Abstract
This study details a one-time ray-tracing optimization method for the optimization of LED illumination systems [S.-C. Chu and H.-L. Yang, "One-time ray-tracing method for the optimization of illumination system," in Proceedings of International Conference on Optics in Precision Engineering and Nanotechnology (icOPEN, 2013), 87692M]. This method optimizes the performance of illumination systems by modifying the light source's radiant intensity distribution with a freeform lens, instead of modifying the illumination system structure. Because illumination system structures are unchanged in the design process, a designer can avoid the common problems faced when designing illumination systems, i.e., the repeated and time-consuming ray-tracing process when optimizing the illumination system parameters. The easy approaches of the proposed optimization method to sample the target illumination areas and to divide the light source radiant intensity distribution make the proposed method can be applied to both direct-lit and non-direct-lit illumination systems. To demonstrate the proposed method, this study designs an illuminator for a tube photo-bioreactor using the proposed one-time ray-tracing method. A comparison shows that in the designing of the photo-bioreactor, tracing all rays one time requires about 13 hours, while optimizing the light source's radiant intensity distribution requires only about twenty minutes. The considerable reduction in the ray-tracing time shows that the proposed method is a fast and effective way to design illumination systems.
Highlights
Because of the advantages over incandescent light sources, such as lower energy consumption, longer lifetime, smaller size and faster switching, light-emitting diodes (LEDs) are widely used in road lighting [1,2], automotive lighting [3,4], interior lighting [5] and LCD backlighting [6]
Since the ray-tracing time is much longer than the time to optimize the LED light intensity distribution curve (LIDC), we suggest designers to use large but reasonable initial divisions of light source and target area under an acceptable condition of his/her calculating equipment
As to the design of the photobioreactor, tracing all rays one-time required around 13 hours, while optimizing the LED LIDC required only about 20 minutes
Summary
Because of the advantages over incandescent light sources, such as lower energy consumption, longer lifetime, smaller size and faster switching, light-emitting diodes (LEDs) are widely used in road lighting [1,2], automotive lighting [3,4], interior lighting [5] and LCD backlighting [6]. Researchers have used LED array lighting (LAL) to achieve uniform illumination [7,8,9,10] Among these LED uniform illumination studies, the “reversing design method” that Liu et al proposed for slim direct-lit LED backlighting [7] has attracted attention for its potential to be modified as a fast design approach for all LED-based illumination systems. In the design process of the proposed method, the system structure remains unchanged as the designer does not need to trace the rays more than once By means of this one-time raytracing and a general optimization process, a good solution for an LED-based illumination system design can be quickly found. The paper is organized as follows: in Section 2, the one-time ray-tracing optimization method is detailed; in Section 3, the proposed method is applied to the design of a tube photobioreactor for cultivating microalgae [23,24]; in Section 4, some concerns regarding the use of the one-time ray-tracing optimization method are discussed; and, in Section 5, a brief summary of this study is given
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