LED 펄스광의 듀티비가 상추의 생장과 광합성 속도에 미치는 영향

Effects of Duty Ratio of Pulsed LED Light on Growth and Photosynthetic Rate of Lettuce Grown in a Plant Factory System

This study was carried out to examine the effect of duty ratio and intensity of pulsed LED light on growth and photosynthetic rate of lettuce(Lactuca sativa L. ‘Cheongchima’ and ’Jeokchima’) grown in a plant factory system. The three-week old seedlings were grown for 4 weeks under the bar-type LEDs(red:blue:white = 5:2:1) with different LED pulse(on/off) of 400/0(continuous), 300/100, 200/200, 133/266, and 100/300 μs by using oscilloscope during 16 h photoperiod. These indicated duty ratio(DR, percentage of on time from one cycle) of 100, 75, 50, 33, and 25%, respectively. Light intensities were two levels(high and low, HL and LL) at DR 100, 75 and 50%. Air temperature and relative humidity in the system were maintained at 20±2°C and 70±10%, respectively. Nutrient solution(initial pH 5.8±0.2, EC 1.2 dSㆍm⁻¹, 20±2°C) was supplied by nutrient film technique method. In ‘Cheongchima’ lettuce, fresh and dry weights at 4 weeks after treatment were highest in DR 100% HL with no significant difference with DR 75% HL and DR 50% HL. Leaf number, leaf area, and leaf thickness represented by the reciprocal of specific leaf area were largest in plants grown under HL of DR 100%, 75% and 50% for 4 weeks. Light use efficiency(LUE) was higher under pulsed light than continuous light irrespective of PPFD. LUE under DR 25% HL was highest and LUE under DR 75% HL and DR 50% HL was higher than that under DR 100% HL. In ‘Jeokchima’, fresh and dry weights at 4 weeks after treatment were largest under DR 100% HL and second-largest under DR 100% LL, DR 75% HL, and DR 50% HL. LUE in was higher under pulsed light than continuous light similarly to ‘Cheongchima’. Photosynthetic rate was proportionally increased to integrated PPFD rather than DR in both cultivars. These results will be utilized for energy saving in the closed plant factory system using LED as a light source.