Photocatalytic efficiency is evaluated using quantum yields (QYs) and the photochemical thermodynamic efficiency factor (PTEF). The PTEF allows establishing reactor efficiency as the ratio of utilized enthalpy for the formation of consumed OH. free radicals over the absorbed photon energy. A key consideration for the evaluation of efficiency factors is the establishment of macroscopic energy balances together with an accurate assessment of evolved and absorbed photons. Of considerable help are the experimental devices developed at the Chemical Reactor Engineering Centre (CREC)/University of Western Ontario (UWO) laboratories. Photoconversion kinetics is required for calculation of the OH. consumption rates and establishment of the related kinetic parameters. PTEFs and QYs have been applied by CREC-UWO researchers for efficiency calculations in photocatalytic reactors for the decontamination of air, water, and hydrogen production.