Smart glass, also called switchable glass or dynamic glazing, refers to any glass technology that can change its light transmission properties in response to an external stimulus, typically an electric voltage, heat, or light. These technologies enable windows to serve dual purposes: transparent when visibility is desired and opaque or tinted when privacy or solar control is needed. The global smart glass market has grown rapidly, with installations in corporate headquarters, hospitals, luxury residences, and automotive applications.
PDLC: Instant Privacy on Demand
Polymer-dispersed liquid crystal, abbreviated PDLC, is the most widely used smart glass technology for privacy applications. A PDLC film consists of microscopic liquid crystal droplets dispersed within a polymer matrix, sandwiched between two transparent conductive films and laminated between two sheets of glass.
When no voltage is applied, the liquid crystal molecules are randomly oriented. This random orientation scatters incident light in all directions, making the glass appear translucent white or frosted. When an AC voltage, typically 48 to 110 volts, is applied across the film, the liquid crystal molecules align parallel to the electric field. Light passes through with minimal scattering, and the glass becomes transparent. The transition is nearly instantaneous, occurring in fractions of a second.
PDLC glass is primarily a privacy product rather than an energy control product. In its transparent state, the visible light transmission is around 75 to 80%. In its translucent state, it drops to approximately 50 to 60%, but still admits significant diffuse light. PDLC does not appreciably block infrared or ultraviolet radiation. Typical applications include conference room walls, bathroom partitions, hospital ICU observation windows, and bank teller screens. Cost ranges from USD 50 to 100 per square foot installed.
PDLC glass has a typical lifespan of 10 to 15 years, after which the polymer matrix can begin to yellow or the liquid crystal droplets can lose alignment uniformity. Power consumption is low, approximately 5 watts per square metre in the transparent state.
Electrochromic Glass: Slow but Energy-Efficient
Electrochromic glass tints gradually through an electrochemical reaction. The active layer typically consists of tungsten oxide, which changes from transparent to deep blue when lithium ions and electrons are injected into it under an applied voltage. The counter-layer, often nickel oxide, balances the charge. When the voltage is reversed, the ions migrate back and the glass clears.
Electrochromic glass requires power only to change state. Once tinted, it holds its darkened condition without consuming electricity. The tinting process takes 3 to 12 minutes depending on the panel size and degree of tint, which is far too slow for privacy but well-suited to building energy management. A fully tinted electrochromic window can reduce solar heat gain by 80% or more while preserving the view.
SageGlass, a subsidiary of Saint-Gobain, is the leading manufacturer of electrochromic glazing. SageGlass Classic offers a range from 60% visible light transmission fully clear to approximately 1% fully tinted, with the option of three intermediate tint levels. The system integrates with building management systems to tint automatically based on sun position, cloud cover, and interior temperature. View Inc., based in Milpitas, California, produces View Dynamic Glass, which also offers four tint levels and cloud-connected control. Cost for electrochromic systems installed ranges from USD 75 to 150 per square foot, though prices have declined significantly as manufacturing has scaled.