This paper examines distributive light pipe (or thick waveguide) systems constructed of fluorescent material. Through consideration of fluorescence efficiency and geometrical optics a general analytical model of fluorescent light propagation in rectangular plastic light pipes is developed. By considering specific material properties the derived general model is applied to LISA material (BAYER KL-3-94000), a commonly used fluorescent additive to Polycarbonate. The fluorescent light propagation model can be used by itself to estimate output surface exitance or in conjunction with optical computer modeling to accurately design and optimize fluorescent light pipe systems. A practical example of instrument cluster pointer design is presented to illustrate how this model is applied.