Light intensity profiles in an annular photoreactor with gas-solid-in-liquid dispersions are measured by means of a newly designed photo-probe which shows a uniform sensitivity to scattered light rays from any directions. The light scattering intensity profiles are approximated by a modified equation which includes two model parameters as a weight coefficient and an effective attenuation coefficient in the light intensity profile equation based on a diffused line light source model for an annular photoreactor with a homogeneous phase. The functional relations between the two parameters, and gas-holdup and solid particles concentration are determined to satisfy the measured profiles. The modified equation can estimate the light absorption rate due to the dispersed solid particles in the reactor. The rate shows a maximum value for the optimum solid concentration with a certain gas hold-up.