a b s t r a c t Numerical simulations of light propagation through capillaries have been reported to a limited extent in the literature for uses such as flow-cell design. These have been restricted to prediction of light path for very specific cases to date. In this paper, a new numerical model of light propagation through multi-walled cylindrical systems, to represent coated and uncoated capillaries is presented. This model allows for light ray paths and light intensity distribution within the capillary to be predicted. Macro-scale (using PMMA and PC cylinders) and micro-scale (using PTFE coated fused silica capillaries) experiments were conducted to validate the model's accuracy. These experimental validations have shown encouragingly good agreement between theoretical predictions and measured results, which could allow for optimisation of associated regions for monolith synthesis and use in fluidic chromatography, optical detection systems and flow cells for capillary electrophoresis and flow injection analysis.