The quality and intensity of light greatly affect the photosynthetic efficiency of plants. In this research, the impact of different light spectral composition on photosynthetic efficiency of three cultivars of Begonia rex (‘Red’, ‘Silver’, and ‘Black Velvet’) was investigated using the OJIP test. Experiment performed with pot-grown plants in a commercial greenhouse consisted of six growth chambers equipped with normal light (control), 100% blue (B), 15%B + 85% red (R), 30%B + 70%R, 15%B + 65%R + 20% white (W), and 30%B + 50%R + 20%W light, based on a completely randomized design with three replications. Photosynthetic biophysical parameters were measured 16 weeks after growth at different light spectra under a 15/9 h light/dark photoperiod and 250 μmol m−2 s−1 PPFD. The highest amounts of quantum yield and Fv/Fo were found in ‘Black Velvet’ plants under 15%B85%R lighting and control conditions. The values of specific energy fluxes per active reaction center (RC) for energy absorption (ABS/RC) and trapped energy flux (TRo/RC) were significantly increased in ‘Black Velvet’ in response to 30%B70%R and 15%B65%R20%W light action. Dissipated energy flux per unit reaction center (DIo/RC) was significantly increased in ‘Black Velvet’ in the treatment with 30%B70%R light. The maximum amount of photosynthetic performance index (PIABS) was recorded under the combination of 30%B50%R20%W spectrum in ‘Black Velvet’. Meanwhile, the lowest amounts of TRo/RC, ABS/RC, DIo/RC, and ETo/RC (unit reaction centers for electron transfer) were detected upon 30%B50%R20%W lighting in ‘Black Velvet’. Therefore, the spectrum combination of 30%B70%R and 15%B65%R20%W, were the most effective treatments for increasing photosynthetic efficiency, whereas blue light and control appeared as low effective source of illumination. Furthermore, light spectra other than RB combination imposed several limits on the growth of begonia plants and the efficiency of electron transport.
