Effects of Pulsed-Red LD Light on the Growth of a Plant

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