## 1 Introduction  
In recent years, LEDs have been used in many different fields. With the highlight of energy savings, long life, and safety for users [1; 2], LEDs are replacing other traditional lamps. However, LEDs have disadvantages of a wide beam angle (from 120\({}^{\circ}\) to 150\({}^{\circ}\)) depending on the type of LEDs [3] and have Lambertian distributions. Illumination should be redistributed using an integrated primary optical system or secondary optical system to control distribution shape and uniformity [4].  
Utilizing free-form optics is a new trend to design secondary optical components for LEDs. The advantages of free-form optics are their unique design, compact size, and precise irradiation control [5]. In order to design a free-form lens, various methods have been proposed. For example, the [PERSON] group developed the simultaneous multiple-surface method (SMS method) [6] to design a collimator for LEDs [7]. This method redistributes light from the source to the reflective surface to produce a parallel beam with a beam angle of \(\pm 1.5^{\circ}\). This method also uses a wave-front theory of geometrical optics [8] to design a Fresnel lens with combined functions of LED collimation and redistribution for uniform illumination. [PERSON] et al. used a light energy mapping method to make a compact freeform lens create an even distribution in many different shapes [5]. In addition, the optimal numerical method can also be used to design free surfaces for LED arrays, such as in [PERSON] et al. [9]. All of the above methods work very well in controlling the distribution shape and producing a uniform light distribution, but they are not flexible in different types of LEDs. Equations for lens surface calculations have parameters dependent on the light source. Therefore, the lens structure must be recalculated when applied to different types of LEDs.  
In this paper, we present a method to fabricate an optical component for a single LED, which can be applied to many types of LEDs with different beam angles to make a uniform distribution. The single LED can be a high-power LED or chip-on-board LED (COB LED). The commercial collimator lens is placed on top of the single LED to collect and collimate the light output from the LED. The collimated beam is redistributed by two linear Fresnel lenses [10] to create a uniform distribution on the receiver, as shown in Figure 1. The surface of the linear Fresnel lens is designed by using the edge-ray principle [11] and Snell's law. The parameters of the linear Fresnel lens are not dependent on the LED chips and the collimators, where poly methyl methacrylate (PMMA) material is used to produce the lens. The results include the simulation of uniformity and efficiency of the system, comparison of simulations, and experimental results. Finally, an experiment on chrysanthemum was conducted to control flowering. Other experiments on flowering control do not present how the uniformity of the light source has an effect on plant growth, and most studies have focused on the wavelength and power of light sources [12]. Therefore, this study will be a useful reference to achieve better quality of agricultural products by improving lighting uniformity.