Patent ID: 7378675

Claim:
A method of indicating a condition of an item, the method comprising: illuminating the item to excite one or both of a first and a second marker incorporated within the item, wherein the first and the second marker are incorporated at different locations within the item; detecting photoluminescent emission from one or both of the first and the second marker in response to the illumination; processing the detected photoluminescent emission to generate a photoluminescent signature, wherein the generated photoluminescent signature comprises a rate of change in photoluminescent emission versus time; comparing the generated photoluminescent signature with a first photoluminescent signature comprising a rate of change in photoluminescent emission versus time associated with the first marker and a second photoluminescent signature comprising a rate of change in photoluminescent emission versus time associated with the second marker, wherein the second photoluminescent signature is different from the first photoluminescent signature; indicating the item is in a first condition when the generated photoluminescent signature corresponds to the first photoluminescent signature; and indicating the item is in a second condition when the generated photoluminescent signature corresponds to the second photoluminescent signature.