The orientation effect of methyl-red (MR) molecules on pentylcyanobiphenyl (5CB) nematic liquid crystal has been investigated in a pump-probe experiment at various concentrations of azo-dye and for different power values of an exciting Ar+ laser beam. Excited dye molecules reorient the LC molecules within their correlation spheres. There is a percolation probability that the whole LC bulk be reoriented. Analyzing the threshold energy necessary for this percolation in terms of dye concentration, the model allows evaluating the lowest concentration of dye molecules (critical concentration), the correlation length and the quantum efficiency of the reorientation process.