Effects of Different Light-emitting Diode (LED) Lights on the Growth Response of Leafy Vegetables in a Closed-type Plant Factory System

Growth of leafy vegetables as lettuce (Lactuca sativa L.), endive (Cichorium endivia L.), pak-choi (Brassica campestris var. chinensis), kale (Brassica oleracea var. acephala), arugula (Eruca sativa), and Treviso (Cichorium intybus L.) were investigated at different types of light sources in closed-type plant factory system. The specific light-emitting diodes (LEDs) chips used for plant cultivation were made by shifting green wavelength to yellow or red in order to promote plant growth. The light source were cool white fluorescent lamps (FL, the control), pink (V1, blue : red = 1:1) LEDs, yellow (V2, blue : green : red = 22:11:67) LEDs or purple (V3, blue : red = 1:3) LEDs, and each light was separately supplied and the intensity of its was adjusted to 100~120 μmol·m^-2·s^-1 at plant level with a photoperiod consisted of 16 hours light and 8 hours darkness. The plants were hydroponically cultured at 23±2 °C, 60~80 % RH and 1,000 μmol·mol^-1 CO₂. Fresh weight and shoot length of all the tested species treated with V3 were the greatest among all the tested light treatments. The number of leaves all tested species, except pak-choi, was greater in LEDs treatments than that in FL. Leaf area of all tested species was the greatest at V3. These results suggested that the V3 which is composed of blue and red wavelengths (1:3) provided the most the suitable light condition for vegetative growth of several leafy vegetables among the tested light sources. To produce high quality of vegetables in plant factory system, the optimum light conditions should be considered such as light intensity, photoperiod and ratios of mixing with other LEDs.