Comparison of the Effects of Monochromic Red Light and Mixed Light on the Growth of Lettuce

The effect of light quality on the growth of lettuce (Lactuca sativa L.) was investigated for cultivation in a plant factory. In this study, we used a mixture of red, green and blue light emitting diodes. The fresh weight of lettuce increased under monochromic red light and a mixture of red and green light. There was no significant difference in the fresh weight of lettuces grown under monochromic red light and those grown under a mixture of red and green light. When a mixture of red and blue light was used, the fresh weight decreased with increase in the ratio of blue light. Stem length decreased and plant shape improved under a mixture of red and blue light. There was no significant difference in the stem length of lettuces grown under monochromic red light and those grown under a mixture of red and green light. Generally, blue light is required to improve plant shape. However, in the case of “Chima sanchu”, which is one of the varieties of lettuce used in this experiment, stem elongation under monochromic red light and that under a mixture of red and green light were acceptable in comparison with that observed lettuces grown outdoors. Energy consumption was the lowest under monochromic red light. These results suggested that monochromic red light was suitable for the cultivation of lettuce.