MODEL RELEASED. Man wearing glasses. Thermogram of the head of a man wearing glasses. Thermography is a technique for visualising the temperature of surfaces (such as skin) by recording their emission of long- wavelength infrared radiation. This heat radiation is detected electronically and displayed with different colours representing different temperatures. In this image, the temperature scale runs from red (warmest) through yellow and green to purple (coldest). The glasses are made of plastic, which is a good insulating material. They are preventing the heat from his eyes from being detected. For images of the same man in visible light see M450/248 and M450/249.