An optical system (10) operatively associated with incident light (50) is provided. The incident light is essentially comprised of a first part (52) and a second part (54). The optical system includes: a photo catalytic reactor (30) comprising a photo catalyst (36) operatively associated with the first part of the incident light, an optical device (20) operatively associated with the second part of the incident light, and a beam splitter (40) for separating the incident light into the first part which is directed to the photo catalyst and the second part which is directed to the optical device.