But here comes the problem of energy conservation. This problem concerns not only the glass in large formats, but also domestic premises: apartments, houses, child care, etc. As a rule, through the wooden box on order (at subject to the application of ordinary glass), lost 40-50% of thermal energy, so all the major manufacturers of glass mastered the production of energy-saving glass. Giving the energy-saving properties of glass connected with drawing on his low-emission surface of the optical coating and the glass itself with such a coating has been called low-emissivity. These coatings provide a passage into the room shortwave, solar radiation, but prevents the exit from the premises longwave thermal radiation, for example, the heater (and therefore low-emission glass is also called selectivity). Characteristic energy is emissivity glass. Coefficient of thermal radiation is a characteristic of the surface rather than the whole body and it is the same physical characteristics, such as density, melting point, etc.
By emissivity glass (emission) to understand the ability of the glass surface to reflect the long-wavelength not visible to the human eye, thermal radiation, whose wavelength is less than 16,000 Nm. Emissitent surface (E) determines the emissivity glass (of conventional E-glass is 0.83, while the less selective 0.04) and, consequently, the possibility as it is reflected back into space thermal radiation. The cause of radiation lies in the movement of free electrons of atoms on the surface of the glass, and the density of moving electrons. Not all metals, well-conductive, have the property to reflect dlinovolnovoe thermal radiation. .