LGE_000694
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`LG Electronics Ex. 1013
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`U.S. Patent
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`Dec. 19, 1995
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`Sheet 1 of 2
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`5,477,422
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`LGE_000695
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`LGE_000695
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`U.S. Patent
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`Dec. 19, 1995
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`Sheet 2 of 2
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`5,477,422
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`Fig. 5.
`Fig. 6.
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`Fig. 7
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`LGE_000696
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`LGE_000696
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`1
`ILLUMINATED LCD APPARATUS
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`5,477,422
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`2
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`This is a continuation of application Ser. No. 08/062,933
`filed on May 17, 1993, abandoned.
`This invention relates to an illuminated liquid crystal
`display apparatus and specifically to a liquid crystal display
`(LCD) which is illuminated from behind.
`
`BACKGROUND OF THE INVENTION
`
`It is common practice to use a light guide (or so—called
`“light pipe”) behind an LCD to distribute light from one or
`more light sources, such as light emitting diodes (LED’s).
`The light guide is generally in the form of a plate-like
`member. Particularly in the case of a low-profile assembly,
`the LEDs are provided, for example, in a recess, at the side
`faces of the light guide. Light enters the light guide through
`the side faces and is distributed through the light guide by
`internal reflection. The front face of the light guide may be
`“roughened” to make it lossy so that light escapes into the
`LCD. The light guide thus acts to distribute light over a wide
`area of the LCD.
`
`However, when relatively few light sources are used,
`there is a tendency for the illumination to be uneven over the
`whole area of the LCD. Generally the light is more intense
`nearer to the LED’s and less intense further away.
`U.S. Pat. No. 4,975,808 discloses a liquid crystal display
`apparatus which aims to provide a more uniform distribution
`of light across a low-profile LCD. In this case the back face
`of the light pipe is selectively painted white. A pattern in the
`form of a border, half-sun and ovals around each lamp is left
`unpainted. The smooth unpainted surfaces of the light pipe
`internally reflect light that has an angle of incidence less than
`the critical angle. The white paint provides diffuse reflection,
`scattering the light. Some of this light escapes the light pipe
`and enters the LCD. The unpainted portion has the eifect of
`dimming the so-called hot spots caused by the proximity of
`the light-sources, and increasing the brightness in the
`painted area. While this arrangement goes some way to
`improving uniformity of illumination, it still leaves room for
`improvement. Moreover, the use of painted and unpainted
`reflected areas provides only limited scope for varying the
`relative intensity in the dimmer areas insofar as the intensity
`is enhanced equally in all painted areas and there is little or
`no control over the degree of intensity enhancement in the
`painted areas.
`
`SUMMARY OF THE INVENTION
`
`According to the present invention there is provided an
`illuminated liquid crystal display apparatus, comprising a
`liquid crystal display, at least one light source, a light guide
`comprising a transparent plate-like member having front,
`back and side faces disposed behind the liquid crystal
`display for distributing light from the light source over an
`area of the liquid crystal display, and light-attenuating means
`disposed adjacent the light guide and including discrete
`areas substantially filled with a pattern of dots for reducing
`the intensity of light reaching portions of the liquid crystal
`display nearest to the light source.
`A back-lit
`liquid crystal display (LCD) apparatus in
`accordance with the invention has the advantage that it is
`very simple and inexpensive to implement, it gives remark-
`ably uniform back illumination, and it offers the potential of
`varying the level of attenuation at would-be hot spots by
`altering the density and/or distribution of the dot pattern.
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`LGE_000697
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`It is noted here that in the present context the term “dot”_
`is not restricted to a small circular area and the expression
`“pattem of dots” is intended to include any discontinuous
`pattern of recurring features such as dashes, ovals, stars,
`squares or other shapes.
`The light-attenuating means may be a thin sheet provided
`against either the front or back face of the light guide. In the
`former case the sheet is translucent, and the dots are non-
`translucent (absorbing or reflective). In the latter case the
`sheet is reflective and the dots are non—reflective. Alterna-
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`tively a reflective layer may be coated directly on the back
`face of the light guide and the spots are formed by selective
`removal or omission of the coating. On the other hand a
`pattern of light-blocking dots may be formed directly on the
`front face of the light guide.
`In each of the four examples mentioned in the preceding
`paragraph the apparatus can be made very slim indeed. It
`will be clear that where the attenuating means is coated
`directly on the front or back face of the light guide that the
`additional space in the thickness direction is negligible.
`However, even when the attenuating member is formed as a
`sheet, the thickness of the sheet can be very small. For
`example the sheet may be a sheet of paper on which the
`pattern of dots is printed with conventional black ink.
`In one example the pattern of dots is substantially uni-
`form, i.e. all the dots have the same shape, size, and pitch.
`In another example the pattern of dots is graduated, i.e. the
`ratio of the black to white, or reflective area to non—reflective
`area, varies gradually so that the intensity of light reaching
`the LCD is reduced less as the distance from the light source
`increases.
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`BRIEF DESCRIPTION OF THE DILAWINGS
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`Embodiments of the invention will now be described, by
`way of example, with reference to the accompanying draw-
`ings, in which:
`FIG. 1 is a schematic cross-section of a liquid crystal
`display apparatus in accordance with the present invention;
`FIG. 2 is a plan view of the liquid crystal display
`apparatus in FIG. 1;
`FIG. 3 is a plan view of an attenuating member for use in
`the liquid crystal display apparatus in FIGS. 1 and 2;
`FIG. 4 is a schematic cross-section of a different liquid
`crystal display apparatus in accordance with the invention;
`FIG. 5 is a plan view of a different attenuating member;
`FIG. 6 is a plan view of a further attenuating member; and
`FIG. 7 is a plan view of another attenuating member.
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`DETAILED DESCRIPTION OF THE
`INVENTION
`
`The apparatus shown in FIG. 1 comprises a conventional
`liquid crystal display (LCD) 1 behind which is mounted in
`contiguous relationship a flat plate-like light guide 2 made,
`for example of acrylic.
`The front face of the light guide 2, i.e. the face adjacent
`the LCD 1, may be roughened in known manner to promote
`the escape of light into the LCD. A number of light emitting
`diodes (LED’s) 3 are provided along opposing side faces of
`the light guide for injecting light into the light guide. As can
`be seen in FIG. 2, a row of three LEDs is used on each of
`the two opposite side faces. The two sets of three LEDs are
`present in a respective recess 4 at the sides of the light guide
`2.
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`LGE_000697
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`5 ,477 ,422
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`Beneath the light guide 2, and in contiguous relationship
`therewith, there is provided a light attenuating member 5, in
`this case a thin sheet of reflective material, e. g. white paper,
`on which is printed in black ink a pattern of dots 6 as shown
`in FIG. 3. The pattern of dots includes two half-elipse shapes
`6 extending respectively from the edge of the attenuation
`sheet 5 adjacent the rows of LEDs 3.
`The half-ellipse shapes 6 are each filled with a regular
`array of equally sized and equally spaced dots printed with
`a conventional black printing ink. The pattern of dots may,
`for example, be printed using a laser printer or a bubble jet
`printer. These two dot patterns reduce the overall level of
`reflection at the back face of the light guide at the two
`half-elliptical areas. This has the effect of attenuating the
`amount of light which escapes from the light guide 5 into the
`LCD 1 at the corresponding areas. Hence a more uniform
`illumination can be achieved over the whole area of the LCD
`1.
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`In practice the Applicant has found that the pattern of dots
`described here provides remarkable results in a low-profile
`LCD apparatus. Moreover, it transpires that the dot pattern
`is not critical. Thus if the pattern varies slightly, either across
`the width of the half—elliptical areas, or from product to
`product; or if the dot pattern is imperfect, e.g. some of the
`dots may be inadvertently omitted or poorly defined; it
`would appear that these defects have virtually no appre-
`ciable elfect on the performance of the attenuator and
`excellent uniformity of illumination is still achieved. On the
`other hand if it is desired to vary the degree of attenuation
`it will be evident that this can be done by varying the size
`and/or frequency of the dots, i.e. altering the proportion of
`black to white areas.
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`The whole LCD apparatus may be supported on a sub-
`strate such as a printed circuit board 7 in conventional
`manner.
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`In FIG. 4 there is shown a modification of the LCD
`apparatus described above. In FIG. 4 the same reference
`numerals are used to denote the corresponding parts as in the
`previous embodiment described with reference to FIGS. 1 to
`3. In this case the attenuating sheet 5 is provided between the
`LCD 1 and the light guide 2. The sheet 5 may be transparent
`(or translucent) and have a pattern of dots printed thereon as
`before. The dots themselves may either be reflective or
`absorbing, in either case they will help to prevent light
`escaping into the LCD at the patterned areas. The patterned
`areas on the attenuating member may be the same as those
`described in the previous embodiment with reference to
`FIG. 3.
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`It is noted here that the attenuating member need not be
`provided as a separate sheet but may be coated directly on
`the relevant surface of the light guide. Suitably the attenu-
`ating coating would be provided selectively on the light
`guide surface. Thus in the first embodiment the reflective
`coating would be provided on the back face of the light
`guide 2, and the pattern of dots would be provided by
`omitting or removing the coating to form the dots. In the
`configuration shown in the second embodiment however the
`coating would be selectively provided (or retained) only at
`the areas corresponding to the dot patterns.
`The dot patterns provided on the attenuating means may
`have a graduated, rather than a uniform distribution, so as to
`attenuate the light less severely at greater distances from the
`light source. Thus for example there is shown in FIG. 5 an
`alternative dot pattern which may be used for the attenuator
`5 in a LCD apparatus which is side lit as in the previous
`embodiments. Here dot patterns 6' comprise a number of
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`parallel bars extending transversely to the longitudial axis of
`the display. These bars provide progressively less attenua-
`tion the further they are away from the side edge of the
`attenuator 5'. This is achieved either by reducing the size or
`frequency of the dots from bar to bar.
`In FIG. 6 there is shown an attenuating member 50 for use
`where the illumination is provided by three LEDs 30 along
`one long side of the display and three further LEDs 30 along
`the opposite long side of the display. Each LED 30 has a
`respective half—elliptical pattern 60 of dots on the attenuator
`50 extending from the edge adjacent the respective LED 30
`towards the longitudial axis of the attenuator. As can be seen
`from FIG. 6 these dot patterns 60 provide gradually less
`attenuation as the distance from the LED 30 increases. This
`is achieved either by reducing the size or frequency of the
`dots.
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`In FIG. 7 there is a shown an attenuator 150 for use in an
`LCD apparatus where the LEDs are provided behind (rather
`than at the edge of) the light guide. In this case, six LEDs
`130 are provided behind the LCD, and six circular dot
`patterns 160 are provided on the attenuator 150, the central
`point of each circular dot pattern being registered with a
`respective LED 130. In this case each pattern of dots 160 is
`graduated radially around the area of the LEDs 130, again to
`provide less attenuation as the distance from the LED 130
`increases, and so provide uniform illumination over the
`whole LCD area.
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`It will be evident in view of the foregoing description that
`various modifications may be made within the scope of the
`present invention. In particular different patterns of dots may
`be used on the attenuator in different circumstances. The
`overall shape of the dot pattern may be varied to suit
`particular needs, as too may the size and frequency of the
`dots making up the pattern. In the case of the graduated dot
`pattern, the graduation may be continuous rather than step-
`wise, in which case the distinct bands visible in FIGS. 5-7
`would not be discernible. Finally,
`it is noted that
`light
`sources other than LEDs may be used for illuminating the
`LCD apparatus.
`What we claim is:
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`1. An illuminated liquid crystal display apparatus, com-
`prising:
`a liquid crystal display,
`a plurality of point light sources generally located behind
`the liquid crystal display,
`a light guide comprising a transparent plate-like member
`having side faces disposed behind the liquid crystal
`display for distributing light from the light sources over
`an area of the liquid crystal display, and
`light-attenuating means disposed adjacent the light guide
`and including a pattern of dots defining a distinct
`individual portion proximate each one of the point light
`sources and spaced from one another for reducing the
`intensity of light reaching portions of the liquid crystal
`display nearest to the individual point light sources.
`2. An illuminated liquid crystal display apparatus as
`claimed in claim 1, wherein the light-attenuating means
`comprises a reflective sheet and the dots provided thereon
`are non-reflective.
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`3. An illuminated liquid crystal display apparatus as
`claimed in claim 1, wherein the light-attenuating means
`comprises a reflective layer coated on the light guide, and
`the dots provided therein are non-reflective.
`4. An illuminated liquid crystal display apparatus as
`claimed in claim 1, wherein the light attenuating means
`comprises a translucent sheet and the dots provided thereon
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`LGE_000698
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`LGE_000698
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`are non-translucent.
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`5,477,422
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`claim 6, wherein the plurality of light sources are disposed
`adjacent at least one of the side faces of the light guide, and
`the pattern of dots is graduated linearly.
`8. An illuminated guide crystal display apparatus as
`claimed in claim 6, wherein the point light sources are
`provided behind the light guide, and the pattern of dots is
`graduated radially around the areas of the individual light
`sources.
`
`5. An illuminated liquid crystal display apparatus as
`claimed in claim 1 wherein the light attenuating means
`comprises a pattern of light-blocking dots.
`6. An illuminated liquid crystal display apparatus as
`claimed in claim 1, wherein the pattern of dots is graduated
`whereby the intensity of light reaching the liquid crystal
`display is reduced less as the distance from the light source
`increases.
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`7. An illuminated crystal display apparatus as claimed in
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`LGE_000699
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`LGE_000699