Light emitting diodes (LEDs) are a potential irradiation source for intensive plant culture systems like plant factories. LEDs have small size, low mass, a long functional life, and narrow spectral output. We have examined the growth profiles of leaf lettuce and other plant species grown under red light with supplemental blue and far-red light of LEDs compared with other artificial light. On the basis of our experimental data, the characteristics of LEDs as irradiation source for plants and the prospects for plant factory equipping LED lighting systems are overviewed in this paper.