Effect of distribution of photosynthetic photon flux density created by leds and condenser lenses on growth of leaf lettuce (lactuca sativa var. angustana)

Abstract

Plant factories have been receiving attention recently as a new vegetable production system. However, the high cost of producing vegetables in plant factories is a problem. An effective irradiation method was investigated to reduce the use of electric energy for light. A combination of LEDs and condenser lenses was constructed with the goal of having most of the light absorbed by a plant. Fresh weight, stem length, and number of leaves of leaf lettuce were measured under 12 different distributions of photosynthetic photon flux density (PPFD) created by the combination of three types of condenser lenses with the Full Width Half Maximum (FWHM) angles of 7°, 13°, and 35° and four LED driving currents of 0.2, 0.3, 0.4, and 0.5 amperes (A). Growth of lettuce was influenced by the distribution of PPFD using the same electric current. The choice of lens increased the fresh weight by 18% under the relatively strong light intensities of 0.4 A and 0.5 A. The combination of an electric current of 0.4 A with a lens of FWHM angle 13° produced the most efficient growth from a growth efficiency point of view.