What is Smart Glass?

In a Nutshell

Smart glass technologies fall into three primary categories:

• glass that filters energy (e.g. absorbing, scattering or reflecting light)
• glass that harvests energy (e.g. converting sunlight into clean electricity)
• glass that displays or channels energy (e.g. optical waveguides in smart spectacles or automotive dashboards)

The following graphic summarises the family:

Further examples of smart glass include:

• microfluidic glass for the healthcare sector
• RF-shielding glass to protect sensitive electronics
• ultra-low reflectance glass for solar panels and semiconductors

Static vs Dynamic Glass

Some equate ‘smart glass’ with ‘dynamic glass’, but we see it a little differently since dynamic glass implies a change in its properties (such as tinting).

However, static glass can also be ‘smart’.

For example, glass that includes a low-emittance (‘low-e’) layer reflects a fixed range of solar infrared wavelengths. It is static but nevertheless smart. 

Let’s take a step back for a moment, shall we? 

What is Glass?

Glass is an amorphous material (Greek: ‘without shape’), which does not follow a continuous pattern in its internal structure. It is normally transparent, brittle and chemically inert.

Crystalline materials, on the other hand, are organized typically in a lattice form. In nature, examples of crystals include snowflakes, diamonds and table salt.

All crystals are solids, whereas amorphous materials can be solids, liquids or gasses.

Visible light passes through most glazing products (both amorphous and crystalline) which can be engineered to block specific wavebands, e.g. visible light, infrared or ultraviolet.

Smart Glass 

‘Smart glass’ is simply ‘engineered glass’ that includes modifications to enhance the inherent properties of the glazing material.

We find applications of smart glass in buildings, transportation, electrical appliances and consumer devices.

It can help to divide the taxonomy by the triggering mechanism, resulting in ‘passive’ and ‘active’ smart glass.

Passive Smart Glass

Natural stimuli trigger passive technologies into changing their properties. Here are some examples:

• Thermochromic glass (triggered by heat)
• Photochromic glass (triggered by visible light and UV)
• Piezochromic glass (triggered by changes in pressure)
• Gasochromic glass (triggered by changes in gaseous concentrations)
• Mechanochromic glass (triggered by changes in mechanical force)

Some of the above are still in the R&D stage, but promise interesting applications across the chemical, pharmaceutical and industrial sectors.

Both thermochromic and photochromic glass find applications in building facades, in eye wear and in transportation. This can minimise air conditioning costs and reduce discomfort and glare for passengers and building occupants.

The biggest advantage of passive materials is that they do not need cabling, which saves on installation costs in buildings and reduces weight in vehicles. 

The disadvantage is that they are harder to control ‘on-demand’, based on user needs.

Active Smart Glass

This type of smart glass operates electrically and thus can connect to building management systems (BMS) and the internet. Recent advances include building facades driven by artificial intelligence based on building occupancy or sky conditions.

Active technologies include:-

• liquid crystals (polymer-dispersed or dyed)
• suspended particle devices (SPD smartglass)
• electrochromic glass
• electrophoretic (‘e-ink’) based glass
• transparent photovoltaics that generate clean electricity from sunlight while maintaining the exterior view
• augmented-reality wearables (think: smart spectacles)
• holographics

Electrical Safety and Smart Glass

Condensation in insulated glazing units can cause short circuits in electrically-activated smart glass, introducing potential safety concerns. This is due to the risk of moisture seeping into nicks and cuts in the cable sheath due to excessive bending.

Even though some technologies operate at low voltages (typically 5-15Vdc), they still require protection against short-circuits and EMI-induced noise.

Smart Glass Powered by Sunlight

Potentially the most exciting technology is transparent photovoltaic (PV) smart glass, since we can combine it with the above technologies to drive the glass using clean energy.

Some windows include opaque PV modules installed on the exterior of the frame.

Some hide the PV layer transparently inside the smart glass, providing a seamless integration and obviating the need for any cables at all.

Yes, you heard that right: the interior PV layer is transparent, conductive and energy-generating!

Use Cases

Applications include:

• privacy screens in a bank or hospital that are triggered by human presence
• auto-tinting glass for buildings or vehicles that block glare under strong sunlight
• retail storefronts that hide objects from view for security reasons
• display cases for art & luxury items that reduce light exposure damage which results in colour fading
• ‘heads-up displays’ with visual information projected onto aircraft or automotive glass to reduce accidents by keeping drivers focussed on the road ahead

Suppliers

If you are looking for manufacturers, distributors or installers, look no further than our parameterised search.

If you press the ‘Show Results’ button, this will produce a list of companies, which you can contact directly, or by posting a request on our Marketplace.

Outlook

Terminology is important.

Recent legislation in the US has confused the term ‘electrochromic’ with ‘any electrically-activated smart glass’, which is not accurate.

We created Smartglass World to educate customers and industry players in the technologies and applications available.

The industry should pay heed to using terminology accurately, so that customers have clarity about which smart glass technology is best suited to their needs.

References

1. “Green Nanotechnology”, Smith & Granqvist, ISBN-13: 978-1420085327

2. “Colour and the Optical Properties of Materials”, Richard Tilley, ISBN-13: 978-0470746950