Many photoelectrodes produce a gaseous product, such as hydrogen or oxygen, from a liquid electrolyte and require light transmission directly through the two-phase mixture forming at the semiconductor–electrolyte interface. Consequently, incidence solar photons will be scattered and reflected from the bubbly mixture leading to an additional optical loss. In this work, these optical losses are quantified for a population of bubbles that evolved from the vertical surface of a transparent conductive electrode (F-SnO2) by measuring the amount of light transmitted. The transmitted photons were collected in an integrating sphere placed directly behind the 15 mm × 15 mm electrode to capture the forward scattered light. The empirical results were compared with a simple dimensionless model. Finally, mitigation strategies are suggested and critically discussed. With progress in the development of large scale prototype photoelectrochemical devices comes the need to understand, quantify, and potentially resolve the issue of optical losses from gas evolving photoelectrodes.