A smart glass is intended to have the ability to control the amount of light, and heat, passing through. With the turn of a button, the glass can change from transparent to completely opaque. Unlike blinds, smart windows are capable of partially blocking light while maintaining a clear view of what lies behind the window.
The “Smart Glasses” provides the advantage of lower energy consumption with the added convenience of a technologically advanced window in place of blinds. While the basic concept behind all smart windows is the same, they can be made in several different ways, each with a different method and properties for blocking light. In this article we will be focusing on three different technologies: liquid-crystal, electrochromic and suspended-particle-device(SPD).
Liquid-crystal glass is a laminated glass, with a minimum of two clear or colored sheets of glass and a liquid crystal film, assembled between at least two plastic interlayers. In this window's normal "off" condition, the glazing is a translucent milky white. When electric current is applied, however, it turns slightly hazy clear. The switch between the two states is nearly instantaneous. As there is little change in performance properties and because it requires constant energy to maintain its clear state, this liquid crystal window provides no energy saving benefits. Liquid crystal glazing is designed for internal applications, including partitions, display cases, bank screens.
SPD smart window is constructed by using two panes of glass separated by a conductive film with suspended, light absorbing, microscopic particles. Microscopic light-absorbing particles are dispersed within a thin film. When no electrical voltage is applied to the film, these particles absorb light, making the glass dark. When voltage is applied, the particles align and allow light to pass through. By simply adjusting the electrical voltage manually or automatically, the amount of light passing through the SPD-glass product can be controlled quickly and precisely. While this type of smart window is capable of changing at the turn of a button, one disadvantage is that electricity is required to keep the window transparent. However, there are some advantages of this type of smart window over the other two types. Electrochromic glass responds slowly, has limited cycle lifetime, and has an “iris effect” where color change begins at the outer edges of the window and trickles its way toward the center. Liquid-crystal glass is either clear or opaque with no in-between states, and merely scatters light rather than blocking it, which limits it to certain interior privacy applications.
A competing technology with SPD smart windows is the electrochromic smart window. Electrochromic windows consist of two glass panes with several layers sandwiched in between. It works by passing low-voltage electrical charges across a microscopically-thin coating on the glass surface, activating an electrochromic layer which changes color from clear to dark. The electric current can be activated manually or by sensors which react to light intensity. One advantage of the electrochromic smart window is that it only requires electricity to change its opacity, but not to maintain a particular shade.