Effects of the Ratio of Red to White Light Using Light-emitting Diodes on the Growth of Watercress

Abstract

The effects of light quality on the growth of watercress were investigated using red light-emitting diodes (LED) and white LED as light sources in the growth chambers. Under conditions of only red LED light irradiation, watercress grew spindly with a markedly decreased fresh weight and stem elongation. Under conditions of only white LED light irradiation, the main stem elongation of watercress was inhibited. Optimal growth could be achieved under the light conditions, whose ratio of red to white LEDs was 50 : 50 based on the photosynthetic photon flux density. This condition increased the fresh weight and satisfied the delivery basis with a more than 10-cm stem length. It also improved almost all the measured values as compared with those of fluorescent light. Therefore, it is desirable to combine red and white LED in watercress cultivation to optimize vegetative growth.