US Application Data
`'
`_
`_
`commuatlon-m'pa? of Sef- No‘ 953,233, Oct- 3’ 1992-
`
`l63l
`
`[51] Int. Cl.5 .............................................. .. G02B 6/04
`[52] US. Cl. ..................................... .. 385/146; 362/32
`[58] Field of Search .............................. .. 385/ 115-119,
`385/900, 901; 362/32, 31, 26, 330, 806; 358/901
`
`[56]
`
`References Cited
`.S. P TENT D CU ENT
`U A
`O M S
`4,917,465 4/1990 Conner et al. .................... .. 350/335
`
`5,050,946 9/1991 Hathaway et a1. 5,187,765 2/1993 Muehlemann et a1. ....... .. 385/901 x
`
`5,202,950 4/1993 Arego et a1. .................. .. 385/901 x
`5,226,105 7/1993 Myers ........................... .. 385/901 X
`inn-man, Examiner__Akm E Unah
`Attorney, Agent, or Firm-Gray Cary Ware &
`Freidenrich
`ABSTRACT
`[57]
`‘
`An assembly for backlighting a liquid crystal ?at panel
`display or other such arrangement requiring backlight
`ing is disclosed herein. The assembly is composed of a
`multi-re?ection light injection system, alight pipe and a
`set of speci?cally con?gured micropnsms WhlCh, coop
`erating with the light pipe, provides an ef?cient back
`lighting technique with a controllable degree of colli
`mation, The disclosed assembly may employ up to four
`light sources to give a brighter backlighting.
`
`30 Claims, 10 Drawing Sheets
`
`Mercedes-Benz Ex. 1007
`
`MBI_001429
`
`

`

`US. Patent
`
`Oct. 25, 1994
`
`Sheet 1 of 10
`
`5,359,691
`
`FIG. 1 l2 / /
`
`1m
`
`l
`28
`\L
`26 \ /,;\ ____________________ --
`
`64'
`
`\
`e
`
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`l
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`I
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`
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`4/‘ r
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`X
`
`2
`
`56
`64
`
`
`/)__ ‘i’: _ ‘ _ — -.J____ ,/ ,1 321
`
`
`/’
`’ 43‘ L
`J ’ 34'
`7%
`
`ll
`
`/\
`
`‘
`
`47,447,474“
`
`MBI_001430
`
`

`

`US. Patent
`
`Oct. 25, 1994
`
`Sheet 2 0f 10
`
`5,359,691
`
`FIG. 3
`
`FIG. 4
`
`MBI_001431
`
`

`

`US. Patent
`
`Oct. 25, 1994
`
`Sheet 3 of 10
`
`‘5,359,691
`
`FIG. 5 12 \/ /
`
`282g! 28...
`
`I
`
`2
`
`FIG. 6A
`Y
`
`98
`1
`
`54
`9% /
`
`96
`
`92
`
`6
`
`_
`
`MBI_001432
`
`

`

`US. Patent “
`
`Oct. 25, 1994
`
`Sheet 4 0f 10
`
`5,359,691
`
`m5 .wE
`
`. .5
`
`L I
`
`ww
`
`MBI_001433
`
`

`

`US. Patent
`
`Oct. 25, 1994
`
`Sheet 5 0f 10
`
`5,359,691
`
`52B
`
`60
`\
`
`FIG. 75
`
`FIG. 7C
`
`MBI_001434
`
`

`

`US. Patent
`
`Oct. 25, 1994
`
`Sheet 6 of 10
`
`1 5,359,691
`
`FIG. 8
`
`FIG. 9B
`
`1030'
`
`MBI_001435
`
`

`

`US. Patent
`
`Oct. 25, 1994
`
`Sheet 7 of 10
`
`5,359,691
`
`l2 \/ /
`
`FIG. l0
`
`Z
`
`Y
`
`11 Z
`
`18'"
`28 \
`
`)~_
`
`'
`
`l,
`/
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`
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`I
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`I
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`I, , I 321
`z
`
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`
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`
`o/y/////////////</////////////l
`FIG. 11 12\/ /
`
`Z Y
`
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`
`I : Z
`
`4- - — — — - - — — - - - - — - - - - — - -
`
`I
`
`I
`
`MBI_001436
`
`

`

`US. Patent
`
`Oct. 25, 1994
`
`Sheet 8 of 10
`
`5,359,691
`
`FIG. 12A
`
`\36.
`
`FIG. 12B
`
`MBI_001437
`
`

`

`US. Patent
`
`Oct. 25, 1994
`
`Sheet 9 of 10
`
`5,359,691
`
`FIG. 15
`
`122
`
`35..
`
`MBI_001438
`
`

`

`US. Patent
`
`0a. 25, 1994
`
`Sheet 10 0f 10
`
`5,359,691
`
`MBI_001439
`
`

`

`1
`
`BACKLIGHTING SYSTEM WITH A
`MULTI-REFLECI'ION LIGHT INJECTION
`SYSTEM AND USING MICRQPRISMS
`- CROSS REFERENCE TO RELATED
`APPLICATIONS
`This application is a continuation-in-part of copend
`ing application Ser. No. 07/958,238, ?led Oct. 8, 1992
`now is being allowed which is incorporated herein by
`reference.
`
`10
`
`5,359,691
`2
`As will be seen hereinafter, with the backlighting
`assembly designed in accordance with the present in
`vention, a compact and power-saving light source,
`which can provide backlighting of both high intensity
`and controllable collimation, may be applied to stacked
`panel displays, colored displays in portable computers
`as well as real time ?at displays.
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`The present invention relates generally to a back
`lighting system especially suitable for use with liquid
`crystal displays. In particular, it contains certain im
`proved features of a backlighting system of the type
`disclosed in the above-recited copending application.
`2. Description of the Related Art
`Liquid crystal displays (LCDs) are commonly used in
`portable computer systems, televisions, and other elec
`tronic display devices. Large area, high performance
`LCDs require a source of lighting for operation. Back
`lighting the LCD has become the most popular source
`of light in personal computers, televisions, as well as
`projector type displays. In general, there is a need to
`obtain a suf?ciently bright backlighting with as little
`power consumption as possible. Backlighting systems
`with a speci?ed degree of collimating, that it is, a lim
`ited divergence angle is necessary for such con?gura
`tions as three cell stacked assembly (T STN). Since most
`LCDs have very low transmission and view-angle de
`pendent characteristics, it is sometimes desirable to use
`more than one light source ef?ciently for brighter pic
`ture presentation. As an example, transmission of a
`color active matrix LCD is only about 2% and a hot
`cathode ?uorescent lamp, which consumes signi?cantly
`more energy than a cold cathode ?uorescent lamp, is
`often needed for its back lighting. With the backlighting
`assembly designed in accordance with the present in
`vention, efficiency in converting light from a linear
`diffuse light source to a ?at display panel, such as LCD,
`can be signi?cantly improved. This invention can there
`fore prolong the life time of a battery powering a porta
`ble LCD display. Uniformity of the backlighting as well
`as small space for convenience of portability are also
`achieved with the present invention.
`In most of the existing backlighting systems, the
`mechanism that brings light out of the light pipe is based
`on the principal of random scattering which is not only
`wavelength dependent, but also not very ef?cient. In
`addition, this approach can not provide collimated
`backlighting which is needed for use in applications like
`stacked liquid crystal displays to avoid parallax effect.
`Although some approaches have been proposed to ob
`tain collimated backlighting for such displays, they all
`need a point light source and an optical system based on
`lenses and mirrors. Since a point light source currently
`available is generally less power-efficient than a ?uores
`cent lamp and in most cases requires a cooling system
`such as a fan, and optical systems based on lenses and
`mirrors which take up a large space, techniques for
`highly collimated light sources presented before were
`not practical for the backlighting of portable computers
`and ?at television sets. For this reason, the stacked
`panel technology is limited to projector type display at
`this moment.
`
`60
`
`65
`
`SUMMARY OF THE INVENTION
`As will be described in more detail hereinafter, an
`assembly for backlighting a liquid crystal display is
`disclosed herein. The assembly includes a generally
`rectangular backlighting light pipe having opposing top
`and bottom surfaces, two pairs of opposing sides, means
`for directing light into the light pipe from one or more
`sides and causing it to move from one end of the light
`pipe towards the opposite end thereof, and an arrange
`ment of immediately adjacent pyramid or triangle mi
`croprisms serving as the bottom surface of the light
`pipe. The microprisms are designed in accordance with
`a number of embodiments of the present invention to
`re?ect light within the light pipe upwards through its
`top surface.
`In one embodiment of the backlighting assembly
`disclosed herein, two linear light sources are coupled to
`the light pipe at two adjacent sides of the light pipe by
`means of light collimating assemblies extending parallel
`to their respective linear light sources. As will be seen,
`each light collimating assembly can collimate light, to a
`certain degree, in the plane perpendicular to the surface
`of the light pipe by means of multi-re?ections inside the
`collimating assembly. There is also disclosed herein a
`backlighting assembly designed in accordance with a
`second embodiment. In this embodiment, the light colli
`mating assembly is divided into a series of longitudinally
`extending laterally adjacent sections or channels which
`extend from the input end of the light collimating as
`sembly to its output end and which are optically iso
`lated from one another along substantially their entire
`lengths, whereby the individual light pipe sections act
`on incoming light substantially independent of one an
`other. As will be seen, this multichannel con?guration
`allows for the use of a linear light source to achieve two
`dimensional collimation of light exiting the assembly. In
`a third and a fourth embodiment of the backlighting
`assembly, only one linear light source is employed.
`Such systems can provide suf?cient backlighting for
`applications needs less intense backlighting such as
`monochromatic LCDs or color STN LCDs. As can be
`seen, up to four light sources can be used if extremely
`intense backlighting is needed.
`While the present invention provides for a number of
`unique backlighting assemblies, it also provides for a
`unique system which includes a backlighting assembly
`in combination with a liquid crystal display and a specif
`ically designed light polarizing arrangement which, in
`combination with the backlighting assembly, ensures
`that substantially all of the light from the backlighting
`assembly for use by the liquid crystal display is appro
`priately polarized. This is to be contrasted with prior art
`polarization schemes in which only at most about one
`half of the available light from the backlighting assem
`bly is properly polarized. In the particular embodiment
`disclosed herein, the polarizing arrangement utilizes a
`retrore?ecting sheet polarizer in cooperation with the
`microprisms forming part of the backlighting assembly
`to provide the appropriate polarization of light exiting
`the backlighting assembly.
`
`MBI_001440
`
`

`

`15
`
`25
`
`5,359,691
`4
`3
`FIG. 14 is a perspective view illustrating the combi
`Other features of the present invention will be appar
`nation of the backlighting assembly of FIG. 1 and the
`ent hereinafter, including the ability to provide a liquid
`retrore?ecting sheet polarizer of FIG. 13;
`crystal display that can be viewed from wide angles
`FIG. 15 diagrammatically illustrates the way in
`without picture degradation.
`which an arrangement of microprisms forming part of
`DESCRIPTION OF THE DRAWINGS
`the backlighting assembly of FIG. 14 cooperates with
`an arrangement of the retrore?ecting sheet polarizer of
`The present invention will be described in more detail
`FIG. 13 in order to polarize light in accordance with
`hereafter in conjunction with the drawings, wherein:
`the present invention; and
`FIG. 1 is a perspective view of a backlighting assem
`FIG. 16 is a diagrammatic illustration, in side eleva
`bly which is designed in accordance with one embodi
`tional view, of an overall liquid crystal display system
`ment of the present invention and which is shown in
`including a liquid crystal display assembly, a backlight
`combination with a liquid crystal display, the backlight
`ing assembly designed in accordance with the present
`ing assembly being shown in an x, y, z coordinate sys
`invention, a polarizing arrangement which, in combina
`tem for purpose of convenience;
`tion with the backlighting assembly, is designed in ac
`FIG. 2 if a sectional view of a light directing assem
`cordance with the present invention, and a light scatter
`bly, taken in x-z plane;
`ing diffusing plate.
`FIG. 3 is a section view of a portion of a backlighting
`pipe forming part of the backlighting assembly of FIG.
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT
`1, speci?cally illustrating the way in which light enters
`and exits the light pipe in cooperation with a sheet of
`Turning now to the drawings, wherein like compo
`pyramid prisms designed in accordance with the pres
`nents are designed by like reference numerals through
`ent invention;
`out the various ?gures, attention is ?rst directed to FIG.
`FIG. 4 is a sectional view of an end of the backlight
`1. As indicated above, this ?gure illustrates in perspec
`ing assembly of FIG. 1, especially illustrating the way in
`tive view an assembly designed in accordance with the
`which light is re?ected by an end mirror;
`present invention for backlighting a liquid crystal dis
`FIG. 5 is a perspective view of a backlighting assem
`play. The assembly is shown at 10 within an x-y-z coor
`bly designed in accordances with another embodiment
`dinate system, and the liquid crystal display is generally
`indicated by the reference number 12. Assembly 10
`of the present invention;
`includes a generally rectangular backlighting light pipe
`FIG. 6A is a sectional view of a lightdirecting chan
`nel which forms part of a multichannel light directing
`14 which extends in both the x-direction and y-direc
`tion, between opposite ends 16 and 18, and opposing
`segment of the backlighting assembly in FIG. 5, taken in
`the x-y planes, respectively;
`sides or ends 20 and 22 and which has opposing top and
`bottom surfaces 24 and 26, respectively, extending hori
`FIG. 6B is a sectional view of a multichannel light
`zontally (in the x-y plane). Two light collimating assem
`directing segment which consists of a row of pyramid
`blies or arrangements generally indicated as 28 and 28’,
`prisms with ?at ends designed in accordance with an
`respectively, are provided for directing light into the
`other embodiment of the present invention;
`light pipe at adjacent entry ends 16 and 20, and for
`FIGS. 7A, 7B, and 7C are sectional views of light
`causing the light to move from entry ends 16 and 20
`directing or light collimating assemblies in accordance
`towards the opposite ends 18 and 22, as indicated gener
`with still other embodiments of the present invention;
`ally by arrows 30 and 30'. Ends 18 and 22 include light
`FIG. 8 is a diagrammatic illustration, in perspective
`re?ecting surfaces, respectively, for re?ecting light
`view, of a portion of a modi?ed sheet of pyramid micro
`back towards entry ends 16 and 20, as indicated gener
`prisms for use as part of the backlighting assembly of
`ally by arrows 34 and 34’.
`FIG. 1;
`Still referring to FIG. 1, backlighting assembly 10
`FIG. 9A is a sectional view of a portion of a back
`also includes an arrangement 36 of immediately adja
`lighting pipe of the present invention employing the
`cent downwardly pointing pyramid shaped micro
`modi?ed sheet of pyramid microprisms in FIG. 8, espe
`prisms or merely pyramid microprisms, as they will also
`cially illustrating the way in which light enters, propa
`be referred to, extending in the x-y plane along the
`gates through and exits light pipe;
`entire extent of and serving as the bottom surface of
`FIG. 9B is a diagrammatic illustration, in side eleva
`light pipe 14. Note that the base of each microprism is
`tion, of a modi?ed backlighting assembly designed in
`immediately adjacent to and in a common plane with
`accordance with the present invention;
`the adjacent pyramid prisms, and that the common
`FIG. 10 is a perspective view of a backlighting assem
`plane is parallel with the x-y axes. In the particular
`bly designed in accordance with still another embodi
`embodiment illustrated in FIG. 1, each of the micro
`ment of the present invention;
`prisms, which is generally indicated at 42 in FIG. 3, is a
`FIG. 11 is a perspective view of a backlighting assem
`regular, four-sided pyramid having a rectangular base
`bly designed in accordance with a further embodiment
`and four triangular (isosceles) light re?ecting sides, a
`of the present invention;
`?rst opposing pair of which re?ects incident light from
`FIG. 12A is a diagrammatic illustration, in perspec
`the x-direction and the second opposing pair of which
`tive view, of a portion of a sheet of microprisms in
`re?ects incident light from the y-direction. One pair of
`accordance with still further embodiment of the present
`opposing sides of each pyramid is shown in FIG. 3 at 44
`invention;
`and 46. For the moment, it suf?ces to say that this ar
`rangement of pyramid microprisms may be constructed
`FIG. 12B is a diagrammatic illustration, in perspec
`of any suitable material such as acrylic glass or polycar
`tive view, of a portion of a modi?ed version of the
`microprism sheet of FIG. 12A;
`bonate having the same or approximately the same
`index of refraction as the light pipe 14. Arrangement 36
`FIG. 13 is a diagrammatic illustration, in side eleva
`may be a separately made, distinct arrangement from
`tion, of a retrore?ecting sheet polarizer;
`
`35
`
`45
`
`65
`
`MBI_001441
`
`

`

`5
`the light pipe, for example in the form of a separate
`sheet having a convex pyramid-featured underside 47,
`as illustrated in FIG. 3, in which case the arrangement
`could be readily bonded to the bottom surface 26 of the
`light pipe by means of suitable adhesive having the
`appropriate index of refraction so as to be transparent to
`light passing between the light pipe and micropyramids.
`On the other hand, as illustrated in FIG. 3, the arrange
`ment of pyramid microprisms could be made as an inte
`gral part of the light pipe. In either case, the size of the
`pyramid microprisms and the height of the light pipe
`sections have been exaggerated in order to more fully
`understand the way in which they act upon light intro
`duced into the light pipe. In the particular embodiment
`illustrated in FIG. 3, each regular pyramid de?nes a
`prism angle of 100° between opposing light re?ecting
`sides. It is to be understood that the present invention is
`not limited to these particular physical parameters. The
`width and the length of the pyramid may also have
`different values and the angles in the x and y directions
`20
`may also have different values. In addition, the two
`angles in x direction and/or the two angles in the y
`direction that the surfaces of the pyramids make with
`the base plane may have different values so that each of
`the four triangular surfaces of the pyramid may not be
`25
`isosceles, as illustrated in FIG. 9B. As will be discussed,
`it may also be desirable to have the angles vary system
`atically in the x-y plane to make the output light propa
`gating in a more desirable direction. The pyramid mi
`croprism sheet can be coated with aluminum or other
`suitable materials on the outer surface of the convex
`pyramids for enhanced re?ection.
`As will be seen hereinafter, as light is introduced into
`the light pipe at its entry end 16, for example, by means
`of arrangement 28, light is re?ected upwards through
`top surface 24 in the direction of liquid crystal display
`12, as indicated generally by means of arrows 38. As
`will also be seen, this arrangement of pyramid micro
`prisms and arrangements 28, 28' can be designed to
`cooperate with one another so as to ensure that the light
`38 exiting the light pipe through surface 24 does so in a
`highly collimated manner.
`'
`Still referring to FIG. 1, overall arrangements 28 and
`28' for introducing light into the light pipe through its
`ends 16 and 20, respectively will now be described in
`more detail. Since the working principle of both ar
`rangements are identical, the following description is
`with reference to arrangement 28 only.
`Turning now to FIG. 2, the light source 64 and its
`associated ?xture 66 is shown in the x-z plane. The
`arrangement 28 includes a re?ection prism 62 extending
`parallel to the entry side 16 of the light pipe. The prism
`62 has opposing top and bottom surfaces 50 and 52, and
`opposite ends 58, 60. Light entering the prism in the x-z
`plane has a maximum divergence angle (the angle of the
`entering light with respect to the x-axis 70) which is
`determined by the index of refraction of the material
`that the prism is made of (about 43° if the prism is made
`of acrylic glass). As will be discussed hereinafter, it is
`important to keep the divergence angles of light in the
`x-z plane which enters the backlighting light pipe sec
`tion 14 to at most a certain maximum angle. If light is
`allowed to propagate down the light directing assembly
`and into the backlighting light pipe at angles greater
`than this maximum angle, the backlight output 38 will
`not have the desired uniformity in distribution of light
`intensity to be suitable for application in LCD back
`lighting. At the entry end 58 of arrangement 28, the
`
`5,359,691
`6
`maximum divergence angle of light is approximately
`equal to arcs in (n1/n2), where n1 and n; are refractive
`indices of air and the collimating prism. When acrylic
`glass is used for the collimating prism, this maximum
`angle of divergence is 43°, as indicated above. Since
`light exiting the light directing assembly 28 and entering
`the light pipe 14 at large divergent angles will, gener
`ally, hit microprisms located at the bottom surface of
`the light pipe along sections close to the light source
`and will therefore give non-uniform intensity distribu
`tion of backlighting, it is important to keep the maxi
`mum divergence angle suf?ciently small to achieve
`uniform backlighting intensity. For arrangement 28 to
`collimate light to within a desired maximum divergence
`range for delivery to the light pipe, for example, i20“,
`the top and bottom surfaces 50 and 52 are constructed at
`a tilted angle, for example about 6°, with respect to the
`x-axis, as illustrated in FIG. 2.
`As an example, light ray 72, which enters the re?ec
`tion prism 62 at a divergence angle of 43° with respect
`to the x-axis, will be re?ected by the top surface 50 and
`then the bottom surface 52 of the reflection prism. With
`each re?ection, the light ray will have its divergence
`angle decreased by 12° for a 6° tilted surface. As a re
`sult, the light ray 82 leaving collimating arrangement 28
`and entering the light pipe will do so at a divergence
`angle of 19° which is within the desired maximum deliv
`ery divergence range of i20°. However, light rays,
`such as ray 74, which has a smaller initial divergence
`angle, for example 12°, will be re?ected by the surface
`of the collimating light pipe only once within the entire
`light collimating assembly and will have its divergence
`angle decreased by 12°. In addition, light with diver
`gence angle less than 6° will not hit either surface 50 and
`52 but rather propagate through the collimating assem
`bly with its direction unchanged. With a properly con
`structed collimating assembly, light rays with initial
`divergence angle greater than 32° will be re?ected by
`surfaces 50 and 52, and will have their divergence an
`gles decreased by a total of 24° before exiting the colli
`mating arrangement 28. Light rays with initial diver
`gence angles greater than 11° but smaller than 32° will
`be re?ected at least once by either surface 50 or 52 and
`will have their divergence angles decreased by at least
`12°. Light rays with initial divergence angles smaller
`than 11° may be re?ected by one of the surfaces 50 or 52
`at most once. Since all changes in propagation direction
`are a result of total internal re?ection, there is no loss in
`light intensity.
`The same principle just described with respect to
`arrangement 28 is applicable to light rays entering the
`arrangement 28' in the y-z plane.
`Having described the way in which light from source
`64 as well 64’ is directed into the light pipe 14 by means
`of the light directing assemblies 28 and 28', attention is
`now directed to the way in which backlighting light
`pipe 14 in cooperation with pyramid microprism ar
`rangement 36 acts on the input light to provide output
`backlighting 38. To this end, reference is directed to
`FIG. 3 which gives a cross sectional view of light pipe
`14 in the x-z plane. Since light propagating in the y-z
`plane is similar to light propagating in the x-z plan,
`because of the symmetry in the arrangement of pyramid
`microprisms, the following discussion also applies to
`light from light directing assembly 28’ propagating in
`the y-z plane. For purpose of this discussion, it will be
`assumed that the maximum divergence angle at which
`light enters the backlighting light pipe is i20°, as de
`
`45
`
`60
`
`65
`
`MBI_001442
`
`

`

`15
`
`20
`
`25
`
`7
`picted in FIG. 3. In the particular embodiment illus
`trated in FIG. 3, each of the regular pyramids de?nes an
`angle of 100° between adjacent pyramids.
`Still referring to FIG. 3, note speci?cally the incom
`ing light beam 76 which deviates by —20° from the
`x-axis will be bent by one surface of a pyramid and then
`propagate in the direction 78 which deviates by + 10°
`from the normal 80. Light beam 82 which propagates
`nearly parallel to the x-axis will be bent by 80° and
`propagate in the direction 84 which deviates by — 10° "
`from the normal to surface 24. Light beam 86 which
`initially deviates by +20° from the x-axis will hit the
`underside of top surface 24 and then propagate down
`wards whereupon it will be re?ected by one surface of
`a pyramid in a way similar to light beam 76, thereby
`propagating upward at an angle of + 10° with the nor
`mal as indicated at 87. This process happens to all light
`beams making a positive angle with the x-axis. Simi
`larly, light beams propagating in the opposite direction
`will also propagate outward with a divergence of :10"
`re?ecting off a micropyramid. As a result, all of the
`light beams exiting the light pipe through top surface 24
`in the x-z plane will be collimated to one-half their
`original divergent angles, that it is, one-half the angles
`at which light enters the light pipe 14.
`In the particular example just described in conjunc
`tion with FIG. 3, it was assumed that the pyramids 42
`de?ne angles 100° between adjacent pyramids and that
`the incoming light does so within a divergence zone of
`120° with respect to the x-axis. For the purpose of
`coupling light into a light pipe, the pyramid array
`should have an angle determined by the allowed diver
`gence angle and the index of refraction of the light pipe.
`The pyramid arrays should have pyramid angles
`roughly equal to 90° plus the allowed divergence angle.
`For practical use, there is no restriction on the size and
`repeat distance of the pyramids as long as they can be
`conveniently manufactured, with the repeating distance
`smaller than the minimum resolving distance of human
`eyes, and can be properly applied for backlighting.
`40
`Nevertheless, it would be wise not to chose pyramid
`repeat distances close to the length of the pitches of a
`liquid crystal display, or their multiples, or dividers so
`that systematic effects on interference may be avoided.
`Now turning to FIG. 4, which illustrates the light
`pipe end 18 with a re?ection mirror layer 88 attached.
`A similar mirror layer is provided at end or side 22,
`although not shown in the ?gures. Since the light enter
`ing the light pipe 14 is collimated, a part of the light can
`propagate through the entire light pipe without interac
`tion with pyramid microprisms and reach the far end 18
`(as well end 22). The mirror layer 88 is intended to turn
`the light rays like ray 90 back to prevent them from
`leaking out as well as to improve uniformity of back
`lighting. Note that the mirror layer is slightly tilted
`toward the micropyramids. As a result, incident light
`rays such as ray 90 which propagate almost parallel to
`the x-axis will be bent downwards after re?ection by
`the mirror. In this way, light 38 exiting the light pipe
`does so more uniformly over the entire backlighting
`area, since otherwise more light 38 tends to leave the
`light pipe nearer to the ends 16 and 20 which are closer
`to the light sources than the ends 18 and 22 which are
`further away from the light sources.
`In the backlighting assembly 10 described in conjunc
`tion with FIG. 1, the output light 38 is provided for
`backlighting LCD displays which do not need highly
`collimated illumination and therefore require no special
`
`5,359,691
`8
`means to achieve collimation of output light in both the
`x and y directions. On the other hand, as described
`previously, in order to backlight some stacked liquid
`crystal displays, a highly collimated output light is de
`sired. FIG. 5 illustrates a backlighting assembly 10’
`designed to collirnate output light in two dimensions.
`The assembly 10' has all of its components identical to
`that of assembly 10 with the exception of its light colli
`mating assemblies 28" and 28"’ which differ somewhat
`from the corresponding light collimating assemblies 28
`and 28’. Light collimating assembly 28" and 28"’ in
`clude the same outermost con?guration as the corre
`sponding light collimating assemblies 28 and 28'. How
`ever, the prism in each of the assemblies 28" and 28”’ is
`divided into a series of longitudinally extending later
`ally adjacent sections or channels which extend from
`the input end of its light directing assembly to its output
`end and which are optically isolated from one another
`along substantially their entire lengths, whereby the
`individual channels or sections act on incoming light
`substantially independent of one another. The collimat
`ing process inside the individual light directing channels
`will be described in detail. Again, since both assemblies
`28" and 28"’ are constructed in the same way, the fol
`lowing description is referred to assembly 28" only.
`For light rays in the x-z plane, collimating process
`inside light collimating assembly 28" is identical to that
`of assembly 28, as illustrated in FIG. 2. As is described
`earlier, the top and the bottom surfaces 50 and 52 of
`each light directing section 62 is constructed with a
`certain tilt angle to accomplish collimating in the x-z
`plane, as illustrated in FIG. 2. However, in the assembly
`28", the multi-channel light pipe con?guration provides
`in addition the ability of collimating light in the x-y
`plane. Attention is now directed to the way in which
`the light enters each of these individual light directing
`sections in the x-y plane, as is illustrated in FIG. 6A. In
`this plane, as in the x-z plane, light will enter the colli
`mating assembly at the entrance end 58 with a divergent
`angle determined by the index of refraction of the mate
`rial that the collimating assembly is made of. This maxi
`mum divergent angle, 43° if the collimating assembly is
`made of acrylic, is usually much greater than the tolera
`ble maximum angle. In order to reduce the maximum
`divergent angle, opposing sides 54 and 56 of each light
`collimating section include appropriate coating 92, for
`example, for limiting the critical angle of total internal
`re?ection within the light directing sections to the value
`of the desired maximum divergent angle, discussed in
`conjunction with FIG. 2. Thus, the light rays entering
`each light collimating section within the allowed diver
`gence angle, for example rays 94 and 96, will be re
`?ected by total internal re?ection from the surface with
`coating 92, passing through the collimating section
`without loss in intensity. On the other hand, light rays
`entering each light directing section at angles outside
`the desired divergence angle, for example light ray 98,
`will be transmitted into the coating layer 92, reaching
`the painted outer surface of the coating and being ab
`sorbed there. As a result, substantially all of the light
`that propagates across each light collimating section
`will be collimated in the x-y plane to the desired degree
`of collimation. The maximum divergence angle, below
`which a light ray can pass through the collimating sec
`tion without any loss, is determined by 90°-arcs in
`(ml/n2), where n1 and 1123.1'6 refractive indices of coating
`92 and the prism 62. In the case of the exempli?ed coat
`ing 92, speci?cally an epoxy of n1 : 1.45, in combination
`
`45
`
`60
`
`65
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`MBI_001443
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`0
`
`35
`
`40
`
`45
`
`9
`with an acrylic prism 62, the maximum divergence
`angle is il3°.
`In the assembly 10’ in FIG. 5, the arrangement 28"’ is
`constructed in-the same way as the arrangement 28".
`Having the light ?eld collimated inside the light pipe,
`the micropyrarnids arrangement 36 will act in the same
`way described earlier, as illustrated in FIG. 3, to pro
`vide collimated backlighting‘38.
`FIG. 6B shows another embodiment which can also
`provide output light collimated to a certain degree in
`both dimensions (x-z and x-y). In this embodiment, the
`multichannel light directi