Instrumentation requirements for sensors based on the measurement of light passing through multi-mode fiber optics are discussed. A model is presented which treats the light source, optics, fiber optic sensor, and photodetector as an integrated system regardless of the mechanism of signal transduction, e.g. absorbance, fluorescence, etc. Analytical models for prediction of the performance of incandescent and flash lamps are presented along with comparative experimental data. Photodetection schemes utilizing solid state photodiodes and photomultiplier tubes are analyzed and analytical models for prediction of detection limits are presented. Criteria for optimization of the overall system performance are laid out.