LED applications in greenhouse and indoor production of horticultural crops

Arrays of light-emitting diodes (LEDs) are increasingly being used in controlled environments to deliver photoperiodic, supplemental, and sole-source lighting to speciality crops. Compared to conventional light fixtures such as high-pressure sodium or fluorescent, LEDs emitting different bands of radiation can be combined to create light spectra that regulate specific plant responses such as extension growth and flowering. LED applications in horticulture can be divided into three major categories: 1) low-intensity lighting to regulate photoperiodic and photomorphogenic responses; 2) supplemental (photosynthetic) lighting in greenhouses to increase growth and yields; and 3) sole-source lighting to consistently produce crops indoors, conceivably with value-added attributes. Potential advantages of LED lighting include greater efficacy at converting electricity into photosynthetic photons; selection and manipulation of the radiation spectrum to elicit specific plant responses; less emission of radiant heat; more focused lighting, resulting in less loss to non-target areas; instant on/off and dimming capabilities; and greater longevity. The primary barrier to commercial implementation of LED lighting in horticulture continues to be return on investment, which is situational. This paper presents a science-based, practical summary of LED applications in the production of horticultural crops grown in controlled environments, especially vegetable and floriculture crops.