System Identification of CO₂ Uptake in Lettuce as Effected by the Pulsed Light Illumination

Abstract

Great progress has been made in the development of plant factory. New artificial light source as called pulsed light illumination has been developed, which is operated on high frequency and could be controlled in different duty ratio. So, electrical power is being expected to be saved by applying the pulsed light illumination in the plant factory.
In this study, system identification method was used to estimate the effect of the pulsed light illumination on the photosynthesis of Okayama Saradana. Impulse responses of net CO₂uptake to 100%, 50%, 30% duty ratio of the pulsed light illumination were estimated in 1000 ppm, 650 ppm, 350 ppm CO₂concentration respectively. Simulation with the estimated impulse responses showed that the net CO₂uptake under low duty ratio of the pulsed light illumination such as 50% could be kept in the level of that under 100% duty ratio, 350 ppm CO₂concentration if CO₂concentration of the environment is increased to two or three times of 350 ppm. So, by means of controlling the duty ratio and the CO₂concentration, much electrical power could be saved in the cultivation of the plant factory.
Furthermore, the estimated changes of net CO₂uptake to various duty ratio of the pulsed light illumination had a good agreement with the changes observed in the short-term. So, it could be concluded that system identification is a very effective method for estimating the effect of the pulsed light illumination for the plant factory.