二次光學於發光二極體照明效率提升之研究

Abstract

白光發光二極體具有壽命長、效率高與節能之優點，已成為新世代照明中極為 重要的光源。發光二極體為指向性光源，故需搭配光學設計才能有效地應用在產品上。傳統的燈泡如白熾燈及螢光燈泡其發光角度都是全周光型，而發光二極體的燈泡卻是半周光型。另外在點光源轉面光源設計中，傳統的背光模組架構需要導光體、增亮片、反射片、擴散片等等零組件，這些都是造成成本無法下降的原因。

於第一部份研究中，由於發光二極體效率的提升和成本降低迅速，使得發光二極體燈泡於照明市場的普及率迅速提昇。目前待改進的一個主要問題是，整體燈泡效率及光型分佈無法滿足“美國能源之星”的全周光規範。在這章節中，由於發光二極體為指向性光源，所以我們應用漫射白反射片（DWRS）與孔的間距設計作為調製光分佈以達到高效率的解決方案。孔的尺寸與間距兩者在滿足全周光規範下進行調整用以得到最佳效率。另外，在散熱部分提出金屬埋入塑膠射出成形的設計概念，金屬屬於高傳導率的材質，導熱塑膠為高輻射率的材質，本文提出利用金屬埋入在塑膠內部用以將熱迅速擴散均勻，再藉由導熱塑膠的高輻射率特性將熱輻射到空氣中作為新穎的散熱體設計，此新概念可達到不須傳統的鰭片式設計，讓外觀更美觀及一體性。

在第二部分研究中，導光板已被廣泛用於將點或線光源轉換為平面光源常見應用於照明和顯示器的平面裝置。傳統背光模組應用導光板設計可達到良好的均勻性，但其有重量及材料吸收的問題，特別是對於大尺寸的應用。中空導光體設計的方式可解決重量的問題，但其均勻性相對較差且效率往往須被犧牲用於提升均勻性。在本章中，應用中空導光與側入式發光二極體光源的架構設計同時解決重量及效能的問題。主要的方法是通過設計連續變化焦距的拋物面與V-CUT來調節光源的發光強度分佈。經調製的光入射中空導光體後可得到一高均勻性及高效率的平面光源，同時不需要額外的光學膜片組件。

I

在第三部分研究中，本章節提出新穎中空光導設計其可同時解決重量、均勻性和效率的問題。其主要設計方法是光通過漫散反射腔且該反射腔的反射面具有連續變化傾斜的角度用以調整光的出光路徑已達到較佳的均勻性。此設計的平面光源模組不須額外再添加光學零組件即可達到高效率高均勻性的效果。 最後本章節提出白光發光二極體在玻璃基板結構下的高效率設計方法，其參雜ZrO2於PDMS膜，應用其高輻射率的特性改善玻璃基板熱的問題，依據實驗證明，此結構的白光發光二極體可得到最小的色溫偏差值(132K)，在此案例最佳為參雜5%的ZrO2在螢光粉膜中，其提升色均勻性及出光效率為最佳效果。

Recently, white light-emitting diodes (LEDs) have been regarded as the next generation of lighting sources because of its long lifetime, high efficiency, and energy-saving properties, especially in solid-state lighting (SSL). Light-emitting diode is directional type light source, so need optical design before used in the product. Traditional bulbs such as incandescent and fluorescent bulbs which light distribution are omnidirectional both, but light-emitting diode bulb is directional type. In the point transfer to area light source design, the traditional architecture requires light guide plate, brightness enhancement film, reflective film, diffusion sheet components, etc., these are the reasons for can’t cost down. In the first part of this study, The penetration of LED light bulbs into lighting market is growing quickly in the recent years due to significant increase of LED efficiency and reduction of cost. One major issue to be improved is the overall light bulb efficiency, which can fulfill “Energy Star for Lamps” while meeting the specification of omnidirectional bulb. The efficiency issue results mainly from the high directionality of the LED sources and the corresponding solutions to make the emission more diverse. In this article, a diffusion white reflection sheet(DWRS) with an array of hole is proposed as a high efficiency solution for modulating light emission profile with SMD type LED source. The hole size is adjusted with fixed hole pitch to both maximize the efficiency and meet the omnidirectional specification. In addition, the concept of thermal plastic insert molding metal is proposed for thermal management without fins for cooling part

III In the second part, light guides have been widely used for transforming line source into planar illuminator for lighting and display applications. Solid light guides provide good uniformity but still have the issues of heavy weight and material absorption, especially for large size applications. Hollow light guides solve the problem of weight, but the uniformity is relatively poor or efficiency could be sacrificed for enhancing uniformity. In this chapter, a hollow light guide with edge lit LED light sources has been proposed to resolve all the weight, uniformity and efficiency issues at the same time for general Lighting application. The major approach is to modulate the LED luminous intensity profile by a cup of parabolic surface with continuously varied focal length. The modulated light emitting profile makes up a sufficient planar uniformity directly and extra components would not be required. Third, a hollow light guide with edge-light LED light sources has been proposed to resolve the issues of weight, uniformity and efficiency simultaneously. The major approach is to modulate the path of light by a diffusion reflection cavity (DRC) with continuously varied tilt angle of the reflecting surface (VTARS). The modulated D.R.C profile directly makes up a sufficient uniformity on a planar surface and extra components would not be required. Finally, demonstrates a highly efficient design of w-LED with COG structure and ZrO2 PDMS films. The w-LED can obtain the least CCT deviations (132K) in the case of the 5wt% ZrO2 blended phosphor film and the use of the ZrO2 film can improve the color uniformity of the w-LED effectively.