## 1 Introduction  
Fruit and vegetables are essential in human health due to the high content in bioactive compounds [1]. Indeed, these nutraceuticaluids have been associated with a reduction in the risk of chronic and pro-inflammatory diseases [2]. Red peppers (_Capsicum annuum_ L.) in particular are demonstrated to be an important source of carotenoids [3], flavonoids, and vitamins [4], being a powerful ingredient able to fight against ageing and prevent chronic diseases [5]. In this context, Spain is the fifth largest producer of bell peppers in the world after China, Mexico, Turkey, and Indonesia [6] and the first European exporter country [7] with 1.4 million tons.  
As light is an essential factor directly related to the synthesis of primary and secondary metabolites [8], the bioaccumulation pathways of these compounds can vary with changes in the quantity and quality of lighting applied. In fact, application of abiotic stresses throughout non-visible spectral regions, such as UV-B (280-315 nm), are reported to have an hormetic effect characterized by positive stimulation of the metabolite pathways under low doses [9, 10], but a negative response of the plant tissues may appear under moderate to high UV doses [11]. In fact, UV RESPONSE LOCUS 8 (UVR8), as the main UV-B receptors,are responsible for regulating carotenoid biosynthesis [12]. Thus, UV-B has shown to improve the contents of carotenoids and flavonoids as the main antioxidant compounds in bell peppers [13]. In this way, UV can be used to induce the expression of antioxidant enzymes, which increase the biosynthesis of vitamins, flavonoids, phenolic acids, and carotenoids, among others [14; 15; 16].  
From another point of view, the environmental conditions in the final steps of the fresh bell pepper retail chain in supermarkets widely apply conventional fluorescent lamps (2 W m\({}^{-2}\) on the floor and 8 W m\({}^{-2}\) on the shelves) for 14 h between 15 to 22 \({}^{\circ}\)C [17]. However, when supermarkets close, the lamps above the horticultural commodities are usually switched off for approximately the next 10 h in order to save energy, with such conditions biologically promoting the accumulation of phytochemicals. In recent years, the use of coloured LEDs in supermarkets and the industry have increased due to their low energy requirements and their possibility to customize the light intensity and spectral properties. In this sense, the use of postharvest LED lighting has already shown potential beneficial effects in broccoli florets [18; 19; 20], brussels sprouts [21], and broccoli sprouts [22].  
However, the effect in quality and phytochemicals accumulation of horticultural commodities of the combination of different postharvest lighting conditions from the visible and non-visible spectrum is mostly unexplored. [PERSON] et al. [23] combined postharvest blue LED and UV-C lighting obtaining promising results in habanero pepper (_Capsicum chinense_) by increasing chlorophyll, carotenoid, capsaicin, phenolic, and flavonoid content.  
The combination of UV illumination and a photoperiod with lights from the visible spectrum during the postharvest shelf life of fruit and vegetables could improve the bioactive compound contents without compromising other quality attributes, or even improving them. Therefore, the aim of the present work was to evaluate the effect on carotenoid accumulation of UV-B radiation treatment jointly with a photoperiod under different illumination spectra during the commercialization of red bell peppers.