The fluorescence excitation spectrum of poly(di-n-hexylsilane) doped into a glass at low temperatures is modelled in the following manner: Each polymer chain is assumed to consist of all-trans segments broken by non-trans defects or by distributed inhomogeneities that limit the excitation coherence length. The probability of a segment consisting of n consecutive all-trans bonds is determined statistically given a fraction of defects. The energy at which such a segment of length n will absorb light is assumed to have the empirically determined form A+B/n. By using this expression for the transition energies, and assuming that the transition for each chain segment length will also be inhomogeneously broadened due to the disordered nature of the glassy environment, the spectrum can be calculated and compared with experiment. Changes in the lineshape following narrowband irradiation at 1.5 K can be modelled in the same manner by including energy transfer and chain scission subsequent to the absorption of light. This very simple model can also be used to describe the two-photon absorption spectrum. © 1990.