In this research, the combined effect of red and blue LED lights on tomato plants and fruit was investigated. Selected tomato plants were illuminated with a combination of red light (RL) and blue light (BL) at a ratio of (1:1) with a combined photosynthetic photon flux density (PPFD) of 138 +/- 5 mu mol m(-2) s(-1). This illumination was installed above the plants and was terminated at different stages of plant growth, namely, at 50% flowering (FLW) and when fruit were mature green (MG). The plants were allowed to receive natural light during the day and were exposed to the light treatments 3 h after sunset and 3 h before sunrise. Control plants received only natural light. Growth, yield, and quality parameters were assessed. Both light treatments, whether terminated at FLW or MG, significantly enhanced plant height, number of leaves, and branching, with light treatment until the MG stage having a lesser, but nonetheless significant, effect. Plants that were treated with additional light until fruit were MG had a significantly increased total fruit mass compared with other treatments. Surprisingly, plants treated until FLW showed a significant increase in number of fruit per plant. Both treatments did not have a significant effect on colour parameters, while light treatments, particularly treatment until MG, were able to significantly enhance chlorophyll degradation in fruit. In addition, both light treatments resulted in a significant increase in fruit lycopene, the most important carotenoid in red tomato, while also potentially increasing the concentration of beta-carotene, as well as total soluble solids (TSS), phenolics, and vitamin C. Treating tomato plants with a combination of LED light sources only until FLW was sufficient to enhance growth, yield, and antioxidant phytonutrients in tomatoes with no additional increase with further light treatment.
