Electrochromic glass speaks to what is electrochromic glass and why use electrochromic glass.
It changes its transparency in response to the passage of electric current. Also called switchable glass, it can be actively controlled by building occupants or automated systems, allowing, in comparison to passive technologies more precise response to requirements for control of solar heat gain, daylighting or occupant privacy.
Smart glass, Magic Glass, or switchable glass, also called smart windows or switchable windows in its application to windows or skylights, refers to electrically switchable glass or glazing which changes light transmission properties when voltage is applied.
Certain types of smart glass allow users to control the amount of light (and thereby heat) transmission. When activated, the glass changes from transparent to translucent, partially blocking light while maintaining a clear view through the glass. Another type of smart glass can provide complete privacy when activated.
Smart glass technologies include electrochromic devices, suspended particle devices, micro-blinds and liquid crystal devices.
The use of smart glass can save costs for heating, air-conditioning and lighting and avoid the cost of installing and maintaining motorized light screens or blinds or curtains. When opaque, liquid crystal or electrochromic smart glass blocks most UV, thereby reducing fabric fading; for SPD-type smart glass, this is achieved when used in conjunction with low emissivity coatings.
Critical aspects of smart glass include installation costs, the use of electricity, durability, as well as functional features such as the speed of control, possibilities for dimming, and the degree of transparency of the glass.
Currently available smart glass products currently rely on solid state liquid crystal technology similar to that used in electronic flat panel displays. These products are limited to interior applications where control over transparency and privacy is desired, but they are not suitable to the conditions to which exterior glazing is subjected.
Other technologies currently under development are expected to result in products that are suitable for both exterior and interior exposures, that can selectively control portions of the solar spectrum, such as infrared radiation and that can switch between transparent and reflective states.
Electrochromic devices change light transmission properties in response to voltage and thus allow control over the amount of light and heat passing through. In electrochromic windows, the electrochromic material changes its opacity: it changes between a colored, translucent state (usually blue) and a transparent state. A burst of electricity is required for changing its opacity, but once the change has been effected, no electricity is needed for maintaining the particular shade which has been reached.
Darkening occurs from the edges, moving inward, and is a slow process, ranging from many seconds to several minutes depending on window size. Smart glass provides visibility even in the darkened state and thus preserves visible contact with the outside environment. It has been used in small-scale applications such as rear view mirrors.
Electrochromic technology also finds use in indoor applications, for example, for protection of objects under the glass of museum display cases and picture frame glass from the damaging effects of the UV and visible wavelengths of artificial light.
Recent advances in electrochromic materials pertaining to transition-metal hydride electrochromics have led to the development of reflective hydrides, which become reflective rather than absorbing, and thus switch states between transparent and mirror-like.
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