200944712 九、發明說明 【發明所屬之技術領域】 本發明係有關面光源裝置，更詳細者係有關使用紅色 發光二極體、綠色二極體及藍色二極體爲光源之面光源裝 置。 【先前技術】 ❹ 作爲如圖3所示之組裝於液晶電視等所使用，之面光源 裝置（3)者，先行技術中被揭示有使用具備光擴散板（1 )與配置於其背面側之光源（2)，於光源（2)之背面側 無反射板者，作爲光擴散板（1)者，由其無色、薄型化 之觀點視之，使用較薄者。又，作爲光源（2)者，由其 省能源之觀點視之，使用LED (發光二極體）爲光源（2 )亦被揭示〔「液晶顯示器用背光技術一液晶照明系統與 構件材料―」、CMC出版'2006年8月31日發行、 © p.148- 149〕、使用合倂對應光的三原色之紅色LED(2R )、綠色 LED(2G)、及藍色 LED ( 2B )爲 LED ( 2 )者 。該面光源裝置（3)中，各LED ( 2R、2G、2B )使分別 發光之光進行混色後時，調整使完全呈白色光之發光強度 、或調整其個數進行使用，因此，由LED之光於透過光 擴散板之間進行混色作成白色光，於面光源裝置（3)之 前面側進行出射。 惟，先行技術之面光源裝置（3’）中，其往前面側之 出射光並未完全成爲白色光，會帶有紅色光者。 200944712 【發明內容】 因此’本發明者’以使用紅色LED、綠色LED、及藍 色LED爲光源’開發一種可出射未帶紅色的白色光之面 光源裝置而進行精密硏討後結果，進而完成本發明。 亦即’本發明係提供一種其特徵爲具備光擴散板（i )與配置於該光擴散板（2)之背面側的紅色LED ( 2R ) ' 、綠色 LED(2G)及藍色 LED(2B)， #| 該光擴散板（1 )由背面側所測定之總光線反射率爲 3 0%以上， 於該紅色LED (2R)、綠色LED (2G)及藍色LED (2B )之背面側中使前面側配置擴散反射面之反射板（4 )之面光源裝置（3)。圖1顯示本發明模式的面光源裝 置（3 )。 本發明之面光源裝置（3 )係以LED作爲光源（2 ) 者，因此不僅消耗電力少，於前面側亦可出射未帶紅色之 〇 完全白色光。 【實施方式】 〔發明實施之最佳形態〕 作爲用於本發明面光源裝置（3)之光擴散板（1)者 ，一般使用未著色之無色（白色）者，該大小係因應其作 爲目的之背光裝置、直立型液晶顯示裝置進行適當的選擇 ，通常爲20型（縱30cm、橫40cm)以上之較大面積者 -5- 200944712 宜。 光擴散板（1)之厚度爲1 mm〜3 mm者宜，較佳者爲 2mm以下。當厚度超出 3mm則不利薄型化。反之未達 1 mm則不利於機械性強度。 作爲該光擴散板者，一般如：由透明樹脂及擴散劑所 成之光擴散性樹脂組成物者，將透明樹脂與擴散劑進行熔 ' 融混煉後，可藉由擠壓成形之擠壓成形法、射出成形之射 φ 出成形法、熱加壓之熱加壓法等之一般成形法進行成形後 取得。 作爲透明樹脂之例者，如：聚碳酸酯樹脂、ABS樹脂 (丙烯腈-苯乙烯-丁二烯共聚物樹脂）、甲基丙烯酸樹脂 、MS樹脂（甲基丙烯酸甲酯-苯乙烯共聚物樹脂）、聚苯 乙烯樹脂、AS樹脂（丙烯腈-苯乙烯共聚物樹脂）、聚乙 烯、聚丙烯等之聚烯烴樹脂等例。 作爲擴散劑之例者，只要構成光擴散板之透光性樹脂 G 與折射率不同之粒子，使透過光經擴散取得者即可，並未 特別限定，一般如：無機玻璃粒子、玻璃纖維、矽粒子、 氫氧化鋁粒子、碳酸鈣粒子、硫酸鋇粒子、氧化鈦粒子、 滑石等無機粒子、亦可如：苯乙烯系聚合物粒子、丙烯酸 系聚合物粒子、矽氧烷系聚合物粒子等之有機粒子。 光擴散劑的粒徑以重量平均粒徑計，一般爲0.8 μηι以 上，ΙΟμπι以下者宜，較佳者爲2~3μιη。 該光擴散板（1 )其由背面側所測定之總光線反射率 (Rt)爲30%以上者宜，較佳者爲35%以上，一般爲50% 200944712 以下者宜。光擴散板之總光線反射率（Rt )如對於透明樹 脂之擴散劑使用量愈多則愈大。總光線反射率（Rt )係依 JIS K-71 05 ( 1 98 1 年）所測定。 光擴散板之總光線透光率（Tt)由其可充分使光混色 之面觀之，通常爲65%以下者宜，由其亮度面視之，爲 5 5%以上。總光線透光率（Tt)如光擴散板之每單位面積 的光擴散劑使用量愈多則壓愈小。總光線透光率（Tt )係 依 JIS K-7361 -1 ( 1997 年）所測定。 光擴散板其由背面側所測定之擴散光線反射率（Rdi )爲22%以上，通常爲40%以下。擴散光線反射率（Rd! )若大量添加光擴散劑之添加量，愈使用與透明樹脂之折 射率差大之光擴散劑，則Rd,愈大。擴散光線反射率（ Rd!)係依 JIS K7 1 05 ( 1 9 8 1 年）所測定。 光源（2 )係發出紅色光之紅色LED ( 2R )、發出綠 色光之綠色LED(2G)、及發出藍色光之藍色LED(2B )。作爲LED者，使用其發光二極體晶片以環氧樹脂製 之透鏡進行被覆之構造者，其指向性可任意爲Lanber Cyan Type、Bat Wing Type、Side emitter Type，而本發 明之面光源裝置（3)爲Lanbercyan Type之LED者較佳 ο 紅色LED ( 2R)、綠色LED ( 2G)及藍色LED ( 2B )係使綠色LED、紅色LED、藍色LED、紅色LED及綠 色LED並排呈直線狀作成一單位，使用多數重覆該單位 200944712 反射板（4)其前面側表面爲擴散反射面，該擴散光 線反射率（Rd4 )通常爲80%以上，90%以下。反射板（4 )之表面的擴散光線反射率（Rd4)係依JIS K7 105 ( 1981 年）所測定。 依據本發明面光源裝置（3)，來自於各LED ( 2 )之 光係藉由光擴散板（1)使其一部份擴散反射。擴散反射 之光到達配置於LED之背面側之反射板（4)，於此再次 到達擴散反射之光擴散板（1)。到達光擴散板之光其一 部份再度擴散反射。如此重覆擴散反射之間，由紅色LED (2R)、綠色LED(2G)及藍色LED(2B)之光充分進 行混色後，進一步於光擴散板（1)之內部擴散，同時藉 由透光後更進一步擴散，呈現完全的白色光，於前面側進 行出射。 〔實施例〕 〇 以下，藉由實施例，針對本發明進行更詳細的說明。 〔實施例1〕 使用具備如圖1所示之光擴散板（1)與配置於其背 面側之LED (2)及配置於其背面側之反射板（4)之面光 源裝置（3)。 作爲光擴散板（1)者係使用於1〇〇質量份之聚苯乙 烯樹脂〔東洋STYRENE公司製「東洋STYROL HRM40」 、折射率1.59〕中，加入1〇質量份之光擴散劑〔丙烯酸 -8 - 200944712 系交聯樹脂粒子、積水化成品工業公司製「ΜΒΧ·2Η」、 重量平均粒徑3μιη、折射率1.49〕’進行混合後’以擠壓 機〔螺旋徑40 mm〕，於210 °C〜2 50 °C下進行熔融混煉’ 經由給料裝置，由245°C~255 °C之T模呈板狀擠出後調製 者。由該光擴散板（1 )之背面側所測定之總光線反射率 (Rt )爲4 3.7 %，由背面側所測定之擴散光線反射率（Rd J )爲35.3%。又，總光線透光率（Tt)爲55%。尺寸爲縱 ’ 100mm ' 橫 100mm、厚度 l_5mm。 ❹ 作爲LED (2)者使用呈直線狀並排綠色LED、紅色 LED、藍色LED、紅色LED及綠色LED者。 作爲反射板（4)者，使用擴散光線反射率（Rd4)爲 8 1 · 4 % 者。 使各LED ( 2 )進行點燈，進行光擴散板（1 )以目測 観察前面側所出射之光後，呈現無帶紅色’完全的白色光 〇 如圖2所示，將各LED ( 2 )進行點燈的狀態下’由 © 該光擴散板（1)之前面側，以光擴散板（1)之中心位置 (◎)測定出射光之色度（Xe、y。）。同時以黑色圓點（ •)所示8點下測定各個出射光之色度（X、y)、求出該 數平均値（xa、xa )。各色度之測定係依 JIS K7105 ( 1 9 8 1年）。以黑色圓點（#)所示之測定點8點係由所有 光擴散板（1 )之端部l〇mm之位置。由所得色度藉由式 (la) 4 X , a 3-2xa+12ya . ... (la) -9 - 200944712 分別求出ua’，藉由式（1 4 X Λ • · · (1 c) 3—2xc+l2y 分別求出，藉由式（2a ) 9y. (2 a) 3-2x.+l2y 分別求出va’，藉由式（2c ) 9yc ❹ 3-2x.+l2y (2 c) 分別求出v c ’，藉由式（3 )BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface light source device, and more particularly to a surface light source device using a red light emitting diode, a green diode, and a blue diode as a light source. [Prior Art] As a surface light source device (3) used in a liquid crystal television or the like as shown in Fig. 3, it is disclosed in the prior art that a light diffusing plate (1) is provided and disposed on the back side thereof. The light source (2) is not reflected on the back side of the light source (2), and is used as the light diffusing plate (1) because it is colorless and thin. Moreover, as a light source (2), from the viewpoint of energy saving, LED (light emitting diode) is also disclosed as a light source (2) ["LCD technology for liquid crystal display - liquid crystal illumination system and component material -" , CMC Publishing 'August 31, 2006 issue, © p.148-149】, using the three primary colors of the corresponding light red LED (2R), green LED (2G), and blue LED (2B) for the LED ( 2). In the surface light source device (3), when each of the LEDs (2R, 2G, and 2B) mixes the light beams that are respectively emitted, the light intensity of the completely white light is adjusted or the number of the lights is adjusted, and the LEDs are used. The light is mixed with the light diffusing plate to form white light, and is emitted on the front side of the surface light source device (3). However, in the surface light source device (3') of the prior art, the light emitted toward the front side is not completely white light, and is red light. 200944712 [Summary of the Invention] Therefore, the 'inventors' developed a method of using a red LED, a green LED, and a blue LED as a light source to develop a surface light source device that can emit white light without red light, and then perform the result of precise begging, thereby completing this invention. That is, the present invention provides a red LED (2R)', a green LED (2G), and a blue LED (2B) which are provided with a light diffusing plate (i) and a back side disposed on the light diffusing plate (2). ), #| The total light reflectance measured by the back side of the light diffusing plate (1) is more than 30%, on the back side of the red LED (2R), the green LED (2G), and the blue LED (2B) The surface light source device (3) of the reflector (4) of the diffuse reflection surface is disposed on the front side. Fig. 1 shows a surface light source device (3) of the mode of the present invention. Since the surface light source device (3) of the present invention uses an LED as the light source (2), it consumes not only a small amount of power, but also emits red light which is not reddish on the front side. [Embodiment] [Best Mode for Carrying Out the Invention] As the light diffusing plate (1) used in the surface light source device (3) of the present invention, an uncolored colorless (white) is generally used, and the size is used for the purpose. The backlight device and the upright liquid crystal display device are appropriately selected, and are generally a large area of 20 type (length 30 cm, width 40 cm) or more - preferably -5,047,712. The thickness of the light diffusing plate (1) is preferably 1 mm to 3 mm, preferably 2 mm or less. When the thickness exceeds 3 mm, it is disadvantageously thinned. Conversely, less than 1 mm is not conducive to mechanical strength. As the light diffusing plate, generally, a light diffusing resin composition made of a transparent resin and a diffusing agent is melted and melted by a transparent resin and a diffusing agent, and can be extruded by extrusion molding. The molding method, the injection molding method, the hot pressing method such as hot pressing, and the like are formed by molding. As a transparent resin, for example, polycarbonate resin, ABS resin (acrylonitrile-styrene-butadiene copolymer resin), methacrylic resin, MS resin (methyl methacrylate-styrene copolymer resin) Examples of polystyrene resins, AS resins (acrylonitrile-styrene copolymer resins), polyolefin resins such as polyethylene and polypropylene, and the like. The example of the diffusing agent is not particularly limited as long as the light-transmitting resin G constituting the light-diffusing sheet and the particles having different refractive indices are obtained by diffusing the transmitted light, and are generally, for example, inorganic glass particles or glass fibers. Inorganic particles such as cerium particles, aluminum hydroxide particles, calcium carbonate particles, barium sulfate particles, titanium oxide particles, and talc, and may also be, for example, styrene polymer particles, acrylic polymer particles, siloxane polymer particles, or the like. Organic particles. The particle diameter of the light diffusing agent is generally 0.8 μηι or more in terms of weight average particle diameter, preferably ΙΟμπι or less, preferably 2 to 3 μιη. The light diffusing plate (1) preferably has a total light reflectance (Rt) of 30% or more as measured by the back side, preferably 35% or more, and usually 50%. The total light reflectance (Rt) of the light diffusing plate is increased as the amount of the diffusing agent for the transparent resin is increased. The total light reflectance (Rt) is determined in accordance with JIS K-71 05 (1981). The total light transmittance (Tt) of the light diffusing plate is preferably such that it is sufficiently light-mixed, and is usually 65% or less, and is 55% or more in terms of brightness. The total light transmittance (Tt), such as the amount of light diffusing agent per unit area of the light diffusing plate, is smaller as the pressure is reduced. The total light transmittance (Tt) is determined in accordance with JIS K-7361-1 (1997). The light diffusing plate has a diffused light reflectance (Rdi) measured by the back side of 22% or more, and usually 40% or less. When a large amount of the light diffusing agent is added in the diffused light reflectance (Rd!), the more the light diffusing agent having a large difference in refractive index from the transparent resin is used, the larger the Rd is. The diffuse light reflectance ( Rd!) is measured in accordance with JIS K7 1 05 (1981). The light source (2) is a red LED (2R) that emits red light, a green LED (2G) that emits green light, and a blue LED (2B) that emits blue light. As a light-emitting device, a light-emitting diode wafer is coated with a lens made of an epoxy resin, and its directivity can be arbitrarily Lanber Cyan Type, Bat Wing Type, and Side emitter Type, and the surface light source device of the present invention ( 3) It is better for Lanbercyan Type LEDs. Red LED (2R), green LED (2G) and blue LED (2B) make green LED, red LED, blue LED, red LED and green LED appear side by side in a straight line. As a unit, a plurality of repeating units of the 200944712 reflector (4) have a front side surface which is a diffuse reflection surface, and the diffused light reflectance (Rd4) is usually 80% or more and 90% or less. The diffused light reflectance (Rd4) of the surface of the reflecting plate (4) was measured in accordance with JIS K7 105 (1981). According to the surface light source device (3) of the present invention, the light from each of the LEDs (2) is diffused and reflected by a portion of the light diffusing plate (1). The diffused and reflected light reaches the reflecting plate (4) disposed on the back side of the LED, and reaches the diffused and reflected light diffusing plate (1) again. Some of the light reaching the light diffusing plate is again diffused and reflected. Between the repeated diffusion reflections, the light of the red LED (2R), the green LED (2G), and the blue LED (2B) is sufficiently mixed, and further diffused inside the light diffusion plate (1) while being transparent. After the light spreads further, it shows complete white light and exits on the front side. [Examples] Hereinafter, the present invention will be described in more detail by way of examples. [Embodiment 1] A surface light source device (3) including a light diffusing plate (1) as shown in Fig. 1 and an LED (2) disposed on the back side thereof and a reflecting plate (4) disposed on the back side thereof was used. As a light-diffusing sheet (1), one part by mass of a polystyrene resin ("Toyo STYROL HRM40" manufactured by Toyo STYRENE Co., Ltd., refractive index: 1.59] was added, and one part by mass of a light diffusing agent [acrylic acid- 8 - 200944712 Cross-linked resin particles, "ΜΒΧ·2Η" manufactured by Sekisui Chemicals Co., Ltd., weight average particle size 3μιη, refractive index 1.49] 'mixed' with extruder [spiral diameter 40 mm] at 210 ° C~2 Melt kneading at 50 °C. After being extruded from a T-die of 245 ° C to 255 ° C through a feeding device, it was prepared. The total light reflectance (Rt) measured by the back side of the light diffusing plate (1) was 43.7 %, and the diffused light reflectance (Rd J ) measured by the back side was 35.3%. Further, the total light transmittance (Tt) was 55%. Dimensions are vertical '100mm' horizontal 100mm, thickness l_5mm. ❹ As the LED (2), use a green LED, a red LED, a blue LED, a red LED, and a green LED in a straight line. As the reflector (4), a diffused light reflectance (Rd4) of 8 1 · 4 % was used. Each LED (2) is turned on, and the light diffusing plate (1) is visually observed to observe the light emitted from the front side, and then presents a reddish-free white light. As shown in Fig. 2, each LED (2) is shown. In the state where the lighting is performed, the chromaticity (Xe, y) of the emitted light is measured by the center position (◎) of the light diffusing plate (1) from the front side of the light diffusing plate (1). At the same time, the chromaticity (X, y) of each of the emitted light is measured at 8 o'clock as indicated by a black dot (•), and the average 値(xa, xa) is obtained. The determination of each color is based on JIS K7105 (1981). The measurement point 8 indicated by the black dot (#) is located at the end of all the light diffusing plates (1) by 10 mm. From the obtained chromaticity, ua' is obtained by the formula (la) 4 X , a 3-2xa + 12ya . ... (la) -9 - 200944712, respectively, by the formula (1 4 X Λ • · · (1 c 3-2xc+l2y is obtained separately, and va' is obtained by equation (2a) 9y. (2 a) 3-2x.+l2y, respectively, by equation (2c) 9yc ❹ 3-2x.+l2y (2 c) Find vc ' separately, by equation (3)
△ U’V’=、/ (Ua’_ Uc’）2+ (va _V (3) 求出均勻色度（△〆▽’）後’爲0.010322。均勻色度 (△ u’ν’）愈小，顯示愈無帶紅色者。 〔實施例2〕 作爲光擴散板（1)者使用將光擴散劑之使用量作成 4.1質量份，與實施例1同法所調製者。該光擴散板（1) 其由背面側所測定之總光線反射率（Rt )爲3 8.4%，由背 面側所測定之擴散反射率（Rd !)爲3 0 · 1 %、總光線透光 率（Tt)爲55%、厚度爲2.0mm。除使用該光擴散板（1 )之外，與實施例1同法作成相同之面光源裝置（3)。 將各LED ( 2 )進行點燈，進行光擴散板（1 )以目測觀察 前面側所出射之光後，呈現未帶紅色，完全的白色光。又 ，此出射光之均勻色度（ΛιΓν’）爲0.010677。 -10- 200944712 〔實施例3~實施例5〕 作爲光擴散板（1)者，使用分別將光擴散劑之使用 量，作成4.5質量份〔實施例3〕、2.4質量份〔實施例4 〕、及3質量份〔實施例5〕，與實施例1同法所調製者 ，實施例3之光擴散板（1 )其由背面側所測定之總光線 反射率（Rt )爲35.4%，由背面側所測定之擴散光線反射 ， 率（Rd!)爲27.1%，總光線透光率（Tt )爲60%、厚度爲 ❹ 1 .5mm。實施例4所使用之光擴散板（1 )其由背面側所測 定之總光線反射率（Rt)爲30.3%，由背面側所測定之擴 散光線反射率（Rdt )爲22.7%，總光線透光率（Tt )爲 6 0%，厚度爲2.0mm者。實施例5所使用之光擴散板（1 )其由背面側所測定之總光線反射率（Rt)爲32.0%，由 背面側所測定之擴散反射率（Rch )爲24.0%，總光線透 光率（Tt)爲65%，厚度爲1.5mm者。除分別使用該各光 擴散板（1)之外，與實施例1同法作成相同之面光源裝 © 置（3 )。將各LED ( 2 )進行點燈，進行光擴散板（1 ) 以目測觀察前面側所出射之之光，結果均呈現無帶紅色， 完全的白色光。又，該出射光之均勻色度（△ u’v’）爲 0.011653〔實施例 3〕、0.012256〔實施例 4〕、0.012864 〔實施例5〕。 〔比較例1〕 作爲光擴散板（1)者，使用將光擴散劑之使用量作 -11 - 200944712 成2質量份，與實施例1同法所調製之光擴散板。該光擴 散板（1 )其由背面側所測定之總光線反射率（Rt )爲 28.2%，由背面側所測定之擴散光線反射率（Rch )爲 20.7%，總光線透光率（Tt)爲65%，厚度爲2mm。除使 用該光擴散板（1)之外，與實施例1同法作成相同的面 光源裝置（3 )。將各LED ( 2 )進行點燈，進行光擴散板 (1 )，以目測觀察前面側所出射之光，結果呈現帶紅色 。又，該出射光之均勻色度（△u’v’）爲0.014298。 〔產業上可利用性〕 本發明之面光源裝置（3)係以LED作爲光源（2) 者’因此’不僅其消耗電力少，亦可於前面側出射呈未帶 紅色之完全的白色光。 【圖式簡單說明】 Ο 圖1係代表本發明面光源裝置一例之模式的截面圖。 圖2係代表實施例中評定均勻色度之測定點的模式圖 0 圖3係代表先行技術之面光源裝置一例之模式的斷面 圖。 【主要元件符號說明】 1 :光擴散板 2 :光源（L E D ) 3 :面光源裝置 -12- 200944712 4 :反射板△ U'V'=, / (Ua'_ Uc')2+ (va _V (3) After obtaining uniform chromaticity (△〆▽'), 'is 0.010322. The uniform chromaticity (△ u'ν') [Example 2] As the light-diffusing sheet (1), the amount of the light-diffusing agent used was 4.1 parts by mass, which was prepared in the same manner as in Example 1. The light-diffusing sheet ( 1) The total light reflectance (Rt) measured from the back side is 3 8.4%, the diffuse reflectance (Rd !) measured from the back side is 3 0 · 1 %, and the total light transmittance (Tt) is 55% and a thickness of 2.0 mm. The same surface light source device (3) was produced in the same manner as in Example 1 except that the light diffusing plate (1) was used. Each LED (2) was turned on to perform a light diffusing plate. (1) After visually observing the light emitted from the front side, it is unreddish, completely white light. Further, the uniform chromaticity (ΛιΓν') of the emitted light is 0.010677. -10-200944712 [Example 3~ Implementation Example 5] As the light-diffusing sheet (1), the amount of the light-diffusing agent used was 4.5 parts by mass [Example 3], 2.4 parts by mass [Example 4], and 3 masses. [Example 5], the light diffusing plate (1) of Example 3, which was prepared by the same method as in Example 1, had a total light reflectance (Rt) measured by the back side of 35.4%, as measured by the back side. The diffused light reflected, the rate (Rd!) was 27.1%, the total light transmittance (Tt) was 60%, and the thickness was ❹1.5 mm. The light diffusing plate (1) used in Example 4 was from the back side. The total light reflectance (Rt) measured was 30.3%, the diffused light reflectance (Rdt) measured by the back side was 22.7%, the total light transmittance (Tt) was 60%, and the thickness was 2.0 mm. The light diffusing plate (1) used in Example 5 had a total light reflectance (Rt) of 32.0% as measured from the back side, and a diffuse reflectance (Rch) of 24.0% as measured by the back side, and total light transmittance. (Tt) is 65%, and the thickness is 1.5 mm. Except that the respective light diffusing plates (1) are used separately, the same surface light source device (3) is formed in the same manner as in the first embodiment. Each LED (2) is used. Light is applied to the light diffusing plate (1) to visually observe the light emitted from the front side, and the result is a reddish, completely white light. The uniform chromaticity (Δ u'v') was 0.011653 [Example 3], 0.012256 [Example 4], and 0.012864 [Example 5]. [Comparative Example 1] As the light diffusing plate (1), light diffusion was used. The amount of the agent used is -11 - 200944712 in 2 parts by mass, and the light diffusing plate prepared by the same method as in Example 1. The light diffusing plate (1) has a total light reflectance (Rt) of 28.2 as measured from the back side. %, the diffused light reflectance (Rch) measured by the back side was 20.7%, the total light transmittance (Tt) was 65%, and the thickness was 2 mm. The same surface light source device (3) was fabricated in the same manner as in the first embodiment except that the light diffusing plate (1) was used. Each of the LEDs (2) was turned on, and the light diffusing plate (1) was subjected to visual observation of the light emitted from the front side, and the result was reddish. Further, the uniform chromaticity (Δu'v') of the emitted light was 0.014298. [Industrial Applicability] The surface light source device (3) of the present invention uses an LED as a light source (2). Therefore, not only does it consume less power, but also complete white light that is not reddish on the front side. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross-sectional view showing an example of a mode of a surface light source device of the present invention. Fig. 2 is a schematic view showing a measurement point for evaluating uniform chromaticity in the embodiment. Fig. 3 is a cross-sectional view showing a mode of an example of a surface light source device of the prior art. [Description of main component symbols] 1 : Light diffusing plate 2 : Light source (L E D ) 3 : Surface light source device -12- 200944712 4 : Reflector
-13--13-