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`“rob [Ted_.5
`
`United States Patent
`
`[191
`
`[11] Patent Number:
`
`4,630,895
`
`[45] Date of Patent:
`Dec. 23, 1986
`Abdala, Jr. et a1.
`
`[54] LCD iIGHTGUIDE
`Julio Abdala, Jr., Miami; Bernard V.
`[75]
`Inventors:
`Camus, Tamarac, both of Fla.
`
`[73] Assignee: Motorola, Inc., Schaumburg, Ill.
`
`[21] Appl. No.: 741,912
`
`[22] Filed:
`
`Jun. 6, 1985
`
`Int. CU ...................................... GOZF 1/13
`[51]
`[52] U.S. Cl. ...................................... 350/345; 362/31;
`362/ 104; 362/297
`[58] Field of Search .................... 350/345; 362/31, 26,
`362/27, 297, 298, 301. 104
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`2,131,471
`9/1938 Carter ................................... 362/31
`
`2,341,658
`.. 362/297
`2/1944 Salani
`
`2,712,593
`7/1955 Merchant ..
`362/27
`2,965,749 12/1960 Hudson ............. 362/27
`
`2/1971 Shotwell ...........
`3,561,145
`362/26 X
`
`6/1973 Takeichi et al. .............. 362/27
`3.740.540
`
`.. 350/345 X
`4,059,916 11/1977 Tachihara et a1.
`................. 362/26 X
`4,258,643
`3/1981 Ishikawa et a].
`
`7/1981 Hehr ............................... 350/345 X
`4,277,817
`4,486,077 12/1984 Torresdal .............................. 362/31
`
`Primary Examiner—L. T. Hix
`Assistant Examiner—Brian W. Brown
`Attorney, Agent. or Firm—Martin J. McKinley; Joseph
`T. Downey; Donald B. Southard
`
`[57]
`
`ABSTRACT
`
`A backlighted diSplay system includes a liquid crystal
`display. a flat light guide behind the display, and light
`emitting diodes (LED’s). The light guide is a molded
`slab of clear polycarbonate material with two planes
`depressed into its rear surface. Four segmented border-
`ing surfaces are approximately arcuate in shape. The
`depressed planes,
`the segmented bordering surfaces,
`and the rear surface are coated with a reflective white
`paint. LED holders are integrally molded with the light
`guide. A central portion of the front surface is option-
`ally textured. The display system provides thin con-
`struction with even light distribution across the width
`of the display, low power consumption, and good out‘
`door visibility at dusk or dawn.
`
`18 Claims, 7 Drawing Figures
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`
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`Page 1 of 10
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`TOYOTA EXHIBIT 1011
`e
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`TOYOTA EXHIBIT 1011
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`

`

`US. Patent Dec. 23, 1986
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`Sheet 1 of4
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`4,630,895
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`
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`FIG.
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`1
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`10’
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`—PR|OR ART—
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`FIG. 2
`—PRIOR ART—
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`Page 2 of 10
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`

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`US. Patent Dec. 23, 1986
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`Sheet 2 of 4‘
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`4,630,895
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`

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`US. Patent Dec. 23, 1986
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`Sheet 3 of 4
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`4,630,895
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`

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`US. Patent Dec. 23, 1986
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`Sheet4of4
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`4,630,895
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`NORMALIZED
`INTENSITY
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`0 0 0 0 60 (PRIOR ART)
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`Page 5 of 10
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`1
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`LCD LIGHTGUIDE
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`prior art light guide any thinner, creates an unaccept-
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`able distribution of light which results in a wide discrep-
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`point on the front surface 12 and another point.
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`The problem is illustrated graphically in FIG. 7,
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`wherein the vertical axis 50 plots the normalized inten-
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`sity of light emitted from the front surface 12. The
`horizontal axis 52 plots the position (that the intensity is
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`measured at) along the sectional
`line 2—2 (FIG. 1).
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`Point 54 on horizontal axis 52 indicates the position of
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`the left-most light source 24, point 56 indicates the posi-
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`‘tion of the right most light source 26, and point 58 is a
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`position equidistant between the two light sources. The
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`graph is normalized, such that the intensity of position
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`54 and 56 is 1.0 (both sources are assumed to be of equal
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`intensity).
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`The curve indicated by dotted line 60 represents the
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`graph of a thin prior art light guide showing its distribu:
`tion of light intensity across the width of the light guide.
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`Specifically, the dip at point 62, being 70% below the
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`intensity at points 64 and 66,
`is unacceptable to the
`average viewer. Curve 60, also illustrates another disad-
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`vantage associated with thin prior art light guides, the
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`problem of “hot spots”. Hot spots are indicated at
`points 68 and 70 on curve 60 and are characterized
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`graphically as peaks in the curve.
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`Generally, prior art light guides are characterized by
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`light transmission inefficiency. To compensate for this,
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`incadescent lamps are used as light sources because they
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`emit more intense light
`than other light sources of
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`equivalent physical size. The use of the higher intensity
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`incadescent lamps, however, requires additional power
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`consumption, a disadvantage in electronic equipment
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`generally, but a particular difficulty in battery operated
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`equipment where power consumption is critical.
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`Furthermore, when using liquid crystal displays spe-
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`cial problems arise when attempting to view the display
`outdoors at dusk or dawn. At these times, atmospheric
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`conditions cause a shift in the ambient solar light spec-
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`trum towards the red. Because of the disportionately
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`greater amount of red light in the atmosphere at these
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`times, it would be advantageous to have a light source
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`that had a spectral output at a wavelength considerably
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`shorter than that of red light. Incadescent bulbs, with
`their characteristic white light output, are therefore not
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`well suited for dusk or dawn visibility. Filtering an
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`incadescent bulb would not provide a solution, because
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`filtering merely selectively eliminates a large portion of
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`the visible light spectrum,
`instead of increasing the
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`intensity of light at the desired wavelength.
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`SUMMARY OF THE INVENTION
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`It is an object of the invention to provide an im-
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`proved backlighted liquid crystal display system.
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`It is another object of the invention to provide a
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`backlighted liquid crystal display system that is very
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`thin, yet has an even distribution of back light intensity.
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`It is another object of the invention to provide a
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`backlighted liquid crystal display system that eliminates
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`the hot spots found in prior art display systems.
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`It is another object of the invention to provide a
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`backlighted liquid crystal display system that has lower
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`power consumption than prior art devices.
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`It is another object of the invention to provide a
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`backlighted display system that provides good visibility
`when operated at dusk or dawn.
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`BACKGROUND OF THE INVENTION
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`This invention relates to the field of display systems
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`and more particularly to backlighted liquid crystal dis-
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`play systems.
`Displays which are capable of forming images of
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`characters or patterns may be broadly broken down
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`into two different categories, active and passive. In
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`active displays, such as light emitting diode (LED)
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`displays, the images are composed of individual diodes
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`which emit their own light. Since active displays are
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`typically characterized by high power consumption,
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`the choice for low power applications, such as portable
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`calculators, watches, portable radios, and pocket pag-
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`is typically the passive display. An example of a
`ers,
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`passive display is the liquid crystal display (LCD).
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`Rather than emitting their own light, LCD images
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`merely reflect or absorb light, therefore, ambient sun
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`light or room light is normally required to view the
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`display. When the ambient light intensity is not suffi-
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`cient to illuminate the display, however, an internal
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`supplemental illumination means is typically provided.
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`In a simple supplemental illumination system one or
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`more light sources,
`typically incadescent lamps, are
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`placed behind or in front of the display. One of the
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`disadvantages of the simple supplemental illumination
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`system is the creation of “hot spots”. “Hot spots” are
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`areas of the display where the light intensity is consider-
`ably greater than in other areas. “Hot spots” result in
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`poor display readability. To correct the problem of “hot
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`spots” and to more evenly distribute the light coming
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`from the light sources, a light guide may be positioned
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`behind the liquid crystal display.
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`A prior art light guide is illustrated in FIGS. 1 and 2.
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`The light guide is normally made from a slab of trans-
`parent plastic material generally designated as 10 and
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`has an upper surface 12, a lower surface 14, and four
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`bordering surfaces 16, 18, 20 and 22. Light sources 24
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`and 26 are positioned respectively in notches 28 and 30
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`which are located at opposite ends of the slab 10. The
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`bottom surface 14 has two planes 32 and 34 depressed
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`into the bottom surface, thereby forming a V-shaped
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`wedge. The t0p surface 12 has two areas 36 and 38
`which are covered with a reflective coating. A reflec-
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`tive coating also covers the bottom surface 14, the de-
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`pressed planes 32 and 34, and the bordering surfaces 16,
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`18, 20 and 22 with the exception of notches 28 and 30
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`which remain transparent.
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`In operation, light emitted from the light sources 24
`and 26 travels the length of the light guide towards the
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`planes 32 and 34, strikes the reflective surface thereon,
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`and is reflected up through the transparent surface 12.
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`The liquid crystal display (not shown) is situated above
`front surface 12 and the light passing through the front
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`surface 12 also passes through the liquid crystal display,
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`thereby improving display visibility.
`Although this prior art light guide more evenly dis-
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`tributes light across the display then the simple supple-
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`mental illumination system, it also has several disadvan-
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`tages, one of which is its thickness. Thinness is ex-
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`tremely important
`in the design of small watches,
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`pocket calculators, pocket pagers, portable radios and
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`any other device in which small packaging size is para-
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`mount. An acceptable design of a 1.8 inch long prior art
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`guide may only be made as thin as 0.070 inches as mea-
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`sured at the thickest point. Any attempt to make the
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`Page 6 of 10
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`Still another object of the invention is to provide a
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`backlighted liquid crystal display system having a light
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`guide that can be manufactured as a one piece molded
`part.
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`Briefly,
`the invention comprises a display system 5
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`including a liquid crystal display and a light guide posi-
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`tioned behind the display. The light guide is made from
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`a transparent slab of material of substantially uniform
`thickness. The slab has a front surface adjacent the
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`display and an opposing rear surface. Six bordering
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`surfaces, substantially perpendicular to the front and
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`rear surfaces, complete the enclosure.
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`Two of the bordering surfaces are substantially mutu-
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`ally parallel and are located at opposite ends of the slab.
`The remaining four bordering surfaces are substantially
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`arcuate in shape.
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`The rear surface has two centrally located substan-
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`tially rectangular planes depressed into it. One edge of
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`each plane intersects the rear surface and the opposite
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`edges mutually terminate at a centerline substantially
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`equidistant between the parallel bordering surfaces and
`between the front and rear surfaces.
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`The arcuate bordering surfaces, the rear surface, and
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`the depressed planes have a light reflecting means.
`Light sources are located adjacent to each of the paral-
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`lel bordering surfaces.
`In another embodiment, the invention includes a liq-
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`uid crystal display and a light guide positioned behind
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`the display. The light guide is made from a transparent
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`slab of polycarbonate material of substantially uniform 30
`thickness. The slab has a centrally textured front surface
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`adjacent the display and an opposing rear surface. Six
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`bordering surfaces, substantially perpendicular to the
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`front and rear surfaces, complete the enclosure.
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`Two of the bordering surfaces are substantially mutu- 35
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`ally parallel and are located at opposite ends of the slab.
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`The remaining four bordering surfaces are approxi-
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`mately arcuate in shape and are segmented into a plural-
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`ity of substantially straight concatenated segments.
`The rear surface has two centrally located substan- 40
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`tially rectangular planes depressed into it. One edge of
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`each plane intersects the rear surface and the opposite
`edges mutually terminate at a centerline substantially
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`equidistant between the parallel bordering surfaces and
`between the front and rear surfaces.
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`The arcuate bordering surfaces, the rear surface, and
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`the depressed planes are provided with a light reflecting
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`means. Light emitting diodes are located adjacent to
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`each of the parallel bordering surfaces.
`In yet another embodiment, the invention includes a 50
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`liquid crystal display and a light guide positioned be-
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`hind the display. The light guide is made from a slab of
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`transparent polycarbonate material having a substan-
`tially uniform thickness of less than 0.050 inches. The
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`slab has a front surface adjacent the display and an 55
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`opposing rear surface. Six bordering surfaces, substan-
`tially perpendicular to the front and rear surfaces com-
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`plete the enclosure.
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`Two of the bordering surfaces are substantially mutu-
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`ally parallel and are located at opposite ends of the slab,
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`the remaining four bordering surfaces are segmented
`into first, second, third, and fourth substantially straight
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`and resPectively concatenated segments. Each of the
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`first segments forms an inside angle of substantially 130°
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`with the adjacent parallel bordering surface. Each of 65
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`the second segments forms an inside angle of substan-
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`tially 150° with the adjacent first segment. Each of the
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`third segments forms an inside angle of substantially
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`45
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`60
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`4
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`170" with the adjacent second segment. Each of the
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`fourth segments forms an inside angle of substantially
`165" with the adjacent third segment.
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`Green light emitting diodes and light emitting diode
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`holders are located adjacent to each of the parallel
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`bordering surfaces.
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`The front surface has a centrally located textured
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`area, untextured areas adjacent to each of the parallel
`bordering surfaces, and boundary lines between the
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`textured area and the untextured areas. The boundary
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`lines are parabolic in shape.
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`The rear surface has two centrally located substan-
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`tially rectangular planes depressed into it. One edge of
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`each plane intersects the rear surface and the opposite
`edges mutually terminate at a centerline substantially
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`equidistant between the parallel bordering surfaces. The
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`angle between the two planes is substantially 172°.
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`The segmented bordering surfaces, the rear surface,
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`and the two depressed planes have a light reflecting
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`means.
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`BRIEF DESCRIPTION OF THE DRAWINGS
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`FIG. 1 is a plane view of the transparent front surface
`of a prior art light guide.
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`FIG. 2 is a sectional view of the prior art light guide
`of FIG. 1, taken along the line 2—2 of FIG. 1.
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`FIG. 3 is a plane view of the light guide of the pre-
`ferred embodiment of the present invention as viewed
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`from the transparent front surface.
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`FIG. 4 is a sectional view of the light guide 0 f FIG.
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`3, taken along the line 4—4 of FIG. 3.
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`FIG. 5 is a schematic light ray analysis of a portion of
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`the light guide of FIG. 3, as viewed fro m the transpar-
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`ent front surface.
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`FIG. 6 is a schematic ray analysis of a cross section of
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`the light guide of FIG. 3, taken along line 6—6 of FIG.
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`5.
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`FIG. 7 is a graph of light intensity versus distance
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`along the dimension line between the sources of the
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`light guide. Curves are shown for a prior art light guide,
`the light guide of the preferred embodiment, and the
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`preferred light guide with the optional central textur-
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`mg.
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`DETAILED DESCRIPTION OF THE
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`PREFERRED EMBODIMENT
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`Referring now to FIGS. 3 and 4 wherein the pre-
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`ferred embodiment of the light guide of the present
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`invention is illustrated. The light guide is manufactured
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`from a transparent slab 100, preferably made from
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`LEXAN 141 clear polycarbonate (LEXAN is a trade-
`mark of the General Electric Corporation). Although
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`LEXAN 141 is the preferred material for the light
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`guide, other materials such as clear acrylic are also
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`suitable. Clear acrylic has better optical properties than
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`polycarbonate but LEXAN 141 has superior molding
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`properties.
`Slab 100 has a front surface 102 adjacent to the liquid
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`crystal display and a rear surface 104 opposite the front
`surface. The slab 100 has six bordering surfaces 106,
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`108, 110, 112, 114 and 116 which are substantially perv
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`pendicular to the front and rear surfaces. The two bor-
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`dering surfaces 106 and 108 are mutually parallel and
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`contain indentations 118 and 120 for aligning light
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`sources 122 and 124 respectively. The remaining four
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`bordering surfaces 110, 112, 114 and 116 have an ap-
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`proximate arcuate shape but are each preferrably com-
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`prised of the concatenation of four straight segments,
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`Page 7 of 10
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`

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`6
`reflective coating. Segments 126, 128, 130 and 132 are
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`optimally positioned to reflect into the image area 200
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`the maximum number of the light rays emitted from any
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`direction of the light source 122.
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`Specifically, light ray 204 is emitted from light source
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`122 whereupon its strikes segment 126 at point 206 and
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`is reflected into the image area 200. Light ray 208 is
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`illustrative of a ray that strikes the reflecting surfaces 3
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`times before being reflected into the image area 200.
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`Ray 208, is emitted from light source 122 and strikes
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`segment 126 at point 210 whereupon it is reflected to
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`segment 128 at point 212. At point 212 it is reflected to
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`line segment 132 at point 214 whereupon it is reflected
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`into the image area 200. Light ray 216 is emitted from
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`light source 122 and strikes segment 128 at point 218
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`whereupon it is reflected into the image area 200. Light
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`ray 220 is emitted from light source 122 whereupon it
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`strikes segment 128 at point 222 and is reflected into the
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`image area 200. Light ray 224 is emitted from light
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`source 122 whereupon it strikes segment 130 at point
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`226 and is reflected into the image area 200. Likewise,
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`light ray 228 is emitted from light source 122 where-
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`upon it strikes segment 130 at point 230 and is reflected
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`into the image area 200.
`The law of total internal reflection is well known in
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`the art and states that under certain conditions a light
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`ray impinging upon a transparent surface will be totally
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`reflected from that surface if the angle of incidence is
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`more than the critical angle. The critical angle is a func-
`tion of the difference between the index of refraction of
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`the two media (slab material and air). The behavior of
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`three light rays in the vertical plane of the slab is illus-
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`trated in FIG. 6. Light ray 300 is emitted from light
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`source 122 and strikes the reflective area 152 of upper
`surface 102 at points 302 and 306 and also the reflective
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`rear surface 104 at points 304 and 308. At all these
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`points, 302, 304, 306, and 308,‘ the light ray 300 is re-
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`flected according to the well known principle that the
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`angle of incidence equals the angle of reflection. After
`being reflected from the lower surface 104 at point308,
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`the light ray strikes the upper surface 102 at point 310.
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`At point 310 the angle of incidence is less than the criti-
`cal angle so the light ray passes through the transparent
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`surface 102 and through the liquid crystal display (not
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`shown, but located ab0ve the slab 100).
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`Light ray 312 originates from light source 122 and
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`strikes reflective area 152 of upper surface 102 at point
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`314 whereupon it is reflected down to the lower reflec-
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`tive surface 104 at point 316. At point 316, light ray 312
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`is reflected up to the transparent upper surface 102 at
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`point 318. At point 318, the angle of incidence is greater
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`than the critical angle, so light ray 312 is. reflected back
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`down towards the lower surface, wherupon it strikes
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`the depressed plane 144, also having a reflective coat-
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`ing, at point 320. At point 320 light ray 312 is again
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`reflected up towards the upper surface 102, whereupon
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`it strikes the upper surface 102 at point 322. Again the
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`angle of incidence is greater than the critical angle, so
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`light ray 312 is reflected down and strikes depressed
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`plane 144 at point 322 whereupon it is reflected up
`towards upper surface 102. Light ray 312 strikes upper
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`surface 102 at point 326, however, this time the angle of
`incidence is less than the critical angle so light ray 312
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`passes through upper surface 102 and through the liquid
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`crystal display (not shown).
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`Light ray 328 is emitted from light source 122 where-
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`upon it strikes reflective lower surface 104 at point 330
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`and is reflected up towards transparent upper surface
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`5
`such as 126, 128, 130 and 132. Bordering surfaces 112,
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`114 and 116 are also preferrably comprised of four con-
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`catenated straight segments as illustrated in FIG. 3,
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`although the—segments are not labeled.
`In the preferred embodiment segment 126 and bor-
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`dering surface 106 intersect at an inside angle 134 of
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`130°. Segments 128 and 126 intersect at an inside angle
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`136 of 150°. Segments 130 and 128 intersect at an inside
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`angle 138 of 170°. Segments 132 and 130 intersect at an
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`inside angle of 165°. Although bordering surfaces 110,
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`112, 114, and 116 are shown broken down into four
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`segments, these bordering surfaces may also be com-
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`prised of any number of concatenated line segments or
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`even a smooth are such as is illustrated by the broken
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`line 142 in FIG. 3.
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`Two planes 144 and 146 are depressed into the bot-
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`tom surface 104 as shown in FIG. 4. The angle between
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`the planes 148 is preferrably 172°. The thickness of the
`slab at the center line 150 is 0.015 inches. Reflective
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`material is applied to top surface 102 at areas 152 and
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`154, to bottom surface 104, to depressed planes 144 and
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`146, and to bordering surfaces 110, 112, 114, 116. Bor-
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`dering surfaces 106 and 108 may have a reflective coat-
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`ing but notches 118 and 120 remain transparent. Al-
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`though any reflective type of coating will suffice, a
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`white surface, such as is provided by a white paint, is
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`preferred because it not only reflects light but also scat-
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`ters light.
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`Two light source holders 156 and 158 are integrally
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`molded with the slab 100 and positioned on bordering
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`surfaces 106 and 108. The holders 156 and 158 are basi-
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`cally cup shaped, being open at the top 160 and 162 and
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`on the sides 164 and 166. The exact shape of the cups
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`will depend on the particular light sources 122 and 124
`utilized but they are generally designed to provide a
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`close fit between the light sources and the interior walls
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`of the holders 156 and 158. Four notches 168, 170, 172
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`and 174 are cut into the sides of the holders 156 and 158
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`such that the leads (not shown) of the light sources 122
`and 124 can be bent through the notches, thereby retain-
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`ing the light sources in their holders.
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`Optionally, a centrally textured area 176 bounded by
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`lines 178 and 180 may be utilized to improve the light
`distribution. The preferred shape for the boundary lines
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`178 and 180 is parabolic.
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`Referring to FIGS. 3 and 4, the dimensions of the
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`light guide of the preferred embodiment are substan-
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`tially as follows. The length of the light guide between
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`bordering surfaces 106 and 108 is 1.62 inches. The width
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`of the light guide along centerline 150 is 0.45 inches.
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`Segment 126 is 0.18 inches long; segment 128 is 0.25
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`inches long; segment 130 is 0.22 inches long; and seg-
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`ment 132 is 0.22 inches long. The thickness of the light
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`guide at its thickest point, not including the lamp hold-
`ers 164 and 166, is 0.45 inches, while at centerline 150
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`the light guide is 0.015 inches thick. The depressed
`planes 144 and 146 are each 0.40 inches wide, as mea-
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`sured along centerline 150, and 0.33 inches long as mea-
`sured along sectional line 4—4.
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`The operation of the light guide is illustrated in
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`FIGS. 5 and 6. FIG. 5 is a light ray analysis in the hori-
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`zontal plane of the light guide, while FIG. 6 is a light
`ray analysis in the vertical plane of the light guide of the
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`present invention. Referring to FIG. 5, the LCD image
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`area 200 is bounded by dotted line 202. This area is
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`generally rectangular in shape although only one quar-
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`ter of the total area is illustrated in FIG. 5. As previ-
`ously discussed, segments 126, 128, 130 and 132 have a
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`25
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`45
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`55
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`65
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`Page 8 of 10
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`Page 8 of 10
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`10
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`7
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`102 at point 332. Because the angle of incidence is
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`greater than the critical angle, the light ray 328 is re-
`flected back down towards reflective lower surface 104
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`at point 334. After striking the lower surface at point
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`334, light ray 328 is reflected back up towards transpar-
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`ent from; surface 102 at point 336. Again, because of the
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`angle of incidence is greater than the critical angle light
`ray 328 is reflected back down towards depressed plane
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`144 whereupon it strikes plane 144 at point 338 and is
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`reflected up towards transparent front surface 102 at
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`point 340. Again the angle of incidence is greater than
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`the critical angle and the ray is reflected back down
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`towards reflective depressed plane 144 at point 342
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`upon which it is reflected up towards transparent front
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`surface 302 to point 344. At point 344, however, the
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`angle of incidence is less than the critical angle so light
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`ray 328 passes through transparent front surface 102 and
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`through the liquid crystal display (not shown).
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`FIG. 7 shows the performance of various light
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`guides. The vertical axis 50 indicates the normalized
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`intensity of light being emitted from the front surface of
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`a light guide. Horizontal axis 52 plots the position (that
`the intensity is measured at) along a line drawn between
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`the two light sources, such as sectional line 4—4 in FIG.
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`3. Appropriate markings indicate the position of the left
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`most light source 54, the center of the light guide 58,
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`and the right most light source 56.
`The curve indicated by dotted line 60 represents the
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`performance of a thin prior a