At the last year's conference, a technique was presented for exploiting substrate fluorescence to embed information into printed documents that was revealed only under pure ultra-violet (UV) light. It required the ability to characterize printed colors under both normal and UV lighting conditions. Printer characterization under normal light has been a very mature technology. This paper will focus on several different approaches for modeling the printer response under UV light. For this security application, it is not necessary to predict all the conventional color appearance attributes, but only the lightness is required. The first and the most straightforward approach was to measure a color target under UV light with a spectroradiometer and to build a printer model for this specific illuminant. While accurate, this approach suffered from the drawback that radiometric measurements were time-consuming and laborious. Two simple alternative approaches were brought forth to model the lightness response under UV light. One was based on a spectrophotometer with and without a UV cutoff filter, and the other was based on a commercial digital camera. Furthermore, visual post-correction method was used together with these two alternative approaches to improve the prediction accuracy of lightness under UV light.