The effect of light quality on growth of lettuce

Plant factory is a plant production system with controlled temperature, carbon dioxide concentration and light environment to enhance plant growth efficiently. Fluorescent lamp is popularly used in a plant factory, however, the spectrum of fluorescent light is broad and some portion of them is not necessary for photosynthesis. On the other hand, LED (light emitting diode) has narrow band width and is getting easy to use these days. The final goal of this project is to develop a new light apparatus with LEDs for plant factory. The specific objective is to investigate the effective light quality for growing plant more rapidly. The effect of light generated by monochromic and mixed radiation from LEDs (blue, green, red) on the response of lettuce (Lactuca sativa L.) were evaluated and compared with the effect of lettuce irradiated by fluorescent lamps. Photosynthesis rate of lettuce increased in monochromic red light and the light mixed with red and blue light. Number of leaves decreased in monochromic blue light. Fresh weight of lettuce was increased in monochromic red and fluorescent light, but monochromic red light significantly decreased dry weight rate. In the view of energy saving, LED is much better than fluorescent lamp. Especially, red LED is good.