LOW-EMISSIVITY

'Low-emissivity' coatings are microscopically thin, virtually invisible, metal or metallic oxide layers deposited on a window or skylight glazing surface primarily to reduce the U-factor by suppressing radiative heat flow. The principal mechanism of heat transfer in multilayer glazing is thermal radiation from warm surfaces to cooler surfaces. Coating a glass surface with a low-emittance material reflects a significant amount of this radiant heat, thus lowering the total heat flow through the window. Low-E coatings are transparent to visible light, and opaque to infrared radiation. Different types of Low-E coatings have been designed to allow for high solar gain, moderate solar gain, or low solar gain.
To make Low-E glass, certain properties such as the iron content may be controlled. Also, some types of glass have natural Low-e properties, such as borosilicate or "pyrex" (tm). Specially designed coatings, often based on metallic oxides, are applied to one or more surfaces of insulated glass. These coatings reflect radiant infrared energy, thus tending to keep radiant heat on the same side of the glass from which it originated. This often results in more efficient windows because: radiant heat originating from indoors is reflected back inside, thus keeping heat inside in the winter, and infrared radiation from the sun is reflected away, keeping it cooler inside in the summer.
['Low-emissivity coating'][1]
Low-emissivity (Low-E) glass has a thin metal coating on the glass within its airspace that reflects thermal radiation back into the interior, and allows solar radiation into the room. Thus, the coating helps to reduce heatloss but allows the room to be warmed by any sunshine.The low-e coating is on the inside pane of glass, if solar control is required then the outside pane of glass would have either a film or a body tint to reflect solar radiation. The principle of operation is similar to the greenhouse effect where short wavelength radiation is transmitted through the pane, but longer wavelength radiation is reflected.