Effects of Blue, Red, and Blue/Red Lights of Two Different PPF Levels on Growth and Morphogenesis of Lettuce Plants

To clarify the possibility of plant production under red and blue monochrome light using light emitting diodes (LEDs), the effects of light quality and photosynthetic photon flux (PPF) on the growth and morphogenesis of lettuce plants were examined. Lettuce plants were hydroponically grown for 20 days, under 3 different light qualities (Red, Blue and Red/Blue) and 2 PPF levels (about 85 and 170 micromoles/m2/s) for a l6hr day and an 8hr night cycle, at a temperature range of 20 to 22 degrees C. Irrespective of the two different PPF levels, the plants grown under the red LEDs developed more leaves than the plants under the blue LEDs, but less leaves than the plants under blue/red light. The curvature rate of the leaf margin in the plants grown under the blue LEDs was less than that of the plants under red LEDs on both PPF levels. The inclination angle of the seventh leaf in the plants grown under the blue LEDs and the blue/red fluorescence lamps was greater than that of the plants under red LEDs on the high PPF level. The whole plant dry weight was greater in the plants grown under the high PPF level than the plants under a low PPF level.