Abstract
Lettuce (Lactuca sativa L.) plants were grown under three irradiating cycles for 24h cycle (8h photoperiod : 16h dark period), 12h cycle (4h photoperiod : 8h dark period) and 8h cycle (2 2/3h photoperiod: 5 1/3h dark period) . The ratio of the photoperiod to the dark period was 1 : 2 in all treatments. The amount of electricity consumed for lighting per 24h period was set to be the same in all treatments. Temperatures in the light period and dark period were 24°C and 20°C throughout the experiments, respectively. Plants grown under 8 and 12 h irradiating cycles had a lower number of leaves, low fresh and dry weights, small leaf area, low photosynthetic rate and less water and mineral (NO3-N, PO4-P and K) uptakes, compared to those grown under 24h irradiating cycle. Plant growth and water and mineral (NO3-N, PO4-P and K) uptakes were found to be similar in both the 8 and 12h irradiating cycles. Plant quality did not change by irradiating cycles.
