發光二極體一般都以外部發光量的變化來探討其發光品質，我們將應用順向偏壓法去量測發光二極體的接面溫度，再以光學顯微鏡配合上高倍數的物鏡，聚焦至發光二極體內部，藉由輸入10mA至240mA的電流，進行熱效應對發光二極體內部發光變化的探討，研究結果得知，接面溫度會隨著輸入電流的增加而跟著上升，兩者呈現一個線性的關係。透過本光學系統，可得知電流在LED內部分佈並非相當的均勻，發光強度較強的區域集中在電極附近，隨著接面溫度的上升，使光出射之臨界角變小，造成光集中從LED中間區域出射，使邊緣之發光強度較弱。受到熱效應的影響，在140mA下其發光強度就會而開始衰減，波長在100mA後即開始往長波長移動，形成紅位移，由研究的結果顯示，受熱效應較大的區域，其發光效率會隨著電流的增加而遞減（約減少7.56 %），受熱效應較小之區域，其發光效率則會隨著電流的增加而稍做增加（約增加5.9 %），透過本系統對發光二極體內部進行量測，可以將發光二極體最真實的發光變化給呈現出來。

In general, the light emitting diodes (LEDs) are discussed its luminous quality by the variation of external light of LED. We applyed the forward voltage method to measure the junction temperature of LED. With optical microscopy in combination of high magnification objective lens, We could focus on the internal regions of LED to investigate the influence of thermal effect by injecting current from 10mA to 240mA. As the injection current increased, the junction temperature would also raise. The results showed a linear relation between injection current and junction temperature. The luminous intensity would be enhanced if input current were increased. Through the optical system we would know the current spreading in the interior regions of LED was not very uniform. The luminous intensity would stronger concentrate in the nearby electrode regions. As the junction temperature raised, the refractive index of gallium nitride would become larger, and the critical angle of total reflection would be smaller. This phenomenon caused the light would only emit from the middle regions of LED and the luminous intensity weaker on the edges. Due to the influence of thermal effect, luminous intensity would decay after 140mA and result in unstable emitting wavelength along with red shift after 100mA. According to the results, Luminous efficiency changed in different zones. The influence of thermal effect was more obvious nearby the electrode regions. The luminous efficiency decreased about 7.56 % when the current increased. The farther distance from the electrode regions, the less influence of thermal effect was observed. The luminous efficiency made a little increase about 5.9% when the current increased. Apply this system to measure in the internal regions of LED, the truly influence of the thermal effect on LED would be performed.

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