Efficient luminescent solar concentrators (LSC) were prepared by deposition of organically modified sol-gel films doped by photostable perylimide dyes on plexiglas substrates. The absorption spectra of these dyes extends from 420 to 620 nm covering the visible part of the solar spectrum and the emission is between 550 and 750 nm, close to the optimum response of silicon and gallium arsenide solar cells. The efficiency of this type of collector was calculated from the absorption coefficients, quantum efficiency of the fluorescence and the overlap between emission and absorption spectra by the method of Monte-Carlo and found to be close to 20%. Optimum concentrations are shown to be strongly dependent on the extent of overlap between the absorption and the emission spectra, which also appears to be the limiting factor in respect to the efficiency of the concentrator.