Low-e Glass:
Low-e or low emissivity coated glass consists of a microscopically thin, virtually invisible, silver and metal oxide layer deposited on the glass pyrolytically (hard coat) or in a vacuum coater (soft coat).
Low-e products are designed to improve the performance of windows in all climates. They reduce heat transfer by providing lower SHGC and U-value ratings compared to ordinary non-coated glass. Because the coating provides an insulation function, they perform day and night year around.
When installed on the #3 surface of an insulated glass unit (IG), the low-e coating will reflect IR (infrared ray) heat from the inside of the room to help reduce the energy loss during the cold months, thereby reducing heating costs.
When installed on the #2 surface of an IG unit, the low-e coating will reflect or absorb IR (infrared ray) heat from the outside, thereby reducing solar gain and cooling costs during the warm months.
Visible Light Transmittance
A fraction of the visible spectrum of sunlight (**0 to **0 nanometers) transmitted through the glass of window, door, or skylight.
Visible Light Reflectance
A fraction of the visible spectrum of sunlight (**0 to **0 nanometers) reflected from the glass surface of window, door, or skylight.
Shading Coefficient (SC)
The total amount of solar energy that passes through a glass is relative to a â…› inch (3 mm) thick clear glass under the same design conditions; it includes both solar energy transmitted directly and any absorbed solar energy subsequently re-radiated into a room.
U-value
Also known as the K-value, the U-value is a measure to test a window's ability of transferring heat (usually given in W/m2K or Btu/hr ft2 oF). Windows with a low U-value, like low emissivity windows, are efficient insulators against heat loss.
Solar Heat Gain Coefficient (SHGC)
The Solar Heat Gain Coefficient (or SHGC) refers to a window's ability to transmit solar radiation. The SHGC ranges from 0 to 1. A value of 0 indicates that the window functions like a wall, essentially preventing any solar energy from entering into the building. A value of 1 indicates that the window functions like an opening, allowing all solar energy in. In cold climates, a high SHGC can lower heating costs by using passive solar heating. In warm climates, a low SHGC is desired to keep unwanted heat out and reduce cooling costs.