What is Low-E?
Low-E is the clear low-emissivity coating on one side of the glass that
is microscopically - thin and has optically transparent layers of silver
sandwiched between layers of metal oxide coatings. This specific process
is known as "sputter coating" and is also referred to as softcoat.
Low-E filters the suns energy in the summer and reduces heat loss in the
winter. Low-E lets in visible sunlight while blocking infrared and reducing
ultraviolet solar energy that fades carpet and furniture.
Low-E glass has been used for nearly two decades. Until now, Low-E has
been a product usually recommended for cold climates. With our introduction
of SunCoat Low-E we can use this product in the heat of Southern Nevada
Desert or in the cold climate of Alaska.
What Low-E does
Winter Time TOP
The sun's energy is "short wave radiation" that passes through
the window and is absorbed by carpet, furniture, etc. The energy is then
transformed into long wave radiation. The long wave radiation wants to
flow from warm to cool. Naturally it will try to escape through the glass.
At night the radiant heat produced from furnaces, wood stoves, etc. will
also want to escape out. The Low-E coating prevents this when the radiant
room side heat is reflected back in to the home. This results in a lower
winter U-value. For winter comfort, the higher the indoor glass temperature,
the better the product is for comfort.
The Low-E coating manages the suns heat in the summer by reducing the
amount of heat transferred through the window in the summer. The Low-E
coating filters the suns short wave radiation which cuts down on the amount
of solar heat gain into your home. For summer comfort, the lower the indoor
glass temperature, the better the product is for comfort.
Throughout the year, Low-E reduces Ultraviolet rays which can damage
curtains, flooring, furniture, etc.
What Low-E does
The Low-E allows most natural light to enter freely but reflects a significant
portion of short-wave heat energy.
In the summer, long-wave heat energy radiating from objects is reflected
back outside, lowering cooling cost.
In winter, internal long-wave heat energy is reflected back inside, lowering
When heat or light energy is absorbed by glass, it is either convected
away by moving air or reradiated by the glass surface. The ability of
a material to radiate energy is called its emissivity. All materials,
including windows, emit (or radiate) heat in the form of long-wave, far-infrared
energy depending on their temperature (see Chapter 2). This emission of
radiant heat is one of the important components of heat transfer for a
window. Thus reducing the window's emittance can greatly improve its insulating
The solar reflectance of low-E coatings can be manipulated to include
specific parts of the visible and infrared spectrum. This is the origin
of the term spectrally selective coatings, which selects specific portions
of the energy spectrum, so that desirable wavelengths of energy are transmitted
and others specifically reflected. A glazing material can then be designed
to optimize energy flows for solar heating, daylighting, and cooling.
A glazing designed to minimize summer heat gains, but allow for some
daylighting, would allow most visible light through, but would block all
other portions of the solar spectrum, including ultraviolet and near-infrared
radiation, as well as long-wave heat radiated from outside objects, such
as pavement and adjacent buildings. These low-E coatings still maintain
a low U-factor, but are designed to reflect the solar near-infrared radiation,
thus reducing the total SHGC while providing high levels of daylight transmission