Artificial light systems are designed for 2 main purposes: 1) Photo-periodic lighting  is meant to modulate processes underlying the growth and the flowering cycles of plants that are regulated by the duration of the day / night; 2) Photo-synthetic lighting is meant to promote photosynthesis activity in the plants, i.e., serve as a “back-up” for the sun-light in cloudy days and elongate the diurnal activity of the plants.  The lighting systems operate in a range of wave-length and magnitudes, depending on the demands of the crop, and the indoor conditions.