Effects of the irradiation patterns of red and blue LED lights on the growth of leaf lettuce were investigated. Seedlings of leaf lettuce (Lactuca sativa L."Greenwave") were transplanted and grown under four irradiation patterns consisted of simultaneous irradiation of blue light with PPFD of 120 μmol m-2 s-1 and red light with PPFD of 120 μmol m-2 s-1 during a 12 h photoperiod (RB 12 h/dark period 12 h), 4 h shifted irradiation of blue light (R 4 h/RB 8 h/B 4 h/dark period 8 h), 8 h shifted irradiation of blue light (R 8 h/RB 4 h/B 8 h/dark period 4 h), and alternating irradiation (R 12 h/B 12 h). The results demonstrated that larger shifts in irradiation times between red and blue lights led to increasing fresh/dry weight of leaf lettuce. A similar trend was observed under the irradiation patterns that replaced the red and blue. An experiment to examine the effects of simultaneous or alternating irradiation of red and blue light under equal day length and light integral was also conducted. As a result, alternating red and blue light irradiation produced better results compared to simultaneous treatment for Greenwave in both experiments.