Effects of Pulsed White LED Light on the Growth of Lettuce

Abstract

Lettuce was grown under pulsed white LED light at variation pulse cycles and DT ratios (illuminated period/cycle), and the relative growth rate per unit luminous energy and photosynthetic rate were examined. Both the growth rate and photosynthetic rate were generally increased (except at a pulse cycle of 10ms and a DT ratio of 50%) compared with continuous illumination. Particularly, both the growth rate and photosynthetic rate were increased by 20% or more at a pulse cycle of 400μs and a DT ratio of 50%. A further slight increase in the growth rate was observed when the DT ratio was 33%. These results may be explained by the presence of a period of 200μs duration in which light is unnecessary (period of electron transport) in the light reaction of photosynthesis. This study supports the feasibility of LED plant factories.