The radiation field in a planar participating and reacting medium was studied. A one-dimensional model with azimuthal symmetry was employed to investigate radiation absorption and scattering phenomena in the reaction space. The mathematical model was solved numerically, and the results were compared with experimental data obtained in a perfectly mixed, isothermal, batch reactor with recycle. Inside the reactor the well-known oxalic acid homogeneous photodecomposition was conducted and scattering was artificially produced by addition of different amounts of small particles of silica that are chemically inert and transparent to radiation in the investigated wavelength range. Model predictions and experiments have good agreement. They demonstrate that scattering in a well-stirred system always produces a decrease in the volume-averaged reaction rate when compared with a purely absorbing system. According to the relative magnitude of the absorption and scattering contributions, there are cases where radiation losses produced by scattering may bring about a significant reduction in the rate of the homogeneous reaction.