A general theory describing light propagation in turbid media is presented, taking into account the effect of scattering on the path length of light propagation. This leads to new relationships between the K-M scattering (S) and absorbing (K) coefficients and the intrinsic scattering (s) and absorbing (a) coefficients of material. It is shown that experimental findings of dyed paper, typical examples that the original K-M theory failed to explain can clearly be understood and accommodated by the theory.