Window construction with UV protecting treatment

In a multiple-pane insulating window assembly having an exterior wall surface and an interior wall surface, said assembly comprising an outer first and an inner second sheet of transparent glazing, each having a perimeter edge surface and an inner surface and an outside surface, the outer first sheet having a sheet thickness with the sheets being held substantially parallel to one another and spaced from one another by an elongated spacer which abuts the inner surfaces of the two sheets at, but inset by a first set distance from, the periphery of the two sheets and extends inward to a second set distance from the periphery, such that the outer surface of the first sheet is the exterior wall surface and the outer surface of the second sheet is the interior wall surface, and a layer of an adherent conforming flexible sealant which sealably surrounds the outside of the spacer and the perimeter edge of the sheets and fills the first distance inset, the improvement comprising an opaque nonreflective light barrier applied directly onto the exterior wall surface and extending inward from the second set distance by a distance which is at least 0.89 times the sheet thickness and extending outward from the second set distance by a distance which is at least 0.89 times the sheet thickness.