FIELD: agriculture.SUBSTANCE: inventions relate to agriculture, in particular to horticulture. In the method, a plurality of blue light-emitting diodes (LEDs) are disposed in the central part of the light source device, a plurality of red LEDs are disposed in the peripheral part of the light source device, mix a plurality of white LEDs with red LEDs and position the white LEDs in the peripheral part of the device, move the light source device to a position, in which the blue LEDs irradiate the top of the stem of the leaf vegetable, and the red LEDs irradiate leaves of the leafy vegetable, during the initial growth period, and terminate the irradiation with light from the blue LEDs and red LEDs. Light is irradiated from the white LEDs and the light source device is moved vertically to a position, in which white LEDs irradiate leaves of leafy vegetables during a late growth period. Device is configured to irradiate leaf vegetables with light to grow them and comprises a plurality of blue LEDs provided in the ce
