Abstract: The present disclosure teaches a UV dosimeter comprising a UV-sensitive layer and a barrier that protects the UV-sensitive layer. The barrier is permeable to oxygen but impermeable to water and, thus, protects the UV-sensitive layer from water while allowing exposure of the UV-sensitive layer to oxygen. The UV-sensitive layer is accessible to both UV radiation and visible light. The UV-sensitive layer comprises a mixture of a semiconductor material, a UV-oxidizable dye, a sacrificial electron donor, and a matrix material. The semiconductor material has a band gap that corresponds to photon energy of the UV radiation. The dye has both an oxidation state and a reduction state. The oxidation state of the dye is visibly distinguishable from the reduction state of the dye. The sacrificial electron donor oxidizes when exposed to UV radiation. The matrix provides structural integrity to the mixture.