A photoresponsive tracer that changed color under ultraviolet (UV) irradiation was prepared by immobilizing a photoacid generator and methyl orange on a poly(vinyl chloride) (PVC) carrier resin to evaluate the performance of dry-type powder photoreactors. The color transition of the tracer during exposure to UV light was recorded using a video camera. By analyzing the recorded images, the color change could be continuously detected as a change in the green component of the tracer's RGB color value. The tracer changed color as a function of the received cumulative radiant energy. Two consecutive reactions occurred on the tracer surface. The first reaction involved the release of a proton upon exposure of the photoacid generator to UV irradiation followed by the reaction of the released proton with methyl orange, which caused the color change. The rate constant of each reaction could be estimated by analyzing the rate of change of the green RGB value under UV irradiation. This photoresponsive tracer enables the visualization of the photoreactions in dry-type powder photoreactors, and allows both the radiant energy received by materials inside the reactor and their reaction kinetics to be determined.