Patent attributes
A product shelf life monitoring system comprises a label substrate bearing upon a limited portion of its area an active indicator composition responsive to varying temperature over time to effect a visible change in color density or the like. The susceptibility of the indicator composition to similarly respond to incidence of vagrant ultraviolet light is ameliorated by application of an area of ultraviolet light absorbent composition in register above the indicator composition and extending at most only slightly beyond the periphery of the area of indicator composition. In this manner, the remaining area of the label is preserved for ultraviolet light responsive implementations, and only a minimal, economical amount of ultraviolet light absorbent composition is expended.
