Smart Glass

Smart glass is window glazing whose light transmission can be changed electronically, by a switch, a timer or a sensor. The name covers two technologies that solve different problems. Electrochromic glazing tints to control solar heat and glare, but it switches slowly and costs the most. PDLC privacy glass switches between clear and opaque for visibility, and it does almost nothing against heat.

What is smart glass and why does the technology matter?

Smart glass, also called switchable glazing, is an insulating or laminated glass unit with a functional layer between the panes. Applying a voltage or removing it changes the optical state of that layer. Because the main technologies do different jobs, a specification that only says "smart glass" is incomplete. Before choosing, ask whether the glass has to reduce heat and glare or simply hide the view from outside.

How does electrochromic glazing work?

Electrochromic (EC) glazing uses a stack of thin films between two panes. A low voltage drives ions between two layers, which changes how much light and heat the stack absorbs, and the glass darkens. Reversing the voltage brings it back to a clear state. Once it reaches the chosen tint, the unit holds that tint with very little power, so most of the electricity is used during switching.

Why does electrochromic glass suit facades and skylights?

Its purpose is solar control. A tinted pane absorbs and reflects part of the sun before the heat enters the room, while still admitting daylight. That makes EC glass useful on south and west facades and in skylights, where the sun is high and strong. It is a slow technology: a full switch takes several minutes, so it follows the sky rather than passing clouds. Control is usually automatic, with light and temperature sensors feeding a building management system.

How does PDLC privacy glass work, and what does it not do?

PDLC (polymer-dispersed liquid crystal) glass holds droplets of liquid crystal in a polymer film, laminated between two panes. With no power applied, the droplets point in random directions and scatter light, so the glass looks milky and opaque. When a voltage is applied, the droplets align and the glass becomes clear. The switch is almost instant, and that is its main strength.

Its limitation is just as clear. PDLC does not tint, so solar energy passes through almost unchanged. It blocks the view but barely changes the heat balance of a room, and it does not improve the thermal performance of the window. Because most PDLC types stay clear only while powered, they also draw current continuously while in use.

How do electrochromic and PDLC glass compare?

The practical split is simple: electrochromic glass is a climate tool for large openings, and PDLC is a privacy tool for interiors.

Feature	Electrochromic (EC)	PDLC privacy glass
Main purpose	Solar heat and glare control	Visibility control
Unpowered state	Holds its last tint	Opaque
Switching speed	Several minutes	Almost instant
Effect on solar heat gain	Significant reduction	Minimal
Typical use	Facades, skylights, large glazed rooms	Bathrooms, interior partitions, meeting rooms
Power use	Mostly during switching	Continuous while clear
Relative cost	High	Lower than EC

How does smart glass compare with external shading?

A solar shading device placed outside the glass stops the sun before it reaches the pane, which is the most effective way to keep solar heat out. Smart glass works inside the glazing, so even in its darkest state it admits more heat than a good external shade would. Its advantage is that the facade stays clean and the view is kept.

Factor	Electrochromic glazing	External shading
Cost per opening	High, plus wiring and control system	Lower for fixed shading, usually below EC for motorised blinds
Speed of response	Several minutes, gradual	Motorised blinds respond in seconds; fixed shading is always active
Heat control	Good, reduces gain through the glass	Very good, stops the sun before the glass
Winter sun	Can stay clear to admit sun	Fixed shading also blocks winter sun unless designed for seasonal angles
Lifespan	No moving parts, but a failed sealed unit is costly to replace	Moving parts exposed to weather; motors, cables and slats wear
Maintenance	Low routine work, specialist repairs	Regular cleaning and mechanical checks
Wind exposure	Unaffected	Motorised systems need wind sensors; fixed systems must carry wind loads

In short, external shading is usually cheaper and more effective against heat. Smart glass is the better answer only where external shading cannot be fitted, such as a rooflight with no room for a blind.

How is smart glass different from a low-e coating?

A low-e coating is a fixed, passive layer. It reduces heat loss through the glass and, depending on its type, limits some solar gain, but it never changes state. Smart glass is active and changes its transmission on command. The two are not alternatives. Smart glass units still rely on the glass package behind the switchable layer for their thermal performance, so the low-e question remains.

Is smart glass a form of dynamic shading?

In a broad sense, yes. Dynamic shading is any shading that adjusts itself to sun, sky or occupant needs. Electrochromic glazing is one way to do it. The difference is location: smart glass is part of the window, while dynamic blinds and louvres sit on the facade and respond faster. External dynamic shading blocks more heat but needs weather-resistant design.

Where does smart glass fit in a Slovak residential project?

In a typical Slovak family house, electrochromic glass is rarely the first choice. Its cost is high for a single room, and it needs a tested control system and an electrician who can commission it. The usual order is to limit the glazed area on the south and west sides, add fixed overhangs or external blinds, and only then specify a high-performance insulating glass package. Overheating is usually solved by shading before any glass technology is needed.

Smart glass becomes relevant in a few specific cases: a large south-facing living room behind a wall of glass, a rooflight above a stairwell that cannot take a blind, or a commercial interior where the boundary between rooms must change. PDLC fits more easily into ordinary homes, for example in a bathroom door or an interior partition between a pracovňa (home office) and a living room. In those cases the reason to choose it is privacy, not energy.

What are the common misconceptions about smart glass?

• Privacy glass reduces summer heat. PDLC leaves solar energy largely untouched, so it does not help with overheating.
• Electrochromic glass replaces shading. In a hot south room it reduces the load, but it does not remove the need for a good shading strategy.
• All smart glass switches instantly. Electrochromic glass takes several minutes, so only PDLC switches almost instantly.
• Smart glass is maintenance free. Sensors, controllers and sealed units still need checking, and a failed unit is expensive to replace.