Effect of artificial light sources on the growth of  green oak lettuce (Lactuca sativa L.) grown in plant factories

Artificial light sources in plant factories offer numerous advantages over traditional plant production. Optimal artificial lighting systems will provide sufficient light to promote plant growth. Thus, this study aimed to determine different artificial light sources on plant growth, especially on internode length, root length, potassium (K), Calcium (Ca), and magnesium (Mg) contents of green oak lettuce (Lactuca sativa L.). Three artificial light sources were utilized in the plant factory: a fluorescent lamp (FL) typically used in plant factories and two light-emitting diodes (LED): bulb-LED and bar-LED lamps. Alternate periods of 12 h of light and dark were applied to the used factories. The results indicated that the lettuce grown under bulb-LED irradiation exhibited the lowest internode length and highest root length of green oak lettuce, regardless to light intensity and the higher photosynthetic photon flux density (PPFD) values of bulb-LED at the growing stage. K, Ca, and Mg contents in the lettuce shoot decreased in the order of K > Ca > Mg for all artificial light sources. The highest K, Ca, and Mg contents were 14.77±3.08, 4.77±0.92 and 108.14±9.36 mg/g dried weight (DW) obtained in lettuce grown under FL irradiation. Lower FL light intensity promotes nutrient deficiency, resulting in increased plant uptake. There was no significant difference in nutrient content between plants grown with bulb-LED and bar-LED. The K/Ca and K/Mg mole ratios were lowest in plants grown under FL irradiation. These findings suggest that FL can be used to control lettuce nutrient levels, whereas bulb-LED can be used to control lettuce growth.