Impact of Supplemental LED Lighting Regimes on Sweet Pepper Growth under Winter Light Deficit

This study investigated the effects of supplemental LED lighting regime (morning, afternoon, and all-day) on the vegetative growth, reproductive development, yield, and water-soluble vitamin content of sweet pepper (Capsicum annuum L.) grown in winter season under deficit sunlight hours.Supplemental lighting regimes included morning lighting from 05:00 to 10:00 (T 1 ), afternoon lighting from 16:00 to 21:00 (T 2 ), all-day lighting for 16 hours from 06:00 to 22:00 (T 3 ), and a control with no supplemental lighting (T 0 ).Results demonstrated that morning lighting (T 1 ) significantly enhanced plant height, leaf length, number of leaves and leaf area, indicating effective promotion of vigorous vegetative growth during early development.In contrast, all-day lighting (T 3 ) reduced vegetative growth but significantly increased stem diameter, node length to first flower, and fruit set, suggesting facilitation of the transition to reproductive growth.Accordingly, T 3 resulted in significantly higher cumulative yield and fruit weight compared to the control, with a marketable fruit rate of 92.0%.Afternoon lighting (T 2 ) showed positive effects on overall growth and yield, particularly contributing to increased fruit size during the enlargement stage.Analysis of fruit water-soluble vitamins revealed distinct responses to lighting periods: T 1 elevated vitamins B 1 and B 5 contents, while T 3 markedly increased vitamin B 2 concentration.Vitamin C content was highest in T 3 and T 0 , possibly reflecting physiological stress and antioxidant accumulation under differing light environments.These findings suggest that a growth stage specific supplemental lighting strategy such as morning lighting to maintain vegetative vigor during early growth and all-day lighting to enhance reproductive growth and yield can optimize sweet pepper production under winter light deficit conditions in a greenhouse.