We studied the effect of 16- and 24-h photoperiods on mitochondrial respiration in the darkness (RDark), in the light (RLight), their ratio RLight/RDark (reflecting the degree of inhibition of respiration by light), and the ratio of respiration to gross photosynthesis (Ag) in Solanaceae plants: eggplant (Solanum melongena L.), sweet pepper (Capsicum annuum L.), and tomato (Solanum lycopersicum L.). The leaf RLight rate was lower than RDark, regardless of plant species and photoperiod. At a 16-h photoperiod, light inhibited up to 19, 31, and 34% of respiration, respectively, in eggplant, sweet pepper, and tomato. Continuous lighting increased the degree of light inhibition of respiration to 36 and 46% in eggplant and sweet pepper but did not affect this value in tomato. An increase in respiration inhibition could be associated with structural changes in the leaf and a decrease in the oxygenase activity of RuBisCO/O. Continuous lighting reduced Ag to a greater extent than RDark and RLight, reflecting a shift in the carbon balance towards losses. Increase in RDark/Ag and RLight/Ag ratios, due to a significant decrease in the photosynthetic activity with a relative stability of the respiratory metabolism, may reflect the negative effect of continuous lighting on the productivity of the studied species. The obtained results also showed that the photoperiod duration can be one of the environmental factors influencing the degree of light inhibition of respiration.