照明用電佔了總用電比例的1/3並快速的消耗有限且應用於發電的石化能源。日光照明系統因此在近年來成為熱門的研究議題之一。在許多的日照系統當中，有一知名的系統為向日葵日照系統，是由日本團隊所研發。此系統具有極高的效率並提供室內充沛的自然光進行照明。然而，像是這樣的系統是屬於動態式的日照系統，需要額外的電力來驅動追日馬達進行追日收集太陽光。與靜態式的日照系統相比較，靜態式日照系統則是具有高容忍角的設計而不像是向日葵日照系統般需要追日馬達來收集日光。而在眾多的靜態式日照系統當中，自然光照明系為一新穎的日照系統，利用直角稜鏡結構壓縮並傳導自然光進行室內照明。自然光照明系統具有許多的優點，例如可堆疊以及可模組化使得整個系統便於安裝以及維護。

自然光照明系統又可細分為集光、傳光以及放光子系統。整個系統的效率為三個子系統效率的相互疊加。由於本篇論文主要是研究集光子系統以及傳光子系統之間的探討，因此我們主要探討如何增加傳光子系統的方法。而關於傳光子系統，光纖以及傳光管是兩種主要用於傳光的元件。傳光管是由管子以及透鏡所構成,經由透鏡的發散以及聚焦的能力，傳光管可長距離的進行光線的傳遞而不會有太大的損耗。由於光纖對於長距離的傳遞其成本太過高昂，因此在傳光元件的選擇上將選擇傳光管進行研究與探討。

經過研究顯示傳光管的容忍角為±〖10〗^°並且經過集光模組後的光線角度遠大於10度，這會造成傳光管低效率且無法傳遞足夠的光進行室內照明。為了要解決此一問題，我們根據自由曲面的方法設計了一準直透鏡作為集光以及傳光子系統之間的耦合器。此透鏡的材質為BK7玻璃材質，當光經過此一透鏡時，光線會根據透鏡上的曲面而被收斂。而曲面的建立方式則是藉由建立並切割虛擬網格並藉由每一網格上的光源分布找出切平面向量以建立自由曲面離散面。最後將每一自由曲面離散面連結便可得到完整的自由曲面透鏡且可將光線收斂為近平行光最終使得傳光子系統的效率大幅度的上升。

Electrical lighting consumes around 1/3 of the total electricity, it depletes rapidly the limited fosil energy sources used to generate electricity. Daylighting systems therefore become one of the most popular research issues recently. Among various daylighting systems, one is the well-known HIMAWARI, designed by a team from Japan. The system is highly efficient and provides sufficient light for indoor illumination. However, such systems are dynamic systems, which need additional electricity to drive the suntracker for gathering sunlight. Comparing with the static systems, in which the tolerance angle of the light collectors are usually designed larger rather than with the suntrackor of the HIMAWALI. Among on these static systems, the Natural Light Illumination System (NLIS) is an innovative static system, using rectangular prisms structure to compress and transmit the sunlight indoor for illumination . There are many advantages of NLIS like cascadable and modulized that is easier for installation and maintenance the system.
The NLIS system is composed of three sub-systems, light collection, light transmission, and light emission. The overall efficiency of the NLIS is the sum of the three subsystems. Since this paper is mainly focus on the reaearch between the light collection subsystem and the transmission subsystem. We mainly explore the way to enhance the efficiency of the light transmission subsystem. Regarding to the transmission subsystem, there are two often-used component, the light pipe and the optical fiber. The light pipe is composed of tubes and lenses. With the properties of focusing and divergence, the lenses in the light pipe allow the light be transmitted to a large distance without substantial loss. Due to the cost of the fiber is too high for long distance to transmit, the light transmission component we choose to study is the light pipe.
The research shows that the numerical aperture of the lightpipe is ±〖10〗^° and the angles behind the collection module are larger than〖 10〗^°. It would cause low efficiency and lead to insufficient light for indoor illumination. To solve this problem, we design a collimating lens based on free-form method to be a light coupler between the collection subsystem and the light transmission subsystem. The free-form lens is made of BK7 glass. When the light passing through the lens, the light will be converged according to the shape of the lens. The surface is constructed based on parting the light source into cells and calculateing the tangent vector of the refractive surface on the basis of the light distribution on each cells. Finally, we connect each free-form lens together to form the complete free-form lens and the light passing through the lens are converged as nearly parallel light. With the nearly parallel light, the efficiency of transmission part can be greatly enhanced.

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