A non-linear equation from photopolymerization kinetics
  In a medium where a photoreactive species produces N equally photoreactive radicals, by combining the Lambert-Beer law for the decay of light intensity, as a beam propagates into the medium, with the kinetic equation, one obtains a generalization of the Wegscheider equation from photobleaching theory. It is shown that this equation can be solved exactly, but implicitly, and can be reduced to a first order ordinary differential equation in a single reduced variable. 
M. L. Glasser