CEO Additude Innovation

If Technology doesn’t fix the problem … we need more technology!

1999 I was hunting technology for my new home. Apart from the obvious with lightning and electricity under computer control via KNX or similar I wanted electrochromatic windows.

Note: I am an engineer. I am built to see things from an engineering perspective, as default mode of operation. Anything else take willpower and Joule. I also seriously lack any competence regarding "nice drapes make for a cozy home". So for me this is a mystery that this technology is so non-existent.

I finally got hold of a company called Research Frontiers that had a technology called SPD which could change the tint of the window. Unfortunately it fell short on two accounts.

  1. Cost. This was 20 years ago seriously expensive. Although I could eat noodles for the coming 25 years just to have these windows, my wife was not that interested. Cool technology, but not that cool.
  2. Research Frontiers could deliver glass sheets, but not complete 3 pane windows as used in Sweden. Not a single Swedish windows maker had a clue what I was talking about when I called around. Still the interest is low and the knowledge weak, and that is a bit of the question.

Smart Windows

So what is Smart Windows? First Smart Windows seam to go by quite many different names. Switch Glass, Smart Glass, Smart Windows, Intelligent Glass, Dynamic Glass, Electronic Glass, and so on.

There is two different groups of smart windows. Passive and Active.


This is a group where the tinting of the windows come from the material properties itself and the switching is autonomous. Two examples here is photochromatic and thermochromatic. Photochromatic reacts on the available light and thermochromatic, as expected, on temperature.

Photochromatic is probably the most well known since it has been available in glasses for very long time. Glasses which turns dark in bright sunlight.


Active glass is glass that can change its properties in a controllable way from external stimuli. These glasses changes their chromatic properties when voltage is applied.

There are three types, somewhat readily available on the market. PDLC, EC and SPD. They are often confused regarding what function they bring to the end user. Despite being somewhat similar in design and operation the transmission function is very different. The PDLC controls the haze of the light and is white in nature. The SPD and EC changes the transmission of the actual light, and is bluish in tint.


PDLC (Polymer Dispersed Liquid Crystal)

PDLC glass can be found a dime a dozen on the Internet. Mostly in the form of a sheet that you attach/bond to the window. You then attach the "buzzbar" on top on both sides. Typically it is made with copper tape. They can be cut in any shape or form. Some also come in different colors.

PDLC is often constructed as a sandwich with PET film on both sides and a polymer with liquid crystals molecules in between. In the off state the LC is ordered randomly thus dispersing the light. As with many of these technologies the transparent state requires constant power/voltage applied.

PDLC is an on/off technology. Either it is clear or very hazed. Although there is some difference in clarity depending on how high voltage you apply.

Below is the untainted windows from my kitchen.

And here is an example of two of the windows with PDLC tinting. The actual light transmission does not change (or not in any noticeable way), but the haze does. The windows turn "milky white". So these windows are more for privacy, than changing light.
NOTE: The picture is simulated, although I also have done experiments with PDLC.

Some Experiments

As I mentioned I had done some real experiments with PDLC film. In the video below you can see (sort of) how one kind of them work. Bought on Alliexpress 2015. The film was attached to a 230V AC variable isolation transformer set to 100V AC.

SPD (Suspended Particle Device)

This was actually the first technology I researched some 20 years ago. At that time it was very expensive. I got an offer for around 30 000 USD for 11 panes. Unfortunately no Swedish window maker could help me, turn that into real windows.

All the electric installations was done though. You never know when I can install some real windows for the 21st century.

It is used in premium buildings, cars and yachts. In the auto industry it is seen in sunroofs, but also since mid 80's in rear view mirrors with automatic dimming.

SPD are constructed with microscopic light-absorbing particles dispersed in droplets within a film. The film is layered between glass sheets. As with PDLC the "off" state is stopping light because of the particles suspended in random. When a voltage is applied the particles aligns and light can pass.

The tint is bluish.

SPD technology can be gradually changed from clear to fully blocked.

Below is the same untainted windows from my kitchen.

And here are two windows tinted 50 percent and 80 percent. Notice in this case that the light drops in the room. SPD actually reduces the light transmission of the windows.
NOTE: The picture is also simulated. I have tried many times to get development kits from the manufacturer, but it has turned out extremely hard.

EC (Electrochromatic)

EC like SPD also controls the light transmission through the glass. It changes between a clear, and slightly yellowish tint, to a blocking and bluish hue. There are two major differences between SPD and EC.

  1. The switching process is very slow. Ranging from seconds through several minutes. This depends on the size of the window. The change of transparency changes from the edges and inwards.
    There has been recent development to speed up the switching and also to remove the yellow tint.

  2. EC only need power when switching transparency states or levels. This is obviously a very beneficial property.

Recent advances in electrochromatic materials pertaining to transition-metal hydride electrochromics have led to the development of reflective hydrides, which become reflective rather than absorbing, and thus switch states between transparent and mirror-like.

Other recent developments has been around using nano structures.

Driver ... buzzbar

All technologies available uses a "buzzbar" in the top or bottom. This is what connects the electrodes on both sides of the films where the light altering particles is suspended, to a power source.

Typically around 100V AC is used and the power requirements is around 5W per sq. meter. This in itself is of course a drawback. 5W per sq. m is turned into heat and needs to be taken into account.


Eureka Tower in Melbourne has a glass cube which projects 3 m (10 ft) out from the building with visitors inside, suspended almost 300 m above the ground. When one enters, the glass is opaque as the cube moves out over the edge of the building. Once fully extended over the edge, the glass becomes clear.

The Boeing 787 Dreamliner features smart windows using electrochromatic glass which replace the pull down window shades on existing aircraft.

Smart glass has been used in some small-production cars including the Ferrari 575 M Superamerica.[8]

ICE 3 high speed trains use electrochromatic glass panels between the passenger compartment and the driver's cabin.

The elevators in the Washington Monument use smart glass in order for passengers to view the commemorative stones inside the monument.

The city's restroom in Amsterdam's Museumplein square features smart glass for ease of determining the occupancy status of an empty stall when the door is shut, and then for privacy when occupied.

Bombardier Transportation has intelligent on-blur windows in the Bombardier Innovia APM 100 operating on Singapore's Bukit Panjang LRT Line, to prevent passengers from peering into apartments as the trains pass by.

In the original Blade Runner movie there is also a early version in a scene where a room is darkened with smart glass shades.

The white PDLC type of glass has been seen plentiful in conference rooms for privacy and to stop prying eyes in your typical secret police/spy movies.


Well this was a short blogg entry on one of the cooler technologies in the architectural community, as well as other places where tinted glass could be useful. Still waiting for this to start being available in a larger scale.

Industry estimates indicate a current (2017) global market for smart glass of over US$3 billion, and project the market will grow in excess of 15% CAGR to ~$7 billion by 2022 and ~$10 billion by 2025.

End use is split roughly 50/50 between transportation (Automotive, Aircraft, Rail and Marine) and architectural. With some small uses in electronics and power generation from solar energy.