An optical detection system that utilizes an electroluminescent (EL) illumination source is provided. Unlike illumination sources used with some conventional optical detection systems, an EL device isrelatively homogeneous and diffuse, and thus may provide uniform illumination to the test sample. In addition, the emitted light intensity of the EL device may be easily controlled by simply varyingthe voltage or the frequency of the applied current. The relatively flexibility of EL devices may also allow them to be readily incorporated into a chromatographic-based assay device for detecting thepresence or absence of an analyte within a test sample.