This chapter addresses issues related to light–object interaction along with its resulting phenomena, taking into consideration materiality issues. It presents light and its role in artefacts studies, either as a tool for finds analysis or as a corrosion agent. It attempts a balanced investigation into past and contemporary approaches towards light from the conservator’s perspective. It discusses traditional raking and oblique light examination, along with its advanced digital analogue, Reflectance Transformation Imaging (RTI), which bridges the gap between digital photography and three-dimensional modelling. Applications of dome and/or Highlight RTI in a wide variety of material and artefact types, as well as in a wide range of conservation states, using macroscopic and microscopic means, indicate that the technique contributes considerably in prevention, investigation, examination and analysis, documentation, communication, dissemination, and presentation, as well as being a conservation monitoring tool.