Refractive index of materials changes per the change of the temperature. Temperature coefficients of refractive index show the changes of refractive indices of the material when the temperature of the material raises by 1 degree C. Usually the coefficient is achieved by averaging the change of the refractive indices of 20 degree C temperature range. We have various measuring methods per the type of the materials :

Typically the temperature coefficients of refractive index are measured by our original measuring equipment which measures the amount of the variation of refractive indices per the change of the temperature. The other way is that they are derived from the refractive indices at 2 different temperature measured by suing refractometer or spectrometer.