United States Patent [191
`Ishikawa et a].
`
`US005779338A
`Patent Number:
`[11]
`[45] Date of Patent:
`
`5,779,338
`Jul. 14, 1998
`
`[54]
`
`[75]
`
`[73]
`
`[21]
`[22]
`
`[62]
`
`[51]
`
`[53]
`
`[56]
`
`SURFACE LIGHT SOURCE DEVICE
`
`Inventors: Tsuyoshi Ishikawa. Nerima-ku:
`Kayoko Watai. Hasuda: Kazuaki
`Yokoyama. Ageo. all of Japan
`
`Assignee: Enplas Corporation. Kawaguchi. Japan
`
`Appl. No.: 709,118
`Filed:
`Sep. 6, 1996
`
`Related US. Application Data
`
`Division of Ser. No. 290,087, Aug. 12. 1994, Pat. No.
`5.575.549.
`
`Int. Cl.6 ...................................................... .. F21V 8/00
`US. Cl. ............................................... .. 362/31: 362/27
`Field of Search ................................. .. 362/26. 27. 31
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`5/1995 DuNah et a1. .......................... .. 362/31
`5,420,761
`5,461,547 10/1995 Ciupke et a1,
`........ .. 362/31
`
`5.485.291
`1/1996 Qiao et a], . . . . . . . . . .
`. . . . .. 362/31 X
`5,485,354
`1/1996 Ciupke et a1, .......................... .. 362/31
`FOREIGN PATENT DOCUMENTS
`
`3/1991 Japan ,
`3-31782
`3-189679 8/1991 Japan .
`94802-1993 12/1993 Japan .
`Primary Examiner-Stephen F. Husar
`Attorney, Agent, or F‘irm—FinnegaI1~ Henderson. Farabow.
`Garrett & Dunner. L.L.P.
`[57]
`ABSTRACT
`
`A surface light source device using a light conducting
`member, in which a multiplicity of concave portions are
`formed on an opposite surface of a light emitting surface of
`the light conducting member and the concave portions are
`arranged to have speci?c shapes to obtain a bright surface
`light source with a uniform brightness. A light diffusing
`material is ful?lled within the concave portions of the light
`conducting member so that a more uniform brightness can
`be obtained in an easy manner.
`
`9/1994 Blonder et a1. ......................... .. 362/31
`5.349.503
`5,377,034 12/1994 Kojima et a1. ..... ..
`
`14 Claims, 13 Drawing Sheets
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`US. Patent
`
`Jul. 14, 1998
`
`Sheet 1 of 13
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`5,779,338
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`Jul. 14, 1998
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`US. Patent
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`Jul. 14, 1998
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`Jul. 14, 1998
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`Jul. 14, 1998
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`US. Patent
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`Jul. 14, 1998
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`Sheet 6 of 13
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`US. Patent
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`Jul. 14, 1993
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`Sheet 7 of 13
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`U.S. Patent
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`Jul. 14, 1993
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`Sheet 8 of 13
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`

`
`US. Patent
`
`Jul. 14, 1998
`
`Sheet 9 0f 13
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`5,779,338
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`US. Patent
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`Jul. 14, 1998
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`US. Patent
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`Jul. 14, 1998
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`Sheet 11 of 13
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`
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`
`US. Patent
`
`Jul. 14, 1998
`
`Sheet 12 0f 13
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`5,779,338
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`
`US. Patent
`
`Jul. 14, 1998
`
`Sheet 13 0f 13
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`5,779,338
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`5.779.338
`
`1
`SURFACE LIGHT SOURCE DEVICE
`
`This is a division of application Ser. No. 08/290087.
`?led Aug. 12. 1994. now US. Pat. No. 5.575.549.
`
`BACKGROUND OF THE INVENTION
`
`a) Field of the Invention
`The present invention relates to a surface light source
`device using a light conducting member.
`b) Description of the Prior Art
`FIG. 1 shows a construction of a conventional surface
`light source device using a light conducting member. This
`device comprises a light conducting member 11. a linear
`light source 12 arranged in the vicinity of one of edge
`surface 11a (light incident surface) of the light conducting
`member. a diffusion plate 13 located on or adjacent to a light
`emitting surface 11b of the light conducting member 11 and.
`a re?ective surface 14 disposed on or adjacent to an opposite
`side surface 11c of the light emitting surface of the light
`conducting member 11. In this surface light source device.
`a light emitted from the light source 12 is made incident
`upon the light incident surface 110 of the light conducting
`member 11. and then transmitted inside of the light con
`ducting member toward an opposite edge surface of the light
`incident surface 110. The light directed into the light con
`ducting member 11 in this manner is emitted from the light
`emitting surface 11b while being transmitted inside of the
`light conducting member 11. Then the light emitted from the
`light emitting surface 11b passes through the diffusing plate
`13 to form a diifused light. which is available for use as a
`surface light source.
`In such a surface light source device. a pattern of fine
`diffusing portion 20 is formed on the opposite side surface
`110 of the light emitting surface 11b of the light conducting
`member 11 in order to increase a light emitting ef?cient of
`the light which is made incident into the light conducting
`member 11. and to get a uniform brightness distribution on
`the diffusing plate 13. which allows to have a uniform and
`bright surface light source. The pattern is formed by printing
`or something like that with the aid of painting material
`having a light dilfusing function.
`Since such a surface light source device is used. for
`example. as a backlight for a liquid crystal display unit. it is
`required to produce a brighter light. However. the above
`explained conventional surface light source device cannot
`provide an enough brightness for such an application.
`Therefore. various means are suggested on such type of the
`surface light source devices to increase the brightness of the
`emitting light.
`As typical surface light source devices to which means for
`increasing the brightness is applied. there are disclosed in
`Japanese Patent Kokai Publication No. 3-189679 and Japa
`nese utility Kokai Publication No. 3-31782. In the conven
`tional surface light source devices disclosed in these
`publications. a large number of pyramid-shaped convex or
`concave portions are formed on the opposite side surface of
`the light emitting surface of the light conducting member in
`order to increase the brightness. Further. these convex or
`concave portions are arranged to be varied according to the
`area chosen to produce a uniform brightness distribution.
`The conventional devices. however. have a problem in
`that the amount of the emitting light of the device is larger
`in the area closer to the light source 12 and decreases as
`farther from the light source 12. so that a uni-form surface
`light source device cannot be obtained. Particularly. in case
`
`2
`that the light source 12 is provided only one of the edge
`surfaces of the light conducting member and the distance
`between the edge surface of the light source side and the
`opposite side edge surface is long. the difference of the
`amount of the emitting light between the area closer to the
`light source and the area far from the light source becomes
`extremely large.
`In order to solve this problem. there is suggested another
`surface light source device in which a light re?ecting
`member is provided on the edge surface opposite to the light
`incident edge surface of the light conducting member.
`However. in this device. the amount of the emitting light is
`decreased even in the area which is only a little far from the
`light re?ective member. Thus no good effect can be obtained
`by the light re?ective member and it is di?icult to get a
`uniform brightness distribution even from the newly sug
`gested light source device.
`Further. in the above-explained conventional devices. the
`light re?ected on the surfaces of the convex or concave
`portions formed on the opposite side surface of the light
`conducting member is directly emitted from the light emit
`ting surface. Therefore. the amount of the emitting light
`emitted from the portions of the light emitting surface
`corresponding to the convex or concave portions on the
`opposite side surface becomes large. so that there is a
`difference in brightness between the portions corresponding
`to the convex or concave portions and the other portions.
`which causes an unevenness of brightness.
`In order to solve this problem. it is suggested to arrange
`as a coarse surface on an inclined surface of the conical or
`polygonal pyramid»shaped concave portions. In such
`devices. the light arrived at the inclined surfaces of the
`concave portions is diffused by the coarse surface and
`therefore. it is possible to prevent that the brightness
`becomes partially large due to that the emitting light emitted
`from the portions corresponding to the concave portions is
`larger in comparison with the light emitted from the other
`portions.
`However. such devices are not in practice use. be cause it
`is difficult to make coarse surfaces on the in lined surfaces
`of the ?ne concave portions. each of whose diameter is
`extremely small. i.e. about 0.1-1.0 mm. Particularly. it is
`much more di?icult to control the coarse ratio of the inclined
`surfaces of the small concave portions to be uniform and
`obtain the ?rstly demanded coarse ratio. Therefore. even if
`the coarse surfaces can be arranged inclined surface of the
`concave portions. the coarse ratio would not become uni
`form and as demanded. and thus it would be difficult to
`obtain a uniform emitting light from the light conducting
`member.
`
`25
`
`30
`
`35
`
`45
`
`SUMMARY OF THE INVENTION
`An object of the present invention is to provide a surface
`light source device comprising a light conducting member
`made of transparent material. a linear light source which is
`located in the vicinity of at least one edge surface of the light
`conducting member. a diffusion plate located on a light
`emitting surface of the light conducting member. and a
`re?ective member disposed on the opposite side surface of
`the light emitting surface of the light conducting member.
`the opposite side surface of the light conducting member has
`a multiplicity of ?ne conical or polygonal pyramid-shaped
`concave portions formed thereon and top angles and inclined
`angles with respect to the opposite side surface of the
`concave portions are set within a given range to obtain a
`bright surface light source device with a uniform brightness
`distribution.
`
`55
`
`65
`
`LGE_001277
`
`

`
`5.779.338
`
`3
`Another object of the present invention is to provide a
`surface light source device comprising a light conducting
`member made of transparent material. a linear light surface
`which is located in the vicinity of at least one edge surface
`of the light conducting member. a diffusion plate located on
`a light emitting surface of the light conducting member. and
`a re?ective member disposed on the other surface opposite
`to the light emitting sluface of the light conducting member.
`a multiplicity of concave portions are provided on the
`opposite side surface of the light conducting member and the
`concave portions are ful?lled with a light diffusion material
`or a light scattering material.
`A still another object of the present invention is to provide
`a surface light source device in which a multiplicity of
`concave or convex portions are formed on the opposite side
`surface of the light conducting member. and the opposite
`side surface as a whole. on which the concave or convex
`portions are formed. is covered with a light diffusion mate
`rial or a light scattering material.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a schematic view showing a conventional
`surface light source device using a light conducting member:
`FIG. 2 is a schematic view depicting a ?rst embodiment
`of a surface light source device according to the present
`invention;
`FIG. 3 is a schematic view illustrating a shape of the
`concave portion formed on the light conducting member of
`the ?rst embodiment in an enlarged scale;
`FIG. 4 is a schematic view representing a second embodi
`ment of a surface light source device according to the
`present invention;
`FIG. 5 is a schematic view showing a shape of the
`concave portion formed on the light conducting member of
`the opposite side embodiruent in an enlarged scale;
`FIGS. 6 and 7 are schematic views depicting third and
`fourth embodiments of surface light source devices accord
`ing to the present invention;
`FIGS. 8 to 32 are schematic views illustrating the other
`embodiments in which the present invention is applied to
`light conducting members having various shaped concave or
`convex portions;
`FIGS. 33 to 40 are schematic views representing
`examples of light conducting members to which the present
`invention can be applied.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`FIG. 2 shows a sectional view of a ?rst embodiment of a
`surface light source device according to the present inven
`tion. In FIG. 2. the numerical reference 1 represents a light
`conducting member. 2 a linear light source. 3 a diffusion
`plate. 4 a re?ective plate and 8 represents another re?ective
`member. In this embodiment. there are provided a multi
`plicity of conical or polygonal pyramid-shaped concave
`portions 5 on an opposite side surfaces 1c of a light emitting
`surface lb of the light conducting member 1. One of the
`conical or polygonal pyramid-shaped concave portions 5 is
`illustrated in FIG. 3 in an enlarged scale. The conical or
`polygonal pyramid-shaped concave portion 5 has its cross
`section cut by a plane which extends in perpendicular to a
`longitudinal direction of the linear light source 2 and passes
`through the top portion 5a of the concave portion 5. as
`shown in FIG. 3. and the top angle or and the inclined angle
`B on the light source side of the concave portion are arranged
`to satisfy the following conditions.
`
`15
`
`25
`
`35
`
`45
`
`55
`
`65
`
`wherein the reference symbol 0 represents a value given by
`the formula shown in below when the light refracting index
`of the light conducting member is n.
`
`In the surface light source device according to the ?rst
`embodiment. the light emitted from the light source 2 is
`made incident upon a light incident edge surface In of the
`light conducting member 1 to be directed inside thereof and
`then transmitted A part of the transmitted light is made
`incident upon the inclined surfaces of the conical or polygo
`nal pyramid-shaped concave portions 5 on the light source
`side and then passes through the inclined surfaces to be
`directed to the light re?ecting surface of the re?ective
`member 4. A most of the light directed to the re?ecting
`member 4 is then re?ected there to be returned into the light
`conducting member 1 via the opposite side surface is
`thereof.
`When the light passes through the inclined surface of the
`concave portion 5 or the opposite side surface 1c of the light
`conducting member 1. the light is refracted there by and
`diffused by the coarse surface of the re?ective sheet 4. As a
`result. the light re?ected by the re?ective sheet is directed in
`all directions.
`FIGS. 4 andS show the second embodiment of the surface
`light source device according to the present invention. In the
`second embodiment. the device is so designed that the
`thickness of the light conducting member 1 is larger on the
`light incident edge surface and smaller on the other edge
`surface side. and the opposite side surface 1c of the light
`conducting member 1 is inclined with respect to the light
`emitting surface lb. Further. as shown in FIG. 5. the shape
`of the conical or polygonal pyramid-shaped concave portion
`5 is arranged such that the inclined angle [3 of the inclined
`surface thereof with respect to the plane which is parallel to
`the light emim'ng surface 1b of the light conducting member
`1 satisfies the conditions in below. That is to say. the angles
`alpha and beta of the concave portion 5 shown in FIG. 5
`satis?es the following conditions.
`
`By such arrangement of the shape of the concave portion
`5. the same effect as that of the ?rst embodiment also can be
`obtained in the second embodiment of the surface light
`source device having its construction shown in FIG. 4.
`FIG. 6 shows the third embodiment of a surface light
`source device according to the present invention. In this
`embodiment. on the opposite side surface 10 of the light
`conducting member 1 are provided the same conical or
`polygonal pyramid-shaped concave portions having the
`same shapes and the same dimensions; and the pitches
`therebetween are arranged to be larger in the light source
`side (the light incident edge surface side) and smaller as
`farther from the light source in order to obtain a compara
`tively uniform brightness distribution. Furthermore. these
`concave portions are ?lled with light diffusing material or
`light scattering material. Therefore. when the light transmit
`ted inside of the light conducting member 1 is re?ected by
`the concave portions 5 or re?ected by the re?ective member
`4 after passing through the concave portions 5. the light is
`diffused or dispersed in all directions. and thus a surface
`
`LGE_001278
`
`

`
`5.779.338
`
`5
`light source having an extremely uniform brightness distri
`bution can be obtained.
`The surface light source device according to the third
`embodiment can be easily manufactured by ful?lling the
`light di?tusing material or light scattering material within the
`concave portions 5.
`It is desired to use a foamed resin such as
`polyethyleneterephthalate. paints containing a powder of
`light re?ective material such as silica. titanium oxide. and
`barium sulfate. or synthetic resin for molding containing
`such re?ective material.
`The light di?iusing material or light scattering material
`can be ful?lled within the concave portions 5 of the light
`conducting member 1 as in the following manner. That is to
`say. the light diffusing material or light scattering material is
`firstly applied on the opposite side surface 10 of the light
`emitting surface 1b of the light conducting member 1 to
`ful?ll the light diffusing material or light scattering material
`Within the concave portions 5: and then. Wipe the material
`out from the opposite side surface 1c of the light conducting
`member 1. The alternative method is to mold a synthetic
`resin containing a light re?ective material by two color
`injection molding method. when the light conducting mate
`rial 1 is molded.
`FIG. 7 shows the fourth embodiment of a surface light
`source device according to the present invention. In the
`fourth embodiment. the opposite side surface 1c of the light
`conducing member 1. on which a multiplicity of conical or
`polygonal pyramid-shaped concave portions 5 are provided.
`is covered with the light diffusing material or the light
`scattering material.
`In the fOLI?h embodiment. since the opposite side surface
`10 of the light conducting member 1 as a whole is coated
`with the light diffusing material or the light scattering
`material. the light directed to the opposite side surface 1c out
`of the light being made incident into the light conducting
`member 1 is re?ected in all directions by the light diffusing
`material or the light scattering material. Therefore. in this
`embodiment. it is not necessary to provide a light re?ective
`member or a light re?ective sheet on the opposite side
`surface 10 side of the light conducting member 1. Further.
`since there is no space between the light conducting member
`1 and the light di?using material or the light scattering
`material. it is easier to design and manufacture the device in
`comparison with the third embodiment shown in FIG. 6. in
`which an air space exists between the surface 10 of the light
`conducting member 1 and the re?ective member 4.
`As shown in FIGS. 6 and 7. the surface light source
`devices according to the third and fourth embodiments are
`so designed that the conical or polygonal pyramid-shaped
`concave portions 5 having the same shape and the same
`dimension are formed on the opposite side surface 10 of the
`light conducting member 1 but the pitch of the concave
`portions 5 are varied as shown in these ?gures. It may be
`possible to form concave portions having the other shapes
`on the opposite side surface 10 of the light conducting
`member 1. In the surface light source devices disclosed in
`Japanese Utility Model Kokai Publication No. Hei 5-94802
`and in US. patent application (U.S. Ser. No. 07/982942).
`both of which are ?led by the present applicant. a light
`conducting member has ?ne concave or convex portions
`with various shapes on a surface opposite to a light emitting
`surface; and the inclined surfaces of the concave or convex
`portions are arranged to be coarse.
`In the following embodiments. the present invention is
`applied on the light conducting member. which is disclosed
`in Japanese Utility Model Kokai No. Hei 594802 or in US.
`
`20
`
`25
`
`35
`
`50
`
`55
`
`65
`
`6
`Ser. No. 07/982942. in which concave or convex portions 5
`having various shapes are formed on the opposite side
`surface 10 of the light conducting member 1 but a light
`dilfusing material or light scattering material is ful?lled in
`the concave portions or a light diffusing material or a light
`scattering material is coated on the surface of the light
`conducting member 1 as a whole instead of making coarse
`surface on the inclined surfaces of the concave or convex
`portions.
`In the embodiment shown in FIG. 8. a multiplicity of
`concave portions 5. whose shapes are not conical or polygo
`nal pyramid. are formed on the opposite side surface 10 of
`the light emitting surface lb of the light conducting member
`1. These concave portions 5 have the same shapes and the
`same dimensions and are arranged at the same pitch. And the
`light dilfusing material or the light scattering material 6 is
`ful?lled within these concave portions 5.
`In the embodiment shown in FIG. 9. the concave portions
`5 have the same shapes and are arranged in the same manner
`as those of the embodiment shown in FIG. 8. but the light
`diffusing material or the light scattering material 6 is coated
`on the opposite side surface 1c of the light conducting
`member 1 so as to cover the surface 1c as a whole.
`In the embodiment shown in FIG. 10. the concave por
`tions 5 formed on the opposite side surface 10 of the light
`conducting member 1 are arranged such that the heights
`(depths) of the concave portions 5 are constant and the areas
`of the openings of the concave portions 5 are smaller on the
`light source 2 side and become larger as farther from the
`light source 2. And. the light diffusing material or the light
`scattering material 6 is ful?lled within the concave portions
`5.
`In the embodiment shown in FIG. 11. the concave por
`tions 5 formed on the opposite side surface 1c of the light
`conducting member 1 have the same shapes and are distrib
`uted in the same manner as those of the embodiment shown
`in FIG. 10. but the surface 10 as a whole is coated by the
`light diffusing material or the light scattering matmial 6.
`In the embodiment shown in FIG. 12. the concave por
`tions 5 are formed on the opposite side surface 1c of the light
`conducting member 1 such that the areas of the openings of
`the concave portions 5 are the same but the heights (depths)
`are arranged to be smaller in the light source 2 side and
`become larger as farther from the light source 2; and the light
`diffusing material or the light scattering material 6 is ful?lled
`within the concave portions 5.
`In the embodiment shown in FIG. 13. the concave por
`tions 5 are arranged on the opposite side surface 10 of the
`light conducting member 1 in the same manner as that of the
`embodiment shown in FIG. 12. But. the opposite side
`surface 10 as a whole is coated by the light diffusing material
`or the light scattering material 6.
`In the embodiment shown in FIG. 14. each of the concave
`portion 5 formed on the opposite side surface 1c of the light
`conducting member 1 has a asymmetric shape. That is to say.
`each of the concave portion 5 is formed in an asymmetrical
`manner with respect to a direction X—X in FIG. 14. Further.
`the top portion 5a of each concave portion 5 is directed
`toward the linear light sources 2 and 2. As same as the above
`embodiments. the light diffusing material or the light scat
`tering material 6 is fulfilled within the concave portions 5.
`In the surface light source device shown in FIG. 14. linear
`light sources 2 are disposed on both edge surfaces (on the
`left side edge surface la and the right side edge surface 1d
`in FIG. 14). which are opposite to each other. Therefore. the
`tops Sa of the left side half of the concave portions 5 are
`directed to the left side and the right side half to the right side
`according to the center of the both edge surfaces la and 1d.
`
`LGE_001279
`
`

`
`5.779.338
`
`7
`In case only one linear light source 2 is arranged on one
`of the edge surfaces. each of the asymmetrical concave
`portions 5 should be arranged that the direction of the top 5a
`of the concave portion 5 is directed toward the same
`direction. i.e. the light source side direction.
`In the embodiment shown in FIG. 15. the concave por
`tions 5 formed on the opposite side surface 10 of the light
`conducting member 1 have the same shapes as those of the
`embodiment shown in FIG. 14 and are arranged in the same
`manner. but the opposite side surface 10 as a whole is coated
`by the light diffusing material or the light scattering material
`6
`In the embodiment shown in FIG. 16. the opposite side
`surface 1c of the light conducting member 1 is arranged to
`be concave and a multiplicity of ?ne concave portions 5 with
`asymmetrical shapes are formed on the concaved surface 1c.
`In this embodiment. two linear light sources 2. 2 are
`arranged in the vicinity of the both edge surface In and 1d.
`Thus the tops 50 of the concave portions 5 are directed
`toward the light sources 2 and 2 as well as the embodiments
`shown in FIGS. 14 and 15. And. the light diffusing material
`or the light scattering material 6 is ful?lled within the
`concave portions 5.
`In the embodiment shown in FIG. 17. the concave por
`tions 5 are arranged in the same manner as those of the
`embodiment shown in FIG. 16. but the opposite side surface
`1c of the light conducting member 1 as a whole is coated by
`the light di?using material or the light scattering material 6.
`In the embodiment shown in FIG. 18. the opposite side
`surface 10 of the light conducting member 1 is arranged as
`a concave surface and two linear light sources 2 and 2 are
`disposed on the both edge surface sides la and 1d of the light
`conducting member 1. In this embodiment. the concave
`portions 5 formed on the opposite side surface 1c have
`symmetrical conical or polygonal pyramid shapes in the
`same manner. Therefore. the openings of the concave por
`tions 5 are also arranged to be concave and thus the tops 50
`are actually directed toward to the light source sides. The
`light di?using material or the light scattering material 6 is
`ful?lled within the concave portions 5.
`In the embodiment shown in FIG. 19. the opposite side
`surface 10 and the concave portions 5 are arranged in the
`same manner as those of the embodiment shown in FIG. 18.
`but the opposite side surface 10 of the light conducting
`member 1 as a whole is covered with the light diffusing
`material or the light scattering material 6.
`In the following embodiments shown in FIGS. 20 to 27.
`the present invention is applied to the surface light source
`devices disclosed in US. Ser. No. 07/982942.
`In the embodiment shown in FIG. 20. a multiplicity of
`conical or polygonal pyramid-shaped concave portions 5 are
`formed on the opposite side surface 10 of the light conduct
`ing member 1. These concave portions 5 have the same
`shape and the same dimension and are arranged with a
`constant pitch. The light di?’using material or the light
`scattering 6 is ful?lled within the concave portions 5.
`In the embodiment shown in FIG. 21. the concave por
`tions 5 are formed on the opposite side surface 10 of the light
`conducting member 1 in the same manner as that of the
`embodiment shown in FIG. 20. however. the opposite side
`surface 10 as a whole is coated by the light diffusing material
`or the light scattering material.
`In an embodiment shown in FIG. 22. the shapes of the
`concave portions 5 are semi-spherical; and the radius of
`curvatures of the concave portions 5 are smaller on the linear
`light source 2 side and become larger as farther from the
`light source 2. The light diffusing material or the light
`scattering material is ful?lled within the concave portions 5.
`
`15
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`8
`In an embodiment shown in FIG. 73. the concave portions
`5 have the same shapes as those of the embodiment shown
`in FIG. 22 and are arranged in the same manner. but the light
`dilfusing material or the light scattering material 6 is coated
`on the opposite side surface 10 as a whole of the light
`conducting member 1.
`In an embodiment shown in FIG. 24. a cylindrical-shaped
`concave portions 5 are formed on the opposite side surface
`10 of the light conducting member 1 in such a manner that
`the diameter and the heights (depths) of the concave portions
`5 are arranged to be smaller on the linear light source 2 side
`and become larger as farther from the light source 2. The
`light diffusing material or the light scattering material 6 is
`fulfilled within the concave portions 5.
`In an embodiment shown in FIG. 25. the concave portions
`5 are formed on the opposite side surface 10 of the light
`conducting member 1 in the same manner as that of the
`embodiment shown in FIG. 24. but the light diffusing
`material or the light scattering material 6 coats over the
`opposite side surface 10 as a whole.
`In embodiments shown in FIGS. 26 and 27. the shapes of
`the concave portions 5 are almost the same as those of the
`embodiments shown in FIGS. 24 and 25. but the top surfaces
`5a of the concave portions 5 are arranged to be curved. The
`other constructions of these embodiments are the same as
`those of the previous two embodiments. respectively.
`In the following embodiments shown in FIGS. 28 to 32.
`the present invention is applied to some of surface light
`source devices disclosed in Japanese Utility Model Kokai
`Publication No. Hei 5-94802 and US. Ser. No. 982942. in
`which a multiplicity of depressions are formed on the
`Opposite side surface 1c of the light conducting member 1.
`In these embodiments. the projections (convex portions) are
`formed on the surface opposite to the light emitting surface
`of the light conducting member 1. and the light ditfusing
`material or the light scattering material 6 should be applied
`on the opposite side surface 1c as a whole so as to com
`pletely cover all over the depressions.
`In the embodiment shown in FIG. 28. the convex portions
`7 are formed on the opposite side surface 10 of the light
`conducting member such that the heights of the convex
`portions are shorter on the most light source 2 side and
`becomes higher as farther from the light source 2.
`In the embodiments shown in FIGS. 29 to 32. the present
`invention is applied to the surface light source device
`disclosed in US. Ser. No. 07/982942. In FIG. 29. the
`semi-sphen'cal-shaped convex portions are formed on the
`opposite side surface 1c of the light conducting member 1;
`and the radius of curvatures of the convex portions 7 are
`smaller on the light source 2 side and become larger as
`farther from the light source 2.
`In the embodiment shown in FIG. 30. the cylindrical
`shaped convex portions are formed on the opposite side
`surface 10 of the light conducting member 1. and the heights
`of the convex portions 7 are shorter on the light source 2 side
`and become higher as farther from the l