K.J. Pretech Ex. 1020
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`Pretech_000807
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`EP 0 500 960 A1
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`TECHNICAL FIELD
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`The present invention relates to a surface light source element used for a surface light source device, in
`particular, to a surface light source element which can be used as a back light device for a liquid crystal
`display element.
`
`TECHNICAL BACKGROUND
`
`Conventionally, a structure which comprises a tubular lamp as a light source located at the focal point
`of a paraboloid of revolution type of reflector and an opalescent diffusing plate located above the lamp, is
`generally used. Such a device is improved by adjustment of the shape of the reflector or of the diffusion
`coefficient of the diffusing plate.
`There exists a device having a combination of a tubular lamp and a light guide with a shape which is
`simulated by an approximation of a point-like source of light and is formed in the shape of the approximated
`curve so that lights in a direction are emitted, a device having a light guide the thickness of which varies
`along the advance direction of light, a device using a lenticular member having angles of prisms which vary
`according to the distance from a light source, and a device having a combination of these elements.
`Recently, surface light source elements have been used as liquid crystal display elements. However,
`the display device, which uses a conventional surface light source element to obtain a high quality display,
`requires a thick surface light source element. In particular, a surface light source element for a large display
`of 10 to 12 inches requires a thickness of 20 to 30 mm. Therefore,
`it is impossible to function as a thin
`surface light source element.
`Various edge-light types of surface light source devices have been proposed. Each of the devices has a
`transparent light guide comprising a plate-shape transparent material such as an acrylic resin. Light incident
`on an edge portion of the transparent light guide is then emitted from the upper or lower surface of the light
`guide. However, such a large liquid crystal display device with a size of 10 to 12 inches results in a display
`with darkness corresponding to the distance from the light source or an uneven display, so that a display of
`high quality cannot often be obtained.
`In order to solve this problem, a light guide having a thickness which varies according to the distance
`from a lamp, or a member which varies light path geometrically,
`is provided. However, such a member
`requires a precise processing to form a specific shape, and high processing costs. Furthermore,
`the
`member provides a low utilization rate of light.
`Recently, Japanese Patent Application Laid-open No. (Tokukai-Hei) 1-245220 discloses a surface light
`source element which is an edge-light type. The surface light source element has a light guide with a layer
`of a light diffusing material which is applied or adhered on the surface thereof opposed to a light emitting
`surface or on a light diffusing surface of a provided member. The density of the provided light diffusing
`material increases as the distance from the light incident portion increases. Japanese Patent Application
`Laid-open No. (Tokukai-Hei) 1-107406 discloses a surface illuminating device which can uniformly illuminate
`the whole surface of a light diffusing plate. The device has a plurality of piled transparent plates, each of
`which has a different pattern of fine dots (light diffusing material) thereon.
`Since a non-light-transmissive inorganic material (e.g., white pigment such as titanium oxide or barium
`sulfate) is used, a loss of light occurs to lower the luminance of the emitted light.
`Oe has reported a light diffusing device which comprises a light guide, a diffusing layer provided on the
`light guide through a layer having a middle characteristic between those of the light guide and the diffusing
`layer, and a light
`regulation member for obtaining a uniform emitting light on the diffusing layer,
`in
`Japanese Utility Model Application Laid-open No. (Jitsukai—Sho) 61—171001 and in United States Patent No.
`4729068.
`
`The inventors have proposed a surface light source element which is an edge-light type, as described
`in Japanese Patent Application Laid-open Nos. (Tokukai-Hei) 1-244490 and 1-252933. The element has a
`lens-like surface or a satin finished surface provided on at least one of a light emitting surface of a light
`guide and the opposed surface thereof, and a light regulation member having a light reflecting pattern which
`corresponds to the reciprocal of an emitting light distribution and a light diffusing plate provided on the
`emitting surface of the light guide.
`The light diffusing device and the surface light source element using the light regulation member show
`excellent effects regarding the uniformity of the emitted light. The device and the element, however, cannot
`reuse the light which is reflected by the emitting light regulating member, so that the luminance of the
`emitted light lowers near the minimum value of the luminance before regulation.
`The object of the present invention is to provide a very thin type of surface light source element which
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`Pretech_000808
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`Pretech_000808
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`EP 0 500 960 A1
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`can supply emitted light with a uniform and high luminance.
`
`DISCLOSURE OF THE INVENTION
`
`The surface light source element according to the present invention comprises a transparent light guide
`(1) which has a side end surface as a light incident surface, a surface perpendicular to the light incident
`surface as a light emitting surface, and a light reflecting layer provided on an opposed surface to the light
`emitting surface; and a diffusing member (2) for diffusing light from the light emitting surface of the
`transparent light guide; wherein at least one of the light emitting surface and the opposed surface of said
`transparent light guide has a directional light emitting function which radiates the incident light from the light
`incident surface of
`the transparent
`light guide in an oblique direction to the incident
`light and has a
`regulation function which makes the luminance of the light through the light emitting surface uniform over
`the whole surface thereof.
`
`light from the light emitting surface which is incident on the light guide
`the amount of
`Generally,
`decreases as the distance from the light incident surface increases due to light emitting through the light
`emitting surface and light absorption inside the light guide. In the surface light source element according to
`the present invention, the ratio of the flat areas increases as the distance from the light incident surface
`decreases. Therefore, even if the transparent light guide is thin,
`it
`is possible to emit light with a uniform
`luminance over the entire emitting surface on the basis of the incident
`light. The incident light
`into the
`transparent light guide is not wasted and has a high utilization rate. Consequently, it is possible to produce
`emitted light having a high luminance without
`increasing the wattage of the light source. Therefore, the
`present invention provides a very thin type of surface light source element which can supply an emitting
`light with a uniform and high luminance.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIGS.
`element.
`
`1
`
`(a) and (b) are sectional views showing a construction of a conventional surface light source
`
`FIG. 2 is a view showing the change of luminance to the distance from the light incident surface of
`various kinds of surface light sources.
`FIG. 3 is a partially fragmentary and perspective view showing a back light device incorporating a
`surface light source element according to an embodiment of the present invention.
`FIG. 4 is a partially sectional view taken along line IV-IV of FIG. 3.
`FIGS. 5 (a)-(e) are schematic views showing embodiments of plan patterns of flat areas.
`FIGS. 6 (a)-(c) are schematic sectional views showing various kinds of lens units.
`FIGS. 7 and 8 are partially sectional views showing modified embodiments of the surface light source
`element of the present invention.
`FIG. 9 is a schematic side view showing a modified embodiment of a back light device.
`FIG. 10 is a graph showing an area ratio distribution of flat areas in a pattern formed on a mold for
`manufacturing a light guide used for embodiments of the present invention.
`FIGS. 11 (a) and (b) are plan views showing a manufactured light guide.
`FIG. 12 is a graph showing a measurement result of a luminance distribution of the respective surface
`light source elements.
`FIG. 13 is a schematic view showing a method for measuring directional emitting angles of a
`manufactured surface light source element.
`FIGS. 14 (a) and (b) are graphs showing a measurement result of directional emitting angles of a
`manufactured surface light source element.
`
`BEST MODE OF CARRYING OUT THE INVENTION
`
`The surface light source element of the present invention will be described in detail.
`First, the basic principle of a surface light source element according to the present invention will be
`explained. The refractive indexes n of a transition from light guide to air are approximately 1.4 to 1.6.
`In the
`system of edge-light of which the_incident surface 7 is perpendicular to an emitting surface 6 as shown in
`FIG.
`1
`(a), light theoretically cannot radiate from the emitting surface 6 when the critical angle of incidence
`is about 45°. In FIG. 1(a), the numeral 4 indicates a light source such as a fluorescent lamp, the numeral 5
`indicates the reflector therefor, and the numeral 2 indicates reflective surface formed at the opposed side of
`the emitting surface 6 of the light guide 1.
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`The emitting surface 6 is generally formed to be a surface 6a treated in light diffusion or the reflective
`surface 2 is formed to a diffusing reflective surface 9a.
`The inventors have studied diffusing treatment for at least the surfaces of a light guide and the opposed
`surface thereof,
`in order to increase the amount of emitted light. Consequently,
`it has been found that a
`method using surface roughening on these surfaces as uniformly as possible and a method using a plurality
`of lens units for radiating light
`in a predetermined direction is effective rather than the method of using
`application of a light diffusing material on at least one of the surface of the light guide and the opposed
`surface thereof or the method of using formation of a light diffusing material layer on the surface when an
`acrylic plate is made by polymerization.
`A surface light source element which comprises a light guide with a roughened surface, a fluorescent
`lamp with a surrounded silver—evaporated polyester film as a reflector provided on an end surface thereof,
`and a white film as a reflective member provided in contact with the roughened surface, was made to
`measure the luminance of the light emitted therefrom. Consequently, the luminance of the emitted light
`decreases as the distance from the fluorescent lamp increases. When the distance is 70 to 80 times the
`thickness of the light guide, the luminance is about 1/10 that at the distance zero. This is shown by the line
`1
`in FIG. 2. The inventors have proposed uniformization of luminance by a light transmissive sheet for
`regulating the emitting light in Japanese Patent Application Laid-open Nos. (Tokukai-Hei) 1-244490 and 1-
`252933, as described above.
`
`is possible to make the luminance of the emitted light uniform. However,
`it
`According to the method,
`this method lowers the value of luminance of the overall emitted light to about 1/10 to 1.5/10 of that near the
`incident end portion.
`In this method, utilization of the incident light energy passing through the light guide
`was not performed efficiently. This is shown by the line 2 in FIG. 2. The reason for this is that the light
`transmissive sheet for regulating the emitting light can cut the emitting light but cannot reuse the cut light
`because of a regulating pattern reflecting the light.
`Therefore, the inventors have developed a surface light source element so as to use the incident light
`as efficiently as possible,
`in view of the above situation. In the surface light source element, light emission
`is not performed by using the regulating pattern of the light transmissive sheet for regulating the emitted
`light, or by applying a light diffusing material on the opposed surface of the light emitting surface so that
`the density of the material is greater as the distance from the light incident portion is greater, as disclosed
`in Japanese Patent Application Laid-open No. (Tokukai-Hei) 1-245220. In the surface light source element, a
`transparent light guide which was reported in Japanese Patent Application Laid-open Nos. (Tokukai-Hei) 2-
`17, 2-84618 and 2-176629 and emits a large amount of light, and an interface for reflection having a small
`optical loss of light are used to regulate the amount of emitted light so as to make the luminance value on
`the light emitting surface uniform.
`That is,
`in the surface light source element according to the present invention, roughened surfaces or a
`plurality of lens units, each of which has a directional light emitting function which radiates the incident light
`from the light incident surface of the transparent light guide at an oblique direction to the incident light, are
`provided on at least one of the light emitting surface and the opposed surface thereof; and flat areas are
`provided on the roughened surfaces or the plural
`lens units so that the ratio of the flat areas thereon
`increases as the distance from the light incident surface decreases, thereby the transparent light guide has
`a regulation function which makes the luminance of the light through the light emitting surface uniform over
`the whole surface thereof. Accordingly,
`it is possible to increase the value of luminance of overall emitted
`light to about 3/10 of that near the incident end portion and to obtain a surface light source element showing
`a uniform luminance value over the entirety of the light emitting surface. This is shown by the line 3 in FIG.
`2.
`
`EMBODIMENT
`
`The surface light source element of
`embodiments.
`
`the present
`
`invention will be described concretely via the
`
`Surface light source element
`
`FIG. 3 shows an embodiment of a back light device incorporating a surface light source element
`according to the present invention. FIG. 4 shows a partially sectional view taken on line IV-IV of FIG. 3.
`The device comprises a light guide 1 with a rectangular plate shape, a film-like light diffusing member 3
`provided over the light emitting surface 6 thereof, a light source 4 such as a fluorescent lamp provided on
`the side end surface (a light incident surface 7) of the light guide 1, and a reflector 5 for holding the light
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`source 4 and reflecting light to the incident surface by the reflective surface provided on the inner surface
`thereof. The opposite side of the light emitting surface 6 of the light guide 1 has a light reflective layer 2.
`The surface light source element according to the present invention is characterized in that roughened
`surfaces or a plurality of lens units, each of which has a directional light emitting function which radiates the
`incident light from the light incident surface of the transparent light guide in an oblique direction to the
`incident light, are provided on at least one of the light emitting surface and the opposed surface thereof;
`and flat areas are provided on the roughened surfaces or the plural lens units so that the ratio of the flat
`areas thereon increases as the distance from the light incident surface decreases, thereby said transparent
`light guide has a regulation function which makes the luminance of the light through the light emitting
`surface uniform over the entire surface thereof.
`
`In this embodiment, flat areas 8 are provided on the roughened opposed surface 9 to the light emitting
`surface 6, so that the flat areas 8 are more numerous as the distance from the light incident surface 7
`decreases, as shown by arrow A in FIG. 4.
`The increasing ratio of the flat areas in the light guide can be selected, changed and determined
`appropriately according to the shape or pattern of the flat areas, the material or shape of the light guide, the
`kind of the light source, the treatment degree of the light emitting or reflecting surface or the like.
`Pattern examples of the flat areas are shown in FIGS. 5 (a) to (e). In every example, the area ratio of the
`flat areas 8 becomes increases as a position is nearer the light incident surface 7, as shown by arrow A in
`FIG. 5.
`
`The diffusing member 3 which can be used for the present invention may be any structure or material
`which can diffuse light from the light guide nondirectionally. The diffusing member 3 can be provided on the
`light guide 1 by the end portion of the light guide adhering to the diffusing member 3 by an adhesive, by
`compulsory close contact through pressure, or by merely positioning the diffusing member 3 on the light
`guide. Furthermore,
`it
`is possible to laminate the light guide 1 and the diffusing member 3 directly or
`through a layer of air.
`in the present invention can be obtained by a transparent resin such as an acrylic
`The light guide 1
`resin, a polycarbonate resin or a vinyl chloride resin.
`In particular,
`it is preferable to use an acrylic resin
`having a large transmission coefficient of visible light. The method of molding the light guide 1 can be
`selected or changed appropriately.
`The light source 4 in the present invention is not limited. A fluorescent lamp or a filament lamp which is
`a continuous tubular light source, a plurality of point-like sources of
`light arranged along the incident
`surface, or a light source device comprising a combination of a light transmissive member which can
`receive light through a side surface and a light source provided near the end portion incident surface of the
`light transmissive member, can be used as a light source.
`The reflecting layer 2 of the surface light source element according to the present invention can be
`formed by laminating a reflecting film or the like which comprises a film and an evaporated metal such as
`Ag, Al or the like.
`It is preferable to use a reflecting material having a high reflectivity.
`In this invention, the light guide requires at least one of the light emitting surface 6 and the opposed
`surface being roughened, or a plurality of lens units being formed. Furthermore, it is necessary to provide
`flat areas on the roughened surface or on the surface on which a plurality of lens units are formed, so that
`the ratio of the flat areas thereon increases as the distance from the light incident surface decreases.
`is
`In a preferred embodiment of the present invention, the surface of the flat areas 8 in the light guide 1
`preferably an optically flat surface,
`in particular, to be a mirror surface. The incident light with an incident
`angle more than the critical reflective angle to the optical flat surface can be reflected almost without loss.
`Since the light does not leak,
`it is possible to use the light effectively to increase the luminance of the
`entire light emitting surface.
`The shape of the lens unit which is used in the present invention is not limited. For example, a lens unit
`with a shape proposed in Japanese Patent Application Laid-open No. (Tokukai-Hei) 2-17 by the inventors
`can be used. Lenses 20 having various shapes are shown in FIGS. 6(a) and (b).
`The roughened surface which is used in the present invention preferably has a haze value of not less
`than 30%, and more preferably, not less than 50% in the roughened surface portion.
`limited to the above
`The surface light source element according to the present
`invention is not
`embodiment. Various changes or modifications in form and details may be made therein. For example, in
`the above embodiment, flat areas 8 are provided on the roughened surface 9 opposed to the light emitting
`surface 6. However, flat areas 8 can be provided on the roughened light emitting surface 6, as shown in
`FIG. 7.
`It is possible to provide a structure so that the area ratio of the flat areas thereon increases as the
`distance from the light incident surface 7 decreases, as shown by arrow A in FIG. 7.
`Furthermore,
`it
`is possible to provide the flat areas on both roughened surfaces of the light emitting
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`It is possible to provide a structure so that the
`surface 6 and of the opposed surface 9, as shown in FIG. 8.
`area ratio of the flat areas thereon increases as the distance from the light incident surface 7 decreases, as
`shown by arrow A in FIG. 8.
`In the above embodiment, the light source 4 is provided only on one end side of the light guide 1.
`possible to provide the light source 4 on both ends sides of the light guide 1, as shown in FIG. 9.
`
`It is
`
`Regulating method of the surface light source element
`
`The surface light source element according to the present invention can be regulated and manufactured
`by various kinds of methods.
`For example, when the flat areas are provided on a roughened surface of the light guide or on a surface
`having lens units,
`it is possible to manufacture desired light guides by using a method in which flat areas
`are provided on a roughened surface or on a surface having lens units or by using a method in which
`roughened parts or lens units are provided on a flat surface.
`A die having a desired roughened pattern or a surface roughness, or a die having specific lens units
`and flat areas is prepared by surface roughening treatments such as sandblasting, etching or the like. A
`light guide, which has predetermined flat areas on at
`least one of a light emitting surface having a
`roughened surface or lens units and an opposed surface thereof, can be obtained by an injection molding of
`a resin or by a heat-press using such a die.
`In particular,
`the injection molding method is preferable
`because of high precision and high molding speed.
`The manufacture of the surface light source element can be performed by preparation of necessary
`members such as a light guide, a diffusing member, a reflecting material and the like, and by then
`assembling them.
`
`Detailed embodiment
`
`(Manufacture of a die for a light guide)
`
`Glass beads were blown on a polished surface of a brass plate, so that a metal plate on which surface
`roughening is carried out by a usual forming process was manufactured (Die 1).
`A gradation pattern having a distribution of area ratio of the flat areas as shown in FIG. 10 was formed
`by using CAD. A pattern was developed and printed photo-optically on the surface of the Die 1 by a usual
`photolithography process. The portion to remain as roughened surfaces, that is the portion similar to the
`rough parts 22 as shown in FIG. 11(a), was protected by a film. The remaining portion was polished to a
`degree of roughness with an emery-paper No. 800. Thereafter, a die having predetermined flat areas was
`made by removing the protecting film (Die 2).
`A surface of a brass plate was polished by a buff with an emery-paper No. 800, and then a mirror plate
`was made (Die 3).
`A combined die for injection molding which had one surface with a state similar to that of the Die 2 and
`had the other surface with a state similar to that of the Die 3, was made (Die 4).
`
`(Manufacture of a light guide)
`
`An acrylic resin plate of 150 mm x 250 mm with a thickness of 3 mm was sandwiched between the Die
`2 and the Die 3 and a replica was formed by a conventional heat-press process. Then, the replica was cut
`to the size and pattern position as shown in FIGS. 11(a) and (b). The four out sides were polished to have
`mirror surfaces in a conventional manner (Light guide 1).
`In FIG. 11(a), numeral 22 indicates roughened surface parts. In FIG. 11(b), the light guide 1 has a length
`(B) of 225 mm, a width (C) of 132 mm, a width of a zone "0" (D) of 15 mm, an effective width (E: a width of
`zones "1 " to "11") of 205 mm, and a width (F) of zone "12" of 5 mm.
`An acrylic resin plate of 150 mm x 250 mm with a thickness of 3 mm was sandwiched between the Die
`1 and the Die 3 using a process similar to the above process and a replica was formed by heat-pressing.
`Then, the replica was cut and polished to produce a light guide (Light guide 2).
`A negative EP picture was made as a comparative example so that ink could be applied on the rough
`corresponding parts of the Die 2 by a screen printing process. A print form for screen printing was made by
`using this. Screen printing was carried out on a surface of an acrylic resin plate of 150 mm x 250 mm with
`a thickness of 3 mm using a commercially available white ink (VIC 120 White made by Seiko-Advance Co..
`LTD.). Thereafter, this was cut and polished in a similar manner to that of the light guide 1 or of the light
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`guide 2 to make a light guide for comparison (Light guide 3).
`Light guides were made from acrylic resin pellets (Acrypet VH made by Mitsubishi Rayon Co.) at a
`cylinder temperature of 240° C by using a 200 t-injection molding machine and the Die 4.
`
`(Measurement of the haze value of the light guide 2)
`
`Pieces of sample of 50 mm x 50 mm were cut out from the roughened surface parts of the light guide
`2, and the haze value thereof was measured according to ASTM-D 1003-61. The haze value was calculated
`according to the following equation.
`
`Haze value = {(Transmittance of diffused light) / (Total transmittance light)} x 100%
`
`Consequently, the haze value of the light guide 2 was 64.8.
`
`(Assembly of the surface light source element)
`
`A crystal white plate produced by Sky Aluminium Co. (an aluminum plate with a thickness of 0.25 mm,
`a surface of which is coated with a white paint) was positioned in a folded state with an inner white surface
`so that the plate had a rib with a width of 3 mm and a flat portion with a size of 132 mm x 225 mm. At least
`one of two short sides had no rib, so that the short side can function as a light incident surface. This plate is
`the light reflecting member. A milk white polyethyleneterephthalate film "EK 300 W" produced by Somar
`Co., with a thickness of 0.075 mm, was cut to size of 132 mm x 225 mm to use as a diffusing member.
`A cylindrical member having an inner diameter of 6 mm and a crystal white inner surface was produced
`as a lamp case. The lamp case has an aperture with an opening width of 3 mm.
`The light guide was placed on the light reflecting member so that the "0" zone as shown in FIG. 11(b)
`was adjacent to the short side without rib of the light reflecting member and the roughened surface or the
`printed surface was close to the white surface thereof. The diffusing member was placed on the light guide.
`These three members were inserted into the aperture of the lamp case together. A lamp "KC 130 T4E74"
`produced by Matsushita Electric Industry Corporation with a diameter of 4 mm and a length of 130 mm was
`set in the lamp case as a surface light source element. "CXA-L10L" produced by TDK Corporation was
`used as an inverter for lighting a lamp. The lamp was lighted by application of DC 12V.
`
`(Measurement of luminance of the surface light source element)
`
`Luminance of the surface light source element was measured by a luminance meter "BM-5" produced
`by Topcon Co. through a view angle of 1° and a measurement circle of 10 to 15 mm in diameter. The
`measurement was carried out at the central portion of the zones "1" to "11" as shown in FIG. 11. The
`surface light source element was fixed at a predetermined measurement pedestal perpendicularly thereto
`so that the lamp was in an upper side. After lighting had been carried out by application of DC 12 V, the
`measurement was carried out
`through a lamp aging time of more than 15 minutes. The condition of
`temperature for measurement was 23° C 1 2° C.
`
`(Result of luminance measurement)
`
`Results of the luminance measurement is shown in Table 1 and FIG. 12.
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`Pretech_000813
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`COMPARATIVEEXAMPLE
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`HVIBODIMENTOFTHEINVENTION
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`LIGHTGUIDE-l
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`LUMINANCEDIS'I‘RIBU'I‘ION
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`AVERAGE
`
`VALUE
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`According to the light guide 1 which is an embodiment of the present invention, it is possible to radiate
`emitted light with an approximately uniform luminance over the whole of the light emitting surface and to
`illuminate a display surface with a uniform luminance. The light guide 1 has a utilization rate of light higher
`than that of the light guide 3. Therefore, even if the same light source is used,
`it
`is possible to obtain
`emitted light having a high luminance. The surface light source element using the light guide 4 can provide
`a result similar to that of the surface light source element using the light guide 1.
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`(Measurement of directional emitting angle of the light guide)
`
`A sample was placed on a measurement pedestal so that a lamp y was at the left side. The luminances
`at predetermined angles were measured, rotating the sample as shown in FIG. 13.
`A sample in which a diffusing member was removed from a surface light source element using the light
`guide 1
`is indicated as 1-1. A sample with a diffusing member is indicated as 1-2.
`A sample in which a diffusing member was removed from a surface light source element using the light
`guide 3 is indicated as 3-1. A sample with a diffusing member is indicated as 3-2.
`The measurement position was fixed at the central portion of the zone 6 as shown in FIG. 11. The
`results are shown in FIGS. 14(a) and (b).
`
`UTILIZATION POSSIBILITY IN INDUSTRY
`
`As described above, in the surface light source element according to the present invention, at least one
`of the light emitting surface and the opposed surface of said transparent light guide has a directional light
`emitting function which radiates the incident
`light from the light incident surface of the transparent light
`guide at an oblique direction to the incident light and has a regulation function which makes the luminance
`of the light uniform over the light emitting surface in the whole surface thereof. Therefore, even if the
`transparent light guide is thin,
`it is possible to emit light with a uniform luminance over the entire emitting
`surface on the basis of the incident light. The incident light into the transparent light guide is not wasted and
`has a high utilization rate. Consequently, it is possible to produce an emitted light having a high luminance
`without increasing the wattage of the light source. Therefore, the present invention provides a very thin type
`of surface light source element which can supply emitted light with a uniform and high luminance.
`
`Claims
`
`A surface light source element comprising a transparent light guide (1) having a side end surface as a
`light incident surface, a surface perpendicular to the light incident surface as a light emitting surface,
`and a light reflecting layer provided on a surface opposed to the light emitting surface; and a diffusing
`member (2) for diffusing light from the light emitting surface of the transparent light guide;
`wherein at least one of the light emitting surface and the opposed surface of said transparent light
`guide has a directional
`light emitting function which radiates the incident light from the light incident
`surface of the transparent light guide at an oblique direction to the incident light and has a regulation
`function which makes the luminance of the light uniform over the entire light emitting surface.
`
`light guide has a
`A surface light source element as claimed in claim 1; wherein said transparent
`roughened light emitting surface having a directional
`light emitting function, a light incident surface
`provided on at least one of the side end surfaces thereof, and a light reflecting layer provided on the
`opposed surface to the light emitting surface; and said roughened light emitting surface having flat
`areas so that the ratio of the flat areas thereon increases as the distance from the light incident surface
`decreases, whereby said transparent
`light guide regulates the luminance of the light so as to be
`uniform through the light emitting surface over the entirety of the surface thereof.
`
`A surface light source element as claimed in claim 1, wherein said transparent light guide having a light
`emitting surface, a light incident surface provided on at least one of the side end surfaces thereof, a
`roughened surface having a directional light emitting function opposed to the light emitting surface, and
`a light reflecting layer provided on the opposed surface; and said roughened opposed surface having
`flat areas so that the ratio of the fla