the amount of illumination to which a plant is exposed; the illumination may be sunlight or light from one of various artificial sources. The light regime is determined by the influx of radiant energy and its distribution in a biocenosis or crop planting. Of particular importance are the intensity and spectral composition of the radiation and changes therein in time and space. The ratio of day length to night length is also significant.
An evaluation of light regime takes into account visible (physiologically active) radiation, during the absorption of which by pigments photosynthesis and other photobiological processes are carried out. Also important are invisible ultraviolet and infrared rays, which play a major role in the water and heat regimes of plants. Favorable light conditions are achieved by regulating the density of crop plantings and selecting the direction of rows in relation to the source of light. In hothouses plants are exposed to photosynthesis-effecting radiation from incandescent, xenon, or fluorescent lamps. To prevent a plant from growing toward the light all sides should be evenly illuminated.
I. A. SHUL’GIN