At the moment, the most recommended switchable windows are based on electrochromic technology. It is actually a thin film – usually less than a micron in thickness – applied to a glass substrate. This stack is made up of a stoneware metal oxide coat that is surrounded by two electrical conductors. When an electric current passes through these conductors, they switch from being clear to being a dull blue transparent shade, that looks almost similar to photochromic shades.
Compared to other similar technologies, EC windows typically require a lower voltage (at most 10 volts) to operate. Besides, they can be precisely adjusted to any shade between being clear and being fully tinted. When they’re full colored, they absorb solar radiation just as tinted glass does, even though research is currently being done to come up with a way of modifying their reflection rate.
They typically reduce transferring solar heat to the unit’s interior using their absorptive layer. During the day, low visibility transmissions work best for ensuring privacy and in eliminating the sun’s glare. When the sun isn’t shining straight through the window, a high transmission works best. This high transmission could even be used for solar heating in the cold winter season. With a wider control of the transmission, electrochromic dimmable windows could be adjusted to fit any environment.
Electrochromic windows using polymer laminate are even more desirable. Once the film has been adjusted to the desired shade, there is no current required to keep it in that state. They could even last up to 5 days once switched.
all-solid-state ECs are the most economical in the sense that they require the least voltage to stay in a given state (less than 0.03 W/SF). After being powered off, they gradually switch from being tinted to being clear. This is why they are more durable than polymer-based EC’s. Recent studies also suggest that they can withstand extreme weather changes such as being subjected to relatively cold conditions and then being subjected to the sun’s scorching rays. They have been tested on durability where they are being continuously switched from being clear to shaded to guarantee that they would last at least 20 years when installed correctly.
Their switching speed is dependent on how large the window is and how hot it is. On average, they shade slower than they discolor. On the typical 3 by 5 window, they switch from being clear to maximum tint in about 10 minutes. It takes longer during cold weather. Luckily, most consumers wouldn’t want to tint glass during cold weather to maximize heating from the sun’s heat. Biologically speaking, slower color changes are more beneficial as they allow our eyes to adjust to the lighting conditions without causing any discomfort. Lighting designers prefer slower switching as the distraction is subtler.
Wires extend from one edge of the film onto a low voltage switching system supplied by the manufacturer. In situations where wiring the glass would be aesthetically unappealing, they could be powered by solar voltaic cells. I learned this from MH Dimmable Tint and I think they are more skilled when it comes to handling Electrochromic glazing.