Patent ID: 8034398

Claim:
A secure tag coding method comprising: providing a first type of secure tag having a first luminescence profile to indicate a first level code; providing a second type of secure tag having a second luminescence profile different from the first luminescence profile to indicate a second level code; mixing secure tags of the first type with secure tags of the second type in a predetermined ratio to produce a mixture so that excitation of the mixture produces a composite of the first luminescence profile and the second luminescence profile, from which composite a multi-level code can be ascertained, the mixture at the predetermined ratio enables simultaneous measurement of both the first luminescence profile and the second luminescence profile and mixing the two types of secure tags to ensure that the ratio of (i) the intensity of one or more emission peaks from the second luminescence profile, to (ii) the intensity of one or more emission peaks from the first luminescence profile, meets a predetermined criterion, the predetermined criterion is a ratio that enables simultaneous measurement of both the first luminescence profile and the second luminescence profile, wherein the second level code is related to the relative intensity of the one or more emission peaks from the second luminescence profile to the one or more emission peaks from the first luminescence profile; and applying the mixture of first and second types of secure tags to a substrate.