發光二極體(Light Emitting Diode,LED)燈具取代傳統燈源是世界的潮流，在水下照明領域亦是。傳統水下燈源是以輻射狀的發光角度傳遞，因為輻射狀光源在水下的散射，各方向光強度一致，導致散射被涵蓋在衰減係數中一併討論，並無出光角度之問題。而LED光源具有高指向性的特性，使得光在水中的光場會因為散射而改變，造成在分析水下照明時，不能引用傳統燈具既定的理論去探討。因此本文利用平均餘弦方法分析LED光束在水下的散射模式，修正傳統輻射狀光源的分析方法，並且簡化複雜的隨機散射計算，來表現各方向之光照強度，接著將LED光源模組量化，結合水中LED光束傳遞模式，分析不同的燈源排列、光照強度及配光曲線等參數，LED光源模組在水中光照強度的分布。以此LED光束在水中傳遞之分析方法，所獲得的最佳設計參數可作為後續設計高亮度LED水下燈之基礎。最後由實驗結果顯示，使用水下LED光源模組在各方向上的光照強度和模擬的誤差量約在10%以內，由此證明使用平均餘弦分析水下LED燈具是具可行性。

The LED lamps replaced the traditional light source is a global trend. It is also in the underwater. Traditional light source’s emitting angle is like radial, so the light intensity in the every direction is same. It lead to scattering coefficient and emitting angle became not important in the calculation. However, the LED light source has the characteristical of high directivity that will change the light field by scattering. Because of the characteristical, we can not analyse and apply the LED in the underwater illumination by using the way of analysing the traditional light source. This research analytically calculate the light scattering models in underwater by average cosine and revise the traditional analysis about light transmitted in underwater and simplify the complex random scattering to express the light intensity in every direction. Then quantify the LED light source and combined the transmitting model. By using this way, we can select the best light intensity curves and power and array. Finally, experimental results show the deviation of the simulation is no more than 10%.

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