A conventional Fresnel lens is suitable to be used in the reading light system due to its features of directing and collecting light rays, as well as its properties of being essentially flat, plastic, lightweight, and cost efficient. However, it is not suitable for a reading light system with multiple light sources. To a reading light system with multiple light sources, a Fresnel lens with suitably designed groove angles can be used to improve the performance of that system in both illuminance and uniformity. Nevertheless, suitable groove angles are rather difficult to find if a Fresnel lens consists of a lot of groove angles and each angle covers a wide range of degrees. We develop a hierarchical genetic algorithm (HGA) to search for a set of optimal groove angles to design a Fresnel lens for a reading light system with multiple light sources from an enormous searching space. In addition, the groove angles of the Fresnel lens are directly derived from a conventional Fresnel lens database. The design goal is to maximize the illuminance and simultaneously maintain the uniformity of light rays incident to a specified reading surface. As a result, we can demonstrate that a HGA really works better than a genetic algorithm and the optimally designed Fresnel lens, indeed, offers a better light-guiding performance than a conventional Fresnel lens for a multiple-LED reading light system.

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A two-layered Hierarchical Genetic Algorithm (HGA) was proposed in a previous paper to solve the design problem of a large scale Fresnel lens used in a multiple-source lighting system. The research objective of this paper is to extend the previous work by utilizing a three-layered HGA. The goal of the suggested approach is to decrease the reliance on deciding the number of groove segments for the designed Fresnel lenses, as well as to increase the variety of groove angles in a segment to improve the performance of the designed Fresnel lens. The proposed algorithm will be applied on a simulated reading light system, and the simulation results demonstrate that the proposed approach not only makes the design of a large scale Fresnel lens more feasible but also works better than the previous one in both illuminance and uniformity for a simulated reading light system.

This paper presents the design of a reading light system consisted of multiple R, G, and B white light LEDs with Fresnel lens located before the light source. First, we use a general Fresnel lens and a Genetic Algorithm (phaseΙ) to search the best arrangement of multiple LEDs, then use another Genetic Algorithm (phaseΠ) to the result obtained before to get a better Fresnel lens of width-varied grooves. Experimental results show that the special arrangement of LEDs and the special structure of Fresnel lens make the reading light system more efficient in illuminance than the reading light system of no Fresnel lens.

A typical Fresnel lens is not suitable to a reading light system with multiple light sources since it is designed in such a way that each groove is at a slightly different angle from the next but with the same focal length. Therefore, a Fresnel lens with suitably designed groove angles is needed for this kind of light system. In this paper, a more efficient three-layered Hierarchical Genetic Algorithm (3LHGA) is proposed to find an optimal set of groove angles for a designed Fresnel lens to optimize both the illuminace and uniformity for a reading light system with multiple light sources. The groove angles of a designed Fresnel lens are directly derived from a Fresnel lens database by two layers of control genes in the proposed 3LHGA. The proposed 3LHGA not only makes it possible to evolve a lot of groove angles as parametric genes but also further improve the performance of a Fresnel lens and increase the speed of evolution. From the simulation results we can demonstrate that the designed Fresnel lens indeed offers improvement of light-guiding performance for a multiple-LED reading light system.