After the introduction to the principles behind the description of the interaction of charged particles with matter in the first lecture and the detailed discussion about the momentum measurement in the second lecture , Dr. Christoph Schaefer builds on the presented material to explain bremsstrahlung as an additional detection mechanisms, that leads naturally to the possibility of detecting also photons and not only charged particles. With this preparation Christoph Schaefer summarizes the effects of the electro-magnetic interaction and extends the understanding of the detector principles to nuclear interactions and the interactions of neutrinos. As a second part Dr. Christoph Schaefer focuses on the detection of light in the optical domain and explains the principles of photo-detection and the application in high energy physics. The overview over the current state-of-the-art detectors together with an outlook at the research and development for each specific detector type finishes this third lecture.