Abstract: An optical system is provided for viewing a sterilization indicator including a receptacle, the receptacle having a translucent portion and being carried interiorally of an incubator. The optical system comprises a light source, and first light transmission structure located intermediate the light source and the receptacle for redirecting light from the light source through the translucent portion of the receptacle. A viewing window is located in an external surface of said incubator; and second light transmission structure is located on a side of the receptacle generally opposite the first light transmission means for redirecting light transmitted through the translucent portion of said receptacle to the viewing window.