LGD_000742
`
`LG Display Ex. 1017
`
`

`
`U.S. Patent
`
`Dec. 17, 1996
`
`Sheet 1 of 9
`
`5,584,556 A
`
`FIG.
`
`7 PRIOR ART
`2
`2b
`
`3
`
`1.
`
`“ ;
`
`2d
`
`FIG. 2
`2
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`2b
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`3
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`2d
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`4
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`5
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`2c
`
`<2
`
`1
`
`2a
`
`9
`
`28
`
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`
`FIG. 3
`
`11
`
`2
`
`9
`
`4
`
`5
`
`LG D_000743
`
`LGD_000743
`
`

`
`U.S. Patent
`
`Dec. 17, 1996
`
`Sheet 2 of 9
`
`5,584,556
`
`FIG. 4
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`<
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`2
`
`1
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`3
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`4
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`5
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`FIG. 6
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`2
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`1
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`LG D_000744
`
`LGD_000744
`
`

`
`U.S. Patent
`
`Dec. 17, 1996
`
`Sheet 3 of 9
`
`5,584,556
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`FIG. 7
`
`2
`
`Q
`
`2
`
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`3
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`
`FIG. 9
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`FIG. 70
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`6b
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`6b
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`4
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`9
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`2
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`9
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`LG D_000745
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`LGD_000745
`
`

`
`‘US. Patent
`
`Dec. 17,1996
`
`Sheet4of9
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`.
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`5,584,556
`
`FIG. 77
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`2a
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`
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`1
`
`23
`
`1
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`2c
`
`LG D_000746
`
`LGD_000746
`
`

`
`U.S. Patent
`
`Dec. 17, 1996
`
`Sheet 5 of 9
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`5,584,556
`
`ms“ ‘
`
`2
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`128
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`3
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`LG D_000747
`
`LGD_000747
`
`

`
`U.S. Patent
`
`Dec. 17, 1996
`
`Sheet 6 of 9
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`5,584,556
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`2b
`
`3
`
`2d
`
`1
`
`2a
`
`2c
`
`
`
`.
`
`FIG. 20
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`LG D_000748
`
`LGD_000748
`
`

`
`U.S. Patent
`
`Dec. 17, 1996
`
`Sheet 7 of 9
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`5,584,556
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`/-70. 23
`
`2
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`<3 E317“/CS3
`
`FIG. 24
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`2
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`FIG. 25
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`H6. 26
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`LG D_000749
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`LGD_000749
`
`

`
`U.S. Patent
`
`Dec. 17, 1996
`
`Sheet 8 of 9
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`5,584,556
`
`FIG. 27
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`LG D_000750
`
`LGD_000750
`
`

`
`U.S. Patent
`
`Dec. 17, 1996
`
`Sheet 9 of 9
`
`5,584,556
`
`F/G. 30
`
`17
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`17a
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`15a
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`15
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`LGD_000751
`
`LGD_000751
`
`

`
`1
`SURFACE LIGHT SOURCE DEVICE
`
`5,584,556
`
`2
`
`member has a disadvantage in that the light will shine at
`their corners.
`
`BACKGROUND OF THE INVENTION
`
`SUMMARY OF THE INVENTION
`
`a) Field of the Invention
`
`This invention relates to a surface light source device to
`be used as a backlight for a liquid crystal display unit.
`b) Description of the Prior Art
`FIG. 1 shows a conventional surface light source device
`that has a light-conducting member. This device comprises
`a linear light source 1, such as a cold-cathode fluorescent
`tube, a light-conducting member 2 that has an edge surface
`of incidence 2a disposed adjacent the light source 1, a
`diffusion plate 3 that is located on or adjacent a front surface
`2b (a top surface in FIG. 1) of the light-conducting member
`2, and a reflective surface that is disposed adjacent a rear
`surface 2c (a lower surface in FIG. 1) of the light conducting
`member 2. In this surface light source device, an incident
`light from the source 1 is directed toward the edge surface
`of incidence 2a of the light-conducting member 2. The
`light-conducting member 2 conducts the light
`toward a
`rearward edge surface 2d by total internal reflection from the
`surfaces 2b and 2c.
`
`In the conventional device, however, the surface 2c of the
`light-conducting member 2 is provided with either a rough-
`ened surface or spots 2e formed by painting to scatter part
`of the conducted light, in such a way that part of the light,
`while travelling toward the surface 2d, spreads out from the
`surface 2b without being reflected by the surface. Thus, in
`the surface light source device of FIG. 1, when the rear
`surface 2c of the light-conducting member 2 has a rough
`surface or forms an array of spots 2e, as shown in FIG. 1, so
`that, while the incident light from the source 1 is advanced
`passing through the light-conducting member 2, part of this
`light spreads out from the surface 212 and then passes through
`the dilfusion plate 3 to form a diffused light, which is
`available for use as a surface light source.
`In this surface light source device, it is necessary to ensure
`that the diffused light that has passed through the diffusion
`plate 3 should appear uniformly over an entire surface of the
`diffusion plate 3.
`Also, because this surface light source device can be used,
`for example, as a back-light of a liquid crystal display, this
`requires the diffused light to be bright enough for such an
`application. Thus, the surface light source device is provided
`with means to increase the brightness.
`Typical surface light source devices of the prior art that
`have means to increase the brightness, are disclosed in
`Japanese Patent Kokai Publication No. 3—l89679A and
`Japanese Utility Kokai Publication No. 3-3l782A. Like the
`device of FIG. 1, each of these devices comprises a light
`source, a light-conducting member, a diffusion plate and a
`reflective plate. The surface 20 of the light-conducting
`member 2, which is opposite to the front or emitting surface
`2b, i.e. the surface 2c adjacent to the reflective surface 4,
`forms a large number of minute pyramids which are
`arranged concavely or convexly to increase the brightness
`on the diffusion plate. Various sizes of these pyramids are
`arranged according to the area chosen to produce a uniform
`brightness distribution.
`These prior art devices, however, have a problem in that,
`although it is possible to increase the brightness if the
`pyramid has a relatively large surface area, it is diflicult to
`produce a uniform brightness distribution on the diffusion
`plate 3. Also, the pyramid formed on the light-conducting
`
`An object of this invention is to provide a surface light
`source device comprising a planar light-conducting member
`of transparent material, a linear light source which is located
`adjacent at least one edge surface of the light-conducting
`member, a diffusion plate located on the front surface of the
`light-conducting member, and a reflective surface disposed
`on or adjacent
`the rear surface of the light-conducting
`member, characterized that the rear surface of the light-
`condueting member has a multiplicity of minute projections
`or depressions formed thereon and that these projections or
`depressions have rought surfaces.
`The rough surface has a multiplicity of microscopic
`projections and depressions, and resembles the face of a
`sand-paper in a configuration. The light reflected by, or
`transmitted through,
`the rough surface is scattered as a
`diflfused light. The greater the roughness of the rough surface
`is, the greater the extent of the diffusion of the scattered light
`is. The fact that
`the roughness is great means that,
`in
`considering the depth and the width of both the microscopic
`projection and depression, and the pitch of the projections
`and depressions in their vertical cross-section, when both the
`width and the pitch are constant, the depth is great, when
`both the depth and the pitch are constant, the width is great,
`and when both the depth and the width are constant, the pitch
`is small.
`
`Another object of this invention is to provide a surface
`light source device wherein various shapes and sizes of
`minute projections or depressions are formed on the rear
`surface of the light-conducting member, each of these pro-
`jections or depressions having a rough surface.
`A still another object of this invention is to provide a
`surface light source device wherein the rear surface of the
`light-conducting member has continuous cormgations, each
`of these corrugations having a rough surface.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a sectional view of a surface light source device
`of the prior art.
`FIG. 2 is a sectional view of a first embodiment of this
`invention.
`
`FIG. 3 is an enlarged section View of a light-conducting
`member used in the first embodiment.
`FIG. 4 is a section View of a second embodiment of this
`invention.
`
`FIG. 5 is an enlarged section view of a light-conducting
`member used in the second embodiment.
`
`15
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`20
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`25
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`30
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`35
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`40
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`55
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`FIG. 6 is an enlarged section view of a light-conducting
`member used in a third embodiment of this invention.
`
`FIG. 7 is a sectional view of a variation of a light-
`conducting member used in the third embodiment.
`FIG. 8 through FIG. 10 are views of variants of a
`light-conducting member shown in FIG. 5 through FIG. 7,
`respectively.
`'
`
`60
`
`FIG. 11 is an enlarged section view of a light-conducting
`member used in a fourth embodiment of this invention.
`
`65
`
`FIG. 12 is an enlarged section view of a light-conducting
`member used in a fifth embodiment of this invention.
`
`FIG. 13 is an enlarged section view of a light~conducting
`member used in a sixth embodiment of this invention.
`
`LG D_000752
`
`LGD_000752
`
`

`
`3
`
`4
`
`5,584,556
`
`FIG. 14 through FIG. 16 are views of variants of a
`light-conducting member shown in FIG. 11 through FIG. 13,
`respectively.
`FIG. 17 is a sectional view of a seventh embodiment of
`this invention.
`FIG. 18 is a view of a variation of the seventh embodi-
`ment of this invention.
`
`FIG. 19 is a sectional view of an eighth embodiment of
`this invention.
`
`FIG. 20 is a View of the light-conducting member as
`viewed from its top (from its light-emitting side).
`FIGS. 21 and 22 are views of the curves of corrugations
`in the light-conducting member used in the eighth embodi-
`ment of this invention.
`
`FIG. 23 through FIG. 29 are views of variants of the
`light-conducting member used in the eighth embodiment of
`this invention, respectively.
`FIG. 30 is a view showing the configuration of a metal
`mold with rough surfaces that is used to form a light-
`conducting member having corresponding rough surfaces.
`FIG. 31 is a view of a pattern of rough surfaces.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`FIG. 2 is a sectional view of a first embodiment of a
`surface light source device of this invention. The device of
`FIG. 1 comprises a light source 1, a light-conducting mem-
`ber 2, a difiusion plate 3 and a reflective plate 4. A pair of
`the light source 1 are located adjacent to both ends 2a, 2a’ of
`the light-conducting member 2. A surface 2c of the light-
`conducting member 2, which is opposite to an emitting
`surface 2b, has a multiplicity of small depressions 5 formed
`thereon. Each of these depression a has a rough surface.
`In this first embodiment, because the surface 2c of the
`light-conducting member 2 has a large number of depres-
`sions 5, the direction of total reflection from the surface 2c
`will be altered by the depressions 5. Thus, if the size, shape
`and position of the depression 5 is appropriately selected, it
`is possible to produce a relatively uniform brightness dis-
`tribution on the diffusion plate 3. Further, due to the rough
`surface 11 formed on the depression 5, it is possible to make
`more uniform the brightness distribution.
`.
`FIG. 3 is an enlarged view of a light-conducting member
`2 for use in the first embodiment. This light-conducting
`member 2 has a number of conical-, or pyramidal-shaped
`depressions 5 formed thereon. If a multiplicity of conical or
`pyramidal depressions are formed and their size, shape and
`position is appropriately selected, it is possible to provide a
`uniform brightness distribution on the surface light source
`device.
`
`As shown in FIG. 2, this embodiment has a pair of light
`sources. However, if four units of light sources are used, one
`each on the surface 2b on four sides of the square-, or
`rectangular—shaped light-conducting member 2, it is possible
`to enhance the brightness of a surface light source device.
`Alternatively, only one light source may be adequate for a
`certain need.
`
`In this first embodiment, by increasing the number of light
`sources used and providing a light-conducting member with
`depressions, it is possible to provide a bright surface light
`source device. Also, by appropriately selecting the size etc.
`of the depressions,
`it
`is possible to produce a uniform
`brightness distribution.
`
`This embodiment has a disadvantage in that, as the
`depressions of the light-conducting member 2 have conical
`or pyramidal shape, only their apex or comers etc. will
`appear recognizably bright with emitted light.
`Throughout this embodiment as well as other embodi-
`ments that will be described hereafter, this invention has a
`major feature in providing depressions on the rear surface of
`the light-conducting member 2, as well as in the shapes etc.
`of these depressions. Thus, to enable clear understanding,
`these depressions and their shapes are shown in expanded
`form in the drawings. In practice, however, the depression or
`projection has a size of about 0.1 to 1 mm.
`FIG. 4 is a sectional view of a second embodiment of this
`invention. This embodiment has a light source 1, a light-
`conducting member 2, a diffusion plate 3 and a reflective
`plate 4, in the same configuration as that of the surface light
`source device of FIG. 2. In this second embodiment, how-
`ever, as shown in FIG. 5, a surface 2c has hemispherical
`depressions 5 formed thereon. These depressions 5 are
`formed in a pattern such that the radius of curvature becomes
`the smallest for those which are located close to the light
`source 1 and gradually increases along the length of the
`surface 20.
`In this way, by providing a multiplicity of
`hemispherical depressions that have differences in the radius
`of curvature, it is possible to make uniform a brightness
`distribution on the diffusion plate 3, as can be achieved in the
`first embodiment. Also, the problem of a local shining can be
`overcome as hemispherical depressions are provided.
`In this embodiment, depressions on the surface 2c may be
`formed in a pattern such that they will have the increased
`depth along its length as they lie farther from the light source
`1, with the most shallow ones close to the light source 1.
`FIG. 6 is an enlarged sectional view of a third embodi-
`ment of this invention wherein a light-conducting member 2
`has differently shaped depressions 6, which are of cylinderi-
`cal form. The depressions 6 have the increased dimensions
`as they lie farther apart from the light source 1.
`In this embodiment, while FIG. 6 shows depressions 6
`having a change in the length t1 as well as depth t2, it is
`possible to achieve the same efl°ect by changing either the
`length t1 or the depth t2 alone.
`‘
`FIG. 7 is a sectional view of a variation of the third
`
`embodiment of the light-conducting member, shown in FIG.
`6, wherein the light-conducting member 2 has depressions
`of cylindrical form, whose innermost surface 6:: is spherical.
`Also, as shown in FIGS. 8, 9 and 10, a surface 2c of the
`light-conducting member 2 may have projections in place of
`depressions. These projections may be spherical, as shown
`in FIG. 8, or cylindrical, as shown in FIGS. 9 and 10. These
`projections have the increased dimensions as they lie farther
`from the light source 1.
`to make more uniform the
`In this third embodiment,
`brightness distribution on the diffusion plate 3, the projec-
`tions or depressions of the light-conducting member 2
`should preferably have rough surfaces on their surfaces 5a,
`6a, 5b, 6b, respectively. Further,
`the roughness of the
`surfaces should preferably become greater as they lie farther
`from the light source 1.
`FIGS. 11 through 13 are enlarged views of a light-
`conducting member for use in a fourth embodiment of this
`invention. In the first, second and third embodiments, the
`depressions used therein are of conical, pyramidal, or hemi-
`spherical form, etc. By contrast, the depressions shown in
`FIGS. 11 to 13 may be of any shape consisting of curves, and
`each of the depressions has a rough surface. Further, in
`FIGS. 12 and 13, the depressions have various sizes and
`
`5
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`10
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`15
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`20
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`25
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`30
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`35
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`40
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`45
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`50
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`55
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`60
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`65
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`LG D_000753
`
`LGD_000753
`
`

`
`5
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`6
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`5,584,556
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`depths. These depressions have different degrees of rough-
`ness. Thus, it is possible to cause the light to be uniformly
`emitted from the entire surface 2b.
`
`In the fourth embodiment of FIG. 11, a surface 2c of the
`light-conducting member 2 has depressions of the same
`shape and size that are equally spaced. This embodiment has
`a depression 10 with a rough surface 11 formed thereon. Due
`to the distribution of these rough surfaces 11,
`the light
`emitted from the surface 2b becomes uniform throughout the
`surface 217, thereby providing a uniform brightness distri-
`bution of a diffuse light that has passed through the diffusion
`plate 3. More particularly, the roughness of the surfaces 11
`becomes greater as they lie farther from an edge surface of
`incidence 2a.
`
`In this fourth embodiment of FIG. 11, because the surface
`2c of the light-conducting member 2 has a multiplicity of
`depressions 10, the light that is incident on the edge 2a is
`reflected from the depressions 10 and then emitted from the
`emitting surface 212. The emitted light passes through the
`diffusion plate 3 to form a diffuse light. The light that is
`incident on the surface 2a, but that is transmitted through the
`depressions 10 is reflected from the reflective plate 4 and
`re-enter into the light-conducting member 2. The reflected
`light is then emitted from the emitting surface 2}) and passes
`through the diffusion plate 3 to form a diffuse light. In this
`case, the light emitted from the light-conducting member 2
`tends to have the declining intensity with respect to its areas
`lying farther from the edge surface of incidence 2a. In this
`fourth embodiment having a distribution of depressions
`mentioned above, it is possible to provide a uniform bright-
`ness distribution.
`FIG. 12 is a sectional view of a fifth embodiment of a
`light-conducting member for use in this invention, wherein
`depressions 12 have different sizes in different areas. More
`particularly, while having the same depth, the depressions 10
`have the increased width as they lie farther from the edge
`surface of incidence. Due to the distribution of depressions
`as noted above, this embodiment provides a substantially
`uniform brightness distribution. In this embodiment, each of
`the depressions have substantially the same roughness.
`FIG. 13 is a sectional view of a sixth embodiment of a
`light-conducting member for use in this invention, wherein
`the light-conducting member 2 has depressions 13 with
`different depths in different areas. More particularly, depres-
`sions 13 have the increased depths as they lie farther from
`the edge surface of incidence. In this way, as with the
`light-conducting member of FIG. 12, it is possible to cause
`the light to be uniformly emitted from the entire emitting
`surface 2b.
`
`FIGS. 14, 15 and 16 are views of variants of the light-
`conducting member 2 of FIGS. 11, 12 and 13, wherein
`depressions 10, 12 and 13 are replaced by projections 10',
`12' and 13', respectively. The light-conducting member 2 of
`FIG. 14 has each of projections of the same size and shape.
`Also, the protrusions have different roughness in different
`areas, as in FIG. 11. By contrast,
`the light-conducting
`member of FIGS. 15 and 16 have projections 12' or 13' of
`different sizes in different areas.
`
`In the above-mentioned embodiments, it must be noted
`that the surface 2c of the light-conducting member 2 has
`depressions or projections each of which is symmetrical
`with respect to its vertical center line.
`FIG. 17 is a sectional view of a seventh embodiment of a
`light-conducting member, wherein the light-conducting
`member 2 has depressions 12 of asymmetrical form about
`the x—x line. This embodiment is accomplished in such a
`
`15
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`20
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`25
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`30
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`35
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`45
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`way that conical or pyramidal depressions of the light-
`conducting member 2 in the first embodiment of FIG. 3 are
`replaced by those of asymmetrical form. Alternatively, coni-
`cal or pyramidal projections may be replaced by those of
`asymmetrical form. Further, regarding the light-conducting
`member of FIGS. 11 through 13, symmetrical depressions
`may be replaced by those of asymmetrical form. Also,
`regarding the light-conducting member of FIGS. 15, 16 and
`17, projections shown therein may be replaced by those of
`asymmetrical form.
`FIG. 18 is a view of a variant of the light-conducting
`member of FIG. 17, wherein a surface 2c of the light-
`conducting member is of curved form. In the embodiments
`of FIGS. 17 and 18, the apexes 12a of the depressions 12
`should preferably have curved surfaces.
`In the first through seventh embodiments, noted above,
`the rough surfaces 11 are formed only on depressions or
`projections of the light-conducting member 2. However, the
`rough surfaces may be formed in portions between depres-
`sions or projections.
`FIG. 19 is a view of an eighth embodiment of a light-
`conducting member. In this embodiment, a surface 2c of the
`light-conducting member 2 has smooth, continuous corru-
`gations in all the directions along its surface. FIG. 19 is a
`sectional View of the light-conducting member taken in a
`direction of the arrow A—A of FIG. 20, which is a plan view
`of the member as viewed from its top. The section of the
`surface 2c in a direction of an arrow B—B, which is at right
`angles to the direction of the arrow A—A,
`is also of
`corrugation. Further,
`the section of the surface 2c in an
`oblique direction of the arrow C—C, set at an angle to the
`directions of the arrows A—A and B—B, has also a corru-
`gated one.
`In this eighth embodiment, the light that is directed onto
`the incidence surface 2a of the light-conducting member 2
`is totally reflected from the surfaces 217 and 2c as it travels
`toward the surface 2d. While traveling toward the surface
`2d, the light is totally reflected in different directions by the
`provision of corrugations. Also, part of the light is refracted
`by, and transmitted through, the corrugations.
`The transmitted light is reflected by the reflective plate 4
`and, after having been refracted by the corrugations,
`it
`re-enters
`into the light-conducting member 2 passing
`through the corrugations. Thus, a diffused light, i.e., the light
`that has emitted through the surface 2b and then passed
`through the diffusion plate 3 will appear substantially uni-
`form and in large amounts on the diffusion plate 3. The
`diffused light thus obtained is so uniform that there occurs
`no bright spots at all.
`In this embodiment, to provide a more uniform light on
`the diffusion plate 3, it will be effective that the corrugations
`have rough surfaces.
`In this embodiment, there occurs no bright spots at all
`because the surface 2c of the light-conducting member 2 has
`continuous corrugations in all directions, as noted above.
`Further, it is relatively easy to provide rough surfaces for the
`corrugations.
`Corrugations of FIG. 19 may be changed with respect to
`their size and shape etc. FIGS. 21 and 22 are views of the
`corrugation shape. The corrugation shape of FIG. 21 may be
`altered with respect to its various dimensions, such as height
`h, spacing between adjacent corrugations f, and incline of
`slope g, that is, angle 6 of FIG. 22.
`FIGS. 23 through 27 are views of variants of a light-
`conducting member for use in an eighth embodiemnt of this
`invention, wherein corrugations of different sizes and shapes
`etc. are provided in different locations.
`
`LG D_000754
`
`LGD_000754
`
`

`
`5,584,556
`
`7
`
`The light-conducting member 2 of FIG. 23 has corruga-
`tions with an increased height as they lie farther from the
`light source. Thus, a light is uniformly emitted through the
`surface 2b of the light-conducting member 2.
`In the light-conducting member 2 of FIG. 24, the surface
`2c has corrugations with an decreased spacing between
`adjacent corrugations as they lie farther from the light
`source. Thus, as in FIG. 23, a light
`is allowed to be
`uniformly emitted through the surface 2b of the light-
`conducting member 2.
`The light-conducting member 2 of FIG. 25 is intended for
`use in a surface light source device, wherein a pair of light
`sources 1 are placed adjacent both edge surfaces 2a and 2d
`of the light-conducting member 2. The surface 2c of the
`light-conducting member 2 has corrugations in such a way
`that their height at both edge surfaces 2a and 2d,
`is the
`lowest and it is the highest at
`the center of the light-
`conducting member 2.
`In the light-conducting member 2 of FIG. 26, the surface
`2c has corrugations with an increased angle 0 of the slope g
`as they lie farther from the light source. The angle 6 at the
`edge surface 2d is 45° to 60°.
`The light-conducting member 2 of FIG. 27 has an edge
`surface 2d opposite to an edge surface of incidence 2a, and
`the edge surface acts as a reflective surface. The light that is
`directed onto the edge surface 2a is reflected back from the
`opposite edge surface 2d after having reaching it. The light
`will not escape through the edge surface 2d. As a result, the
`region adjacent to a reflective plate 7 shines brightly and
`thus it is impossible to provide a uniform brightness distri-
`bution. To provide a uniform brightness, the light-conduct-
`ing member 2 of FIG. 27 has a surface 2c formed with
`corrugations in such way that their height is the lowest for
`those close to the edge surface 2a and it becomes gradually
`higher as they lie farther away from the edge surface 2a, and
`then their height becomes lower toward the edge surface 2d.
`The light-conducting member 2 of FIG. 28 is tapered in
`thickness. It has a thickest portion close to the light source
`and has an decreased thickness along its length. The tapered
`surface 2c has corrugations.
`The light-conducting member 2 of FIG. 29 is tapered in
`thickness toward its center where it has a thinnest portion. A
`pair of light sources are positioned adjacent opposite edge
`surfaces of the light-conducting member 2. A lower surface
`2c has corrugations.
`In the light-conducting member of FIGS. 23 to 29, noted
`above, it is possible to provide the corrugations with rough
`surfaces.
`
`Now, description will be made on means to form rough
`surfaces on a surface 2c of the light-conducting member in
`the first through eighth embodiments. The light-conducting
`member is generally made of transparent synthetic resins.
`Thus, a mold used in molding the light-conducting member
`of synthetic resins should have rough surfaces.
`To form rough surfaces on the mold, an electric—discharge
`machining (a spark erosion process) may be used for this
`invention. As a typical example, a light-conducting member
`2 requires to have a pattern with a multiplicity of tiny spots
`16, as shown in FIG. 31. The mold is prepared by a spark
`erosion process to form a corresponding pattern of spots.
`In this process, as shown in FIG. 30, an electrode 17 is
`maintained very close to a mold 15. The electrode 17 of male
`form has a large number of projections 17a that correspond
`to tiny spots 16 in FIG. 31. As shown in FIG. 30, the mold
`15 and electrode 17 are positioned in opposed relation. The
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`mold 15 is made to act as the other electrode so that the
`electric-spark machining is carried out. In this way, a surface
`15a of the mold 15 which is placed very close to the
`electrode 17 will be machined in areas facing the projections
`17a of the electrode 17 to form a desired pattern of the
`roughness on the rough surfaces. Typically, the electric-
`spark machining is made with the current of 3-7 A, and at
`a pulse duration of 5-20 microseconds. By changing the
`operating conditions of the electric—spark machining pro-
`cess,
`it
`is possible to provide different patterns of the
`roughness on the rough surfaces.
`When a multiplicity of dots are fonned on the projections
`or depressions of the rear surface 2c of the light conductive
`member 2 by printing in place of providing the rough surface
`on them, the extent of the diffusion of the scattered light is
`substantially the same as in the later ease. The fact that a
`number of the dots per unit area is great corresponds to that
`the roughness of the rough surface is great.
`We claim:
`
`1. A surface light source device comprising: a light-
`conducting member, a linear light source disposed adjacent
`to an edge surface of incidence of said light-conducting
`member, a diffusion plate disposed along a front surface of
`said light-conducting member, and a reflective surface dis-
`posed along a rear exterior surface of said light-conducting
`member opposite said dilfusion plate, said rear exterior
`surface comprising a plurality of depressions
`formed
`therein, said rear exterior surface comprising rough portions
`only in said depressions.
`2. The surface light source device of claim 1 wherein said
`depressions are of conical shape.
`3. The surface light source device of claim 1 wherein said
`depressions are of pyramidal form.
`4. The surface light source device of claim 1 wherein said
`depressions are of hemispherical form and have an increased
`size as they lie farther from said edge surface of incidence,
`with depressions of the smallest size being disposed close to
`said edge surface of incidence.
`5. The surface light source device of claim 1 wherein said
`depressions are of cylindrical shape and have an increased
`size as they lie farther from said edge surface of incidence,
`with depressions of the smallest size being disposed close to
`said edge surface of incidence.
`6. The surface light source device of claim 5 wherein the
`innermost surface of said depressions has a spherical form.
`7. The surface light source device of claim 1 wherein said
`depressions are identically shaped and sized and equally
`spaced and wherein said depressions have rough surfaces
`and the roughness of said rough surfaces become greater as
`said rough surfaces lie farther from said edge surface of
`incidence.
`
`8. The surface light source device of claim 1 wherein said
`depressions are identically shaped and wherein said depres-
`sions become larger as said depressions lie farther from said
`edge surface of incidence with the largest depressions lying
`close to said edge surface of incidence.
`9. The surface light source device of claim 1 wherein said
`depressions have an identical depth, but said depressions
`have an increased diameter as said depressions lie farther
`from said edge surface of incidence with the depressions of
`the smallest breadth lying close to said edge surface of
`incidence, and wherein said depressions have rough sur-
`faces.
`
`10. The surface light source device of claim 1 wherein
`said depressions have an identical diameter, but said depres-
`sions have an increased depth as said depressions lie farther
`from said edge surface of incidence with the depressions of
`
`LG D_000755
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`LGD_000755
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`5,584,556
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`9
`the smallest depth lying close to said edge surface of
`incidence.
`
`11. The surface light source device of any of claims 8, 9,
`or 10 wherein the roughness of said rough surfaces become
`greater as said rough surfaces lie farther from said edge
`surface of incidence.
`
`12. A surface light source device comprising a linear light
`source, a light-conducting member having an edge surface
`of incidence disposed adjacent to said light source, a diffu-
`sion plate disposed on a front surface of said light-conduct-
`ing member, and a reflective surface disposed on a surface
`of said light-conducting member opposite to said diifusion
`plate, said device comprising a multiplicity of corrugations
`formed on said surface of said light-conducting member
`close to said reflective surface, said corrugations having
`either curved surfaces or a combination of curved and planar
`surfaces continuously formed in all directions, and said
`corrugations having rough surfaces.
`13. The surface light source device of claim 12 wherein
`said curved surfaces have an increased height as said curved
`surface lie farther from said edge surface of incidence, with
`lowest ones lying adjacent to said edge surface of incidence.
`14. The surface light source device of claim 12 wherein
`said corrugations have a decreased spacing between adjacent
`corrugations as said corrugations lie farther from said edge
`surface of incidence and the ones with the largest spacing
`lying closest to said edge surface of incidence.
`15. The surface light source device of claim 12 wherein
`said corrugations have one of an increased and decreased
`incline between a crest and a base of a waveform as said
`corrugations lie farther from said edge surface of incidence,
`in such a way that the incline is about 45° to 60° for the
`corrugations lying at the farthest position.
`16. The surface light source device of claim 12 wherein
`roughness of said rough surfaces becomes greater as said
`rough surfaces lie farther from said edge surface of inci-
`dcnce.
`
`17. The surface light source device of claim 12 wherein
`said corrugations are varied by selecting and changing at
`least
`two factors from the group comprising a height,
`spacing, incline between a crest and base of a waveform and
`roughness of said rough surfaces.
`18. A surface light source device comprising a linear light
`source, a light-conducting member having an edge surface
`of incidence disposed adjacent to said light source, a light-
`reflective member placed on a surface of said light-conduct-
`ing member opposite to said edge surface of incidence, a
`diffusion plate disposed on an emitting surface of said
`light-conducting member, and a reflective surface disposed
`on a surface of said light-conducting member, opposite said
`diffusion plate said device further comprising corrugations
`formed on said reflective surface of said light-conducting
`member, said corrugations having one of curved surfaces
`and a combination of c