Transparent zinc oxide (ZnO) films that were prepared via a spin-spray process using sodium citrate as a surfactant were exposed to UV light of varying wavelengths and irradiation times. The effects of the UV irradiation on the optical and electrical properties of the ZnO films were examined. The band gap of the as-prepared ZnO film (3.46 eV) increased after UV irradiation, even when exposed to relatively long wavelengths (> 365 nm) with a low power density (similar to 0.55 W/cm(2)). The modifications in the band gap and conductivity of the spin-sprayed ZnO films were primarily caused by the persistent photo-conductivity effect and photodecomposition-induced doping. Examination of the ZnO films using FTIR indicated that irradiation with shorter UV wavelengths (<= 350 nm) improved the photodecomposition of carbon impurities that were inside the ZnO films, which resulted in enhanced conductivity and electrical stability for > 1 days.