Updated from an article in GLASS DIGEST, the leading U.S. architectural glass industry journal.

The technologies which have expanded the glass industry during this century are the float process, lamination, sealed windows, tempering, and Low-E It is becoming apparent that the glass industry expects its next major market expansion to come from the technology of optical shutters, or smart windows. One industry expert estimates that about one half a billion dollars (€320) has been spent,(1) worldwide, developing electrochromic shutter technology, which is now being used to dim automobile rear view mirrors at night. About a quarter of that amount has been spent developing liquid crystal technology for the architectural markets, to which it was introduced, and then withdrawn. Although these technologies address only a small fraction of the optical shutter markets - due to cost and performance limitations - the level of development effort shows that the industry takes these approaching markets quite seriously.

The markets for optical shutters are as diverse as the technologies, and in some cases the fit looks good. The major market segments are: passive solar heating, skylights, view and illumination windows, sunrooms, greenhouses, and automobile sun roofs and windows. Each segment is divided into new and retrofit, and also divided into improvements on existing products and products which require developing consumer awareness.

The services which the various optical shutters provide to these markets are: control of passive solar heaters, reduced air conditioning costs from skylights and windows, control of solar glare, controllable privacy, increased plant growth and health, and control of summer solar heating in automobiles.

The shutter technologies which have received the most attention to date are: electrochromic, liquid crystal, suspended particle and Cloud Gel. Let's take a quick look at the most interesting points in this matrix of markets, services, and technologies: noticing that, for most markets, there is a strong synergy between some optical shutters and Low-E.

Electrochromic shutters are switched electrically to turn from semi-transparent into a dark semi-mirror which absorbs, reflects and transmits light. Because they are activated electrically, electrochromics require both an external control system and electrical power. External control is desirable primarily for the privacy market. In this market however, the mirror property is objectionable, although it can be eliminated.(2) Electrochromic shutters allow one to see through them even when they are in their less transmissive state, provided the viewer is on the darker side of the shutter. This property has a negative market value, however, since at night the darker side is outside. For reducing air conditioning loads, the high light absorption of this shutter is a severe problem, even if it is on the outermost lite of a glazing system. The installed cost will be approximately $50 per square foot. Most of the major glass companies and a few governments have had electrochromic projects, although most of these have been dropped.

Liquid Crystal shutter technology is in the $100 per square foot installed price range, and is also electrically activated. Because it does not become a mirror in its opaque state, this shutter is more suitable than electrochromic shutters for the privacy market. Its cost, however, limits it to end of this market. Liquid crystal shutters transmit much of the visible and more suitable than electrochromic shutters for the privacy market. Its cost, however, limits it to the top all of the infrared portions of the solar spectrum and so are not suitable for controlling solar heat gains. In the U.S., 3M and Marvin Windows have marketed and then withdrawn liquid crystal shutter windows, while in Europe and Japan, Saint-Roch and NSG have done the same.

Suspended particle shutters, like electrochromic shutters, are electrically activated and provide one-way viewing only in the daytime. However, like electrochromics and liquid crystals, these shutters provide no privacy at night. This shutter turns absorbing when in its non-transmitting state, and so can not control solar gains. Its installed cost will also be approximately $100 per square foot. Remarkably, they have had an IPO and signed licensing agreements with major glass manufacturers a decade ago, but have not yet completed product development.

Cloud Gel shutters differ from the previous technologies in three important ways:

In summary, these are the market/technology matches: Electrochromics are suitable for high value per square foot markets which require reflectivity and electrical activation, such as automobile rear view mirrors or airplane windows. Liquid crystal and suspended particle shutters (if they work) are good for high value privacy markets, such as some view windows and conference room walls. A dramatic cost reduction would greatly increase the market size accessed by these two technologies, but after many years and hundreds of millions of dollars spent on development, this appears unlikely. Cloud Gel shutters are useful in the markets for rejecting unwanted solar heat - the mass markets where low cost is essential. Because Cloud Gel shutters can be activated automatically by light or heat or manually by electricity, they can provide all of the services previously listed, except daytime one-way view windows and automobile rear view mirrors. Where Cloud Gel shutters are used not to create new products (such as solar heating), but only to improve the performance of existing ones, the world market size is about a billion square feet per year for new construction, and 20 billion square feet for retrofit applications.

For aesthetic reasons, it is doubtful that any optical shutter technology will replace curtains in the window market. There are, however, enough other small architectural and automobile market niches for several varieties of shutter technology. It is my opinion that the technologies which will successfully address all of the architectural markets will come from basic research, rather than from the adaptation to civilian markets of technology originally intended for military displays.

It is not surprising that optical shutters go well with high performance transparent insulations such as Low-E, as both were invented as parts of the same building component. Because the major market for optical shutters is the reflecting away of unwanted solar gains, and because glazing apertures are responsible for a disproportionately large amount of a building's unwanted heat gains in the summer and unwanted heat losses in the winter, optical shutters and transparent insulations both address the same market: the energy used to cool and heat glazings. Thus it is natural that, for example, a skylight whose energy performance is being upgraded by the incorporation of an optical shutter would also use a transparent insulation to further upgrade its energy performance. Combining an optical shutter with a transparent insulation to form a building panel makes a Weather Panel, so named for its ability to transform foul weather into fair. These panels can be made to provide either natural illumination or natural space heat, and they constitute by far the largest potential markets for optical shutters and glass. In the case of passive space heat, consumer awareness is growing rapidly, especially outside the U.S.

Low-E and Cloud Gel shutters were intended to be the driving force behind an emerging architecture which places buildings and their occupants in a healthy relation with their environment. They may also be perceived as the glass industry's next major step after Low-E toward expanding market size while increasing profitability.

(1) personal communication, A. D. Little, Inc; (2) U.S. Patent 5,198,922