Effects of combined Red and Blue light spectra as supplemental light on yield and fruit quality of sweet pepper

Purpose: The use of supplementary light in regions with low natural sunlight is necessary to fulfill the increasing consumer requests for fresh vegetables. This study aimed to investigate the effect of different combinations of red and blue LEDs on yield and quality of greenhouse-grown sweet pepper (Capsicum annuum L.) fruits during the growth period. Research method: The experiments were conducted in Rasht, Iran as split plots in the form of a completely randomized design in three repetitions (four plants per plot) on two cultivars of sweet pepper (Padra and Shadlin). With the appearance of the first flower buds, plants were exposed to different light treatments including: three combinations of red (R) and blue (B) LEDs (T۱:R۸B۱, T۲:R۷B۲, and T۳:R۶B۳), with a same intensity of ۲۰۰ μmolm-۲s-۱ as supplement light to the natural light, together with natural light as control treatment (CT). Sweet pepper fruits were harvested weekly over ۲۷ weeks and fruit yield and quality were assessed. Findings: Supplemental light using LEDs significantly increased yield and fruit quality parameters (except titratable acidity and maturity index) compared to the control. Marketable yield was differed among the light treatments and plants exposed to T۳ showed the highest marketable yield (۱۴.۵۸ kg/m۲). The effect of supplemental light on total yield was more detectable when the average daily light integral was the lowest (for example, the difference between T۳ and the control treatment in January was ۱.۲۷ kg/m۲, while this difference was ۰.۶۸ kg/m۲ in June). No significant difference was observed between cultivars and T۳ was the best treatment in most parameters. Research limitations: No limitations were found. Originality/Value: In the northern regions of Iran, even in the months that do not seem to have light limitations, the use of supplementary light is recommended to increase the yield of sweet peppers in the greenhouse.