What is switchable glass & how does it work?

What is switchable glass?

In the most simple terms, switchable glass is a glass panel that can ‘switch’ between a crystal clear state and an opaque one (meaning you can’t see through it) at the push of a button.

This might sound a little ‘space age’, but it’s very much a reality. Indeed, these kinds of installations are increasingly being chosen for their versatility and multitude of practical applications in both residential and commercial properties.

How does switchable glass work?

There are a few ways that glass can be turned from transparent to opaque (and back again), with each method having its own relevant application. Broadly speaking, there are three popular methods for achieving switchable glass: light exposure, heat exposure, or the application of an electric current. While they all provide the same effect, the mechanics differ slightly:

How photochromic glass works

Photochromic glass contains small molecules of silver halide, suspended in the glass itself. When these are exposed to sunlight, a reaction takes place, and electrons in the glass combine with the molecules to create elemental silver; as silver isn’t transparent (it’s, well, silver), this causes the glass to darken. The process usually takes around 30 seconds to fully complete, and between 2 and 5 minutes to revert once the glass is no longer exposed to UV.

This type of switchable glass isn’t normally used in building construction, because the only effect of the glass is to darken and shield you from light, with no other real benefits. Considering the many benefits of natural light, it’s easy to see why specialists prefer to opt for thermochromic or electrochromic solutions (see below). Instead, this is the technology normally used to make eyeglasses that can act as both reading spectacles and sunglasses.

How thermochromic glass works

Thermochromic glass acts in a very similar way to photochromic, except it isn’t light that causes the reaction: it’s heat. As the sun heats the pane, it tints and darkens, thereby letting less light through. There are several different types of thermochromic material, each with slightly different properties. Arguably the most popular is Vanadium dioxide, which takes on a distinctive reflective metallic tint when exposed to heat.

This type of glass technology isused more often in building construction, as counterintuitive as it may seem. After all, darkening a room when the sun comes out doesn’t seem to make a lot of sense. But it’s not the way these panels interact with light that matters; it’s the way they block out radiation and heat.

When it’s cold, you ideally want a window to take heat in and stop it getting out – and when it’s hot, you generally want the opposite. A perfect concept when deployed as part of a glass box extension, for example. Thermochromic dynamic windows essentially swap between the two as required, making them extremely efficient at climate control.

How electrochromic glass works

When people envisage ‘switchable’ glass, what they’re usually imagining is electrochromic glass. Unlike thermochromic or photochromic glass, electrochromic panels don’t gradually tint as their surrounding environments change – they switch quickly from clear to opaque at the push of a button.

These panels contain several thin layers, or ‘coatings’, which can be charged with a large number of lithium ions. When a current is applied, the lithium ions and electrons are transferred from one layer to another, giving the glass a tinted effect. Once the current is stopped, they return, and the glass becomes totally clear again.

This kind of switchable glass is the most popular for use in buildings and homes, mainly because the inhabitants of the building have full control over it. Electrochromic glass also offers many of the insulating and energy-efficient properties of thermochromic glass, with the added accessibility and flexibility of being manually operated.

What is switchable glass used for?

There are all kinds of uses for switchable glass in building design, but there are two main reasons people choose to have it installed: energy efficiency and privacy.

Thermochromic and electrochromic glass can both reduce the amount of heat that enters and escapes through a glass surface, and for this reason they are often chosen for modern designs with a focus on reducing energy costs (in the form of heating or air conditioning).

However, while this practical application is certainly important, the privacy afforded by switchable glass is the main reason many people choose to include it in their homes and commercial properties. There are all kinds of situations when switchable privacy glass can make a big quality-of-life difference to the inhabitants of a space, such as:

Office windows

If you work in office with a shared meeting room space, there will undoubtedly be the odd occasion when it isn’t appropriate for someone to peek in. Private meetings, sensitive discussions with employees — the list goes on.

While simply rolling down the blinds might be a time-honoured way of handling this, switchable glass offers a faster, more modern, and more aesthetically pleasing way around this situation – and as ‘smart buildings’ become increasingly popular for modern enterprises, this granular level of control over your facility will become ever more useful.

Hospitals and hygienic interiors

While functional, blinds and curtains are fundamentally not that hygienic. Dust accumulates on them at a staggering pace, and their proximity to outdoor elements can make them a breeding ground for bacteria. This doesn’t matter too much at home, or in the average office, but in hospitals, surgeries and other areas in which hygiene is paramount, this can create a problem.

Switchable glass eliminates the need for any physical contact, as it can be controlled in any number of manual or automated ways. Timers, light sensors, and even motion detectors can all be integrated with switchable glass to eliminate any potential transference of germs.

Bathrooms

On the residential side of things, switchable glass can also provide a practical and convenient upgrade to a bath or shower room. In a space where privacy is important, having the option to quickly flick a switch and ensure no one can peer in through the window is endlessly helpful.

Homeowners will be able to ensure privacy while still having the option of enjoying a view to the outside world when needed, and will also be spared the inevitable and awkward towel-covered dash for the curtains or blinds when they realise they forgot to prepare before stepping into the shower.

What does the future hold for switchable glass?

The market for smart glass is expected to reach $7.5 billion by 2028. Certain types of smart windows can already be found in a variety of places, including aeroplanes, cars and boats, and it is also beginning to find a home in offices and airport terminals too (with privacy screens, display panels, boat windows, aircraft windows and some car sunroofs).

Looking to the future, smart glass might also play an important role in making residential spaces more energy efficient, experts say. As buildings account for a huge amount of energy consumption, a lot of which is associated with heating and ventilation, smart windows can help to bring down those energy needs.

This is because the hydrogel (placed within the two panes of glass) expands when temperatures dip under 30 degrees Celsius, turning the glass transparent. Above this threshold, the chains crumple like paper and entangle with each other to create a tint, scattering near-infrared and visible light. Thanks to the water in the mixture, which can hold high amounts of heat, hydroliquid absorbs the warmth, gradually releasing it over time. This can reduce heating, ventilation and air conditioning energy needs by 35% compared to double-pane glass.

In the future, says materials physicist Claes-Göran Granqvist, “there’s no reason really to have any other windows than these smart windows.”