Patent ID: 7767605

Claim:
Phosphate optical glass comprising, in terms of percent by mass: P 2 O 5 15 to 35%, Nb 2 O 5 35 to 60%, Na 2 O 0.1 to less than 15%, BaO 0 to less than 25%, Gd 2 O 3 0 to 5%, K 2 O 0 to 10%, Li 2 O 0 to 10%, Bi 2 O 3 0 to 15%, MgO 0 to 10%, CaO 0 to 10%, SrO 0 to 10%, ZnO 0 to 3%, SiO 2 0 to 5%, B 2 O 3 0 to 5%, Al 2 O 3 0 to 4%, Ta 2 O 5 0 to 5%, ZrO 2 0 to 3%, TiO 2 0 to 10%, WO 3 0 to 20% and Sb 2 O 3 0 to 0.1%, wherein the phosphate optical glass contains Pt no more than 0.8 ppm, and wherein, when a sample of the glass polished on both surfaces and having an internal transmittance to light and a thickness of 10 mm is irradiated with UV and/or visible light at a light-receiving energy of at most 0.4 mW·cm −2 for at least 200 hours, then a difference in the internal transmittance to light having a wavelength of 420 nm, before and after the irradiation (before irradiation—after irradiation) of the sample, as calculated in terms of the sample having a thickness of 10 mm, is at most 0.1.