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Understanding Low-e Window Coatings

Sep 7, 2010; 12:53 PM ET

Low-e coatings, which are microscopically thin layers of metallic oxide that's bonded to the surface of a window's glass, are so thin you can see right through them yet they prevent heat and ultra-violet (UV) rays from passing through glass. The result? A window with low-e glass does a better job keeping heat in during the winter and out during the summer.

Letting Light In

When you look outside on a sunny day, you're seeing the visible part of the light spectrum. But only 38 percent of the solar energy that reaches the surface of the earth is visible. The rest of the light that lands in your yard is invisible. 59 percent is infrared and 3 percent is ultraviolet (UV rays). Even though they're invisible, infrared and UV rays do affect the interior of your home. Infrared rays can pass in out out through glass windows, which increases your home's heat load in the winter and cooling load in the summer. As for UV light, the same rays that burn your skin can enter through glazing to fade and degrade your fabrics and furnishings.

Coating Types

A low-e coating works like an invisible mirror to reflect selected portions of the light spectrum back out or back in through windows. There are three major types of coatings on the market: soft, hard, and Heat Mirror.

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