The device physics necessary to gain theoretical insight into the relationship between the bias conditions and the associated electric field for semiconductor structures in various failure conditions such as forward and reverse biased junctions, MOSFET saturation, latchup, and gate oxide breakdown are examined. The relationships are verified by light emission spectra collected from test samples under various bias conditions. Several examples are included that demonstrate the utility and limitations of spectral analysis techniques for defect identification and the associated, non-electric field related information contained in the spectra.