The UNL trichromatic colorimeter was designed to perform color-matching experiments under a range of stimulus conditions. The colorimeter can be set up with a conventional 10 degrees structure-free bipartite viewing field (either horizontally or vertically bisected) but can also be configured for field sizes as large as 102 degrees (wide) X 50 degrees (high), and depth cites can be introduced into the viewing field. This article documents the construction and performance of the apparatus, including the structural components, light sources, optics, filters, and instrumentation. Maxwell method CMFs measured at a homogeneous 10 degrees horizontally bisected field are reported with results that compare favorably with CMFs reported by Thornton under similar stimulus conditions. (c) 2005 Wiley Periodicals, Inc.