Drawing on methods currently used in chemical thermodynamics, apparent and partial molar refractions of mixing for the components of a liquid mixture are defined. These optical properties are calculated from the experimentally measured refractive index and density of aqueous 2-diethylaminoethanol mixtures at five different temperatures between 283.15 and 303.15 K and at least at 37 different mole fractions spanning the entire composition range at each temperature. The new optical properties, partial molar refractions of mixing, are discussed in terms of their composition dependence and the effect of temperature on the limiting apparent molar refraction of mixing of the organic component dispersed in water is examined. These profiles are compared with the corresponding profiles obtained for volumetric excess partial molar properties using literature data. This advanced analysis shows that optical properties are able to give new insights into the mixing process.