If you live in the United States, you've probably heard
recently about the impending energy crunch that is facing
Americans. In the next 20 years, U.S. energy consumption will
increase 45 percent for electricity, 62 percent for natural
gas and 33 percent for oil,
according to the Department
of Energy (DOE). The DOE also says that energy supplies
will be unable to meet demand for the next two decades. For
consumers, this means paying higher prices for electricity,
natural gas and oil.
While the country is concentrating on ways to increase its
energy supply, a few researchers are working on new
low-power-consuming technologies. Among these new technologies
that could make our homes more energy efficient are smart
windows, and we aren't talking about Microsoft's
operating system. With this developing window technology,
consumers can block either all light or
just some by simply turning a knob. This type of light control
could save consumers billions of dollars on heating, cooling
and lighting costs.
Smart windows made with suspended particle devices
are controlled with electricity. To block out the light, take
away electricity by sliding the red knob
down. NOTE: Netscape users may
have difficulty using this file.
Several types of smart-window technologies are being
developed and each are vying for a share of the estimated 20
billion square feet of flat glass
produced worldwide each year. Liquid
crystals, electrochromics and suspended particle devices
(SPDs) are all being touted as the next great technology for
windows. In this edition of How
Stuff WILL Work, you will learn how each of these
technologies work and how they could save you money.
Suspended Particle Devices Windows serve an
important function in homes and commercial buildings. They not
only let light in to cut down on electricity use for lighting,
but the light coming through the window also provides heat.
However, windows are not something people typically associate
with being a cutting edge technology. At least one company is
trying to change that by introducing a new type of window that
can quickly be changed from clear to opaque and anywhere in
between with the flip of a switch.
Although Edwin Land, inventor of the
Polaroid camera, was the first to build a device
using suspended particle devices (SPDs), the actual
discovery of light-absorbing crystals can be credited to
a dog. SPD technology was first discovered more than 100
years ago. As the story goes, the dog of an English
chemist had been fed some quinine bisulfate to settle an
upset stomach. When the dog accidentally urinated on a
tray of iodine, the chemist noticed that green crystals
formed in the tray. Somehow, the chemist discovered that
these crystals had the ability to filter out light. Land
later used these light-absorbing crystals to make a pair
of glasses that could block out light.
Conventionally, curtains and mini-blinds have been used to
block out light and give us privacy, but they don't block out
all of the light. Research
Frontiers is the only company developing a new type of
window that uses small light-absorbing microscopic particles
known as suspended particle devices (SPD), or light
valves. Here's a breakdown of the parts that make up SPD
Two panels of glass or plastic
Conductive material - used to coat the panes of
Suspended particle devices - millions of these
black particles are placed between the two panes of glass
Liquid suspension or film - allows the particles
to float freely between the glass
Control device - automatic or manual
How the SPD windows work is very simple if you think of
SPDs as light valves. In a SPD window, millions of these SPDs
are placed between two panels of glass or plastic, which is
coated with a transparent conductive material. When
electricity comes into contact with the SPDs via the
conductive coating, they line up in a straight line and allow
light to flow through. Once the electricity is taken away,
they move back into a random pattern and block light. When the
amount of voltage is decreased, the window darkens until it's
completely dark after all electricity is taken away.
Control the level of light by increasing or
decreasing the electricity flowing to the window. Slide the
red button down to decrease the amount of
electricity. NOTE: Netscape users
may have difficulty using this file.
Users apply a moderate amount of voltage to the conductive
material on the window panes through a control device. Several
control methods will be offered with the SPD light-control
windows, including automatic and remote devices. Photocells
and other sensing devices could be used to control the level
of light automatically. Or, the windows can be controlled
manually with a rheostat or remote.
Research Frontiers holds about 350 worldwide patents on
this light-control technology. Suspended particle devices
could also be used for a multitude of other consumer products,
including sunroofs, sun visors, rearview mirrors, ski goggles
and flat panel displays for computers. SPD technology isn't
the only smart-window technology being developed. Liquid
crystals have been in use for years, and
electrochromics has the potential to perform the same
functions as suspended particles. In the next section, we will
look at these two technologies.
Competing Technologies Windows are
undergoing a change that hasn't been seen since the horizontal
mini-blind was developed 50 years ago. Soon, curtains and
window blinds could be obsolete. SPD technology is one of the
reasons for this window revolution, but let's look at two of
the other technologies competing with SPD light control.
Here are the two technologies competing with suspended
particle devices in the smart window niche of the glass
You are probably familiar with liquid crystals, which are
found in many of the products you use every day. Portable computers,
calculators, digital clocks and watches, and microwave
ovens all use liquid crystal
displays (LCDs). In these displays, electricity is used to
change the shape of the liquid crystals to allow light to pass
through, thus forming figures and numbers on the display.
The technology behind an LCD is similar to polymer
dispersed liquid crystals (PDLCs) in switchable
windows. In these windows, the liquid crystals respond to
an electrical charge by aligning parallel and letting light
through. When the electrical charge is absent, the liquid
crystals in the window are randomly oriented. With liquid
crystals, you either let all the light in or block all of the
light out. There are no intermediate settings. PDLCs are not a
developing technology. In fact, they can already be found in
some offices and homes.
Suspended particle devices require power to be transparent.
A different smart window technology is in development that
would reverse the process. Electrochromic windows
darken when voltage is added and are transparent when voltage
is taken away. Like suspended particle devices, electrochromic
windows can be adjusted to allow varying levels of light in.
They are not an all or nothing technology like liquid
Electrochromic windows are made by sandwiching several
layers of materials between two panes of glass. Here are the
basic materials inside an electrochromic window and the order
you will find them in:
Glass or plastic panel
Electrochromic, such as tungsten oxide
A second layer of conducting oxide
A second glass or plastic panel
Ions in the sandwiched electrochromic layer are what allow
it to change from opaque to transparent. It's these ions that
allow it to absorb light. A
power source is wired to the two conducting oxide layers, and
a voltage drives the ions from the ion storage layer, through
the ion conducting layer and into the electrochromic layer.
This makes the glass opaque. By shutting off the voltage, the
ions are driven out of the electrochromic layers and into the
ion storage layer. When the ions leave the electrochromic
layer, the window regains its transparency.
We're surrounded by windows everyday, but we probably don't
stop to think about them very often. With advances in smart
window technologies, we could soon begin to see windows in a
whole new light.