微結構陣列應用於遠程螢光粉白光發光二極體改善光色均勻度之研究

Abstract

本篇論文主要是研究在遠程螢光粉白光發光二極體的架構下，將圓錐狀微結構陣列結合螢光粉乘載盤，改善空間色偏的方法。空間色偏為白光發光二極體常見的問題之一，起因於來自發光二極體的激發光源與螢光粉的發散角度不匹配，而導致組合成的白光光源，呈現光色不均的現象。發光二極體的光型大多為高斯分佈，光強度的最高值落在元件的正上方，隨發光角度變大而光強度遞減，導致透過此光源激發的遠程螢光粉白光發光二極體的光譜分佈黃藍光比例，於低角度時偏低而高角度時偏高，產生明顯黃暈的現象。我們透過圓錐狀微結構陣列的光型調變效應，將激發光源的發散角度擴大，使其能夠更均勻的入射螢光粉層，達到提升光色均勻度的效果。 首先透過光學模擬演算以及實測藍光發光二極體光型，驗證當光源通過圓錐狀微結構陣列時，發散角度的調變效應。由實驗結果得知，若將圓錐狀微結構陣列，添加於透光基板的光出射面，則通過此基板的光源其發散角度會縮減；若將圓錐狀微結構陣列，添加於透光基板的光入射面，則通過此基板的光源發散角度分佈，會由原先的高斯分佈轉換成雙鋒型或三鋒型的分佈，而使發散角度擴大。本研究中我們使用無添加結構設計的平面基板作為對照組，透過結構設計將光源發散角度由131.5度擴大至139.5度。 接著將圓錐狀微結構陣列結合於螢光粉乘載盤，使入射至螢光粉層的發光二極體激發光源，先經由圓錐狀微結構陣列的調變效應，增加其發散角度，更均勻的進入螢光粉層，使不同角度的黃藍光比例更一致，降低變角度色溫分佈差異(∆CCT)，並直接反應在光色的均勻度上。本實驗的最佳結果為，當白光相關色溫為5200K時，∆CCT可由3285K下降至375K；於相關色溫3000K時，∆CCT可由806K下降至169K，在亮度損失低於7%的狀況下達到光色均勻度改善的效果。 最後經由模組化遠程螢光粉白光發光二極體的實驗佐證，以圓錐狀微結構陣列結合於遠程螢光粉白光發光二極體改善空間色偏的方法，能夠有效的適用於不同白光色溫的螢光粉組合、不同發光二極體元件的選擇與排列方式、且不受尺寸限制，於整體光源模組的機構設計上，無須做其於修改，能夠直接套用於平面式的遠程螢光粉白光發光二極體光源模組上，有效改善光色均勻度，提供更高品質的照明光源。

This paper mainly aims to study the cone-shape microstructure array prepared on the phosphor carrier of remote phosphor white LEDs, which can improve the uniformity of angular-dependent correlated color temperature (CCT) and modify spatial color deviation. Spatial color deviation is a common problem in white LEDs caused by the mismatch of radiation patterns from an LED excitation light source and the radiation of the phosphor. This mismatch cause the inhomogeneous chromaticity of the white light source. LEDs show mostly Gaussian distributions, and the maximum light intensity falls just above elements, with the light angle light intensity becomes larger decline, leading to excitation light through the phosphor layer of the remote phosphor white LEDs uniformity. The angular-dependent intensity ratio of yellow to blue rays at low angles is low, whereas that at high angles is high. Thus, a significant yellow halo phenomenon is observed. The transmitted light type modulation effect of cone-shape microstructures array stimulates the expansion of the divergence angle of the light source. Thus, the incident phosphor layer becomes more uniform, and the light and color uniformity is enhanced. First, based on optical simulations and measurements, we discuss the radiation pattern of blue LEDs ,and the modulation effect observed when the light source passes through the cone-shape microstructures array. Based on the experimental results, if the light output passes through the cone-shaped microstructures array of the transparent substrate, the divergence angle of the light decreases and the Gaussian distribution will be converted to the original front-type or three front-type distribution, and the divergence angle increases. In this study, we used a flat substrate structure as a reference. This structure expanded the divergence angle of the light source from the 131.5 ° to 139.5 °. An array of cone-shaped microstructures was subsequently bound to a phosphor carrier plate incident to the phosphor layer of the excitation light source. The first effect observed is modulation of the cone-shaped microstructure array to increase its divergence angle. The phosphor layer becomes more uniform, and a yellow-blue light is produced at different angles. Thus, the proportion becomes more consistent, the distribution difference of the variable angle color temperature decreases, and a direct response to the uniformity of light and color is observed. The optimum results of this experiment are obtained when the white light source was of 5200K. The ΔCCT value may decrease from 3285 K to 375 K. When the CCT 3000 K, the ΔCCT decrease from 806 K to 169 K. The brightness of light reaching the loss is less than 7% when the color uniformity is improved. Finally, the experimental results obtained from module level remote phosphor white LEDs with an array of cone-shape microstructures show that the color deviation was improved and that the proposed method can effectively be used in different color temperatures and phosphor compositions. The selection and arrangement of different LED components and sizes should not be limited to the overall design of the light source module. The proposed method can be directly used for planar remote phosphor white LED light source modules improved light color uniformity to obtain better quality lighting.