9. Conclusion

The main emissivity measurement techniques have been described. These descriptions correspond to existing experimental set-ups. The wide variety of methods used is obvious. This great diversity reflects the need to adapt devices to the type of parameter required (directional, hemispherical, total, spectral emissivity, etc.), the nature of the material, the sample configuration and the temperature range. There is no universal device for measuring emissivity, and at present all commercial devices meet only a small proportion of needs. They are, for the most part, limited to measurements at room temperature. Absolute methods, and calorimetric methods in particular, are highly technical and limited to certain types of sample. These methods are reserved for characterizing reference samples, specifically produced samples or coatings that can be easily applied to reusable substrates.