The unique physical phenomenon of photon emission from a variety of defects in ICs has long been exploited for failure analysis. This method provides a fast non-destructive inspection method for failure localization. Several functional failures have a distinctive emission signature that allows functional analysis of the design. The transition to flipchip packaging accelerated the use of Infrared Focal Plane Arrays (IR FPA) such as MgCdTe (MCT). It has been proven that systems that incorporate MCT arrays demonstrate higher sensitivity for emissions in comparison to the traditional Si CCDs; usually the higher sensitivity is compromised with inferior resolution. In this work we will review and demonstrate the optical limitations involved with the use of an MCT camera, yet we shall show a calibration procedure carried out by the analyst to bypass these limitations. By calibrating typical emissions, generated by typical functional defects, we generate calibration curves, which supply a fast reference for detection of the defective transistor, and the correlated current that results from the defect. The calibration of the array response is crucial for evaluation of its sensitivity. It will also enable a clear distinction between emissions, which correlate to small or negligible current flows, and emissions that correlate to significant current flows. We also classify logic failures that lead to emissions, and estimate the level of emission anticipated from these failures.