The 1970’s saw a lot of advancements in home construction. In 1978 a law was passed that forbade the use of highly toxic lead paint. This was also the decade that saw the public released of insulated glass, which has revolutionized private- and commercial use windows. Insulated glass is simply the use of two or more panes to trap a pocket of air. That air pocket slows the heat transfer that occurs between the outdoor air and that found inside.
Though it came a decade later, Low-E coating was also a giant step forward in window manufacturing and could be used with insulated glass to provide consumers with something energy efficient. In order to fully appreciate the benefit added by Low-E coating on replacement windows, one must first understand the breakdown of sunlight.
Of course, window replacements are made to allow light into the home. Natural light is a very desired commodity in the home. However, there are different waves of light that come from the sun and each has a different property. Some of them are very desirable and some are detrimental to the home.
There are three components of sunlight that are of varying wave lengths, which impact the average household. The first is visible light, which is made up of short wave lengths and that is the light that brightens a room. This is the desired wave length. The second component is UV light. This is what sunblock creams and lotions were developed to protect us from. It can be damaging to the skin and also causes fabrics to fade. Blocking UV means prolonging the life of curtains, carpets and other household items. Finally, there is infrared, or IR, light, which is a long wave. IR light is, essentially, heat. While colder climates might welcome it in the depths of winter, here in Texas there is good reason to keep it out of the home.
Because both UV and Infrared light waves are longer than those of visible light, it is possible to block them without blocking the shorter, visible waves. This is the job performed by Low-E when used on window replacement jobs.
There are two varieties of Low-E coating. Hard coat involves the pouring of tin while the glass is molten. As it cools, the two fuse together and the result is a coated window, capable of reducing UV and IR emissions into the home. Soft coat is added between two layers of glass (along with argon to reduce the chances of oxidation). You should talk to your Cy Fair window replacement contractor about the advantages and disadvantages of hard and soft coat.
Perhaps the best part about Low-E is that it can be adjusted to accommodate the intended audience. In the south both UV and IR are considered undesirable, but in the north infrared helps keep heating costs lower, so Low-E can be adjusted to address just the UV, while letting IR pass.