Most of the "abnormal" kinetic behaviour in photopolymerization can be explained by absorbance effect in the system. Absorbance depends on the concentration and extinction coefficient of initiator

the thickness of the system and the wavelength of the incident light. So all the four factors will influence the kinetics of photopolymerization. In low absorbance

the kinetics of photopolymerization is similar to that of thermal polymerization

while in high absorbance

they will be quite different.