A fluorescent solar collector (FSC) is a waveguide device that can concentrate both diffuse and direct sunlight on to a solar cell. The electrical output of the device depends strongly on the photon fluxes that are absorbed, emitted, and trapped inside the FSC plate. For this reason, it is important to study the photon transport losses inside the collector. One of the losses in FSC to be investigated is scattering, which increases the probability of the escape cone losses. We determine the scattering contributions in FSC by using angle dependence of light internally reflected in the FSC. The cause of scattering in spin-coated polymethylmethacrylate on top of the glass collector is identified as roughness from the top surface, rather than bulk losses. This loss can be suppressed to less than 2% using an index-matching planarization layer.