Abstract: A reader for validating a secure tag. The reader comprises: an optical source operable to illuminate the secure tag; a processor coupled to the optical source and operable to activate and de-activate the optical source; and a luminescence detector coupled to the processor and operable to measure a luminescence spectrum after a time delay has elapsed. The time delay may be based on a number generated by the reader in a random or pseudo-random manner, or it may be received across a network from a remote server. The processor is operable to accessing the time delay and to derive a luminescence signature from a luminescence spectrum measured by the luminescence detector. The processor is then operable to create a control signature using the time delay, to compare the derived luminescence signature with the control signature, and to validate the secure tag in the event of a match.