200406619 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（參照曰本 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 亮度大型化。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 200406619 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，本發明的目的是提供 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10%〜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 200406619 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 (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 200406619 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，可抑制燈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 燈管確保足夠的売度。 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 200406619 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%〜40%，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 200406619 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，亮度爲亮度最大値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)， ·200406619 (1) Description of the invention: [Technical field to which the invention belongs] The present invention relates to a direct type backlight assembly applied to a liquid crystal display device and the like. [Prior Art] In recent years, as a liquid crystal display device such as a liquid crystal television is enlarged, a backlight unit that irradiates light to a liquid crystal panel is also required to be large. Although the backlight unit can be divided into an edge-lit type and a direct-lit type, the latter is mostly used for large-sized backlight components. That is, in the direct type, a plurality of lamps (cold-cathode fluorescent lamps) are arranged behind a diffuser made of a synthetic resin such as acrylic or polycarbonate, and the plurality of lamps are arranged on a light emitting surface. On the back side (refer to Japanese Patent Application Laid-Open Nos. 4-350821 and 11-295731 published earlier in this patent), high brightness can be easily obtained even if the size is increased, so it is suitable for high brightness large-scale. In addition, the internal structure of the direct type device is hollow, so that it is lightweight even if it is large. Therefore, it is more suitable for high brightness and large size. However, in the conventional direct type backlight module, it is difficult to maintain good light emitting quality on the light emitting surface during thinning. In particular, when it is desired to further reduce the thickness of the high-brightness large-scale film, it is more difficult to maintain good light emission quality. In other words, since the direct type backlight unit has a lamp tube arranged behind the diffuser plate, it is thicker than the side light type, and it is not easy to reduce the thickness. In addition, as the space between the thinned diffuser plate and the lamp tube becomes smaller, the image of the lamp tube on the light emitting surface of the diffuser plate becomes stronger. Sake), it is difficult to eliminate this lamp 12246pif.doc / 008 4 200406619 tube image, the luminous quality is reduced. In other words, when the thickness of the direct type backlight unit is reduced, the light emitting quality is reduced. In addition, in the case of ensuring the large-scale and high-brightness of the direct type backlight assembly, since the display surface is large, a large number of lamps need to be used, and the heat generated by the lamps also becomes large. In addition, in the conventional direct type backlight assembly, the diffusion plate is made of synthetic resin such as acrylic or polycarbonate. The diffusion plate is easily bent, yellowed, and thermally deformed due to the influence of heat. Low positive shortens the life expectancy. In this way, in the conventional resin diffusion plate, if the light emission quality or the influence of heat generation is to be avoided, it is necessary to increase the distance between the lamp tube and the diffusion plate, which will make the device thicker and thinner, and The brightness will also decrease. In view of the above-mentioned conventional problems, an object of the present invention is to provide a direct type backlight assembly which can maintain good light emission quality and is thin. Another object of the present invention is to provide a novel technical means in a direct type backlight assembly, which can maintain the luminous quality well, can have high brightness and large size, and can be further thinned. [Summary of the Invention] The present invention provides a direct type backlight assembly, which is used to arrange a plurality of lamp tubes behind a diffuser plate at a certain lamp tube interval, and is characterized in that the distance between the diffuser plate and the lamp tube is Below 10mm, it is close to the lamp tube, and the diffuser is made of glass, the haze is more than 95%, and the transmittance is 10% to 40% (preferably 10% to 30%). According to the present invention, because the diffuser plate is made of glass, even if the heat from the lamp tube becomes large, the influence of the lamp tube heat can be avoided, and the diffuser plate 12246pif.doc / 008 5 200406619 can be arranged close to the lamp tube. Therefore, the backlight assembly can be made thin. In other words, the diffuser plate is made of glass and has excellent heat resistance. Therefore, even if the heat generated from the lamp tube becomes large, the distance between the diffuser plate and the lamp tube is 10 mm or less (preferably 5 mm or less). Keep the diffuser close to the tube. Furthermore, the present inventors have found that even if the distance between the diffuser plate and the lamp tube is shortened, by using a diffuser plate with a high haze and a low transmittance, a good luminous quality can still be obtained. That is, even if the distance between the diffuser plate and the lamp tube is reduced to reduce the thickness, the image of the lamp tube is strengthened. The use of a diffuser plate with high haze and low transmittance can effectively suppress the lamp tube. Image, so the luminous quality is good. Specifically, with a diffuser having a haze of more than 95% and a transmittance of 10% to 40%, a good light emitting quality can be obtained. In addition, even if the transmittance of the diffuser is reduced to less than 40%, the distance between the diffuser and the lamp is small, so high brightness can be ensured even if the number of lamps is small. In order to ensure the minimum brightness, a transmittance of 10% or more is desirable. In addition, according to the present invention, since the distance between the diffuser plate and the lamp tube is small, when a large-sized backlight assembly is made, a good light emitting quality with high brightness can be obtained with a small number of lamp tubes. The distance between the diffuser plate and the lamp tube may be 5 mm or more and 10 mm or less. If the distance between the diffuser and the lamp is too small, the image of the lamp is easy to be displayed. In order to suppress this, the transmittance of the diffuser needs to be very small. Once the transmittance becomes smaller, the brightness will decrease. In order to obtain high brightness, the number of lamps needs to be increased, but this will result in increased cost or power consumption. The countermeasure of the present invention is to make the distance between the diffuser plate and the lamps 12246pif.doc / 008 6 200406619 thinner than 5mm to 10mm, so that the number of lamps can be suppressed and the light emitting quality can be good. And a high-brightness / thin type direct type backlight assembly. By suppressing the number of lamps, the distance between the lamps can be set to a larger range of 12mm to 30mm, and the cost / power consumption caused by the increase in the number of lamps can be suppressed. Alternatively, the present invention can make the distance between the lamp tubes very small in the range of 4 mm to 12 mm to increase the number of the lamp tubes, and make the penetration rate of the diffuser plate below 30% very small. The distance between the lamp tubes is 5 mm (preferably 1.5 mm to 5 mm). That is, the lamp pitch is made very small to increase the number of lamp tubes, and the transmittance of the diffuser plate is very low, so that a sufficient penetration can be ensured with a low transmittance and a large number of lamps. In addition, since the transmittance of the diffuser plate is very small, the effect of eliminating the image of the lamp tube is very effective. In addition, because the distance between the tubes is small, there are fewer portions with low brightness between the tubes, so that the occurrence of images of the tubes can be suppressed. Therefore, even if the distance between the diffusion plate and the lamp tube is 5 mm or less (preferably 1.5 mm to 5 mm, and more preferably 3 mm to 5 mm), it is sufficient to suppress the image of the lamp tube. As a result, a high-brightness with good light emission quality and an ultra-thin front-type backlight assembly can be obtained. In addition, in order to prevent an unnecessary increase in the number of lamps, the distance between the lamps is preferably 4 mm or more. In addition, according to another aspect of the present invention, the present invention provides a direct 12246pif.doc / 008 7 200406619 type backlight assembly, which is used to arrange a plurality of lamps behind a diffuser at a certain lamp interval. The reason is that the distance between the diffuser plate and the lamp tube is less than 10mm, so as to be close to these lamps, and the diffuser plate is made of glass, the haze is more than 95%, the transmittance is 10% to 60%, and the lamp tube The pitch is in the range of 4mm ~ 12mm. In this case, since the diffuser plate is made of glass, even if the heat generated from the lamp tube becomes large, the influence of the lamp tube heat can be avoided, and the diffuser plate can be arranged close to the lamp tube, so that the backlight assembly can be made thin. In other words, the diffuser plate is made of glass and has excellent heat resistance, so even if the heat generated from the lamp tube becomes large, the distance between the diffuser plate and the lamp tube is 10 mm or less (or even 5 mm or less), which can diffuse. The board is close to the tube. In addition, because the distance between the diffuser plate and the lamp tube is small and the distance between the lamp tubes is small, an ultra-high-brightness / thin type direct-type backlight assembly with good light emission quality can be obtained. In other words, even if the distance between the diffuser plate and the lamp tube is reduced for the purpose of thinning, the distance between the lamp tubes is small, so that the occurrence of lamp tube images can be suppressed, and the light emission quality is good. In addition, because the small tube spacing is used to suppress the occurrence of tube images, the penetration rate of the diffuser plate can be as large as 60%, and the tube spacing can be suppressed to increase the number of lamp tubes, and the light emitting surface of the diffuser plate can be obtained. A direct-type backlight assembly having a very high brightness (for example, 1000 cd / m2). Furthermore, according to another aspect of the present invention, the present invention provides a direct type backlight assembly, which is used to arrange a plurality of lamp tubes behind a diffuser plate at a certain lamp tube interval, and is characterized by the penetration of the diffuser plate The rate is 20% to 40%, and the distance L between the diffusion plate and a reflecting surface is determined by the following inequality (1). Among them, the expansion corresponding to the middle position of two adjacent lamps is 12246pif.doc / 008 8 200406619. The maximum brightness on one light-emitting surface of the diffuser is 値 Bmax. The distance between the diffuser and a reflective surface is La, and the brightness is When the distance between the diffuser and the reflecting surface, which is 90% of the maximum brightness 値 Bmax, is Lb, and Lb> La, the following inequality (1) is satisfied,
La^ Lb …（1)。 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20〜40%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 200406619 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 卜 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 200406619 [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1的液晶 顯示裝置爲大型，具體而言，爲比10英吋（畫面對角線尺 寸約爲10英吋）大。舉例而言，爲15、17、20、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15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 英吋。且，擴散板2的非有效發光區域是隱藏並被支撐在 殼體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 200406619 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平行地酉己 置。此正下型背光組件1，因爲是用於大型液晶顯示裝慶 用，需有大的有效發光區域，且需具備與此對應的多數個| 螢光燈管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根程度的營 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，殼體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 晶顯不裝置用的背光組件1的場合，殼體3內部的溫度昇 尚將無法避免。 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 200406619 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，把燈管間距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10mm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20mm的程度，然而，在本 實施例中，可做到距離L爲l〇mm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1.5〜5mm。 或者是也可以把距離L做成5mm以上10mm以下。 像本實施例那樣，雖距離L做小會使得發熱的燈管4 接近擴散板2而使擴散板2易受熱的影響，但擴散板2是 12246pif.doc/008 13 200406619 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，因爲是採用咼霧度（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40%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%，30〜40%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 200406619 [實施例1] 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，僅管穿 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 200406619 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 0 1更高的亮度(約l〇〇〇〇cd/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 是安裝在殼體3內部的一面，且在殻體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，在上述殼體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 200406619 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的發熱或殼體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是採用使亮 12246pif.doc/008 17 200406619 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顯示 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 ^ Lb… (1). In the direct type backlight unit configured as described above, a diffusion plate with a low transmittance of 20% to 40% is used. That is, the present inventors focused on reducing the transmittance of the diffusion plate in order to maintain good light emission quality after being thinned. When a diffusion plate with such a low transmittance is used, the brightness of the light emitting surface is also low, and the light emitting surface is likely to be darkened. Here, the inventor noticed that the darkest part of the light-emitting surface after thinning is the place where the image of the tube is most easily recognized, so he paid particular attention to the light emission of the diffuser plate corresponding to the middle position of the two adjacent lamps. Brightness on the surface. Then, based on this brightness, the distance L between the diffuser plate and the reflecting surface is selected within the range prescribed by the above inequality (1). Thereby, the light-emitting surface can ensure a desired brightness, and a tube image can be prevented from being generated on the light-emitting surface as much as possible. Therefore, a direct type backlight assembly can be obtained which can maintain good light-emitting quality and can be made thin. Here, the transmittance of the diffuser plate is 20 to 40%. When a diffuser plate with a transmittance of less than 20% is used, the light passing through the light emitting surface is reduced. If a diffuser with a transmittance exceeding 40% is used, the brightness of the light emitting surface near the upper part of the lamp tube is higher than that corresponding to the above-mentioned intermediate position, and it is difficult to suppress the image of the lamp tube. Therefore, it is difficult to maintain a good quality when the thickness is reduced. Luminous quality. Moreover, the above-mentioned distance L is taken as the edge of 値 in the range of inequality (1) 12246pif.doc / 008 9 200406619. Therefore, if the distance L is selected as the distance between the diffusion plate and the reflection surface which is greater than the maximum brightness 値 Bmax If La is still small, it is difficult to suppress the occurrence of a tube image as in the case of using a diffusion plate with a transmittance exceeding 40%, and it is difficult to maintain good light emission quality during thinning. On the other hand, if the distance L is selected to be larger than the distance Lb between the diffuser and the reflecting surface which is 90% of the maximum brightness 値 Bmax, it is the same as the case where a diffuser with a transmittance of less than 20% is used. It is difficult to ensure the desired brightness of the light emitting surface. In addition, in the above-mentioned direct type backlight assembly, it is preferable that the brightness is in a range of 92% to 95% of the maximum brightness 値 Bmax to determine the distance. In this case, particularly, it can constitute an excellent light emitting quality. Thin backlight assembly. In each of the above-mentioned direct-type backlight assemblies, because it can provide a countermeasure against the heating of the lamps, it is easy to obtain a large backlight assembly with a large number of lamps, that is, the diagonal size of the effective light-emitting area of the backlight assembly is 10 inches or more (compared to A large backlight unit of 15 inches or more is preferred. In addition, in each of the above-mentioned direct-type backlight assemblies, since it can provide a countermeasure against the heating of the lamps, it is easy to obtain a high-brightness backlight assembly with a large number of lamps, that is, the brightness of the light-emitting surface of the diffuser plate is 4000cd / m2 or more It is preferably 5000 cd / m2, and more preferably 7000 cd / m2 or more. In order to make the above and other objects, features, and advantages of the present invention more comprehensible, a preferred embodiment is given below, and in conjunction with the accompanying drawings, the detailed description is as follows: 12246pif.doc / 008 10 200406619 [Implementation Mode] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. Figures 1 to 3 show a direct type backlight unit 1 for a liquid crystal display device such as a liquid crystal display for a television or a computer. The liquid crystal display device in which the direct type backlight assembly 1 is assembled is large, specifically, larger than 10 inches (diagonal screen size is about 10 inches). For example, 15, 17, 20, 30, 50 inches and so on. The direct type backlight assembly 1 has a diffuser plate 2 mounted on one side inside the housing 3, and a plurality of light sources 4 are arranged inside the housing 3. The case 3 is made of metal or synthetic resin, and is formed in a thin box shape with one surface opened. A white reflecting surface is formed on the bottom surface 3a of the casing 3. A diffuser plate 2 made of white glass is attached to the open side of the case 3. The diffusion plate is 1.0 mm to 3.0 mm thick, and preferably a thickness of about 2.0 mm is used. The liquid crystal panel 5 of the liquid crystal display device is provided at a position behind the aforementioned diffuser plate 2. The planar light of the diffuser plate 2 is irradiated to the liquid crystal panel 5 in a uniform manner. Therefore, the diffuser plate 2 is formed to have a larger screen size than that of a liquid crystal display. Specifically, the diffusion plate 2 secures the size of the non-effective light-emitting area on the periphery of the effective light-emitting area, which is slightly equal to the screen size of the liquid crystal display device. Therefore, for example, the diagonal size of the effective light-emitting area of the backlight module diffuser 2 applied to a 15-inch type liquid crystal display device is about 15 inches. The non-effective light-emitting area of the diffuser plate 2 is hidden and supported by the case 3 and the like, and is a range that cannot be irradiated with light toward the liquid crystal panel 5. The light source having an elongated linear shape arranged under the light source 4 behind the diffuser plate 2 is 12246pif.doc / 008 11 200406619. Specifically, it is a cold-cathode tube type fluorescent lamp. These fluorescent tubes 4 are arranged in parallel with a plurality of tubes (eight are shown in the figure) at approximately equal lamp pitches LP. This direct-type backlight assembly 1 is used for large-scale liquid crystal display applications, and needs a large effective light emitting area, and it needs to have a large number of corresponding | fluorescent tubes 4. Moreover, from the standpoint of high-brightness requirements for the use of liquid crystal televisions, multiple fluorescent tubes 4 are also required. Specifically, for a 15-inch type backlight unit, about 8 fluorescent tubes are used, and for a 20-inch type backlight unit, about 12 fluorescent tubes are used. For a 30-inch type backlight unit, approximately 16 camping light tubes 4 are used. The distance between the fluorescent lamp 4 and the reflecting surface 3a is set to about 0.3 to 2 mm, and the lamp tube 4 is a reflecting surface 3a arranged close to the plane. The cold-cathode tube type fluorescent lamp 4 has a diameter of about 2.0 to 4.0 mm (preferably about 3.0 mm), and is suitable for thinning. However, since the electrode part generates a large amount of heat, once it is set to a large number, When each fluorescent tube 4 is heated, the temperature inside the case 3 becomes extremely high due to heat generation. In addition, the fluorescent tube 4 is turned on by a high-frequency lamp (not shown) by a converter (a lighting device, which is generally provided on the back of the housing), but the heat generated by the converter may also promote the housing. 3 The internal temperature rises. In particular, in the case where a plurality of fluorescent tubes are turned on as in the present embodiment ', since the power consumption increases, the heat generation also increases. 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 distance (lamp pitch) LP between the adjacent lamp tubes 4, 4 can be in a range of about 4 to 30 mm. When the distance LP of the lamp tubes is made small, the number of the lamp tubes increases, the heat generation is greater, and the brightness is also larger. On the other hand, when the lamp 12246pif.doc / 008 12 200406619 tube pitch LP is made large, the number of lamp tubes is reduced, the heat generation is small, and the brightness is low. Specifically, when the lamp tube pitch LP is set to 4 to 12 mm, abnormally high temperatures can be avoided and high brightness can be obtained. That is, setting the lamp pitch LP to 12 mm or less can increase the number of lamps and achieve high brightness, and making the lamp pitch LP larger than 4 mm can avoid abnormal heating. On the other hand, when the lamp tube pitch LP is set in the range of 12 to 30 mm, a certain degree of brightness can be ensured, the number of lamp tubes can be reduced, and costs and power can be saved. That is, because the distance LP between the tubes is larger than 12 mm (preferably 15 mm, and more preferably 20 mm), the number of tubes is less and the heat generation is less. And because the lamp pitch LP is smaller than 30mm, it can ensure a certain degree of brightness. In addition, by adopting a lamp pitch LP of 30 mm or less, there are fewer low-luminance portions between two adjacent lamps 4 and 4, thereby suppressing the generation of lamp images. The casing 3 is formed to be thin to support the diffuser plate 2 at a position having a small distance L from the lamp tube 4. In this way, the backlight assembly 1 can be made thin, and the liquid crystal display device can be made thin. Specifically, the distance L between the diffuser plate 2 and the lamp tube 4 is 10 mm or less. It is known that the commercially available backlight assembly for a liquid crystal display device uses a synthetic resin diffuser. In order to generate heat by request, the distance L is not only about 20 mm. However, in this embodiment, the distance L can be achieved. It is significantly thinner than 10 mm. Furthermore, the distance L can be made 5 mm or less, and more preferably 1.5 to 5 mm. Alternatively, the distance L may be 5 mm or more and 10 mm or less. As in this embodiment, although the distance L is small, the heating tube 4 is close to the diffuser plate 2 and the diffuser plate 2 is easily affected by heat. However, the diffuser plate 2 is 12246pif.doc / 008 13 200406619. It is more heat-resistant than synthetic resin. It is made of strong glass and will not be warped, yellowed or deformed by heat. In addition, when the distance L of the conventional diffuser plate is made small, the image of the lamp tube is clearly displayed and the luminous quality is reduced. However, the diffuser plate 2 of this embodiment uses haze (haze) because For those with low transmittance, even if the distance L becomes small, it is difficult to generate a tube image, and the brightness uniformity (luminous quality) of the diffusion plate 2 can be maintained. In addition, although only a diffusion plate with a high haze and a low transmittance may cause a problem of low brightness, in this embodiment, because the distance L becomes small, even if a diffusion with a high haze and a low transmittance is used, The panel also maintains high brightness with a smaller number of lamps. That is, the size, thickness, high brightness, and good light emitting quality of the direct type backlight module 1 can be achieved in all cases. Specifically, the haze 値 of the diffuser plate 2 is 95% or more, and more preferably 97% or more in order to obtain good diffusibility. The transmittance of the diffuser plate 2 may be 60% or less depending on the occasion, and preferably 40% or less. In order to prevent the transmittance from being too low and not to damage the brightness, it is preferable to set it to 10% or more. The transmittance is preferably 20 to 40%, and more preferably 30 to 40%. On the diffuser plate 2 (the surface on the liquid crystal panel 5 side of the diffuser plate 2), an optical plate 6 such as a diffuser plate, a lens plate, a polarizing plate and the like for adjusting the light emission quality is disposed as necessary. In many cases, a diffuser plate for increasing the brightness is used as the optical plate 6. In the following, several experimental results will be taken as a representative and described as examples and comparative examples. 12246pif.doc / 008 14 200406619 [Example 1] In the 15-inch type direct type backlight assembly 1, the distance L is reduced to 10 mm, and the lamp pitch LP is set to 23.5 mm (the number of lamp tubes is 8). Root), when the haze 値 of the diffuser 2 is 97% and the transmittance is 40% (Example 1), good luminous quality with little luminous unevenness can be obtained. In addition, with a low number of tubes (8) and low tube penetration, sufficient brightness of about 5000 cd / m2 can be obtained (brightness in the state without optical plate 6; 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 assembly can be achieved all together, 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. In other words, for the 15-inch type, the direct type backlight module 1 has a thinned distance L of 10 mm, a lamp pitch LP of 23.5 mm, a haze of the diffuser 2 of 値 97%, and a transmittance of 50%. In the above case (Comparative Example 1), it was confirmed that the light emission was uneven on the diffuser plate 2 and the light emission quality was impaired. [Example 2] In a 15-inch type direct type backlight assembly 1, the distance L is thinned to 5 mm, the lamp tube pitch LP is set to 12 mm, and the haze 値 of the diffusion plate 2 is 97%, and the transmittance is When it is 30% (Example 2), good luminous quality with little emission unevenness can be obtained. Further, in Example 2, although the transmittance is lower than that in Example 1, since the distance L is small, it is possible to obtain the same brightness (about 5000 cd / m2) as in Example 1. That is, in Example 2, the size, thickness, and high brightness of the direct type backlight assembly and its good light-emitting product 12246pif.doc / 008 15 200406619 can be achieved without compromising the light-emitting quality. And high brightness, it is possible to achieve a further thinner (ultra-thinner) than in Example 1. [Example 3] In the 15-inch type direct type backlight assembly 1, the distance L is thinned to 10 mm, the lamp tube pitch LP is set to 12 mm, and the haze 値 of the diffuser plate 2 is 97%, penetrating When the rate is 60% (Example 3), good luminous quality with little emission unevenness can be obtained. Moreover, in Example 3, since the transmittance is higher than that in Example 1, and the lamp tube pitch LP is small, a higher brightness (about 1000 cd / m2) than that in Example 01 can be obtained. That is, in the third embodiment, the 'large-scale, thin-type, high-brightness' of the direct type backlight assembly and its good light-emitting quality can be achieved without impairing the light-emitting quality' and ultra-high brightness can be achieved. This embodiment 3 is particularly suitable for a liquid crystal television. [Comparative Example 2] In a 15-inch type direct type backlight assembly 1, the distance L is reduced to 10 mm, the lamp tube pitch LP is set to 23.5 mm, the haze of the diffuser plate 2 is 97%, and the transmittance is When it was 60% or more (Comparative Example 2), it was confirmed that the light emission unevenness on the diffuser plate 2 deteriorated the light emission quality. 4 to 6 illustrate a direct type backlight assembly 1 according to another embodiment. This direct-type backlight assembly 1 is, for example, a milky white diffuser plate 2 mounted on the inside of the casing 3, and a plurality of light sources 4 are arranged inside the casing 3. Figures 4 to 6 show the direct type backlight assembly 1. The parts that are not specifically described are the same as those of the direct type backlight assembly shown in Figures 1 to 3. A reflection plate 8 made of a resin film or a metal film such as aluminum is provided on the bottom surface of the case 3. This reflecting plate 8 is a reflecting surface that reflects the light from the light source 4 toward 12246pif.doc / 008 16 200406619 toward the diffusion plate 2. For example, the surface on the light source 4 side is painted white, and the light can be efficiently reflected to the diffusion plate 2 side to improve the utilization efficiency of the light and the brightness of the diffusion plate 2. The thickness of the reflecting plate 8 is about 0.2 to 0.4 mm so as not to hinder the reduction in thickness of the backlight unit 1. Alternatively, a white or silver paint having a high light reflectance may be applied to the bottom surface of the casing 3, and the reflection layer may be used as a reflection surface instead of the reflection plate 8 described above. Figures 4 to 6 show the direct-type backlight unit 1. Instead of glass, a resin material may be used as the diffusion plate 2. However, compared with the case of synthetic resin, when a heat-resistant glass diffuser 2 is used, it is less likely to be bent or yellowed due to thermal effects such as heat generation of the lamp tube 4 or temperature rise inside the case 3. , Thermal deformation, etc., more ideal. In addition, in the diffusion plate 2 described above, the haze 値 is 88% or more, preferably 95% or more, and more preferably 97% or more. For the liquid crystal panel 5, the light diffusion of the lamp tube can be improved. It is easy to form a high-brightness display image on the panel 5 uniformly. Moreover, the transmittance of the diffuser 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 it to 20% or more, and it is more preferable that the transmittance is 30 to 40% or more. In addition, by reducing the transmittance to 40% or less, even if the thickness is reduced, it is possible to suppress the decrease in brightness and prevent the occurrence of a tube image, and it is easy to maintain good light emission quality. On the diffuser plate 2 (the surface on the liquid crystal panel 5 side of the diffuser plate 2), an optical plate 6 such as a diffuser plate, a lens plate, and a polarizing plate for adjusting the light emission quality may be disposed as necessary. In most cases, as the optical plate 6, a diffuser plate that raises the brightness of 12246pif.doc / 008 17 200406619 is used. The distance L between the diffuser plate 2 and the reflective plate 8 (Fig. 6) is 1/2 of the size of the lamp tube distance LP shown in the middle position of two adjacent lamp tubes 4 (point line C in Fig. 5). The brightness of the light-emitting surface (point X in FIG. 4) of the diffuser plate 2 corresponding to an arbitrary point c) on the line is optimized and can be selected from the range specified by the following inequality (1) of La and Lb値. In the case of a thin backlight assembly, when the measurement is performed without the optical plate 6, the X point on the light emitting surface is the darkest part of the light emitting surface, and it is the place where the image of the tube is most easily seen. In addition, the above-mentioned La is the distance between the diffusion plate 2 and the reflection plate 8 whose luminance on the light emitting surface (point X) above the middle position is maximum 値 Bmax. The Lb is the distance (and Lb> La) between the diffuser plate 2 and the reflective plate 8 whose luminance on the light emitting surface (point X) above the intermediate position is 90% of the maximum 値 Bmax.
La^LSLb ---(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之發熱或殼體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 200406619 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 200406619 [表1] 距離 L(mm) 売度（cd/m2) 擴散板1號 擴散板2號 擴散板3號 擴散板4號 擴散板5號 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 16 木 3728 4300 4783 5478 18 氺 3595 4185 4693 5465 20 * 3365 4061 4607 5452 22 * 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 20 12246pif.doc/008 200406619 板2號〜4號中，上述χ點的亮度是距離L從7mm開始， 隨者距離愈大亮度愈高，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 點売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接近至不出最大売 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%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，根據上述實驗結果，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 200406619 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上方的亮度f 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/ m2l 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/ 由表2可知，穿過率20〜40%的擴散板2號〜4號的最 大亮度値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 22 12246pif.doc/008 200406619 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，可把發光面確保在高亮度。 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，槔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l2mm的場合，不需擔心燈管影 像而可構成具7000 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〜l5.06mm(較佳的是12 16〜13 9〇mm)， 9.00 〜18.65mm(較佳的是 14·82 〜17.08mm)，及 11.00〜21.68mm(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.doc/008 23 200406619 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 200406619 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及殻體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 200406619 若連續使用背光組件1，伴隨著燈管的連續發熱，殻體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。 雖然本發朋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圖繪示第i圖之擴散板與燈管的配置放大斷面 圖0 12246pif.doc/008 26 200406619 第4圖繪不依煦本發明之第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圖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圖之擴散板與燈管的配置放大斷面 圖。 第7圖繪示實驗結果之一例的亮度與距離之關係圖。 [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 ^ LSLb --- (1) To satisfy the above inequality (1), the distance L between the diffuser plate 2 and the reflective plate 8 needs to be selected. Even when the direct type backlight unit is thin, the The two lamp tubes 4 directly or indirectly via the reflection plate 8 can appropriately adjust the light amount of the lamp tube light incident above the intermediate position of the diffuser plate 2 to prevent a lamp image from being generated on the light emitting surface of the diffuser plate. In addition, the light emitting surface can be made to a desired high brightness (for example, 4000 cd / m2 or more), and the heat generated by the lamp tube 4 or the temperature rise in the housing 3 can be further suppressed. Thermal effects. Furthermore, a preferable range of the distance L is a distance range between the diffuser plate 2 and the reflective plate 8 in the range of 92% to 95% of the maximum brightness 値 Bmax. 12246pif.doc / 008 18 200406619 Here, in order to select the transmittance of the diffusion plate 2 and optimize the distance L, please refer to Table 1 and an example of the experimental results performed by the inventor. Fig. 7 illustrates the specific transmission rate of 20 to 40%, and the distance L is optimized according to the above inequality. In this experiment, two cold-cathode lamp tubes 4 with a diameter of 3.0 mm are arranged at a lamp pitch LP of 23.5 mm, and the lower end of the lamp tube 4 is set above a distance of 2 mm from the reflecting plate 8 and changed in a certain unit. The distance between the diffusion plate 2 and the reflection plate 8 (that is, the distance from above the lamp tube to the diffusion plate 2), and the brightness of the light emitting surface of the diffusion plate above the middle position of these lamp tubes 4 was measured. Diffuser plates 1, 2, 3, 4 and 5 with 10%, 20%, 30%, 40%, and 50% transmittance are used, and the light emitting surface above the middle position of each diffuser plate 1 to 5 is measured at any time. (Point X). Table 1 shows the brightness of the diffuser plate with different distances (between the diffuser plate and the reflector plate) and different transmittances. 12246pif.doc / 008 19 200406619 [Table 1] Distance L (mm) 売 Degree (cd / m2) Diffusion plate 1 Diffusion plate 2 Diffusion plate 3 Diffusion plate 4 Diffusion plate 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 16 Wood 3728 4300 4783 5478 18 氺 3595 4185 4693 5465 20 * 3365 4061 4607 5452 22 * 3088 3952 4502 5419 * indicates brightness Low, not measured. From Table 1 and Figure 7, it can be seen that the diffusion plate No. 1 with 10% transmittance has a low brightness peak value of 3855 cd / m2. Compared with other transmittance diffusion plates, the brightness is significantly larger. It can be judged that the utilization efficiency of the lamp light is too poor. The diffusion plate No. 5 with 50% transmittance, although the brightness of the X point at the above measurement position is 4000 cd / m2 or higher, the brightness directly above the lamp is large, even if the maximum brightness of the X point is set距离 Bmax distance L, the brightness difference between the lamp directly above and the X point (above the middle position of the lamp) is large, and the lamp image cannot be erased. That is, when a diffusion plate having a transmittance of 50% is used, good light-emitting quality cannot be ensured when the thickness is reduced. As shown in the corresponding curve in Fig. 7, in the spread of 20 to 40% transmittance 20 12246pif.doc / 008 200406619 No. 2 to No. 4, the brightness of the above-mentioned χ point is a distance L starting from 7 mm, and a follower distance The larger the brightness, the higher the brightness, until the maximum brightness 随着 Bmax is shown, as the distance increases, the brightness decreases. Moreover, the decrease in the X-point degree accompanying this increase in distance L is as shown in the graph, which is much larger than the diffusion plate No. 5 with a transmittance of 50%. Therefore, it can be judged that the diffusion plate No. 2 to No. 4 are used. It is easy to cause the brightness of the light emitting surface to be low. In addition, when the light emitting surface of each diffuser plate No. 2 to No. 4 is smaller than the distance La where the point X is the maximum brightness 値 Bmax, the brightness directly above the lamp is high, and the measured brightness and relative brightness at the point X are high. The difference is large, and the lamp image can be recognized on the light emitting surface. Therefore, if the distance L is approached to a distance La that does not exceed the maximum value 売 Bmax, the above-mentioned relative brightness difference will become smaller. When the distance La is set to the distance La, it is difficult to visually observe the lamp image. After that, up to a distance Lb of 90% of the maximum brightness 値 Bmax, the desired brightness of each light-emitting surface can be ensured, and a good light-emitting quality with less image of the tube can be maintained. In addition, within a distance range of 95% to 92% of the maximum brightness 値 Bmax, it was found from 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 reaches 90% of the maximum brightness 値 Bmax, the brightness at the X point is too low to use the lamp light efficiently. Alas, the brightness directly above the lamp, each of the diffuser plates No. 2 to No. 4 shows a peak 値 at a distance L of 7 mm, and then, as the distance becomes larger, the curve corresponding to FIG. 7 approaches X. The brightness of the dots is low. Moreover, according to the above experimental results, the maximum brightness (100%, 95%, 92%, and 90% of Bmax of the specific distance between the diffuser plate 2 and the reflective plate 8) is shown in the upper paragraph of Table 2, which corresponds to The specific brightness is as shown in the lower paragraph of Table 12246pif.doc / 008 21 200406619. In each of the diffuser plates No. 1 to No. 4 in Table 2, the distances and brightness 95 of 95%, 92%, and 90% are calculated from the curve (experimental result) corresponding to FIG. 4. In addition, in Table 2, the diffuser plate No. 5 which cannot erase the lamp image is omitted. Table 2 shows the distances and brightnesses between the diffusers and reflectors that account for the maximum brightness (different ratios). [Table 2] Upper section: Distance L (mm) between diffuser and reflector. Lower section: Brightness f above the middle position of two adjacent lamps. Straight (cd / m2) to Bmax. No. 3 diffuser No. 3 diffuser 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 / m2l 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 / As can be seen from Table 2, the maximum brightness of the diffuser plates No. 2 to No. 4 with a penetration rate of 20 to 40% is 値 Bmax The above-mentioned distance L is 8, 9, and 11 mm, respectively. For each of the diffuser plates No. 2 to No. 4 in the distance L satisfying the above inequality (1), the lamp tube image 22 12246pif.doc / 008 200406619 hardly appears on the light-emitting surface of the diffuser plate. In addition, even if the distance L of 90% of the above-mentioned maximum brightness maxBmax is selected for diffuser plates 3 and 4, as shown in Table 2, the darkest part of the light emitting surface is The brightness 値 at point X is also 4000 cd / m2 or more, which can ensure the high brightness of the light emitting surface. That is, as shown in Figure 7, compared with the diffusion plate No. 5 with a transmittance of 50%, the distance L When it is made larger, even if the diffuser plates No. 3 and No. 4 with a transmittance of 30% and 40%, where the brightness at point X is easily lowered, use the limit below Lb specified on the right side of the above inequality (1) 値The distance L can prevent the image of the tube from occurring, and can maintain good light emission quality and form a high-brightness light emitting surface. In the diffusion plate No. 2 with a transmittance of 20%, for example, When its maximum brightness is 90% of Bmax, although the brightness at point X is only 3796 cd / m2 and less than 4000 cd / m2, according to other experimental results of the inventor, the lamp tube pitch LP is made 12mm In the following, a thin-type backlight assembly with a distance L of about 7 mm can be constructed without generating a tube image and having a high brightness at the X point of 4000 cd / m2 or more. In addition, according to other experiments, when a diffuser plate with a transmittance of 30% is used to make the lamp tube pitch LP 12 mm, a light emitting surface with a brightness of more than 7000 cd / m2 can be formed without worrying about the image of the lamp tube. Furthermore, as can be seen from Table 2, the distances l of the diffuser plates 2 to 4 are 8.00 to 15.06 mm (preferably 12 16 to 13 9 mm), and 9.00 to 18.65 mm (preferably 14 · 82 ~ 17.08mm), and 11.00 ~ 21.68mm (preferably 16.29 ~ 19.72mm), among the above 20% ~ 40% transmittance, that is the diffuser plate with the maximum transmittance 4 12246pif.doc / 008 23 200406619, the distance L can also be made 21.68mm below 22mm. In the transmittance of 20% to 40%, the higher the transmittance, the larger the allowable range of the distance L. In other words, the higher the transmittance, the wider the freedom of design can be confirmed when the high-brightness light-emitting surface is formed with good light-emitting quality. On the contrary, the backlight unit used in the conventional commercially available liquid crystal display device has a distance of not only about 25 mm, and the product of the present invention can achieve a substantial reduction in thickness compared with the conventional product. Furthermore, when it is known to use a diffusion plate to make the distance L small, the tube image will clearly show that its light emission quality is low. However, because the diffusion plate 2 in this embodiment uses a low transmission rate, even the distance A small L is not easy to generate a tube image, so the brightness uniformity (luminous quality) of the diffusion plate 2 can be maintained. In addition, only the diffusion plate with a low transmission rate will cause a problem of low brightness. Therefore, the distance L in this embodiment is made smaller than the conventional one. Therefore, even if a diffusion plate with a low transmission rate is used, it can be reduced. The number of lamps maintains high brightness. That is, even when the direct type backlight unit 1 is made thin, it is possible to maintain good light emitting quality on the light emitting surface which ensures a desired brightness. As described above, when using a diffuser plate 2 with a low transmittance of 20 to 40%, the distance L is selected to be greater than or equal to La that defines the above-mentioned maximum brightness 値 Bmax, so that the distance between the diffuser plate 2 and the reflective plate 8 can be increased. The separation size is relatively large, so that the problem that the amount of light entering the lamp above the intermediate position is insufficient due to the lamp 4 being too close to the diffuser plate 2 can be prevented. As a result, even if the diffuser plate 2 with the highest transmittance of 40% is used for the transmittance of 20 to 40%, the brightness of the above-mentioned X point of the diffuser plate 2 can be prevented from being higher than the surroundings (for example, a lamp tube). 4 directly above), the brightness is low, so you can avoid recognizing the image of the tube on the smooth surface of the diffuser plate 12246pif.doc / 008 24 200406619. Furthermore, since the lamp tube 4 can be arranged relatively apart from the diffuser plate 2, the influence due to the heat generation of the lamp tube 4 and the like can be suppressed. In addition, by limiting the distance L to Lb which is 90% or less of the above-mentioned maximum brightness 値 Bmax, the separation size between the diffuser 2 and the reflector 8 can be made small, so that the backlight module 1 can be made thinner. In addition, even if a 20% to 40% transmittance is used, even if the diffuser 2 'with the lowest transmittance is used, the problem of low brightness of the light emitting surface caused by the lamp tube 4 being too far away from the diffuser can be prevented. Therefore, a desired brightness can be secured. Furthermore, by limiting the distance L in this way, and then using the diffusion plate 2 with a low transmittance to each other, a high-brightness light emitting surface can be ensured even with a small number of lamps. Therefore, a temperature rise in the diffuser plate 2 and the case 3 can be suppressed, and a backlight unit with low power consumption can be easily constructed. In addition, when visually observed, no lamp image is displayed on the light-emitting surface of the diffuser plate, which ensures good light-emitting quality. The distance L is set in a distance range between the diffuser plate 2 and the reflective plate 8 in a range of 92% to 95% of the maximum brightness 値 Bmax, thereby obtaining a pu-shaped backlight unit 1 with good light emission quality. That is, 値, which is the distance between the expansion plate 2 and the reflection plate 8 whose brightness at the X point is 92% of the maximum brightness 値 Bmax, is selected as the L 値, whereby further thinning can be ensured. Direct light type backlight assembly 1 of brightness. In addition, the above-mentioned distance L is a distance equal to or greater than the distance between the diffuser plate 2 and the reflective plate 8 whose brightness at the X point is 95% of the maximum brightness 値 Bmax, so 'the heat influence of the lamp tube 4 is suppressed as much as possible. In the direct type backlight assembly 1, it is possible to surely prevent degradation of light emission quality. And, for example, in a liquid crystal display for a PC, it may be used continuously for more than ten hours. In such a long time, '12246pif.doc / 008 25 200406619 If the backlight assembly 1 is continuously used, the continuous heating of the lamp tube, the shell The temperature in the body 3 may rise above the expected temperature. For this reason, the distance L is made larger than the distance between the high-brightness diffuser plate 2 and the reflective plate 8 which reaches more than 95% of the above-mentioned maximum brightness 値 Bmax, so that the lamp tube 4 and the diffuser plate 2 are arranged apart. This is preferable because it is possible to suppress the influence of the above-mentioned temperature rise and the like even if the product is continuously used for a long time. That is, in the above description, the backlight unit for a liquid crystal display device that 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 limited. Specifically, instead of the cold cathode tube described above, a hot cathode and other linear light sources, or a point light source such as a metal halide lamp may be used. In addition, the present invention is applicable to a lighting box that irradiates light to a photo negative film, an X-ray film, and the like for visual confirmation, a backlight assembly that illuminates a light-emitting device such as an advertisement provided on a kanban or a station wall, and the like. Although the present disclosure has been disclosed above with a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can make some changes and decorations without departing from the spirit and scope of the present invention. The scope of protection of the invention shall be determined by the scope of the attached patent application. [Brief Description of the Drawings] FIG. 1 is a cross-sectional view of a direct type backlight assembly according to a first embodiment of the present invention. Fig. 2 is a plan view of a direct type backlight assembly in a state where the diffusion plate in Fig. 1 is removed. Fig. 3 is an enlarged sectional view showing the arrangement of the diffuser plate and the lamp tube of Fig. 0 12246pif.doc / 008 26 200406619 Fig. 4 is a sectional view of the direct type backlight assembly which does not rely on the second embodiment of the present invention Illustration. FIG. 5 is a plan view of a direct type backlight assembly with the diffuser plate in FIG. 4 removed. Fig. 6 is an enlarged sectional view showing the arrangement of the diffuser plate and the lamp tube of Fig. 4. FIG. 7 is a graph showing the relationship between brightness and distance as an example of the experimental result. [Schematic description] 1: Direct type backlight assembly, 2: diffuser, 3a: reflector, 4: light source (lamp), 5: liquid crystal panel, 8: reflector (reflective surface). 12246pif.doc / 008 27