Pisum sativum (L.) plants were grown under "white" luminescent lamps, W [45 µ mol(quantum) m-2 s-1] or under the same irradiation supplemented with narrow spectrum red light-emitting diodes (LEDs), RE [λmax = 660 nm, Δλ = 20 nm, 40 µmol(quantum) m-2 s-1]. Significant differences in the chlorophyll (Chl) a fluorescence parameters, degree of State 1-State 2 transition, and the pigment-protein contents were found in plants grown under differing spectral composition. Addition of red LEDs to the "white light" resulted in higher effective quantum yield of photosystem 2 (PS2), i.e. F'v/F'm, linear electron transport (ϕPS2), photochemical quenching (qP), and lower non-photochemical quenching (qN as well as NPQ). The RE plants were characterised by higher degree State 1-State 2 transition, i.e. they were more effective in radiant energy utilisation. Judging from the data of "green" electrophoresis of Chl containing pigment-protein complexes of plants grown under various irradiation qualities, the percentage of Chl in photosystem 2 (PS2) reaction centre complexes in RE plants was higher and there was no difference in the total Chl bound with Chl-proteins of light-harvesting complexes (LHC2). Because the ratio between oligomeric and monomeric LHC2 forms was higher in RE plants, we suggest higher LHC2 stability in these ones. and N. M. Topchyi ... [et al.].