The intensity of light transmitted through an evolving suspension of two-dimensional deformable liquid drops in shear-driven or pressure-driven flow within a channel with parallel-sided walls is studied using a numerical method. The rays enter the suspension normal to upper wall, undergo reflections and refractions at the drop interfaces, and either return to the upper wall or leave from the lower wall. The motion and deformation of the drops are computed using a boundary integral method, and the optics is studied using a standard ray-tracing method. Evidence is presented that, in the case of shear-driven flow, a consistent correlation exists between the intensity of light transmitted through the channel, the geometry of the microstructure, and the global rheological properties of the emulsion. In the case of pressure-driven flow, a correlation between the transmitted intensity and the effective viscosity is also observed, but its features are not entirely consistent. These differences are attributed to the profound effect of variable flow rate or presence of a mean pressure drop on the state of the microstructure and accompanying dynamical features of an emulsion.