光線在建築當中是不可或缺的一部份，不管是空間照明、路線引導或氣氛營造，光線總是設計者最有利的工具之一。自然天光與人造光是現今主要的光線來源，隨著環保意識逐漸抬頭，利用天光取代人造光以節省能源的設計手法越來越常見，卻也因為天光的不斷變化，使得導光設計更加具有挑戰性。

本研究以直射光與固定式控光裝置作為實驗主題，製作了圓形窗與矩形長窗並分別測試其導光效果，在導光策略上以營造視覺舒適區為目標，利用導光窗將光線導向室內高處，再藉由天花板與牆壁的漫反射使光線均勻分布於空間內，進而達到均齊照明以及避免光線直射工作平面之目的。

經研究發現，圓形窗的導光量受限於開口的大小，而開口大小又會影響光線直接穿透的機率，由於天光角度不斷改變以及筒狀反射的維度較多，聚光板與遮光板並無法處理大部分的入射光與反射光，因此對於固定式控光裝置而言，圓形窗較難以實現精準控光之目標；相較之下，矩形長窗的導光結果較符合本研究之導光策略，從實驗結果可以看到天光最終都被引導至天花板，再藉由漫反射散佈於室內，且經過長窗與天花板或牆壁的反射後，工作平面仍能達到一定的亮度，故在室外光源足夠的情況下，透過矩形長窗導光可達到降低人工光源需求以節省能源之目標。

Lighting is an indispensable part of architecture. It’s a good tool for illuminating, guiding, and atmosphere making. Nowadays, daylight and artificial light are the two main lighting resources. As the environmental awareness rising, using daylight to replace artificial light for energy saving becomes more and more common. However, light guiding is full of challenges due to the inconstant direction of daylight.

This research mainly focuses on the efficiency of nonadjustable light guiding
devices under direct light by comparing windows with circular and rectangular sections respectively. To make a visual comfort zone, light was reflected to the upper indoor space from outside by the windows, and then was diffused into whole room evenly by ceiling and walls. Therefore, this light guiding strategy can achieve uniform illumination and block the direct light on the work plane.

By the research, the amount of reflected light limited by the aperture size, and the aperture size affects the probability of light passing through the windows directly. Because of the inconstant daylight and the high dimension of reflection in circular window, the collector and shading board cannot deal with the most incident light and reflected light. For nonadjustable light guiding devices, circular window is difficult to control light precisely. By comparison, the efficiency of light guiding in rectangular window meets the research goal more. The result shows that most light was reflected on the ceiling first and then was diffused into the space. Furthermore, the luminance on the work plane could still maintain a certain level although the light was reflected by such places. Therefore, under the premise that the daylight is strong enough, the light guiding strategy using the rectangular window is a feasible method to reduce the need of artificial light and save energy.

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