1308653 玖、發明說明： [發明所屬之技術領域] 本發明是有關於一種應用於液晶顯示裝置等的正下 型背光組件。 [先前技術] 近年來，因爲液晶電視等的液晶顯示裝置的大畫面 化，將光照射至液晶面板的背光組件也需要大型化。雖然， 背光組件可區分爲側光型及正下型’但大型的背光組件多 採用後者的正下型。 亦即，正下型是在丙烯酸或聚碳酸酯等的合成樹脂 製的擴散板的背後，配置多數個燈管（冷陰極管型的螢光 燈管）’使用多數個燈管配置在發光面的靠裡側（參照日本 專利早期公開之特開平4-350821號及特開平11-295731 號），即使是大型化也可容易獲得高亮度，因而適用於高 売度大型化。且，正下型的裝置內部爲中空結構，即使大 型化也很輕，也因此更適用於高亮度大型化。 然而’在習知的正下型背光組件中，在薄型化時， 難以保持發光面上的良好發光品質。特別是，高亮度大型 化欲進一步薄型化時，欲良好地保持發光品質更爲困難。 亦即因爲直下型背光組件是在擴散板的背後配置 燈管，比側光型要厚，本來就不容易薄型化。 且’因薄型化造擴散板與燈管之間的間隔變小，擴 散板發光面上的燈管影像變強（擴散板的燈管正上方附近 的高度高’燈管間的位置亮度低的緣故），很難消去此燈 12246pif.doc/008 4 1308653 管影像’發光品質降低。換言之，正下型背光組件當謀求 薄型化時’發光品質便會降低。 更’在確保正下型背光組件之大型化及高亮度的場 合’因爲顯示面大，需使用多數個燈管，由燈管造成的發 熱也會變大。且，習知的正下型背光組件，其擴散板是由 丙烯酸或是聚碳酸酯等的合成樹脂製，會因發熱的影響而 易使擴散板彎曲、變黃、產生熱變形，使發光品質低正又 縮短受壽命。 像這樣，在習知的樹脂製擴散板中，若欲避免發光 品質低下或是發熱的影響，需要加大燈管與擴散板之間的 間隔，這樣會使裝置變厚，無法薄型化，且亮度也會降低。 有鑑於上述的習知的問題點，本發萌的目的是提供 一種正下型背光組件，可保持良好的發光品質，且薄型化。 又，本發明的其他目的是，在正下型背光組件中， 提供一種新穎的技術手段，可良好地保持發光品質，可高 亮度又可大型化，更可進一步薄型化。 [發明內容] 本發明提供一種正下型背光組件’應用於以一一定 的燈管間隔在一擴散板的背後配置多數個燈管，其特徵在 於：擴散板與燈管之間的距離爲10mm以下，以接近燈管， 且擴散板爲玻璃製’霧度値爲95%以上，穿透率爲 10%~40%(較佳的是 1〇%~30%)。 根據本發明，因爲擴散板是玻璃製，即使從燈管而 來的發熱變大，仍可避免燈管發熱的影饗，且可把擴散板 12246pif.doc/008 5 1308653 配置得接近燈管，因而可薄型化背光組件。換言之’擴散 板爲玻璃製具有優良的耐熱性，所以即使是從燈管而來的 發熱變大的場合，擴散板與燈管之間的距離爲i〇mm以下 (較佳的是5mm以下），可使擴散板接近燈管。 且，本發明人發現到，即使擴散板與燈管之間的距 離縮短，藉由採用霧度値高且穿透率低的擴散板，仍可獲 得良好的發光品質。 也就是說，即使是爲了薄型化把擴散板與燈管之間 的距離縮小，而使得燈管影像變強，利用高霧度値與低穿 透率的擴散板，便可有效的抑制燈管影像，因而發光品質 良好。具體而言，由霧度値95%以上，穿透率爲10%~40% 的擴散板，便可獲得良好的發光品質。且，即使把擴散板 的穿透率一直降低到40%以下，因爲擴散板與燈管之間的 距離小，因而即使燈管數少也可確保高亮度。又，爲了確 保最低限度的亮度，穿透率10%以上較’爲理想。 又，根據本發明，因爲擴散板與燈管之間的距離小， 當做成大型的背光組件時，以較少的燈管數便可獲得高亮 度的良好發光品質。 前述擴散板與前述燈管之間的距離可做成5mm以上 10mm以下。若擴散板與燈管之間的距離過小，則易顯示 出燈管影像，爲了抑制此情況’擴散板的穿透率需非常地 小。而一旦穿透率變小，亮度就會降低，爲了要得到高亮 度，需增加燈管數，但此舉會導致成本或是消耗電力增大。 本發明針對此點的對策是’使擴散板與些燈管之間 12246pif.doc/008 6 1308653 的距離爲5mm以上l〇mm以下的薄型化程度，因而可獲 得抑制燈管數、發光品質良好且高亮度/薄型的正下型背 光組件。 藉由抑制燈管根數’可把燈管間距做成較大的 12mm〜30mm的範圍’可抑制鐙管根數增多造成的成本/消 耗電力。 或者是，本發明可在前述燈管間距在4mm〜12mm的 範圍內使燈管間距非常小以增加燈管數，並使擴散板的穿 透率爲30%以下非常之小’把擴散板與燈管之間的距離做 成5mm(較佳的是1.5mm〜5mm)以下。 亦即，使燈管間距在非常小以增加燈管根數，並使 擴散板的穿透率非常低’藉此’可利用低穿透率及較多的 燈管確保足夠的亮度。 且，因擴散板的穿透率非常地小’消去燈管影像的 作用便十分有效。又’因爲燈管間距較小，燈管間亮度低 的部分變少，因而可抑制燈管影像的發生。因此’即使擴 散板與燈管之間的距離爲5mm以下（較佳的是 1.5mm~5mm，更佳的是3mm〜5mm)，也足以抑制燈管影 像。 藉此，可得良好發光品質的高亮度’又是超薄型的 正下型背光組件。 且，爲了防止不必要的增加燈管數，燈管間距較佳 的是4mm以上。 又，根據本發明的其他觀點，本發明提供一種正下 12246pif.doc/008 7 1308653 型背光組件，應用於以—定的燈管間隔在一擴散板的背 後配置多數個燈管，其特徵在於：擴散板與燈管之間的距 離爲10mm以下，以接近該些燈管，且擴散板爲玻璃製， 霧度値爲95%以上，穿透率爲10%〜60%，且燈管間距是 在4mm〜12mm的範圍內。 在此場合，因爲擴散板是玻璃製’即使從燈管而來 的發熱變大，仍可避免燈管發熱的影響，且可把擴散板配 置得接近燈管，因而可薄型化背光組件。換言之’擴散板 爲玻璃製具有優良的耐熱性，所以即使是從燈管而來的發 熱變大的場合，擴散板與燈管之間的距離爲10mm以下(甚 至是5mm以下），可使擴散板接近燈管。 且，因爲擴散板與燈管之間的距離小，燈管間距小’ 可得發光品質良好的超高亮度/薄型的正下型背光組件。 換言之，即使是爲了薄型化而使擴散板與燈管的距離縮 小，因爲燈管間距小，是故可抑制燈管影像的發生，其發 光品質良好。更，因爲是利用小燈管間距抑制燈管影像的 發生，可讓擴散板的穿透率一直大到60%爲止，並相互抑 、 制燈管間距而使燈管數增加，可得擴散板發光面之亮度非 常高(例如爲l〇〇〇〇cd/m2)的正下型背光組件。 更，根據本發明的其他觀點，本發明提供一種正下 型背光組件，應用於以一一定的燈管間隔在一擴散板的背 後配置多數個燈管’其特徵在於：擴散板的穿透率爲 20%〜4〇% ’且擴散板與一反射面之間的距離l是由下述不 等式（1)決定之。其中對應於相鄰兩個燈管之中間位置的擴 12246pif.doc/008 8 1308653 散板的一發光面上的亮度最大値爲Bmax之擴散板與一反 射面之間的距離爲La，売度爲亮度最大値Bmax之90%的 擴散板與反射面之間的距離爲Lb，且Lb>La時，滿足下 列不等式（1)， ·1308653 发明Invention Description: [Technical Field] The present invention relates to a direct type backlight assembly applied to a liquid crystal display device or the like. [Prior Art] In recent years, a liquid crystal display device such as a liquid crystal television has a large screen, and a backlight unit that irradiates light to a liquid crystal panel also needs to be enlarged. Although the backlight assembly can be divided into an edge type and a down type, the large backlight assembly mostly uses the latter type. In other words, the positive type is disposed behind a diffusing plate made of synthetic resin such as acrylic or polycarbonate, and a plurality of lamps (cold cathode tube type fluorescent tubes) are disposed. In the case of the large-scale, it is easy to obtain high brightness even if it is large-sized, and it is suitable for large-scale enlargement. Further, since the inside of the device is a hollow structure, it is light in size and is therefore more suitable for high brightness and large size. However, in the conventional direct type backlight assembly, it is difficult to maintain good light-emitting quality on the light-emitting surface when thinning. In particular, when it is desired to further reduce the thickness of the high-intensity, it is more difficult to maintain the light-emitting quality satisfactorily. That is, since the direct type backlight assembly is provided with a lamp tube behind the diffusion plate, it is thicker than the side light type, and it is not easy to be thinned. And 'the interval between the thin diffuser plate and the lamp tube becomes smaller, the image of the lamp on the light-emitting surface of the diffuser plate becomes stronger (the height near the lamp tube of the diffuser plate is high), and the position between the lamps is low. For sake), it is difficult to eliminate this lamp 12246pif.doc/008 4 1308653 tube image 'light quality is reduced. In other words, when the down-type backlight unit is thinned, the light-emitting quality is lowered. Further, in order to ensure an increase in the size and brightness of the down-type backlight unit, since the display surface is large, it is necessary to use a plurality of lamps, and the heat generated by the lamps is also increased. Further, in the conventional direct type backlight assembly, the diffusion plate is made of synthetic resin such as acrylic or polycarbonate, and the diffusion plate is easily bent, yellowed, and thermally deformed due to the influence of heat generation, so that the light quality is improved. Low positive and shortened life expectancy. As described above, in the conventional resin diffusion plate, if it is desired to avoid the influence of low light quality or heat generation, it is necessary to increase the interval between the lamp tube and the diffusion plate, which makes the device thicker and cannot be made thinner, and The brightness will also decrease. In view of the above-mentioned conventional problems, the purpose of the present invention is to provide a direct type backlight assembly which can maintain good light quality and is thin. Further, another object of the present invention is to provide a novel technical means for maintaining a light-emitting quality in a direct-type backlight assembly, which can be high in brightness and large in size, and can be further thinned. SUMMARY OF THE INVENTION The present invention provides a direct-type backlight assembly that is applied to a plurality of lamps disposed behind a diffusion plate with a certain tube interval, wherein the distance between the diffusion plate and the lamp tube is 10mm or less, close to the lamp tube, and the diffuser plate is made of glass, the haze is 95% or more, and the transmittance is 10% to 40% (preferably 1% to 30%). According to the present invention, since the diffusion plate is made of glass, even if the heat generated from the lamp tube becomes large, the influence of the heat generation of the lamp tube can be avoided, and the diffusion plate 12246pif.doc/008 5 1308653 can be disposed close to the lamp tube. Thus, the backlight assembly can be thinned. In other words, the 'diffusion plate has excellent heat resistance from glass. Therefore, even when the heat generated from the tube is increased, the distance between the diffusion plate and the tube is i 〇 mm or less (preferably 5 mm or less). , the diffusion plate can be close to the lamp tube. Further, the inventors have found that even if the distance between the diffusing plate and the bulb is shortened, a good illuminating quality can be obtained by using a diffusing plate having a high haze and a low transmittance. That is to say, even if the distance between the diffusing plate and the tube is reduced for thinning, the image of the tube becomes strong, and the diffusing plate with high haze and low transmittance can effectively suppress the tube. The image is therefore of good quality. Specifically, a good diffusion quality can be obtained by a diffusion plate having a haze of 95% or more and a transmittance of 10% to 40%. Further, even if the transmittance of the diffusion plate is always reduced to 40% or less, since the distance between the diffusion plate and the tube is small, high brightness can be ensured even if the number of lamps is small. Further, in order to ensure the minimum brightness, the transmittance is preferably 10% or more. Further, according to the present invention, since the distance between the diffusing plate and the bulb is small, when a large-sized backlight unit is formed, a high-brightness good light-emitting quality can be obtained with a small number of lamps. The distance between the diffusion plate and the aforementioned tube can be made 5 mm or more and 10 mm or less. If the distance between the diffuser plate and the tube is too small, the tube image is easily displayed, and in order to suppress this, the transmittance of the diffuser plate is required to be extremely small. Once the penetration rate becomes smaller, the brightness is lowered. In order to obtain high brightness, the number of lamps needs to be increased, but this causes an increase in cost or power consumption. The countermeasure against this point of the present invention is to make the distance between the diffuser plate and the lamps 12246pif.doc/008 6 1308653 to be 5 mm or more and less than 10 mm, thereby suppressing the number of lamps and the light emission quality. And a high-brightness/thin positive under-type backlight assembly. By suppressing the number of lamps, the distance between the lamps can be made larger in the range of 12 mm to 30 mm, and the cost/consumption power due to the increase in the number of the tubes can be suppressed. Alternatively, the present invention can make the spacing of the lamps very small in the range of the lamp tube spacing of 4 mm to 12 mm to increase the number of lamps, and make the diffusion rate of the diffusion plate 30% or less very small. The distance between the lamps is made 5 mm (preferably 1.5 mm to 5 mm) or less. That is, the pitch of the lamps is made very small to increase the number of lamps and the transmittance of the diffusion plate is very low 'by this' to ensure sufficient brightness with a low transmittance and a large number of lamps. Moreover, since the transmittance of the diffusing plate is very small, it is very effective in eliminating the image of the lamp. Further, since the interval between the lamps is small, the portion where the brightness between the lamps is low is reduced, so that the occurrence of the image of the lamp can be suppressed. Therefore, even if the distance between the diffusion plate and the tube is 5 mm or less (preferably 1.5 mm to 5 mm, more preferably 3 mm to 5 mm), it is sufficient to suppress the tube image. Thereby, a high brightness of good light quality can be obtained, which is an ultra-thin positive type backlight assembly. Further, in order to prevent unnecessary increase in the number of lamps, the pitch of the lamps is preferably 4 mm or more. Moreover, according to other aspects of the present invention, the present invention provides a backlight assembly of 12246 pif.doc/008 7 1308653 type, which is applied to a plurality of lamps disposed behind a diffusion plate at a time interval of a lamp, characterized in that : The distance between the diffuser plate and the lamp tube is 10 mm or less to approach the lamps, and the diffuser plate is made of glass, the haze is 95% or more, the transmittance is 10% to 60%, and the tube spacing is It is in the range of 4mm~12mm. In this case, since the diffusion plate is made of glass, even if the heat generated from the lamp tube becomes large, the influence of the heat generation of the lamp tube can be avoided, and the diffusion plate can be disposed close to the lamp tube, so that the backlight unit can be made thinner. In other words, the 'diffusion plate has excellent heat resistance from glass. Therefore, even when the heat generated from the tube becomes large, the distance between the diffusion plate and the tube is 10 mm or less (or even 5 mm or less), and diffusion is possible. The board is close to the tube. Moreover, since the distance between the diffusion plate and the lamp tube is small and the pitch of the lamp tube is small, an ultra-high brightness/thin type direct-type backlight assembly having good light-emitting quality can be obtained. In other words, even if the distance between the diffusing plate and the bulb is reduced for thinning, since the pitch of the bulb is small, the occurrence of the bulb image can be suppressed, and the light-emitting quality is good. Moreover, because the small tube spacing is used to suppress the occurrence of the image of the tube, the transmittance of the diffusing plate can be kept up to 60%, and the distance between the tubes is increased, and the number of tubes is increased to obtain a diffusing plate. A direct-type backlight assembly in which the luminance of the light-emitting surface is very high (for example, l〇〇〇〇cd/m2). Further, according to other aspects of the present invention, the present invention provides a direct-type backlight assembly for applying a plurality of lamps disposed behind a diffusion plate with a certain tube interval. The feature is: penetration of the diffusion plate. The rate is 20% to 4%% and the distance l between the diffusion plate and a reflecting surface is determined by the following inequality (1). The distance between the diffusing plate and the reflecting surface of the diffusing plate of the 12236pif.doc/008 8 1308653 diffusing plate corresponding to the middle position of the adjacent two lamps is the maximum brightness, and the distance between the diffusing plate and the reflecting surface is La, The distance between the diffusing plate and the reflecting surface, which is 90% of the maximum brightness 値Bmax, is Lb, and when Lb>La, the following inequality (1) is satisfied,
La ^ L ^ Lb —(1)0 在如上述構成的正下型背光組件中，是使用20%〜40% 的低穿透率的擴散板。亦即，本發明人爲了在薄型化後仍 能保持良好的發光品質，是著眼於降低擴散板的穿透率》 當使用像這樣低穿透率之擴散板的場合時，上述發光面的 亮度也會變低而易使該發光面變暗。在此處，本發明人注 意到薄型化後發光面上最暗的部分是最容易認出燈管影像 的地方，於是便特別注意上述相鄰兩燈管的中間位置所對 應的擴散板的發光面上的亮度。然後，根據此亮度，在上 述不等式（1)規定的範圍內，選擇擴散板與反射面之間的距 離L。藉此，可使發光面確保所希望的亮度，並可極力防 止在該發光面上產生燈管影像，因而能獲得可保持良好的 發光品質又可謀得薄型化的正下型背光組件。 在此處，把擴散板的穿透率做成20〜4〇%的緣故是， 當使用未滿20%穿透率的擴散板時，通過發光面的燈光會 變少。而若使用超過40%穿透率的擴散板的場合，在燈管 正上方附近的發光面亮度比對應上述中間位置的亮度要 高，不易抑制燈管影像，因而在薄型化時難以保持良好的 發光品質。 又，把上述距離L取爲不等式（1)之範圍內的値的緣 12246pif.doc/008 9 1308653 故是’若把距離L選擇成比最大亮度値Bmax之擴散板與 反射面之間的距離La還要小的話，與使用超過40%穿透 率的擴散板的場合同樣的，很難抑制燈管影像的發生，因 而在薄型化時難以保持良好的發光品質。另一方面，若把 距離L選擇成比最大亮度値Bmax之90%的擴散板與反射 面之間的距離Lb還要大時，與使用未滿20%穿透率的擴 散板的場合同樣的，難以確保發光面達所希望的亮度。 .又，在上述正下型背光組件中，較佳的是，亮度是 在亮度最大値Bmax之92%〜95%的範圍內，以決定該距離 L。 在此場合，特別是能構成具優良發光品質的薄型背 光組件。 在上述的各正下型背光組件中，因爲能提供燈管的 發熱對策，所以容易獲得燈管數較多的大型背光組件’即 背光組件有效發光區域之對角尺寸爲10英吋以上（較佳的 是15英吋以上）的大型背光組件。 又，在上述的各正下型背光組件中’因爲能提供燈 管的發熱對策’所以容易獲得燈管數較多的高亮度的背光 組件，即擴散板發光面的亮度爲4000cd/m2以上’較佳的 是5000cd/m2,更佳的是7000cd/m2以上的高亮度背光組 件。 爲讓本發明之上述和其他目的、特徵、和優點能更 明顯易懂，下文特舉一較佳實施例’並配合所附圖式’作 詳細說明如下： 12246pif.doc/008 10 1308653 [實施方式] 以下，根據附圖說明本發明的較佳實施例。第1〜3 圖繪示作爲液晶電視或電腦用液晶顯示器等的液晶顯示裝 置用正下型背光組件1。組裝此正下型背光組件丨的液晶 顯示裝置爲大型，具體而言，爲比英吋（畫面對角線尺 寸約爲10英吋）大。舉例而言，爲15、17、2〇、30、50 英吋型等。 正下型背光組件1是在殼體3内部的一面安裝著擴 散板2，且在殼體3內部配置多數個光源4。殻體3是金 屬製或是合成樹脂製，形成爲一面開口的薄箱狀。且在殼 體3的底面3a上，形成有白色的反射面。 在殼體3開口的一面上安裝白色玻璃製的擴散板2。 擴散板是1.0mm〜3_0mm厚，較佳的是採用2.0mm厚左右 者。 液晶顯示裝置的液晶面板5是被設置在前述擴散板2 背後的位置’擴散板2之面狀光是略均一地被照射至液晶 面板5。因此’擴散板2是形成比液晶顯示裝直的畫面尺 寸還要大。具體而言，擴散板2在與液晶顯示裝置之畫面 尺寸略相等的有效發光區域的周緣側，確保了非有效發光 區域的大小。因此，例如，應用於I5英吋型液晶顯示裝 置的背光組件擴散板2之有效發光區域對角尺寸約爲15 央吋。且，擴散板2的非有效發光區域是隱藏並被支撑在 殻體3等，爲朝往液晶面板5的光所照射不到的範圍。 配置於擴散板2背後的光源4下細長線狀的光源， 12246pif.doc/008 11 1308653 具體而言’是冷陰極管型的螢光燈管。此些螢光燈管4是 把複數根（圖示爲8根）燈管以略等燈管間距LP平行地配 S °此正下型背光組件1，因爲是用於大型液晶顯示裝置 用’需有大的有效發光區域，且需具備與此對應的多數個 m光燈管4 °且，從作爲液晶電視使用場合的高亮度需求 看來’也是需要多個螢光燈管4。具體而言，15英吋型用 的背光組件的話，是使用約8根程度的螢光燈管4，20英 吋型用的背光組件的話，是使用約12根程度的螢光燈管 4 ’ 30英吋型用的背光組件的話，是使用約16根程度的螢 光燈管4。且螢光燈4至反射面3a的距離是設定成約 0.3〜2mm程度，燈管4是接近地配置在平面的反射面3a。 冷陰極管型的螢光燈管4，其直徑約爲2.0〜4.0mm細 (較佳爲3.0mm的程度），適於薄型化，但是，因爲電極部 分的發熱大，一旦設了多數個螢光燈管4時，因發熱的緣 故，殻體3內部的溫度變得非常高。又，螢光燈管4是由 未圖示的換流器（點燈裝置，一般設於殼體的背面）進行高 頻點燈，但是由此換流器而來的發熱也會促使殻體3內部 的溫度上昇。特別是’像本實施例那樣，點燈多數個螢光 燈管的場合，因爲消耗電力變大，發熱也會變大。大型液 晶顯示裝置用的背光組件1的場合，殻體3內部的溫度昇 高將無法避免。 在此，相鄰的燈管4、4彼此之間(燈管間距)LP可做 成4〜30mm程度的範圍。當把燈管間距LP做小時，燈管 的根數增加，發熱較大且亮度亦較大。另一方面，當把燈 12246pif.doc/008 12 1308653 管間距LP做大時，燈管根數就減少，發熱較小且亮度較 低。具體而言，當把燈管間距LP設定成4〜12mm時’可 避免異常高溫且可得高亮度。亦即，杷燈管間距LP設成 12mm以下，可使燈管數變多而得高亮度，把燈管間距LP 做得比4mm大，可避免異常發熱。 另一方面，當把燈管間距LP設定在12~30mm範圍 中時，可確保某程度的亮度且可降低燈管數目，可節約成 本及消耗電力。亦即，因爲燈管間距LP比12mm大(較佳 的是15mm，更佳的是20mm)，燈管根數較少，發熱較少。 且因爲燈管間距LP比30mm小，可確保某程度的亮度。 且，藉由採用30mm以下的燈管間距LP，在相鄰的 2個燈管4、4之間，顯示出亮度低的部分較少，因而可抑 制燈管影像的產生。 殻體3是形成爲薄型，以將擴散板2支撐在距燈管4 距離L小的位置，以此方式，背光組件1可被薄型化，且 可達成液晶顯示裝置的薄型化。具體而言，擴散板2與燈 管4的距離L是做成l〇mm以下。習知，市售的液晶顯示 裝置用的背光組件，因爲是採用合成樹脂製的擴散板，爲 了要約制發熱，距離L不只爲2〇mm的程度，然而，在本 實施例中，可做到距離L爲10mm以下的大幅薄型化。更 進一步’可距離L做成5mm以下’更佳的是做成1 5~5@爪。 或者是也可以把距離L做成5 mm以上1 〇mm以卞· 像本實施例那樣，雖距離L做小會使得發熱的燈管* 接近擴散板2而使擴散板2易受熱的影響，佝撼 目女板2是 12246pif.doc/008 13 1308653 由比合成樹脂製耐熱更強的玻璃製，不會因熱的影響而產 生彎曲、變黃、熱變形等。 此外，當把習知的擴散板距離L做小時，燈管影像 會顯示地很明顯而使發光品質下降，然而，本實施例的擴 散板2，因爲是採用高霧度（曇度，haze)低穿透率者，即 使距離L變小’也不易產生燈管影像，而可維持擴散板2 之亮度均一性（發光品質）。再加上，雖只用高霧度低穿透 率的擴散板會有導致亮度低下的問題，但是在本實施例 中，因爲距離L變小’所以即使採用高霧度低穿透率的擴 散板，也以由較少的燈管數維持高亮度。亦即，正下型背 光組件1的大型化、薄型化、高亮度，及良好的發光品質， 通通都可以達成。 具體而言，擴散板2的霧度値，爲了得到良好的擴 散性爲95%以上，較佳的是97%以上。又，擴散板2的穿 透率，視不同的場合可爲60%以下，代表較佳的爲4〇%以 下。爲了使穿透率不要太低且使亮度不受損，較佳的是設 定10%以上者。較佳的是穿透率爲20〜40%，30〜4〇%則爲 更佳。 在擴散板2上(擴散板2的液晶面板5側的面），視需 要配置調整發光品質的擴散板、透鏡板、偏光板等的光學 板6。在多數的場合，作爲光學板6採用的是使亮度上昇 的擴散板。 以下，以幾個實驗結果爲代表，作爲實施例與比較 例說明之。 12246pif.doc/008 14 1308653 [實施例l] 15英吋型用的正下型背光組件丨中，把距離l薄型 化爲10mm，把燈管間距LP設成23.5mm(燈管根數爲8 根），擴散板2的霧度値爲97%，穿透率爲40%的場合(實 施例1)，可得幾無發光不均的良好發光品質。且，僅管;$ 透率低燈管數又不多（8根），乃可獲得約5000cd/m2的足夠 亮度(無光學板6狀態時的亮度，以下同樣）。亦即，在實 施例1中，正下型背光組件的大型化、薄型化、高亮度， 及其良好的發光品質，通通都可以達成，且燈管數較少， 成本較便宜。 [比較例1] 在比較例1中，改變了實施例1中的穿透率。亦即， 15英吋型用的正下型背光組件1，把距離L薄型化爲 10mm，把燈管間距LP設定成23.5mm，擴散板2的霧度 値97%，穿透率爲50%以上的場合（比較例1)，可確認到 擴散板2上的發光不均，發光品質受損。 [實施例2] 15英吋型用的正下型背光組件1中，把距離L薄型 化爲5mm，把燈管間距LP設成12mm，擴散板2的霧度 値爲97%，穿透率爲30%的場合(實施例2) ’可得幾無發 光不均的良好發光品質。且，在實施例2中，雖穿透率比 實施例1還要低，但因爲距離L較小，所以可得與實施例 1同等亮度(約5000cd/m2)。亦即，在實施例2中’正下型 背光組件的大型化、薄型化、高亮度’及其良好的發光品 12246pif.doc/008 15 1308653 質，通通都可以達成，且未損及發光品質及高亮度，可比 實施例1達成更進一步的薄型化(超薄型化）。 [實施例3] 15英吋型用的正下型背光組件1中，把距離l薄型 化爲10mm，把燈管間距LP設成12mm，擴散板2的霧度 値爲97%，穿透率爲60%的場合(實施例3)，可得幾無發 光不均的良好發光品質。且，在實施例3中，因爲穿透率 比實施例1高，且燈管間距LP較小，所以可得比實施例 1更高的亮度(約10000cd/m2)。亦即，在實施例3中，正 下型背光組件的大型化、薄型化、高亮度，及其良好的發 光品質，通通都可以達成，且未損及發光品質，又可達成 超高亮度。此實施例3特別適用於液晶電視。 [比較例2] 在15英吋型用的正下型背光組件丨，把距離l薄型 化爲10mm ’把燈管間距LP設定成23.5mm，擴散板2的 霧度値97%，穿透率爲60%以上的場合(比較例2)，可確 認到擴散板2上的發光不均，發光品質受損。 第4〜6圖繪示其他實施例的正下型背光組件1。 此正下型背光組件1，舉例而言，乳白色的擴散板2 是安裝在殻體3內部的一面，且在殼體3內部配置著複數 個光源4。第4〜6圖繪示正下型背光組件1，未特別說明 的部分是與第1〜3圖繪示的正下型背光組件相同。 且，在上述殻體3的底面上，設有由合樹脂膜或鋁 等金屬膜構成的反射板8。此反射板8是將光源4的光朝 12246pif.doc/008 16 1308653 向擴散板2反射的反射面。在光源4側的表面，舉例而言， 是被塗裝成白色’可有效率地將上述光反射到擴散板2側， 以提高該光的利用效率及擴散板2的亮度。且，此反射板 8的厚度爲0.2〜0.4mm程度’以不妨礙背光組件1的薄型 化。且’也可以把高光反射率的白色或銀色等的塗料塗佈 在殻體3的底面’並以此反射層當作反射面，取代掉上述 的反射板8。 第4〜6圖繪示在正下型背光組件1中，亦可取代玻 璃材’利用合樹脂材作爲上述擴散板2。但是，比起合成 樹脂製的場合，應用耐熱強的玻璃製的擴散板2的場合的 一方’其不易因燈管4的發熱或殻體3內部的溫度上昇等 的熱影響而彎曲、變黃、熱變形等，較爲理想。 且，在上述擴散板2中，其霧度値爲88%以上，較 佳的是95%以上，更佳的是使用97%以上的話，對液晶面 板5而言，可提高燈管光的擴散性，因而容易地在面板5 上均一地形成高亮度顯示畫像。更，擴散板2的穿透率是 使用20〜40%的低穿透率。爲了使穿透率不要太低而損及 亮度，較佳的是設定20%以上，更佳的是穿透率爲30〜40% 以上。且，藉由把穿透率做成40%以下，即使薄型化也能 抑制亮度低下且可防止燈管影像的發生，易於保持良好的 發光品質。 在擴散板2上（擴散板2的液晶面板5側的面）上’可 視需要配設調整發光品質用的擴散板、透鏡板、偏光板等 的光學板6。在大多數的場合，作爲光學板6是採用使売 12246pif.doc/008 17 1308653 度上昇的擴散板。 上述擴散板2與反射板8之間的距離L(第6圖），是 根據相鄰兩燈管4之中間位置(第5圖中一點鎖線C顯不 的上述燈管間距LP的1/2尺寸線上的任意點c)所對應的 該擴散板2之發光面(第4圖的X點）的亮度而被最適化， 可選自於由下述La及Lb的不等式（1)規定的範圍內的値。 在薄型化背光組件時，在未配置上述光學板6的狀態下測 定的場合，上述發光面上的X點爲該發光面上最暗的部 分，爲最易看到燈管影像的地方。且，上述La是上述中 間位置上方的發光面上(X點）亮度爲最大値Bmax之擴散 板2與反射板8之間的距離。上述Lb是上述中間位置上 方的發光面上(X點)亮度爲最大値Bmax之90%的擴散板2 與反射板8之間的距離（且Lb>La)。La ^ L ^ Lb - (1) 0 In the direct-type backlight assembly constructed as described above, a diffusion plate of low transmittance of 20% to 40% is used. In other words, the present inventors have focused on reducing the transmittance of the diffusing plate in order to maintain good light-emitting quality even after thinning. When using a diffusing plate having such a low transmittance, the brightness of the above-mentioned light-emitting surface It also becomes low and it is easy to darken the luminescent surface. Here, the inventors have noticed that the darkest portion of the light-emitting surface after thinning is the place where the image of the tube is most easily recognized, so that attention is paid to the light emission of the diffusion plate corresponding to the intermediate position of the adjacent two lamps. The brightness on the surface. Then, based on this brightness, the distance L between the diffusion plate and the reflection surface is selected within the range defined by the above inequality (1). Thereby, the light-emitting surface can be made to have a desired brightness, and the tube image can be prevented from being generated on the light-emitting surface as much as possible, so that a down-type backlight unit which can maintain a good light-emitting quality and can be made thinner can be obtained. Here, the transmittance of the diffusion plate is made 20 to 4%, because when a diffusion plate having a transmittance of less than 20% is used, the light passing through the light-emitting surface is reduced. On the other hand, when a diffusing plate having a transmittance of more than 40% is used, the brightness of the light-emitting surface near the upper side of the tube is higher than the brightness corresponding to the intermediate position, and it is difficult to suppress the image of the tube, so that it is difficult to maintain a good shape when the thickness is thinned. Luminous quality. Further, the above-mentioned distance L is taken as the edge 12246pif.doc/008 9 1308653 of the 不 in the range of the inequality (1), so "if the distance L is selected as the distance between the diffusion plate and the reflection surface of the maximum brightness 値 Bmax When La is small, it is difficult to suppress the occurrence of the tube image as in the case of using a diffusion plate having a transmittance of more than 40%, and thus it is difficult to maintain good light-emitting quality at the time of thinning. On the other hand, if the distance L is selected to be larger than the distance Lb between the diffusing plate and the reflecting surface which is 90% of the maximum brightness 値Bmax, the same as in the case of using a diffusing plate having a transmittance of less than 20%. It is difficult to ensure that the luminous surface reaches the desired brightness. Further, in the above-described front type backlight assembly, it is preferable that the luminance is in the range of 92% to 95% of the maximum luminance 値Bmax to determine the distance L. In this case, in particular, a thin backlight assembly having excellent light-emitting quality can be constructed. In each of the above-described direct type backlight assemblies, since it is possible to provide a countermeasure against heat generation of the lamp tube, it is easy to obtain a large-sized backlight unit having a large number of lamps, that is, the diagonal size of the effective light-emitting area of the backlight unit is 10 inches or more (more) The best is a large backlight assembly of 15 inches or more. Further, in the above-described respective direct type backlight assemblies, "the countermeasure for heat generation of the lamp tube can be provided", so that it is easy to obtain a high-brightness backlight unit having a large number of lamps, that is, the luminance of the light-emitting surface of the diffusion plate is 4000 cd/m2 or more' More preferably, it is 5000 cd/m2, more preferably a high-brightness backlight assembly of 7000 cd/m2 or more. The above and other objects, features, and advantages of the present invention will become more apparent and understood from the <RTIgt; <RTIgt; </ RTI> <RTIgt; </ RTI> <RTIgt; Modes Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. The first to third figures show a direct type backlight unit 1 for a liquid crystal display device such as a liquid crystal display or a liquid crystal display for a computer. The liquid crystal display device in which the front type backlight unit is assembled is large, specifically, larger than the inch (the screen diagonal size is about 10 inches). For example, it is 15, 17, 2, 30, 50 inches, and the like. In the direct type backlight unit 1, a diffusion plate 2 is attached to one surface of the inside of the casing 3, and a plurality of light sources 4 are disposed inside the casing 3. The casing 3 is made of metal or synthetic resin and is formed in a thin box shape with one opening. Further, a white reflecting surface is formed on the bottom surface 3a of the casing 3. A diffusing plate 2 made of white glass is attached to one side of the opening of the casing 3. The diffusion plate is 1.0 mm to 3_0 mm thick, preferably 2.0 mm thick. The liquid crystal panel 5 of the liquid crystal display device is disposed at a position behind the diffusing plate 2. The planar light of the diffusing plate 2 is slightly uniformly irradiated onto the liquid crystal panel 5. Therefore, the diffusing plate 2 is formed to be larger than the screen size of the liquid crystal display. Specifically, the diffusion plate 2 ensures the size of the ineffective light-emitting region on the peripheral side of the effective light-emitting region which is slightly equal to the screen size of the liquid crystal display device. Therefore, for example, the effective light-emitting area of the backlight unit diffusion plate 2 applied to the I5 inch type liquid crystal display device has a diagonal size of about 15 Å. Further, the ineffective light-emitting area of the diffusing plate 2 is hidden and supported by the casing 3 or the like in a range that is not irradiated to the light of the liquid crystal panel 5. An elongated linear light source disposed under the light source 4 behind the diffuser plate 12, 12246pif.doc/008 11 1308653 is specifically a cold cathode tube type fluorescent tube. The fluorescent tubes 4 are provided with a plurality of (eight illustrated) lamps in parallel with the lamp pitch LP in parallel with the S-type backlight assembly 1 because it is used for large liquid crystal display devices. It is necessary to have a large effective light-emitting area, and it is necessary to have a plurality of m-light tubes corresponding to this, and it is necessary to have a plurality of fluorescent tubes 4 from the viewpoint of high brightness demand for use as a liquid crystal television. Specifically, the backlight unit for a 15-inch type uses a fluorescent tube of about 8 degrees, and a backlight unit for a 20-inch type, which uses about 12 fluorescent tubes. For a backlight unit of 30 inches, a fluorescent tube 4 of about 16 degrees is used. Further, the distance between the fluorescent lamp 4 and the reflecting surface 3a is set to about 0.3 to 2 mm, and the bulb 4 is a reflecting surface 3a which is disposed close to the plane. The cold cathode tube type fluorescent lamp tube 4 has a diameter of about 2.0 to 4.0 mm (preferably 3.0 mm), and is suitable for thinning. However, since the heat of the electrode portion is large, once a plurality of fireflies are provided In the case of the light tube 4, the temperature inside the casing 3 becomes extremely high due to heat generation. Further, the fluorescent tube 4 is energized by a converter (a lighting device, generally provided on the back surface of the casing) (not shown), but the heat generated by the inverter also causes the housing. 3 The internal temperature rises. In particular, when a plurality of fluorescent tubes are turned on as in the present embodiment, since the power consumption is increased, the heat is also increased. In the case of the backlight unit 1 for a large liquid crystal display device, the temperature rise inside the casing 3 cannot be avoided. Here, the adjacent lamps 4, 4 (lamp spacing) LP can be made to a range of about 4 to 30 mm. When the lamp pitch LP is made small, the number of the lamps increases, and the heat generation is large and the brightness is also large. On the other hand, when the lamp pitch of the lamp 12246pif.doc/008 12 1308653 is made larger, the number of lamps is reduced, the heat generation is small, and the brightness is low. Specifically, when the lamp pitch LP is set to 4 to 12 mm, abnormal high temperature can be avoided and high luminance can be obtained. That is, the pitch of the xenon lamp tube is set to 12 mm or less, so that the number of lamps can be increased to obtain high brightness, and the pitch of the lamp tube LP can be made larger than 4 mm to avoid abnormal heat generation. On the other hand, when the lamp pitch LP is set in the range of 12 to 30 mm, a certain degree of brightness can be ensured and the number of lamps can be reduced, which saves cost and power consumption. That is, since the lamp pitch LP is larger than 12 mm (preferably 15 mm, more preferably 20 mm), the number of lamps is small and the heat generation is small. And because the lamp pitch LP is smaller than 30 mm, a certain degree of brightness can be ensured. Further, by using the lamp pitch LP of 30 mm or less, a portion having a low luminance is displayed between the adjacent two lamps 4 and 4, and generation of a lamp image can be suppressed. The casing 3 is formed in a thin shape to support the diffusion plate 2 at a distance L from the bulb 4. In this manner, the backlight assembly 1 can be made thinner, and the liquid crystal display device can be made thinner. Specifically, the distance L between the diffusing plate 2 and the bulb 4 is not more than 10 mm. Conventionally, a backlight unit for a commercially available liquid crystal display device is a diffusion plate made of a synthetic resin, and the distance L is not limited to about 2 mm in order to heat up. However, in the present embodiment, it can be achieved. The distance L is substantially 10 mm or less. Further, the distance L can be made 5 mm or less. More preferably, it is made into 1 5 to 5 @ claws. Alternatively, the distance L may be made 5 mm or more and 1 mm or less. As in the present embodiment, although the distance L is small, the heat generating lamp * is close to the diffusing plate 2, and the diffusing plate 2 is easily affected by heat. The eye-catching female board 2 is 12246pif.doc/008 13 1308653 made of glass which is more heat-resistant than synthetic resin, and does not cause bending, yellowing, thermal deformation, etc. due to the influence of heat. In addition, when the distance L of the conventional diffusion plate is made small, the image of the lamp tube is displayed to be conspicuous and the quality of the light emission is lowered. However, the diffusion plate 2 of the present embodiment uses high haze (haze). In the case of low transmittance, even if the distance L becomes smaller, the tube image is less likely to be generated, and the brightness uniformity (light emission quality) of the diffusion plate 2 can be maintained. In addition, although only a diffusing plate having a high haze and a low transmittance may cause a problem of low brightness, in the present embodiment, since the distance L becomes small, even a high haze and a low transmittance are used. The board also maintains high brightness with a small number of tubes. That is, the size, thickness, high brightness, and good light quality of the direct type backlight unit 1 can be achieved. Specifically, the haze of the diffusing plate 2 is preferably 95% or more in order to obtain good diffusibility, and is preferably 97% or more. Further, the transmittance of the diffusing plate 2 may be 60% or less depending on the case of the diffusing plate 2, and preferably 4% or less. In order to prevent the transmittance from being too low and the brightness not to be impaired, it is preferable to set it to 10% or more. Preferably, the transmittance is 20 to 40%, and 30 to 4% by weight is more preferable. On the diffusion plate 2 (the surface on the liquid crystal panel 5 side of the diffusion plate 2), an optical plate 6 such as a diffusion plate, a lens plate, or a polarizing plate for adjusting the light-emitting quality is disposed as needed. In many cases, a diffusing plate for increasing the brightness is used as the optical plate 6. Hereinafter, several experimental results are representative, and the examples and comparative examples are explained. 12246pif.doc/008 14 1308653 [Embodiment 1] In a down-type backlight assembly for a 15-inch type, the distance l is thinned to 10 mm, and the lamp pitch LP is set to 23.5 mm (the number of lamps is 8) In the case where the haze 値 of the diffusing plate 2 is 97% and the transmittance is 40% (Example 1), a good illuminating quality with no unevenness in luminescence can be obtained. Moreover, the number of lamps having a low transmittance is not much (8), and sufficient brightness of about 5000 cd/m2 is obtained (the brightness in the absence of the optical plate 6 state, the same applies hereinafter). That is, in the first embodiment, the size, thickness, high brightness, and good light-emitting quality of the direct-type backlight unit can be achieved, and the number of lamps is small and the cost is relatively low. [Comparative Example 1] In Comparative Example 1, the transmittance in Example 1 was changed. That is, the direct-type backlight unit 1 for the 15-inch type has a thinner distance L of 10 mm, a lamp pitch LP of 23.5 mm, a diffusing plate 2 of haze of 97%, and a transmittance of 50%. In the above case (Comparative Example 1), unevenness in light emission on the diffusing plate 2 was observed, and the light-emitting quality was impaired. [Embodiment 2] In the direct-type backlight unit 1 for a 15-inch type, the distance L is reduced to 5 mm, the tube pitch LP is set to 12 mm, and the haze of the diffusion plate 2 is 97%. In the case of 30% (Example 2), a good luminescence quality with no unevenness in luminescence was obtained. Further, in the second embodiment, although the transmittance is lower than that of the first embodiment, since the distance L is small, the brightness (about 5000 cd/m2) equivalent to that of the first embodiment can be obtained. In other words, in the second embodiment, the size, thickness, and brightness of the backlight module are excellent, and the good illuminating product 12246pif.doc/008 15 1308653 can be achieved without damaging the illuminating quality. With high brightness, it is possible to achieve further thinning (ultra-thinning) than in the first embodiment. [Embodiment 3] In the direct-type backlight unit 1 for a 15-inch type, the distance l is reduced to 10 mm, the tube pitch LP is set to 12 mm, and the haze of the diffusion plate 2 is 97%. In the case of 60% (Example 3), a good luminescence quality with no unevenness in luminescence was obtained. Further, in Embodiment 3, since the transmittance is higher than that of Embodiment 1, and the lamp pitch LP is small, a higher luminance (about 10000 cd/m2) than that of Embodiment 1 can be obtained. That is, in the third embodiment, the size, thickness, high brightness, and good light-emitting quality of the direct-type backlight unit can be achieved, and the high-brightness can be achieved without impairing the light-emitting quality. This embodiment 3 is particularly suitable for a liquid crystal television. [Comparative Example 2] In a direct-type backlight assembly for a 15-inch type, the distance l is reduced to 10 mm. The lamp pitch LP is set to 23.5 mm, and the diffuser 2 has a haze of 97%. In the case of 60% or more (Comparative Example 2), unevenness in light emission on the diffusion plate 2 was confirmed, and the light-emitting quality was impaired. 4 to 6 show a direct type backlight assembly 1 of another embodiment. The front-back type backlight unit 1 is, for example, a milky white diffusing plate 2 which is mounted on the inside of the casing 3, and a plurality of light sources 4 are disposed inside the casing 3. Figs. 4 to 6 show the direct type backlight unit 1, and the portions which are not particularly described are the same as those of the down type backlight unit shown in Figs. Further, a reflecting plate 8 made of a metal film such as a resin film or aluminum is provided on the bottom surface of the casing 3. This reflecting plate 8 is a reflecting surface that reflects the light of the light source 4 toward the diffusing plate 2 toward 12246 pif.doc/008 16 1308653. The surface on the side of the light source 4, for example, is painted white, and the light can be efficiently reflected to the side of the diffusion plate 2 to improve the utilization efficiency of the light and the brightness of the diffusion plate 2. Further, the thickness of the reflecting plate 8 is about 0.2 to 0.4 mm so as not to impede the thinning of the backlight unit 1. Further, a paint such as white or silver having a high light reflectance may be applied to the bottom surface of the casing 3, and the reflecting layer may be used as a reflecting surface instead of the reflecting plate 8 described above. Figs. 4 to 6 show that in the direct type backlight unit 1, the glass material 'may be replaced with a resin material as the diffusion plate 2. However, in the case where a diffusing plate made of glass having high heat resistance is used, it is hard to bend or yellow due to heat generation of the bulb 4 or temperature rise inside the casing 3. , thermal deformation, etc., is ideal. Further, in the diffusing plate 2, the haze 値 is 88% or more, preferably 95% or more, and more preferably 97% or more, the liquid crystal panel 5 can improve the light diffusion of the tube. Therefore, it is easy to form a high-brightness image uniformly on the panel 5. Further, the transmittance of the diffusion plate 2 is a low transmittance of 20 to 40%. In order to prevent the transmittance from being too low to impair the brightness, it is preferable to set 20% or more, and more preferably, the transmittance is 30 to 40% or more. Further, by setting the transmittance to 40% or less, it is possible to suppress the occurrence of the image of the lamp tube even if the thickness is reduced, and it is easy to maintain good light-emitting quality. On the diffusing plate 2 (on the surface on the liquid crystal panel 5 side of the diffusing plate 2), an optical plate 6 such as a diffusing plate, a lens plate, or a polarizing plate for adjusting the light-emitting quality may be disposed as needed. In most cases, as the optical plate 6, a diffusion plate which raises the height of 売 12246pif.doc/008 17 1308653 is employed. The distance L between the diffuser plate 2 and the reflector 8 (Fig. 6) is based on the intermediate position of the adjacent two bulbs 4 (1/2 of the above-mentioned lamp pitch LP shown by the one-point lock line C in Fig. 5) The brightness of the light-emitting surface (X point in FIG. 4) of the diffusing plate 2 corresponding to any point c) on the dimension line is optimized, and may be selected from the range defined by the inequality (1) of La and Lb described below. Inside. In the case where the backlight unit is thinned, when the optical plate 6 is not disposed, the X point on the light-emitting surface is the darkest portion of the light-emitting surface, and is the place where the image of the tube is most easily seen. Further, the above La is a distance between the diffusion plate 2 and the reflection plate 8 whose luminance on the light-emitting surface (X point) above the intermediate position is the maximum 値Bmax. The above Lb is a distance (and Lb > La) between the diffusing plate 2 and the reflecting plate 8 whose luminance (X point) luminance above the intermediate position is 90% of the maximum 値Bmax.
La^ L ^ Lb ---(1) 要滿足上述不等式（1)，需選擇擴散板2與反射板8 之間的距離L，即使是把正下型背光組件薄型化的場合， 可從相鄰的兩燈管4直接地或是經由反射板8間接地，適 當地調整入射至擴散板2的上述中間位置上方的燈管光的 光量，可防止在擴散板發光面上產生燈管影像。且，在上 述發光面上可將亮度做成所需的高亮度(例如爲4000cd/m2 以上）’且可進一步地抑制燈管4之發熱或殻體3內的溫 度上昇等對擴散板2的熱影響。 更，上述距離L的較佳範圍，是上述最大亮度値Bmax 之92%〜95%範圍的擴散板2與反射板8之間的距離範圍。 12246pif.doc/008 18 1308653 在此處，爲了上述擴散板2之穿透率的選定及上述 距離L·的最佳化’請參照本發明人所實施的實驗結果之一 例的表1及將之圖形化的第7圖，其具體的說明了穿透率 爲20〜40%，及根據上述不等式最佳化距離l。 在此實驗中，以23.5mm的燈管間距LP配置直徑 3.0mm的兩個冷陰極燈管4，並把燈管4下端設置在距反 射板8距離2mm上方的狀態下，以一定的單位變更擴散 板2與反射板8之間的距離(即，從燈管上方到擴散板2 爲止的距離），並測定此些燈管4之中間位置上方的擴散 板發光面的亮度。採用穿透率10%、20%、30%、40%及50% 的擴散板1、2、3、4及5號，隨時測定各擴散板1〜5號 之上述中間位置上方的發光面上(X點）的亮度。 表1列示出不同（擴散板與反射板之間）的距離與不同 穿透率之擴散板的亮度値。 12246pif.doc/008 19 1308653 [表1] 距離 ------ ---^ 亮度（cd/m2) _ L(mm) 擴散板1號 擴散板2號 擴散板3號 擴散板4號 擴散板5! 7 3855 4164 4418 4696 4909 __ 8 3764 4218 4527 4836 5145 . 9 3455 4200 4606 4992 5273 11 2837 4091 4592 5021 5445 ___. 14 氺 3873 4429 4906 5491 一 16 木 3728 4300 4783 5478 18 氺 3595 4185 4693 5465 一 20 氺 3365 4061 4607 5452 __ 22 本 3088 3952 4502 5419__ #表示亮度低，未測定 由表1及第7圖可知，10%穿透率的擴散板1號，即 使是亮度峰値也是3855cd/m2低，比起其他的穿透率的擴 散板，其亮度大幅度的降低，可判定其燈管光的利用效率 太差。 50%穿透率的擴散板5號，其在上述測定處之X點的 亮度雖爲4000cd/m2以上的高亮度，但燈管正上方處的亮 度大，即使設定了其X點之最大亮度値Bmax的距離L ’ 其燈管正上方處與X點（燈管中間位置的上方）的亮度差 大，無法抹去燈管影像。亦即，使用穿透率50%的擴散板 的場合，在薄型化的時候無法確保良好的發光品質。 如第7圖的對應曲線所示，在穿透率20〜40%的擴散 12246pif.doc/008 20 1308653 板2號〜4號中，上述x點的亮度是距離L從7mm開始， 隨著距離愈大亮度愈高，一直到示出最大亮度値Bmax之 後，隨著距離愈大亮度愈低。且，伴隨此距離L增大之X 點亮度降低是如同圖曲線所示，比穿透率50%的擴散板5 號要大得多，因而可判定採用擴散板2號〜4號的場合，易 招致發光面的亮度低下。 且’各擴散板2號〜4號的發光面，在比X點爲最大 亮度値Bmax的距離La還要小的場合，上述燈管正上方 處的亮度高，X點的測定亮度與相對亮度差大，可在發光 面上認出燈管影像。所以，若使距離L接近至示出最大亮 度値Bmax的距離La，上述相對亮度差就會變小，當設成 上述距離La時便不易目視出燈管影像。在此之後，一直 到最大亮度値Bmax之90%之距離Lb爲止，可確保各發 光面所希望的亮度’且可保持燈管影像較少的良好發光品 質。又，在最大亮度値Bmax之95%〜92°/❶的距離範圍內， 由目視觀察可發現其爲發光品質良好，且少有亮度低下 者。當距離L比達最大亮度値Bmax之90%的距離Lb還 要大時，X點的亮度過低而無法有效率地利用燈管光。尙， 上述燈管正上方處的亮度’各擴散板2號〜4號都是在距離 L爲7mm時示出峰値，其後便隨著距離愈大而如第7圖對 應的曲線接近X點的亮度而低下。 更，根據上述貫驗結果’最大亮度値Bmax之100%、 95%、92%、及90%之擴散板2與反射板8之間的具體距 離値是如表2的上段所示’其對應的具體亮度値則如同表 12246pif.doc/008 21 1308653 下段所示。在表2的各擴散板1號〜4號中，95%、92%、 及90%的距離與亮度値是由第4圖對應的曲線(實驗結果) 而來的算出値。且，在表2中省略了無法抹去燈管影像的 擴散板5號。 表2列示出佔最大亮度値不同比例之各擴散板與反 射板之間的距離與亮度値。 [表2] 上段:擴散板與反射板之間的距離L(mm) 下段:相鄰兩燈管之中間位置h方的亮度< 直(cd/m2) 對 Bmax 的比 例 擴散板1號 擴散板2號 擴散板3號 擴散板4號 100% 7.00(mm) 3855(cd/ m2) 8.00(mm) 4218(cd/ m2) 9.00(mm) 4606(cd/ m2) 11.00(mm) 5021(cd/ m2) 95% 8.33(mm) 3662(cd/ m2) 12.16(mm) 4007(cd/ m2) 14.82(mm) 4376(cd/ m2) 16.29(mm) 4770(cd/ m2) 92% 8.70(mm) 3547(cd/ m2) 13.90(mm) 3881(cd/ m2) 17.08(mm) 4238(cd/ m2) 19.72(mm) 4619(cd/ m2) 90% 8.95(mm) 3470(cd/ m2) 15.06(mm) 3796(cd/ m2) 18.65(mm) 4145(cd/ m2) 21.68(mm) 4519(cd/ m2) 由表2可知’穿過率20〜40%的擴散板2號〜4號的最 大売度値Bmax的上述距離L分別爲8、9、11mm，各擴 散板2號〜4號在滿足上述不等式（1)的距離L中，燈管影 12246pif.doc/008 22 1308653 像幾乎不會在擴散板發光面上發生。且，擴散板3號及4 號，即使選擇了上述最大亮度値Bmax的90%的距離L， 如表2所示的那樣，其發光面最暗的地方之上述X點的亮 度値也有4000 cd/ m2以上，可把發光面確保在局売度。 亦即，如第7圖所示，與穿透率50%的擴散板5號 相比，當把距離L做得較大時，即使是使用X點的亮度易 低下的穿透率30%及40%的擴散板3號及4號的場合，採 用限制在上述不等式（1)右邊所規定的Lb以下値的距離L， 藉此，可防止燈管影像的發生，且可保持良好的發光品質 並可構成高亮度的發光面。 又，在穿透率爲20%的擴散板2號中，舉例而言， 其最大亮度値Bmax之90%的場合，X點的亮度雖僅爲3796 cd/ m2與4000 cd/ m2以下，根據本發明人之其他實驗結果， 藉由把燈管間距LP做成12mm以下，便不會產生燈管影 像且可使該X點的亮度達4000 cd/ m2以上的高亮度，同 時可構成上述距離L爲7mm程度的薄型背光組件。 且，根據其他的實驗，使用穿透率30%的擴散板， 把上述燈管間距LP做成12mm的場合，不需擔心燈管影 像而可構成具7〇00 cd/ m2以上亮度的發光面。 更，由表2可知，擴散板2號〜4號的各距離L，分 別爲 8.00〜15.06mm(較佳的是 12.16〜13.90mm)， 9.00~18,65mm(較佳的是 14.82 〜17.08mm)，及 ll.00~21.68mm(較佳的是 16.29〜19.72mm)，在上述 20%〜40%的穿透率中，即是使用最大穿透率的擴散板4 12246pif.d〇c/008 23 1308653 號，也可把距離L做成22mm以下的21.68mm。更在 20%〜40%的穿透率中，穿透率愈高其距離L的容許範圍愈 大。也就是說，穿透率愈高時，在以良好發光品質構成高 亮度發光面的時候，可確認設計寬廣的自由度。 相反地，習知市售的液晶顯示裝置所用的背光組件， 其距離不只25mm的程度，本發明品與習知品相比，確實 可達大幅度的薄型化。更，當習知利用擴散板把距離L做 小時，燈管影像便會明顯地顯示出，其發光品質低下，然 而，因爲在本實施例的擴散板2是採用低穿透率者，即使 距離L小也不易產生燈管影像，因而可維持擴散板2的亮 度均一性（發光品質）。再加上，只採用低穿透率的擴散板 會有招致亮度低下的問題，所以本實施例的距離L做得比 習知小，因而即使採用低穿透率的擴散板，也可以較少的 燈管數目維持高.亮度。亦即，即使是把正下型背光組件1 薄型化的場合，也可在確保所希望亮度的發光面上保持良 好的發光品質。 如以上那樣，使用20〜40%的低穿透率的擴散板2的 場合，選擇距離L爲規定出上述最大亮度値Bmax之La 以上，藉此，可使擴散板2與反射板8之間的分開尺寸較 寬裕，因而可防止燈管4太接近擴散板2造成的入射於上 述中間位置上方處之燈管光量不足的問題。結果是，在 20〜40%的穿透率中，即使用了穿透率最高的40%的擴散 板2，也可防止該擴散板2之上述X點的亮度比其周圍（例 如是燈管4正上方處）的亮度低，因而可避免在擴散板發 12246pif.doc/008 24 1308653 光面上認出燈管影像。且，因爲可使燈管4配置成相對於 擴散板2離得較開，因而可抑制因燈管4之發熱等的影響。 又，藉由把距離L限制在規定出上述最大亮度値Bmax 之90%的Lb以下，可使擴散板2與反射板8之間的離開 尺寸小，因而可較容易地進行背光組件1的薄型化，且在 20〜40%的穿透率中，即使使用了穿透率最低的20%的擴 散板2，仍可防止燈管4離該擴散板太開所造成的發光面 亮度低下的問題，因而可確保所希望的亮度。更，藉由像 這樣子的限制距離L，再相互採用低穿透率的擴散板2， 即使使用較少的燈管數也可確保高亮度的發光面。因此， 可抑制擴散板2及殼體3內的溫度上昇，且可以容易地構 成消耗電力少的背光組件。且由目視觀察時，不會在擴散 板發光面上示出燈管影像，可確保良好的發光品質。 把上述距離L做成在最大亮度値Bmax之92%〜95% 範圍的擴散板2與反射板8之間的距離範圍中，藉此，可 得發光品質良好的蒲型背光組件1。亦即，選擇上述X點 的亮度爲最大亮度値Bmax之92%之擴板板2與反射板8 之間的距離以下的値作爲上述L値，藉此，可更進一地薄 型化已確保希望亮度的正下型背光組件1。且，上述距離 L，因爲是採用在上述X點之亮度爲最大亮度値Bmax之 95%的擴散板2與反射板8之間的距離以上的値，所以’ 在極力抑制燈管4之發熱影響的正下型背光組件1中’可 確實防止發光品質的低下。且，例如在PC用的液晶顯示 器中，有可能連續使用了十多小時，在這樣長的時間中’ 12246pif.doc/008 25 1308653 若連續使用背光組件1 ’伴隨著燈管的連續發熱，殼體3 內的溫度有可能上昇到預想的溫度以上。爲此，把上述距 離L做得比達上述最大亮度値Bmax之95%以上之高亮度 擴散板2與反射板8之間的距離還要大，使燈管4與擴散 板2配置成離得較開’藉此，即使長時間連續使用，也可 抑制上述溫度上昇等的影響，此較爲理想。 尙，在上述的說明中，雖說明了把光源4的光照射 至液晶面板5上之液晶顯示裝置用的背光組件，但並不需 限定光源的種類。具體而言，也可以取代上述的冷陰極管， 而使用熱陰極及其他的線狀光源，或是金屬鹵素燈等的點 狀光源。且，對於把光照射至相片負片、X光片等以進行 目視確認的照明箱、點亮設於看板，或是車站內壁面等的 廣告等的發光裝置之背光組件等，本發明皆適用。 雖然本發明已以較佳實施例揭露如上，然其並非用 以限定本發明’任何熟習此技藝者，在不脫離本發明之精 神和範圍內’當可作些許之更動與潤飾，因此本發明之保 護範圍當視後附之申請專利範圍所界定者爲準。 [圖式簡單說明] 第1圖繪示依照本發明之第1實施例的正下型背光 組件的斷面圖。 第2圖'繪示取下第1圖中之擴散板之狀態的正下型 背光組件平面圖。 第3 Η繪示第1圖之擴散板與燈管的配置放大斷面 圖。 12246pif.doc/0〇8 26 1308653 第4圖繪示_本_之第2實施例之正下型背光 組件的斷面圖。 第5圖繪示取下第4 _中之擴散板之狀態的正下型 背光組件平面圖。 第6圖繪示第4 »之—_随_放大斷面 圖。 第7圖繪示實驗結果之〆例的亮度與距離之隱圖。 [圖式標示說明] 1:正下型背光組件，2:擴散板’ 3a:反射板’ 4:光源(燈管），5:液晶面板，8:反射板(反射面）。 12246pif.doc/008 27La^ L ^ Lb ---(1) To satisfy the above inequality (1), the distance L between the diffusion plate 2 and the reflection plate 8 needs to be selected, and even if the front type backlight assembly is thinned, the phase can be obtained. The adjacent two tubes 4 directly or indirectly via the reflecting plate 8 appropriately adjust the amount of light of the tube light incident above the intermediate position of the diffusing plate 2, thereby preventing the occurrence of a tube image on the emitting surface of the diffusing plate. Further, the luminance can be made to have a desired high luminance (for example, 4000 cd/m 2 or more) on the light-emitting surface, and the heat generation of the bulb 4 or the temperature rise in the casing 3 can be further suppressed to the diffusion plate 2. Heat impact. Further, a preferable range of the distance L is a range of a distance between the diffusing plate 2 and the reflecting plate 8 in the range of 92% to 95% of the maximum brightness 値Bmax. 12246pif.doc/008 18 1308653 Here, in order to select the transmittance of the diffusion plate 2 and to optimize the distance L·, please refer to Table 1 of an example of the experimental results performed by the inventors and Graphical Figure 7, which specifically illustrates a penetration of 20 to 40%, and optimizes the distance l according to the above inequality. In this experiment, two cold cathode fluorescent tubes 4 having a diameter of 3.0 mm were arranged at a lamp pitch LP of 23.5 mm, and the lower end of the fluorescent tube 4 was placed at a distance of 2 mm from the reflecting plate 8, and was changed in a certain unit. The distance between the diffusion plate 2 and the reflection plate 8 (i.e., the distance from the upper side of the tube to the diffusion plate 2), and the brightness of the light-emitting surface of the diffusion plate above the intermediate position of the lamps 4 is measured. The diffusing plates 1, 2, 3, 4, and 5 having a transmittance of 10%, 20%, 30%, 40%, and 50% are used to measure the light-emitting surface above the intermediate position of each of the diffusing plates 1 to 5 at any time. (X point) brightness. Table 1 shows the difference between the distance (between the diffuser plate and the reflector) and the brightness of the diffuser plate with different transmittances. 12246pif.doc/008 19 1308653 [Table 1] Distance ------ ---^ Brightness (cd/m2) _ L(mm) Diffusion plate No. 1 diffusion plate No. 2 diffusion plate No. 3 diffusion plate No. 4 diffusion Board 5! 7 3855 4164 4418 4696 4909 __ 8 3764 4218 4527 4836 5145 . 9 3455 4200 4606 4992 5273 11 2837 4091 4592 5021 5445 ___. 14 氺 3873 4429 4906 5491 A 16 wood 3728 4300 4783 5478 18 氺 3595 4185 4693 5465 A 20 氺 3365 4061 4607 5452 __ 22 Ben 3088 3952 4502 5419__ # indicates low brightness, not measured by Table 1 and Figure 7, the diffusion plate No. 1 of 10% transmittance, even the brightness peak is 3855cd/m2 Low, compared with other transmittance diffusers, the brightness is greatly reduced, and it can be judged that the utilization efficiency of the lamp light is too poor. 50% transmittance diffuser No. 5, the brightness at the X point of the above measurement is high brightness of 4000 cd/m2 or more, but the brightness directly above the tube is large, even if the maximum brightness of the X point is set距离Bmax distance L 'The difference in brightness between the front of the tube and the X point (above the middle of the tube) is large, and the tube image cannot be erased. In other words, when a diffusing plate having a transmittance of 50% is used, good light quality cannot be ensured when the thickness is reduced. As shown in the corresponding curve of Fig. 7, in the diffusion of 12246pif.doc/008 20 1308653 plates 2 to 4 in the transmittance of 20 to 40%, the brightness of the above x point is the distance L from 7 mm, with the distance The higher the brightness, the higher the brightness until the maximum brightness 値Bmax is shown, and the brightness becomes lower as the distance increases. Moreover, the decrease in the brightness of the X point accompanying the increase of the distance L is as shown in the graph curve, and is much larger than the number of the diffusion plate No. 5 having a transmittance of 50%. Therefore, it can be judged that the diffusion plate No. 2 to No. 4 are used. It is easy to incur the low brightness of the luminous surface. Further, when the light-emitting surface of each of the diffusion plates No. 2 to No. 4 is smaller than the distance La of the maximum brightness 値 Bmax at the X point, the brightness immediately above the tube is high, and the measured brightness and relative brightness of the X point are high. The difference is large, and the image of the tube can be recognized on the light-emitting surface. Therefore, if the distance L is made close to the distance La showing the maximum brightness 値Bmax, the relative luminance difference becomes small, and when the distance La is set, it is difficult to visually recognize the tube image. After that, the desired brightness of each of the light-emitting surfaces is ensured until the distance Lb of 90% of the maximum brightness 値Bmax, and the good illuminating quality of the lamp image can be maintained. Further, in the range of the maximum brightness 値Bmax of 95% to 92°/❶, it was found by visual observation that the light emission quality was good and the brightness was low. When the distance L is larger than the distance Lb which is 90% of the maximum brightness 値Bmax, the brightness of the X point is too low to efficiently utilize the lamp light.尙, the brightness above the lamp tube 'different diffuser plates No. 2 to No. 4 are peaks when the distance L is 7 mm, and then the curve corresponding to the seventh figure is close to X as the distance is larger. The brightness of the dots is low. Further, according to the above-mentioned test result, the specific distance 扩散 between the diffusion plate 2 and the reflection plate 8 of 100%, 95%, 92%, and 90% of the maximum brightness 値Bmax is as shown in the upper part of Table 2 The specific brightness is shown in the next paragraph of Table 12246pif.doc/008 21 1308653. In each of the diffusing plates No. 1 to No. 4 of Table 2, the distances and luminances of 95%, 92%, and 90% were calculated from the curve (experimental result) corresponding to Fig. 4 . Further, in Table 2, the diffusion plate No. 5 in which the lamp image cannot be erased is omitted. Table 2 shows the distance and brightness 各 between the diffuser plates and the reflector plates in different proportions of the maximum brightness 値. [Table 2] Upper section: Distance between diffuser plate and reflector L (mm) Lower section: Brightness of h-position in the middle of adjacent two lamps < Straight (cd/m2) Proportion of Bmax diffusion plate No. 1 diffusion Plate No. 2 diffuser plate No. 3 diffuser plate No. 4 100% 7.00 (mm) 3855 (cd / m2) 8.00 (mm) 4218 (cd / m2) 9.00 (mm) 4606 (cd / m2) 11.00 (mm) 5021 (cd / m2) 95% 8.33 (mm) 3662 (cd / m2) 12.16 (mm) 4007 (cd / m2) 14.82 (mm) 4376 (cd / m2) 16.29 (mm) 4770 (cd / m2) 92% 8.70 (mm 3547(cd/ m2) 13.90(mm) 3881(cd/ m2) 17.08(mm) 4238(cd/ m2) 19.72(mm) 4619(cd/ m2) 90% 8.95(mm) 3470(cd/ m2) 15.06 (mm) 3796 (cd/m2) 18.65 (mm) 4145 (cd/m2) 21.68 (mm) 4519 (cd/m2) As shown in Table 2, the diffusion plate of No. 2 to No. 4 having a penetration rate of 20 to 40% The above-mentioned distance L of the maximum twist 値Bmax is 8, 9, 11 mm, respectively, and each of the diffusers 2 to 4 is in the distance L satisfying the above inequality (1), and the tube shadow 12246pif.doc/008 22 1308653 is almost no Will occur on the diffusing surface of the diffuser. Further, even if the diffusion plate No. 3 and No. 4 have a distance L of 90% of the maximum brightness 値Bmax, as shown in Table 2, the brightness of the X point at the darkest point of the light-emitting surface is 4000 cd. / m2 or more, the luminous surface can be ensured in the degree of eccentricity. That is, as shown in Fig. 7, when the distance L is made larger than the diffusion plate No. 5 having a transmittance of 50%, even if the brightness of the X-point is easily lowered, the transmittance is 30% and In the case of 40% diffuser plates No. 3 and No. 4, the distance L which is limited to Lb or less defined by the right side of the inequality (1) is used, thereby preventing the occurrence of the lamp image and maintaining good light quality. It can form a high-brightness light-emitting surface. Further, in the diffuser plate No. 2 having a transmittance of 20%, for example, when the maximum brightness 値Bmax is 90%, the brightness of the X point is only 3796 cd/m2 and 4000 cd/m2 or less, according to As a result of other experiments by the present inventors, by setting the lamp pitch LP to 12 mm or less, the lamp image is not generated and the brightness of the X point can be made high by 4000 cd/m2 or more, and the distance can be formed. L is a thin backlight assembly of about 7 mm. Further, according to other experiments, when the above-mentioned lamp pitch LP is 12 mm using a diffusing plate having a transmittance of 30%, a light-emitting surface having a brightness of 7 〇 00 cd/m 2 or more can be formed without worrying about the tube image. . Further, as can be seen from Table 2, the respective distances L of the diffusion plates 2 to 4 are 8.00 to 15.06 mm (preferably 12.16 to 13.90 mm), 9.00 to 18, 65 mm (preferably 14.82 to 17.08 mm). ), and ll.00~21.68mm (preferably 16.29~19.72mm), in the above 20%~40% transmittance, that is, the diffusion plate using the maximum penetration rate 4 12246pif.d〇c/ 008 23 1308653, the distance L can also be made 21.35mm below 22mm. In the penetration rate of 20% to 40%, the higher the penetration rate, the larger the allowable range of the distance L. In other words, when the transmittance is higher, when the high-luminance light-emitting surface is formed with good light-emitting quality, a wide degree of freedom in design can be confirmed. On the other hand, in the backlight unit used in the commercially available liquid crystal display device, the distance of the present invention is as large as that of the conventional product, and the thickness of the present invention can be made substantially smaller than that of the conventional product. Further, when it is conventionally known that the distance L is made small by using the diffusion plate, the lamp image is clearly displayed, and the light-emitting quality thereof is low, however, since the diffusion plate 2 of the present embodiment employs a low transmittance, even if the distance is It is also difficult for L-light to generate a tube image, and thus the brightness uniformity (light-emitting quality) of the diffusion plate 2 can be maintained. In addition, the use of a diffusing plate having a low transmittance may cause a problem of low brightness, so the distance L of the present embodiment is made smaller than conventionally, and thus even a diffusing plate having a low transmittance can be used. The number of lamps remains high. Brightness. In other words, even when the down-type backlight unit 1 is made thinner, it is possible to maintain good light-emitting quality on a light-emitting surface that secures desired brightness. When the diffusing plate 2 having a low transmittance of 20 to 40% is used as described above, the selection distance L is equal to or greater than La which defines the maximum brightness 値Bmax, whereby the diffusing plate 2 and the reflecting plate 8 can be formed. The separation size is relatively large, so that the problem that the lamp tube 4 is too close to the diffuser plate 2 and the amount of light incident on the lamp above the intermediate position is insufficient is prevented. As a result, in the transmittance of 20 to 40%, that is, the diffusion plate 2 having the highest transmittance of 40% is used, the brightness of the above-mentioned X point of the diffusion plate 2 can be prevented from being more than the surrounding (for example, a lamp tube). The brightness at the top of the 4 is low, so that the lamp image can be avoided on the diffuser board 12246pif.doc/008 24 1308653. Further, since the bulb 4 can be disposed to be relatively open with respect to the diffusion plate 2, the influence of heat generation or the like by the bulb 4 can be suppressed. Further, by limiting the distance L to Lb or less which is 90% of the maximum brightness 値Bmax, the distance between the diffusion plate 2 and the reflection plate 8 can be made small, and the backlight unit 1 can be easily made thin. And in the transmittance of 20 to 40%, even if the diffusion plate 2 having the lowest penetration rate of 20% is used, the problem that the brightness of the light-emitting surface caused by the lamp tube 4 being too open from the diffusion plate can be prevented from being lowered. Thus, the desired brightness can be ensured. Further, by using the diffusion plate 2 having a low transmittance as the above-described restriction distance L, it is possible to secure a high-luminance light-emitting surface even if a small number of lamps is used. Therefore, the temperature rise in the diffusion plate 2 and the casing 3 can be suppressed, and the backlight assembly with less power consumption can be easily formed. Further, when visually observed, the tube image is not displayed on the light-emitting surface of the diffusing plate, and good light-emitting quality can be ensured. The distance L is set to a distance between the diffusing plate 2 and the reflecting plate 8 in the range of 92% to 95% of the maximum brightness 値Bmax, whereby the PU-type backlight unit 1 having good light-emitting quality can be obtained. In other words, 値 which is equal to or less than the distance between the expanded plate 2 and the reflecting plate 8 whose brightness of the X point is 92% of the maximum brightness 値Bmax is selected as the above L値, whereby the thickness can be further reduced and the hope is ensured. The front type backlight assembly 1 of brightness. Further, since the distance L is equal to or greater than the distance between the diffusing plate 2 and the reflecting plate 8 at which the luminance at the X point is 95% of the maximum luminance 値Bmax, the influence of the heat generation of the bulb 4 is suppressed as much as possible. In the direct type backlight assembly 1 'the light quality can be reliably prevented from being lowered. Moreover, for example, in a liquid crystal display for a PC, it is possible to continuously use it for more than ten hours, in such a long time ' 12246 pif. doc / 008 25 1308653 if the backlight assembly 1 is continuously used 'with continuous heating of the lamp, the case The temperature inside the body 3 may rise above the expected temperature. Therefore, the distance L is made larger than the distance between the high-intensity diffusion plate 2 and the reflection plate 8 which is greater than 95% of the maximum brightness 値Bmax, so that the lamp tube 4 and the diffusion plate 2 are disposed apart from each other. This is preferable because it is possible to suppress the influence of the temperature rise or the like even if it is continuously used for a long period of time. In the above description, the backlight unit for the liquid crystal display device which irradiates the light from the light source 4 to the liquid crystal panel 5 has been described, but the type of the light source is not necessarily limited. Specifically, instead of the above-described cold cathode tube, a hot cathode and other linear light sources or a point light source such as a metal halide lamp may be used. Further, the present invention is applicable to a lighting box that illuminates a photo negative film, an X-ray film, or the like for visual inspection, a lighting device that illuminates an illumination device such as an advertisement provided on a kanban, or an inner wall surface of a station. While the present invention has been described in its preferred embodiments, the present invention is not intended to limit the invention, and the invention may be modified and modified without departing from the spirit and scope of the invention. The scope of protection is subject to the definition of the scope of the patent application. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross-sectional view showing a direct type backlight unit according to a first embodiment of the present invention. Fig. 2' is a plan view showing a direct type backlight assembly in which the state of the diffusion plate in Fig. 1 is removed. Figure 3 is an enlarged cross-sectional view showing the arrangement of the diffuser plate and the lamp tube of Fig. 1. 12246pif.doc/0〇8 26 1308653 Fig. 4 is a cross-sectional view showing the direct type backlight assembly of the second embodiment of the present invention. Fig. 5 is a plan view showing the direct type backlight assembly in which the state of the diffusion plate in the fourth embodiment is removed. Figure 6 shows the 4th - _ _ enlarged section. Figure 7 is a diagram showing the brightness and distance of the example of the experimental results. [Illustration description] 1: Down-type backlight assembly, 2: diffuser plate '3a: reflector plate' 4: light source (lamp), 5: liquid crystal panel, 8: reflector (reflection surface). 12246pif.doc/008 27