Natural Light Control: Why We Should Care
- by Glenn A. (Tony) Lovette: DWC March 2004

     The window treatments industry is in prim position to capitalize on or disregard a challenge that offers a brighter and profitable future. (MORE)

     Remember the 1970s? That’s when Congress blamed automakers and Midwest manufacturing plants for poor national air quality. This ill was ultimately remedied, in part, by legislation, catalytic converter design and smokestack restrictions. The good news is that Americans probably do live healthier lives because of fewer carbon dioxide particles, less acid rain and improved breathing space. The bad news is that other daunting issues have replaced the old.

     Today the window treatments and shadings business also faces a call to arms. Regulation issues aside, some of the same needs for improvement urged upon the automakers and other industrialists will soon be standard operating procedure for our businesses as well. Here’s why: Quite simply, the world can no longer afford to be non-energy efficient. For a preview, one only needs to look east across the Atlantic Ocean and study the shading methods of Europeans who have practiced energy conservation for most of the 20th century.

     At the risk of understatement, the deal is simply this. The sun can be our friend or enemy. Depending on how we treat this power source, we can make it an energy efficient partner, as the Europeans do, or a continued lost opportunity with ultimate dire consequences for our grandchildren and ourselves.

     Let’s be honest, no living person would dispute the sun’s power as a dynamic energy source for all life. Intensity and duration of natural light not only affect our vision, but also trigger biological, physiological and psychological responses. It especially affects melatonin, the blood hormone that influences sleep, waking and the manner in which we conduct our day-to-day work and leisure activities.

BALANCING FORM AND FUNCTION
     Aesthetically, daylight has always been integral to good building design. It is dynamic because it adds visual interest to interiors by reflecting various sky conditions. As a result of its cool, blue temperature color, daylight renders colors quite naturally except at sunrise and sunset when it is a warm red. It is no wonder that artists prefer northern daylight as a source of illumination.

     The art and science of daylighting design also involves a critical balance of form and function, particularly when applied to public spaces, such as malls and lobbies. Because available daylight controls many natural light considerations, one of the first concerns of architects and designers is the typical sky at the building site. Meteorologically, clear skies are defined as those with 0 to 30 percent cloud cover. Cloudy or overcast skies range from 70 to 100 percent. The 30 to 70 percent range contains myriad possibilities and requires that a design perform well in a variety of conditions.

     Were those the only variables architects had to consider, natural light control might be reasonably simple. However, the planning process is complicated by a host of other important factors, including sky conditions, light source (direct sun, sky and/or reflected ground or surround) and solar position.

     Experts must also weigh the critical issue of daylight delivery systems, architectural elements that permit daylight to enter buildings and provide a means for distributing light within interiors. The most common systems are skylights, windows, light sleeves, monitors and clerestories. The best choice for a particular building (commercial or residential) depends on space function, design flexibility and general site daylight conditions.

DAYLIGHT CONTROLS
     Daylight control is affected by both exterior and/or interior means. Most daylighting systems are devoted to the exclusion of direct sunlight, and therefore, affect the amount, quality and distribution of general daylight inside buildings to varying degrees. The five chief exterior means are overhangs, fins, louvers, fenestration (window systems) and specialty fenestration.

     With large glazed surfaces again popular with architects, fenestration is an overriding element in natural light control. For purposes here, we define fenestration (from the Latin fenestra for window) as glass or plastic materials. That includes single-, double- or triple-pane for insulation and annealed, heat strengthened, tempered and laminated glass for different degrees of strength and safety. When considering glaze, architects look at the following performance parameters in material choice: daylight transmittance, U-value, shading coefficient, color appearance and glass reflectance.

     Specialty fenestration incorporates a variety of glass, plastic products and other materials. Specialty glass includes fritted, frosted and block glass. Fritted is a ceramic pattern superimposed on clear glass. It has clear and opaque areas that offer a distorted view through an opaque surface. Frosted glass is frequently found in skylights and is double-layered to diffuse light and enhance insulation. Glass block is a non see-through decorative material with outstanding prismatic and insulating qualities that is often used in public places.

     In many applications, plastics and other materials can be suitable and, in some cases, stronger substitutes for clear glass. Translucent and insulting properties make them ideal for windows, skylights and even wall panels. The addition of fiberglass fibers between glass layers also provides an attractive diffuse effect.

OPTIMAL LIGHT FOR LIVING TASKS
     Short of sunglasses, there is no one all-purpose shading system that allows optimal light for living tasks and accompanying ergonomic regulation that influences mood, perception and eye strain itself. As a result, natural light engineers are continuing to explore technological limits to bring comfort and productivity to a world at home, work and play.

     For outdoor leisure activities, visors, hats and sunglasses generally provide sufficient visual protection and comfort. Inside, most Americans rely on various shading options (blinds, louvers, etc.) and direct task lighting to operate productively. Rising energy costs and an industry response to the burgeoning home automation trend promise a plethora of new residential natural light control advances.

     In the workplace, the issue of optimal light levels and proper utilization of interior controls has a direct effect on energy costs, productivity, comfort, security, privacy and convenience. It also means less need for artificial light, which while not the focus of this article is a discipline unto itself and is of critical concern for architects and engineers who must integrate these light sources and, ultimately, for building occupants who must live with the result.

     Proper interior natural light control invariably supplies solar protection, glare and interior heat gain reduction, diffused light and the elimination of interior furnishing fading. Typical controls include horizontal and vertical blinds, draperies and shades and products such as film that can be applied directly to the glazing. Horizontal blinds are effective on north and south exposures blocking high-angle sunlight. Vertical blinds work well on east and west exposures because they mitigate low-angle sunlight. Draperies, while stylish, are not as effective in admitting sunlight and limit adjustment flexibility.

     In the late 20th century, the emergent choice of natural light control became exterior and, particularly, interior shades. The trendy term is performance daylighting, in which the goals are comfort, energy efficiency, aesthetically pleasing glare reduction and relatively uniform light distribution.

     An early objective for engineers was, and remains, visual comfort. In either setting, an ideal shading system should permit sufficient natural light without glare. The most common sources of glare are direct sunlight, skylight, reflected ground or opposite façade light.

     Manufacturers and trade organizations, such as the Illuminating Engineering Society of North America (IESNA), have published guidelines for designing daylighted spaces. For instance, IESNA recommends a maximum of 3:1 for the ratio of near surround luminance to task luminance and 10:1 for the ratio of far surround to task luminance. Adherence to such formulas goes a long way in combating ocular fatigue and eliminating uncomfortable glare in daylighted space.

     Shades also can prevent problems associated with veiling reflections, i.e., light from external sources that strike work surfaces at mirror angles with respect to tasks. Examples are desks directly in front of unobstructed windows or computer monitors situated so that screens face windows. One solution is to position computer monitor viewing direction parallel to window faces. Better yet, get some shades.

MAKING EVERY DOLLAR COUNT
     Proper management of direct sunlight and the resulting excessive solar heat gain is one of the continuing challenges faced by today’s natural light control experts. As a consequence, energy efficiency is a huge reason shades have become a staple of modern office building architecture. Not only do they conserve energy by minimizing interior lighting loads, but they also reduce associated heating and cooling costs. As modern building elevations return to the use of large glazed surfaces (that capture natural light and create solar radiation problems inside buildings), shades have come to be recognized as a fundamental construction requisite.

     Consider this: Normal glazing admits 88 percent of solar radiation, 80 percent of which is transmitted directly. That solar radiation is absorbed by walls and furniture and is converted to long wave radiation, which in turn is blocked by the glass creating a greenhouse effect. In buildings with 50 percent or more of unprotected windows exposed to the sun, the temperature in closed rooms (which is most of them) is 10 to 15 degrees higher than those outside. This phenomenon is known as solar gain. Exterior blocking devices, and especially solar shades, mitigate that heat, allow for higher temperature settings and permit visibility. Resulting cost savings for the very largest buildings can surpass $100,000 a year. An added bonus is that such interior shades are virtually maintenance free.

WAKEUP CALL
     Recent studies by the National Engineering School of State Public Works (ENTPE) in Lyon, France, reveal the following:

• Americans represent four percent of the world’s population and use 40 percent of the world’s energy.

• Exterior solar screening shades can reduce air conditioning loads by more than 60 percent.

• Interior solar screening shades can reduce air conditioning loads by more than 23 percent.

     These are impressive numbers, particularly when viewed in the context of dwindling global resources. Theoretically, we all accept as fact that someday natural resources will expire. We just don’t know when. Unfortunately, we conspicuous consumers continue our mode of ecological brinkmanship hoping against hope that there will be enough fuel for the Porsche, the powerboat, the furnace and maybe our grandchildren. Beyond that, our horizon pales, our vision grows dimmer and level of concern dissipates.

     The wakeup call is just around the corner. With architects reconsidering the role of light and increasingly returning to glazed surfaces, it is time that we, in the window treatments industry, realize that we are in a prime position to influence national solar protection preplanning and energy management.

     Here’s a final thought: North Americans are subject to 4,000 hours of natural light per year. Our decision in these first years of the 21st century is either to capitalize on this gift or disregard it. Accepting the challenge of conservation offers a far brighter and more profitable future.