Ag coated polymer film is widely used as the lamp reflector of backlights of liquid crystal displays (LCD). We investigated the degradation behavior of Ag and Ag alloy thin film mirrors sputtered on poly(ethylene terephthalate) (PET) substrates under intense visible light irradiation at elevated temperatures. Ag and Ag alloy thin films were prepared on PET substrates by DC magnetron sputtering at room temperature. The interface was exposed to visible light from a Xe lamp with an intensity of 500 mW/cm(2) through the PET substrate. In order to avoid the deterioration of PET itself, the component of the ultraviolet (UV) light was excluded by placing a UV cut filter between the light source and the specimen. The reflectance was measured with a light spectrometer with an integrating sphere. While deposition of 0.5 mm of metals such as Ti on PET before the deposition of Ag was found quite effective to maintain the high reflectance of the Ag thin film, the deposition of Al, Mg and Si accelerated the degradation. The alloys of Ag with Au, Pd or Pt were found to be not effective. Results of the observation of the initial growth of Ag thin films with and without Ti pre-deposition on PET with the use of atomic force microscope (AFM) will be also reported. (C) 2003 Elsevier B.V. All rights reserved.