Low emissivity (low e or low thermal emissivity) refers to a surface condition that emits low levels of radiant thermal (heat) energy. All materials absorb, reflect and emit radiant energy according to Planck's Law but here, the primary concern is a special wavelength interval of radiant energy, namely thermal radiation of materials. In common use, especially building application, the temperature range of approximately -40 to +80 degrees Celsius is the focus, but in aerospace and industrial process engineering, much broader ranges are of practical concern.