In Sect. 3.1, a number of thermography and lock-in thermography approaches from literature are described and discussed, both steady-state and non-steady-state, showing the large variety of thermography measurement possibilities. Many of these systems are not called thermography but rather thermo-AFM, or photothermal or thermo-elastic investigations. But, in principle, they are all designed to measure lateral surface temperature distributions, and can be used to investigate also electronic components. At the end of this chapter, the figures of merit of different lock-in thermography systems are compared in terms of the pixel-related system noise density, defined in Sect. 2.6. In Sect. 3.2 the design philosophies of different commercial lock-in thermography systems are compared. Since many novel techniques for investigating solar cells are working with homogeneous irradiation of light, in Sect. 3.3 different systems for illuminating the sample are compared. In Sect. 3.4 the application of solid immersion lenses for improving the spatial resolution of lock-in thermography investigations is described. Finally, Sect. 3.5 introduces the special demands of the realization of different non-thermal carrier density imaging techniques, which also make use of the illumination systems described in Sect. 3.3.