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Gilkey Window Company

August 11, 2015
Get the Latest in Glass Technology: Low-E Coatings

Get the Latest in Glass Technology: Low-E Coatings

Chicago Casement Windows

Windows may seem a simple part of your home, but they matter more than you realize. Much like your home's walls, windows act as an important barrier between the outside world and the comfort within.

You want a variety of things, like light, heat, and air, in your home-but only at specified levels. Windows allow you to have all these elements in just the right amounts. It wasn't always this way though.

Windows in History

Until the late 20th century, manufactures yielded poorly made, drafty, and thin windows. Most homes lost valuable hot or cool air because their glass couldn't maintain the home's internal temperature.

Early window manufacturers tried to use extra glass layers, increased thickness, and many other traits to fix this problem. But these advancements couldn't completely stop external temperatures from leaking inside. Luckily, all that changed for the better at the end of the century, when windows began to have many of the technologies and designs we use today.

In the 1970s, window technology went through a revolution. A group of researchers from MIT started a company that developed very thin silver coatings.

Using a vacuum, the researchers deposited this transparent coating onto thin plastic. They then placed this plastic between two layers of glass. Marketed as the "heat mirror," this invention allowed heat to bounce back into a room instead of escaping out of the house through the window.

By the 1980s, many other companies began to develop and sell low-e glass for windows to help residents maintain comfortable temperatures. This change in glass design significantly increased the R-value, or energy efficiency, of windows.

Now, instead of putting a plastic film between layers of glass, most manufacturers directly coat glass with low-e materials. But what does "low-e" mean?

Low-E Coatings

The "e" in low-e stands for "emissivity." A material's ability to radiate heat energy is called emissivity. Generally, darker materials have high emissivity and reflective surfaces have low emissivity.

For homeowners, it's useful to have low-emissivity windows, as this characteristic helps reflect radiant energy back into their home. However, "reflect" isn't quite the right word-rather, low-e coatings slow the emission of radiant energy.

But why does it matter if radiant energy escapes or comes into a home from the outside? Most homeowners want to keep the interior temperature different than the exterior one. They wouldn't purchase heaters or air conditioners otherwise. These advanced windows give them better control over their home's temperature.

The Science Behind Low-E Coatings

Light comes in different wavelengths, and depending on the wavelength, it may travel more easily through certain materials. UV and infrared light each have wavelengths that allow them to penetrate glass windows.

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