PLANT LIGHTING IN CONTROLLED ENVIRONMENTS FOR SPACE AND EARTH APPLICATIONS

Light is a requirement for plant growth and development that interacts powerfully with other environmental variables to define plant responses to the environment. Protected cultivation can eliminate off-nominal conditions that prevent plants from achieving their productivity potential. Light hardens plants off against growth-inhibiting effects of mechanical stresses in protected environments, and likely contributes to hardening in the field. Growth-dynamic and gas-exchange metrics reveal interactions of light level, CO₂ concentration, temperature, and nitrogen nutrition in stimulating crop productivity and nutritional composition while saving energy for lighting. Intracanopy lighting of planophile crops growing in controlled environments with low-power lamps overcomes aspects of dense plantings and mutual shading that occur with overhead lighting. For more than 20 years, plant researchers have experimented with solid-state light-emitting diodes (LEDs). LEDs have numerous technical advantages for plant lighting, including cool emitters that allow close placement to plant surfaces without scorching them. Thus, reduced power can be used to achieve adequate photon flux. When used as sole sources for photosynthetic, photomorphogenic, and/or photoperiod lighting, narrow-spectrum LEDs must be proportioned carefully to obtain desired plant responses. Potential exists for significant electrical energy savings using LEDs, but undesirable effects of wavelength deficiencies on plants also are being revealed by ongoing LED research. Intracanopy and close-canopy “smart lighting” with LEDs hold additional promise for plant-lighting effectiveness and efficacy. A natural extension of sole-source LED lighting approaches for space applications to supplemental LED lighting approaches has implications for improved profitability of the greenhouse industry.