Effect of LED Light Quality on Appearance Quality of Leafy Vegetables

The appearance quality of vegetables produced in artificial light closed environment is particularly important. Plant factory is a closed space, the loose leaf lettuce growing in the plant factory is clean and free from disease and insect pests, but when fluorescent lamp is used as the light source, the burning of plants is more serious.

Edge burning can affect the appearance quality and taste of leaf lettuce, and reduce the economic benefit of it. Supplying air to the inner leaves of loose leaf lettuce can effectively prevent or reduce the incidence of burn due to calcium imbalance.

In the plant factory of the affiliated farm of the Department of Horticulture, Chiba University, scientists have studied different light qualities such as white fluorescent lamps (310-750nm), red LEDs (660nm), blue LEDs (460nm), red and blue LEDs ((Red and blue light intensity ratio 89:11) )under the conditions of the plant factory. The effect on leaf lettuce growth and burnt edge (Tipbum) under the same light intensity.

The results showed that compared with white fluorescent lamps, both red LED light and blue LED light significantly reduced the disease index of burnt edge of leaf lettuce, while red LED and blue LED had no effect. The main reason is that the loose leaf lettuce under red LED light has a longer stem and a smaller leaf area, which makes the airflow and exchange around the leaves relatively faster, accelerates transpiration and improves the absorption of water and calcium by the roots. At the same time because blue LED inhibited the growth rate and leaf enlargement of lettuce, the calcium absorbed by roots could meet the needs of leaves, and burning edge was not easy to occur.

The content of calcium, potassium and magnesium in leaf of lettuce showed an opposite trend, This is consistent with the results of Barta et al. 's study on early leaf enlargement of loose leaf lettuce. Magnesium accumulation may be due to cellular dysfunction during edge burn, whereas potassium accumulation in leaf margins exacerbates calcium dysregulation by requiring more calcium loss to maintain cell membrane integrity.