A photon-emission microscope method and system are described which allow both emission spot localization and continuous spectral analysis of the emited light from the emission spot of a biased electronic circuit. The system includes an emission microscope, a detector and an in-line, direct vision, chromatically dispersing prismatic device. The microscope system advantageously uses only one detector which does not need to be moved to be able to detect both the localization and spectral images. In a particular embodiment, localization of emission spots may be performed using monochromatic light which allows sharp images of the electronic circuit despite the fact that the electronic circuit is viewed through the dispersing device. Further, an improved procedure is described for overcoming errors caused by saturation of the detector at high sensitivities.