But sunlight creates problems indoors. In the summer heat comes through the windows with the light, making your air conditioning work harder.
In the winter, heat escapes through the windows, making your furnace work harder. Ultraviolet rays fade the colors of your walls, carpets, furniture, and artwork year-round.
Wouldn’t it be nice if windows were smart enough to let in the cheery sunlight without the damaging ultraviolet and without wreaking havoc on indoor temperatures? Smart windows exist, and advancing technology is making them both less expensive and more flexible.
Smart glass technology has mostly been limited to commercial buildings, aircraft, and the like. In a few years, smart windows (and skylights) suitable for your house and car will become available. Heat blocking window treatments are available now.
Three smart glass technologies
Smart windows use one of three competing technologies: Suspended Particle Devices (SPD), Polymer Dispersed Liquid Crystal (PDLC), and Electrochromic glass (EC). If you’re tired of the hassle of getting window treatments cleaned, you won’t need them with smart windows.
The photo above shows PDLC windows filtering light. The diagram also explains SPD windows, except they block light.
SPDs operate with millions of black particles suspended in a liquid or film between two panes of glass. Current can be turned on and off with a rheostat, a remote, or sensing devices like photocells.
With no current, the particles take a random pattern and block all light. With current, they line up in straight lines like ranks and files of soldiers, which allows light to pass. Voltage can be increased or decreased to admit as much or as little light as desired. The electricity is cheap. Powering 15 large windows in a house uses less electricity than a night light.
Of course, replacing all the windows in your home is not cheap. Research Frontiers has recently taken a patent on a way to apply SPD technology to existing windows.
PDLCs work similarly, except that they use liquid crystals dispersed in a liquid polymer instead of black particles. They are translucent, not opaque when a current flows through them. Also unlike SPDs, they are either on or off. Because they do not block all light, they are useful inside homes and offices for privacy.
EC windows use materials that change color when current is applied. Like SPDs and PDLCs, this material is built into a double pane window. With no charge, EC windows are transparent. Electricity causes a chemical reaction that causes the electrochromic material to change color by absorbing light.
Like SPDs, EC windows offer degrees of transparency, but with a crucial difference; they require electricity to achieve a particular opacity, but not to maintain it. In other words, turn on electricity until the window is the way you want it, turn it off, and then turn it on the next time you want to change it.
EC works much more slowly than SPD or PDLC. It can take a very long time complete adjustment of the light, and very large windows begin to change tint at the outside edge of the window and gradually move inward. But that’s already “old fashioned” EC.
New EC technology promises exciting possibilities of not only adjusting light but saving energy.
Controlling heat is now possible because of recent innovations using nanotechnology developed at the University of Texas at Austin by Delia Milliron.
Colloidal nanocrystals and other nanomaterials can block not only visible light but also near-infrared light. In other words, EC nanotechnology has produced smart glass that can not only regulate the intensity of light but also heat. Not only that, but it is less expensive to manufacture than traditional EC.
Windows with this new EC can regulate heat and light separately. In the summertime, the windows can admit sunlight and block heat. In the winter, they can reduce the glare of sunlight but admit heat. Current dual-pane windows are made with argon gas or “Low E” coatings between the panes. They provide insulation but don’t regulate light.
Many houses still have single-pane windows. Replacing these windows with the new nano EC could save 10-25% of a house’s heating and cooling bill. Replacing non-EC windows would result in lesser but still noticeable savings. A startup called Heliotrope Technologies hopes to have a commercial product available in 2017.
The smart windows and inner shades make curtains and blinds obsolete, but who would ever think bare windows look like home?
Cellular shades, or honeycomb shades, will block heat and maintain all the decorative choices of ordinary curtains and blinds.
They are widely available. When I searched for information about them on Google, most of the first 10 pages of results were companies that sell them. Even Walmart did not appear till the third page, and Wikipedia not until the fourth!
Like traditional shades, blinds, and curtains, you have a choice between light filtering and light blocking. They come with a wide variety of styles and colors, which you can choose according to your own taste in decorating. They will be either open or closed, so you can’t use them and look out the window at the same time, except . . .
You can choose a top-down/bottom-up design that mounts in the middle of the window. You can raise the top part and lower the bottom part separately. That way, you can have both privacy and natural light and still get improved insulation.
Instead of slats, like traditional blinds, or a single layer of fabric or plastic like traditional shades, cellular shades are made of hollow air cells. From the side, they resemble a honeycomb. Thus the names.
Each shade has one, two, or three rows of cells between the room and the window. The fabrics can either block or filter light, but they don’t conduct heat. The air within the cells doesn’t change temperature, or only minimally. Therefore heat does not come into the house with sunlight in the summer or leak through the windows in the winter. I expect they block noise, too.
Cellular shades are heavier than regular shades. Using a cord can present problems, but cords are a safety hazard anyway. You can get cordless shades or even motorized shades. With motorized shades, you can get a remote control—very handy for hard-to-reach windows.
If you have leaky windows, the shades won’t insulate very well, but caulk and/or storm windows plus cellular shades are still cheaper than buying new smart windows, or even new dual-pane windows.
How Smart Windows Work / Kevin Bonsor (How Stuff Works)
Smart Windows That Separate Light from Heat / Dan Acks (Wall Street Journal, August 28, 2015)
Smart Windows Just Got Cooler / Mike Orcutt (MIT Technology Review, August 5, 2015)
Insulating Window Shades / Marc Rosenbaum (Green Building Advisor, January 8, 2013)
Pros and Cons of Honeycomb Shades / A Little Design Help, June 12, 2012.