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 (T1:R8B1, T2:R7B2, and T3:R6B3), with a same intensity of 200 μmolm-2s-1 as supplement light to the natural light, together with natural light as control treatment (CT). Sweet pepper fruits were harvested weekly over 27 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 T3 showed the highest marketable yield (14.58 kg/m2). 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 T3 and the control treatment in January was 1.27 kg/m2, while this difference was 0.68 kg/m2 in June). No significant difference was observed between cultivars and T3 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.

The postharvest quality of vegetables and fruits is significantly influenced by environmental factors, including light exposure. Light-emitting diodes (LEDs) offer a versatile tool for manipulating light spectra to enhance the preservation and quality of produce. This review examines the impact of different LED light spectra on the postharvest quality of vegetables and fruits. The research problem addressed is the optimization of LED lighting conditions to extend shelf life and maintain nutritional and aesthetic qualities of produce. The methodology involved a comprehensive analysis of existing literature on the effects of various LED light spectra, including red, blue, green, ultraviolet and combinations thereof, on postharvest attributes such as color, texture, and nutrient retention. Key findings indicate that specific LED spectra can delay senescence, reduce spoilage, and enhance antioxidant content in certain produce types. For instance, red light often promotes ethylene production, while blue light can suppress microbial growth. The main conclusions highlight the potential of tailored LED lighting strategies to improve postharvest management practices. These findings have significant implications for the development of more efficient storage and transportation systems, potentially reducing food waste and enhancing consumer satisfaction. Future research directions include exploring the molecular mechanisms underlying light-induced responses in produce and integrating LED technology into commercial postharvest handling systems. Overall, this review underscores the importance of light spectrum optimization in maintaining the quality and extending the shelf life of vegetables and fruits, contributing to a more sustainable food supply chain.

Artificial light source is one of the most important factors for high quality and quantity vegetable production in a plant factory. Aiming to investigate the role of light spectra on growth, chlorophyll fluorescence, photosynthesis and stomata parameters in lettuce plants grown in a plant factory, a factorial experiment was conducted based on a completely randomized design with two lettuce cultivars (Lollo Rossa and Lollo Bionda) and four spectra LED illumination red (656 nm), red/blue (3:1) (656 nm), blue (450 nm) and white (449 nm). The results showed that the combination of red and blue LED light had the greatest effect on stomatal conductance (gs), number of stomata, length and width of stomata in both lettuce cultivars. Also the maximum substomatal CO2 concentration (Ci) was observed in both lettuce cultivars when they were treated with red LED light. The results also showed that the maximum CO2 assimilation rate (PN) was observed in Rossa variety under white LED and in Bionda cultivar under blue LED light. Contrary to the results related to some of photosynthetic parameters, the highest values of vegetative traits (plant height, dry and fresh mass of shoots and roots, leaf number and leaf area) of plants were observed in the treatment of red and blue light combination. It is concluded that plant growth, chlorophyll fluorescence characteristics, photosynthetic and stomatal properties can be affected by different spectra and cultivars of lettuce, so that the choice of proper lighting is a fundamental requirement for the cultivation of this plant

The aim of this study was to explore how various spectra of complementary light impact the growth and development of strawberry plants under stress conditions caused by salinity and alkalinity. The experiment involved cultivating plants in a greenhouse with ambient light, subjecting them to blue (460 nm), red (660 nm), blue/red (1:3), and white/yellow (400-700 nm) light at different developmental stages. Stress treatments included control (without stress), alkalinity (40 mM NaHCO3), and salinity (80 mM NaCl). Results indicated a decrease in dry weights under salinity and alkalinity stress. The blue and red spectra were more effective in mitigating stress effects compared to other spectra. While stress conditions led to a reduction in SPAD, blue light increased SPAD under stress. Stress conditions decreased RWC, and blue/red light increased RWC under stress conditions. Blue/red and white/yellow light had the most significant impact on reproductive traits. Salinity and alkalinity stress reduced OJIP curves compared to the control, but the blue and red spectra increased OJIP curves under their respective stress conditions. In conclusion, manipulating the supplemental light spectrum can alleviate the effects of salinity and alkalinity stresses, suggesting the potential extension of artificial light use in stress conditions.