A radically different process also triggered by light has been develop without the use of photo-initiation. This process involves the light excilation of a photoreducible component, such as a quinone, followed by its photoreduction. This new photoreduced species is then oxidized by the oxygen that it scavenges. In this case the polymer was inactive until exposure to, for example, ultraviolet light – something that might not be applied until immediately before package filling (Rooney, 1993). The species reactive towards oxygen is therefore not present during thermal processes such as extrusion and blow molding.