The effect of fluorescence on the spectral modeling of inks printed on optically brightened substrates was investigated. Color differences were computed between print measurements with ultraviolet included (UVI) and excluded (UVX) instrument setups. Heat-set, CMYK process inks printed at SWOP density on non-optically brightened substrates exhibited color differences less than 1 ΔE*_ab. The same inks printed on optically brightened substrates had color differences greater than 3 ΔE*_ab as a result of fluorescence due to UV component inclusion. A modified spectral Neugebauer printer model was used to model desktop printer ink on optically brightened substrates using both UVI and UVX measurement setups. Results indicate although UVI/UVX model parameters are similar, their output colors are quite different. Printer models using the optically brightened substrates could plug directly into printer models of non-fluorescent substrates.