Effect of LED-light Stimulation at Specific Frequencies on Lettuce Growth

Abstract

Plant growth rate can be controlled by adjusting both the light quality and during light and dark transition. Light intensity and time also have an effect on growth rate. We investigated the effects of low-intensity light irradiation of specific frequency on the growth and inorganic contents of lettuce in the field. Lettuce was cultivated using three types of nutrient solution (complete nutrition, NO3-N-excessive, NO3-N-deficient) . Light sources were red and yellow LEDs, which are low-cost artificial light sources used in plant production. Leaves were irradiated by pulsed LED-light for several hours each day. Red and yellow LED-light stimulation of specific frequency (20 Hz, 50 Hz) increased the lettuce yield in nutrient solutions with lower NO3-N concentrations, despite of the fact that the chlorophyll in lettuce does not response much yellow light. Changes in light stimulation frequency affected NO3-N concentrations in lettuce sap. These results suggest that stimula-tion by red or yellow LED-light in the field has a positive effect on photosynthetic activity.