## 3 Experiment
### Outdoor Test  
An LED with an optical component in this study was applied to control chrysanthemum flowering. Chrysanthemum is a short-day plant, which flowers only when the provided photoperiod is shorter than the \"critical period\" [17]. We used night break phenomenon [12] as show in Figure 15 to control chrysanthemum flowering. We made a short flash of light in the middle of the night so the plant would behave as if it had been exposed to a long day. The differences of chrysanthemum growth between controlled flowering and uncontrolled flowering are shown in Figures 15 and 15, respectively. When chrysanthemums were under uncontrolled flowering, it flowered at a time of no demand. Flower sizes were small, and the quality was also low. Chrysanthemums under controlled flowering had a longer vegetative process, resulting in taller chrysanthemums. With time-controlled flowering, the quality of the product improved.  
Figure 14: Experiment results of the distribution measuring system. (**a**) Distribution on the target surface. (**b**) Comparison of the simulation and experiment distribution along the X axis across the center of the target surface.  
The flowering process takes 20 to 30 days after stopping the night break phenomenon. The wavelength that is suitable for illumination is 630 nm [18]. In this experiment, we used two flowerbeds of chrysanthemums. The first flowerbed was under a 5W COB LED with 630 nm wavelength with optical components we designed, and the second flowerbed was under the same LED with a traditional parabolic reflector. Chrysanthemums were illuminated at night with a projection time of 2 h per day, and the distance between stems was \(10\times 16\) cm. The area of the flowerbed was 4 m\({}^{2}\) (\(2\times 2\) m). Thus, 250 flowers were planted in each flowerbed. After two months, the results are shown in Figure 16.  
As shown in Figure 16a, chrysanthemums under LED with parabolic reflectors had non-uniform heights; the plants on the edge of the area were shorter than the plants at the center, which results in a lower-quality commercial product. On the other hand, chrysanthemums under LED with our optical components showed quite uniform heights, which is important in the market. Specific numerical results are shown in Table 2.  
Based on the data in Table 2, we can see that both samples had good results in controlled flowering; more than 94% of plants had no flowers before stopping the night break illumination. The LED with  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **LED with Double Fresnel Lenses** & **LED with Parabolic Reflector** \\ \hline Number of stems surveyed & 216 & 207 \\ Rate of early flowering & 4.2\% & 5.9\% \\ Lowest height of the stems & 75 cm & 58 cm \\ Highest height of the stems & 84 cm & 80 cm \\ Average height of the stems & 82 cm & 72 cm \\ Average diameter of the flower & 7.8 cm & 7.3 cm \\ \hline \hline \end{tabular}
\end{table}
Table 2: Results of chrysanthemums after 2 months of testing.  
Figure 16: Chrysanthemums under controlled flowering (**a**) By LED with a parabolic reflector. (**b**) By LED with our optical component.  
Figure 15: Night break phenomenon (**a**) Principle; (**b**) Chrysanthemum with controlled flowering by LED. (**c**) Chrysanthemum without controlled flowering.  
our optical components was better than the LED with a parabolic reflector for controlling the flowering effect in terms of uniformity in height. Also, the overall height of flowers under our light source was higher than those under the conventional LED source by 12%. The flower size was also 6% larger in our case.  
A uniform light distribution on the cultivated area using our proposed design is a very promising solution in the field of high-value-added agriculture. Our method can be applied to many types of LEDs, reducing costs and achieving high efficiency.