Effect of Artificial Light Sources on Growth and Quality Characteristics of Leaf Lettuce in Closed Plant Factory System

The growth and quality of lettuce were evaluated in a plant factory system with three types of artificial lights including fluorescent lamp (FL), light-emitting diode (LED) and external electrode fluorescent lamp (EEFL). Air temperature, relative humidity, CO2 concentration, and wind velocity in the plant factory system were maintained at about 25°C, 60%, 400 ppm, and 0.5 m·s, respectively. The photosynthetic photon flux densities (PPFD) of FL, LED, EEFL 7000K, EEFL 9000K and EEFL 12000K were 200, 300, 215, 265, and 235 μmol.m-2.s-1, respectively, with all same 24 hour photoperiod per day. Among lettcue cultivar ‘Manchudae' plants grown for three weeks under different artificial lights, plants under LED showed the highest fresh weight, followed *Corresponding author: Yeong Cheol Um Tel: +82-31-240-3657 Fax: +82-31-240-3669 E-mail: ycum0403@korea.kr 24 ... Journal of Agriculture & Life Science 47(6) by those under EEFL 9000K. In contrast, the lowest fresh weight was observed in plants grown under FL. The number of leaves showed the same trend as fresh weight. There was no significant difference in both leaf area and photosynthetic rate among plants grown in different light sources, although they were relatively low in those under FL. The contents of phenolic compound and total flavonoid were highest in plants under FL and LED but lowest in those under EEFL. In conclusion, the EEFL promoted growth in lettuce compared to FL although the growth response varied depending on the types of EEFL. Thus, EEFL can replace FL considering production-cost and energy saving in closed-type plant factories. Further studies are needed on the growth conditions such as temperature, light intensity, and relative humidity to increase antioxidant chemicals in lettuce grown in plant factories.