Low E Glass

Emissivity is a measure of a material’s ability to re-radiate energy into a space. Every type of glass has an emissivity rating — when a normal glass window is exposed to sunlight, it absorbs heat, light, and UV rays, and radiates that energy into the indoor space. Low-emissivity glass, as you might guess, has a reduced capacity for absorbing and re-radiating heat and UV energy. It is common for a double or triple-paned window to incorporate at least one low-e pane to reduce excess heat energy.

Low-e glass works to reduce the unwanted side effects of natural light. Visible light generally occurs at wavelengths of between 380 and 780 nanometres. Ultraviolet (UV) radiation occurs at wavelengths just under 380nm (usually between 310nm and 380nm), while infrared light has longer wavelengths, usually beginning at a minimum of 780nm.

Both these types of energy can be detrimental at high concentrations and depending on the intended use and climate of a building project. UV radiation is responsible for sunburns and other undesirable long-term health effects, while infrared light produces a significant amount of heat energy. A room full of windows that absorb and re-radiate infrared rays will quickly heat up under direct sunlight. High quality low-e glass allows light within the visible wavelength spectrum (wavelengths between 380nm and 780nm) to pass through while minimizing the amount of heat passing from indoors to outdoors and vice versa.

How does low-e do this? During processing, low-e glass is coated with a microscopic chemical layer thinner than the average thickness of a human hair. This coating is made with material that absorbs and re-radiates visible light while reflecting the majority of longer-wavelength infrared rays, minimizing the amount of heat loss or gain that occurs via windows in homes, offices, and other indoor spaces. In some manufacturing scenarios, this chemical coating is applied to the glass before it is cut into panes, as it cools on the float line. This is known as the pyrolytic process. Another method for coating low-e glass is the Magnetron Sputtering Vapor Deposition (MSVD) process, in which the coating is sealed onto cooled and cut panes of glass at the end of manufacturing.

Passive low-e coatings are designed to maximize solar heating in a home — windows with passive low-e coatings reflect infrared energy coming from inside a home, minimizing heat loss in cooler climates, and helping to reduce energy bills. Solar-control low-e coatings, on the other hand, keep infrared energy from entering a space, keeping homes and offices cooler in the summer and reducing reliance on air conditioning. Coniston distributes low-e glass with a range of coatings and quality ratings to adhere to the highest building code standards.