Fluorescence of the peripheral LH2 antenna complex from the photosynthetic bacterium Rhodobacter sphaeroides has been studied at 5 K upon selective excitation into the B870 exciton absorption band. Heterogeneous nature of the LH2 emission band has been confirmed by a double spectral selection technique simultaneously utilizing hole burning and fluorescence line narrowing spectroscopy. The phonon structure of the spectra related to the B870 band has been analyzed resulting in a genuine single-exciton state absorption/emission profile. The total electron-phonon coupling strength S = 0.8 +/- 0.2, larger than previously assumed, has been determined. (C) 2003 Published by Elsevier B.V.