Abstract: A method includes illuminating a mixture of materials in a wet-end of a paper process, where the mixture includes an ultraviolet-activated material. The method also includes measuring light from the mixture and determining a property of the ultraviolet-activated material based on the measured light. The method may further include adjusting an operation in the wet-end of the paper process based on the determined property of the ultraviolet-activated material. The determined property could include a quantity of fluorescent material in recycled material used to form stock for a paper machine and/or a quantity of fluorescent material in stock provided to a headbox in the paper process. Adjusting the operation in the wet-end could include adjusting an amount of one or more materials used to form stock provided to the headbox, such as a fluorescent whitening agent, fixative, fluorescent fiber, fluorescent pigment, fluorescent particle, fluorescent highlight, fluorescent planchette, or fluorescent quencher.