Plant Cultivation Under Artificial Illumination

Artificial illumination is used for the early cultivation of vegetable seedlings, for the winter cultivation of vegetables (especially in the Far North), for the forcing of flowering plants, and for year-round breeding and seed production under an optimal light regime. Plants are often raised under artificial illumination for research purposes. Artificial lighting is also used in hothouses and greenhouses during the winter months to lengthen the day and augment the weak sunlight.

The Russian botanist A. S. Famintsyn was the first to use in 1868 kerosine lamps for the cultivation of plants. In the 20th century the American scientist R. Harvey (1922) and the Soviet physiologist N. A. Maksimov (1925) cultivated plants “from seed to seed” under the light of powerful incandescent lamps. In commercial plant cultivation, incandescent, fluorescent, xenon, and mercury-vapor lamps are used. For the normal growth and development of plants under artificial illumination, the intensity of the light in the physiological range (380–710 nanometers) must be not less than 30–150 watts per sq m; the intensity varies for different plant species and varieties. Ultraviolet radiation with a wavelength less than 300 nanometers must be absent in the spectrum of the light source. To remove excess amounts of infrared radiation, which causes overheating of the plants, water screens are used or the air temperature in the room is lowered. The spectral composition of the light, the radiation intensity, and the duration of the photoperiod have considerable significance in plant cultivation under artificial illumination. The best results are obtained by using lamps whose visible spectrum is close to the spectrum of sunlight (for example, xenon lamps).

By utilizing the spectral and photoperiodic sensitivity of a particular plant, one can accelerate or retard the development of seed or fruit. As a result, the yield of leaves (for example, in lettuce and cabbage), root crops (for example, in garden radishes), fruits (for example, in tomatoes), or seeds (for example, in summer wheat) may be greatly increased. The maximum crop may be obtained with day lengths of 16 to 24 hours.