Low E Window Facts

Insulated Glass Unit

Low E window facts start with an insulated glass unit (IGU). The glass surface of a window acts chiefly to absorb heat energy or shift that energy away in the form of moving air. Low E (low emissivity) coating applied to the glass surface helps to reduce the penetration of infrared and ultraviolet light. The protective layers, actually thinner than a human hair, actually act to prevent excess heat from entering the room in warm weather and, conversely, act to reverse heat loss from inside the home in the colder months.

Low Emissivity

Low E Window Facts stands for low emissivity. Generally, light colored materials have a lower emissivity and dark colors a higher emissivity. These energy-efficient coatings were developed to lower the amount of ultraviolet and infrared light that can pass through the glass. In turn, the amount of visible light is not compromised. Light wavelengths determine what you should consider in a window coating. Ultraviolet light is the wavelength that fades fabrics in the home. Most important, heat transfer occurs with infrared wavelengths. Short-wave infrared is referred to as solar infrared. Long-wave infrared is produced by heat radiating from warm objects.

Passive and Solar Control

​In a Low E coated window, two different coatings work in unison on the glass layers. Firstly, Passive Low E coatings maximize solar heat gain to produce a desired heat gain in the home which reduces heating costs. On the other hand, Solar Control Low E coatings are made with air conditioning in mind. Secondly, Solar Control greatly limits the amount of heat transfer. The two layers on the glass function simultaneously. In the diagram, Solar Control is the layer closest to the sun (#2 surface) and Passive is the layer furthest from the sun (#4 surface).