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The phenomenon of variation in a substance’s properties of light admittance and transference using electric current is known as electrochromatism.
Those of us who have seen the first installment of the popular science fiction movie Iron Man will know about his rather innovative alarm clock. Built as a function of the artificial house assistant Jarvis, it was capable of ‘switching’ curtains on and off to allow sunlight into the room.
Light by itself is a very destructive form of energy. It must be filtered in some way or another before it can be utilized. Here are a few examples for your consideration.
The ozone layer is responsible for keeping UV radiation from reaching us, as it can otherwise cause rapid skin deterioration and various forms of skin cancer. Overexposure to UV radiation is also detrimental to the integrity of fibers and pigments.
The human eye is equipped with an iris that dilates and contracts to admit light. Ophthalmologists, therefore, suggest using sunglasses when outside, as constant exposure to glare for extended periods can result in permanent corneal damage.
Cameras are equipped with shutters to prevent exposing the sensor to unnecessary levels of radiation. At the same time, camera makers also advise against prolonged exposure as a preventive measure. Until now, light control has been achieved on a large scale by either mechanical (apertures, filters, polarizers) or chemical means (photochromism).
Concept or practical?
While the technology of electronic light control is not new, it has found mainstream applications only recently, primarily in the automotive industry, where it’s used in panoramic sunroofs and auto-dimming rearview mirrors. Given that more sectors embrace this concept, we should examine the science of electrochromatism in greater detail.
Electrochromatism in detail
The phenomenon in question is called electrochromatism (electro – electric current, chromo – color). It refers to a change in the transparency of an object, mostly glass, upon the passage of an electric current.
Certain electrolytes or fluid-conducting media exhibit particle movement at the atomic level upon the passage of electricity. Electrochromism leverages this phenomenon to achieve control over the admittance and transference of light. The general anatomy of an electrochromatic device (ECD) is explained in the following diagram:
An ECD is composed of the following main parts:
Layer 1: The outer glass surface
Layer 2: A transparent conducting layer to which voltage is applied
Layer 3: Liquid or gel-based electrolyte
Based on this structure, different types of voltage-based light control technologies have been derived. The devices differ from each other based on the electrolyte used, as we will explore further below.
Suspended particle device (SPD) glass
In SPD glass, the electrolyte consists of light-absorbing particles in suspension. The glass becomes transparent to incident light when AC voltage (110V) is applied. Upon ceasing the current flow, the alignment of these particles randomizes to make the glass opaque. The transition between transparent and opaque states can occur in a matter of seconds.
Polymer dispersed liquid crystal (PDLC) glass
In PDLC glass, the electrolyte consists of large liquid crystals dispersed in a liquid medium. Upon the passage of electricity (110V AC), they become parallel to incident light, allowing it to pass through. When the current ceases, their alignment changes in order to wholly or partially block incident light.
However, PDLCs have a minor disadvantage in that they cannot achieve complete opacity upon voltage removal. The transition between states takes place in a matter of seconds.
Conventional ECDs are different from both SPDs and PDLCs in various aspects. The architecture of a conventional ECD comprises a lithium electrolyte sandwiched between a nickel oxide and amorphous tungsten trioxide layer. Upon the passage of electricity (5V DC), a transfer of ions takes place from the nickel oxide and tungsten oxide layer, resulting in opacity. Thus, conventional ECDs are transparent in their unpowered state. The transition time between states is longer compared to SPDs and PDLCs. They generally only find usage in exterior applications.
Benefits of using electrochromatic glass
Electrochromatic glass can switch between states of opacity in a matter of seconds while blocking up to 99% of UV radiation. It is also capable of holding the desired level of transparency for the length of the time for which voltage is applied. They can be up to 60 times darker than tinted glass, and twice as clear.
These characteristics help in reducing air conditioning costs, as cooling is difficult to sustain in the presence of light radiation.
They also help in selective reflection and glare reduction, while maintaining clear visibility. This is particularly useful when driving at night.
Current applications of electrochromatic glass
As of now, electrochromatic glass has not found widespread usage due to high costs. Some common applications include:
- Airplane windows: Instead of using window shades, electrochromatic glass can help achieve a more continuous state of illumination or darkness. Seen here is a segment of Boeing’s Dreamliner, where electrochromatic windows were first used commercially.
2. Auto-dimming rearview mirrors: The use of electrochromatic films on rearview mirrors in cars can help eliminate glare from vehicles driving behind. This is essential for safe driving at night time, as bright lights can otherwise dazzle the driver.
3. Privacy barriers and sunroofs: The use of electrochromatic glass in sunroofs and privacy barriers in luxury automobiles and limousines is increasingly popular as a stylish and more effective way to achieve isolation and privacy.
Scope and potential applications
Electrochromatism finds use mainly in the luxury automobile and aircraft industry. However, this technology can also be extensively applied to architectural establishments. Here is a list of potential applications:
- Electronic curtains and blinds – The use of electrochromatic glass for domestic purposes, such as curtains, can help improve the cooling efficiency of air conditioning.
- Solar architecture (e.g., skylights and vision panels) – Electrochromatism in solar features, such as skylights and vision panels, can help illuminate establishments optimally and naturally without having to resort to LEDs or incandescent lamps during the day time.
- Conservatory roofs – Electrochromatic glass, as stated earlier, can be made up to twice as clear compared to normal glass. This can be applied in greenhouses and conservatories where a greenhouse effect is desired.
- Display cases and counters – Electrochromatic glass can be used in places where valuable and light-sensitive substances are stored, such as in a jewelry shop or drug store.
- Room partitions and privacy barriers – Electrochromatic glass can find extensive use in corporate offices that have clear glass walls to demarcate work stations and private cabins.
Commercially popular as Smart Glass, electrochromatic glass is still an unaffordable luxury due to the high associated costs. However, we can expect this technology to get more and more popular as stricter environmental compliance norms are implemented in the near future!