Photon emission (PE) is one of the major optical techniques for contactless isolation of functional faults in integrated circuits (ICs) in full electrical operation. This article describes the fundamental mechanisms of PE in silicon based ICs. It presents the opportunities of contactless characterization for the most important electronic device, the MOS - Field Effect Transistor, the heart of ICs and their basic digital element, the CMOS inverter. The article discusses the specification and selection of detectors for proper PE applications. The main topics are image resolution, sensitivity, and spectral range of the detectors. The article also discusses the value...