Abstract: Disclosed are a method and an apparatus for irradiation of plants using optoelectronic devices. In accordance with this invention, optoelectronic devices that emit radiant energy at the appropriate wavelength are operated in a continuous mode or pulsed asymmetrically at a frequency and level of electrical power that results in sufficient irradiance to support plant growth and development. The apparatus consists of: (1) an array of optoelectronic devices, primarily light emitting diodes, for producing irradiance in each of three different wavelength regions necessary for specific plant photobiological reactions, (2) a pulse generator and associated electric power driving components, and (3) an electric direct current (D.C.) power supply.