What is the purpose of a low E coating on windows?

A low E (low emissivity) coating on windows serves to reflect infrared radiation while still allowing visible light to pass through. This is essential because it enhances the energy efficiency of a building. By reflecting infrared radiation—essentially heat that can enter from the outside during warm months or escape from inside during colder months—low E coatings help maintain a comfortable indoor temperature and reduce reliance on heating and cooling systems.

These coatings do not block all light, as that would be counterproductive for allowing natural illumination into buildings. Instead, they are designed specifically to let visible light through to maintain brightness while minimizing heat transfer. The structural strength of the windows is not enhanced by low E coatings; rather, they are primarily a thermal management feature. Similarly, while a low E coating could contribute indirectly to the aesthetics by eliminating the need for heavy draperies due to decreased glare from sunlight, it is not primarily designed for appearance purposes. Therefore, the primary function of low E coatings is centered around energy efficiency by managing heat transfer through reflection of infrared radiation.