Windows, such as those used in commercial and residential buildings, have long been a source of energy loss and are therefore associated with significantly increased energy costs. Despite efforts in the last three decades to reduce energy costs associated with windows, an estimated 2.7 quadrillion BTU's of energy utilized to heat and cool buildings in the United States in 2006 (out of estimated total of 10 quadrillion BTU's expended) were attributable to windows, an amount roughly equivalent to the nation's entire Strategic Petroleum Reserve. Energy inefficiencies associated with windows include heat loss through the window in cold weather, heat gain through the window in hot weather, or both.
Many technologies that reduce energy losses from windows have developed in the past few years. For example, today's windows can employ multiple glazing, high-tech materials like aerogel between the glazing, and low-emissivity (low-E) coatings to minimize heat loss. There are also coatings that are much more reflective of infrared light than visible light. However, even windows which employ all these advances have significant energy losses. This is because they are designed for single climate use and cannot adapt to changing weather conditions.
Accordingly, there remains a need for variable light attenuating devices, such as windows, that have the ability to reduce the amount of light transmission through the window at various times. It is also desirable to be able to provide a “privacy” mode, where the window is translucent or “frosted” in appearance. Therefore, there is a need for a device with variable light absorption, light transmission and light scattering states that can be controlled according to need.
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