According to a popular early 70s song, if your mother tells you not to look into the sun and you do it anyway, you’ll be “Blinded by the Light” (spoiler, the “deuce” in “revved like a deuce” was a 1932 Ford Coupe).
The reality is that damage can occur in just a few seconds as ultraviolet light, focused by the lens and absorbed by the retina at the back of the eye, oxidizes and ultimately destroys surrounding tissue. Our precious photoreceptors! The technical term is solar retinopathy, and the sad part is that you likely wouldn’t even realize when it’s happening, as the associated eye pain may not be felt until 12 hours later. So how do you avoid it? Don’t look into the sun, or any other bright source for that matter. Follow your instinct to squint or look away when the sun is in direct view or reflected in your line of sight, especially if it is bright enough to cause pain or discomfort. This can be difficult to do in some circumstances, particularly in spaces with a surplus of natural light and little-to-no conditioning to negate its potentially harmful effects. So what is the solution?
Today, there is a dazzling array of glazing-related products that fall under the general term “smart glass.” Stated simply, this is a type of glazing whose visible transmittance, spectral content, or pattern of light distribution is altered when voltage, light or heat is applied. In this “smart glass” family of technologies are electrochromic, photochromic, thermochromic, suspended particle, micro-blind and polymer liquid crystal devices.
In this article we’ll focus on the use of electrochromic glazing (EC) in architectural applications – specifically, integrated into the exterior building envelope in an Insulated Glazing Unit (IGU). The concept is simple: voltage is applied to the glazing, which controls the amount of light and heat that passes through and allows the glazing to act as a climate-adaptive building shell. This specific product has been around for several decades and undergone several generations of development. The transition is not lightning-fast, nor is it completely invariable. Depending on the specific EC technology, it may take several seconds to several minutes, with darkening occurring from the outside edges in or happening more uniformly over the entire unit. One manufacturer even offers a unique iris-like pixel effect. The typical offering is four distinct states: clear, light tint, medium tint and dark tint. The intent is to maintain some degree of view, though even in its darkest state, typically 0.5% to 1% it still is unsafe for solar viewing. One recent development is the offering of a gradated tint, from clear to dark, which can be oriented to suit the distribution of luminance in a particular view.
And now for the elephant in the room – color! First generation EC technologies had a distinctive honey-yellow cast in their clear state, and a bright blue cast in their tinted states, which altered the view out and tinted daylight coming in. Generally speaking, the more you tint the EC, the bluer your daylight experience gets. This is tied to how EC glass works – changing the properties of the glass by applying a voltage to it so that it blocks specific wavelengths of lighting. With the way that many of these technologies were developed, this means that most of the actual blocking of light happens in the form of red wavelengths, leaving only the crisper blues to pass through.
In application, this means that the daylight – which is already quite blue compared to most interior electric lighting – becomes even more blue, and the blocking of large sections of the visual spectrum means that colors are rendered poorly with a muddy feel. The poor color quality of daylight can then be offset in a space either by using electric lighting to supplement it, or by making sure that additional daylight is coming from a different orientation where the EC glazing isn’t tinted as dark.
Beyond the energy benefits of EC, though, there are two potential health benefits associated with its application. First, it allows for more daylight to enter a space, raising the overall light levels while mitigating some concerns about glare and solar heat gain. Ongoing research examining the impact of light on our circadian rhythms generally points to the conclusion that the presence of daylight is important during morning hours to help synchronize our daily rhythms, and that the effect is more strongly tied to providing high light levels than the spectrum of light. Providing high amounts of carefully controlled daylight is a huge factor in helping to increase interior light levels to respond to this basic human need. The second health benefit is that, unlike many shade products, EC glass preserves a view to the outside. Numerous studies have demonstrated the value of having a view, everything from reducing stress-related cortisol levels in Wall Street traders to minimizing the amount of pain medications needed by hospital patients.
A new generation of EC is hitting the market with technological advancements seemingly every day. Many of the challenges from the past – extremely blue tints, large control zones, heat absorption in the unit, latency in the system – have been overcome with new technologies that are making EC glazing a feasible option for more project types. With these new developments comes more opportunities to integrate EC glazing into projects that might benefit from what EC glazing can provide: a way to help integrate daylighting into a space to support occupant health while preserving views.
