Photoelasticity is a method of experimental stress analysis based on the principle of birefringence. Birefringence appears as an intrinsic property of some optical materials, such as anisotropic crystals, or it can be induced by stress in certain noncrystalline transparent materials, such as glass. This property of glass is used in glass industry and research to obtain direct quantitative data and phenomenological understanding for various problems. This paper gives an overview of several applications of photoelasticity in the field of structural glass. Photoelasticity is primarily applied in the measurement of residual stresses induced by the process of thermal toughening. Thermally treated glass is a type of glass in which a permanent surface compressive stress has been induced by a controlled heating and cooling process in order to give it greatly increased resistance to mechanical and thermal stress and prescribed fragmentation characteristics to reduce the consequences of glass failure. Current standards define the level of prestress in glass based on the number of fragments within a given area of a broken glass specimen, which is a very rough characterisation considering the importance of this measure in relation to glass strength. Specialised techniques applying photoelasticity are thus used to obtain residual stress distribution at the glass surface (differential refractometry) and through the glass thickness (scattered light method). Futhermore, the paper presents several examples of data acquisition (qualitative and quantitative) through photoelasticity in the scope of glass research at Steel Structures Laboratory (ICOM) at EPFL.