Application of Red Laser Diode as a Light Source for Plant Production

Abstract

As a new type of light source for plant production, high-power and high electrical-to-optical power conversion efficiency AlGalnP laser-diode lamps with the continuous wave output power of 500 mW that have peak emission of 680 nm have been developed. To confirm the possibility of growing plants under this new light source, the effects of laser-diode light on growth of lettuce (Lactuca sativa L.) plants were studied. In experiment 1, lettuce plants were grown under 350 μmol · m^-2 · s^-1 photosynthetic photon flux (PPF) of the laser-diode light with a 12-hour photoperiod. In experiment 2, lettuce plants were grown under laser-diode light supplemented with blue light with a total PPF of 350 μmol · m^-2 · s^-1. The lettuce plants were able to grow even under the 680 nm laser-diode light. However, the leaves of the lettuce plants grown under the laser-diode light were long and thin, and their dry weight was low compared to lettuce plants simultaneously grown under high-pressure sodium lamps. By supplementation with the blue light, the shape of the leaves was much improved and the dry weights were much increased. These results indicate that red laser-diode lamps combined with blue LED light have a possibility for efficient plant production, including transplant production.