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Since the oil crunch of the 1970s, architects, engineers and homeowners have sought new ways to reduce America's reliance on traditional energy sources for heating and lighting homes. Certainly one of the most popular and promising answers to emerge has been solar energy. "Although nobody has officially counted, we project there are well over half a million passive solar houses in the United States," says Helen English, the Executive Director of the Passive Solar Industries Council.
With the solar heating movement, a less known but highly regarded design science has stepped to the fore--daylighting, the use of natural light to illuminate building interiors. Of course, this concept is as old as the window, but relatively recent advances in lighting research, window and glazing technology and lighting controls have opened up new horizons for daylighting.
DAYLIGHTING DEFINED
Daylighting is really just the act of illuminating rooms naturally. Any time you're able to light a room with a window or skylight instead of flipping on a light switch, you are daylighting. It's that simple.
On the other hand, most designers note that daylighting also involves control. Kristine Anstead, of the ENSAR Group, a Boulder, Colorado, based architectural and consulting firm that specializes in daylighting, says, "I see daylighting as the art of bringing natural light into a space in the best way for that space...understanding what light does and how to manipulate it to meet the needs of the people in that space."
Daylighting solutions can be quite simple or very complex, depending upon the building and the situation. A comprehensive approach, particularly in commercial and institutional building design, must consider many factors: the climate, the sources of natural light, the necessary measures for controlling light, heat gain and heat loss, occupancy and use of the building, and so forth. Such solutions often involve special glazing, coatings or films; shading and light reflecting and diffusing surfaces; special controls that reduce artificial light when it isn't needed; and more. Very sophisticated systems may even include sun-tracking mirrors and lenses, light pipes and fiber-optic cables.
But these types of comprehensive daylighting design are not common for houses. "Daylighting isn't really a term that's normally applied to a house," says Helen English, the Executive Director of the Passive Solar Council. "You can daylight a library or a school, but for a home, true daylighting is pretty unusual."
THE COMMERCIAL CASE
Because commercial and institutional buildings operate primarily during daylight hours and with clearly-defined schedules and because specific tasks are conducted in given areas, these kinds of buildings often lend themselves to comprehensive, systemized daylighting plans. And in these buildings, daylighting makes sense because of both energy savings and worker satisfaction.
When a building is flooded with well-controlled natural light, the amount of electricity needed for lighting may plummet. It's estimated that 25% to 40% of a commercial or institutional building's energy is needed for lighting, often at peak-demand prices; daylighting may save up to about 50% of that, depending upon how natural light is used.
That's significant, particularly in view of national energy picture. In the United States, electric lighting consumes about one fourth of all the energy generated. According to the Rocky Mountain Institute, a nonprofit research and educational organization that fosters efficient use of resources, this usage equals the energy produced by 170 large powerplants.
Workers prefer brighter, more naturally-lit environments, too. In fact, a number of studies support the idea that natural light has positive psychological effects on people. They suggest both that our brain perceives the color properties of natural light as "normal" and that we respond in a positive, physical way to its intensity. Russell Leslie, Associate Director of the Lighting Research Center at Rensselaer Polytechnic Institute in New York, points to evidence that shows high light levels can contribute to good health, comfort and productivity. He notes that depression caused by seasonal affective disorder (SAD), a sometimes debilitating condition that occurs at high latitudes where people are deprived of sufficient winter daylight, can be successfully treated with high light levels.
THE HOUSE ADVANTAGE
Clearly, the case for daylighting commercial and institutional buildings is a strong one. But what about houses? We know that homeowners love the qualities of natural light--billions of dollars are spent each year on remodeling, often in an effort to achieve more light and spaciousness. But how far should homeowners go? Do they really need sophisticated daylighting systems? The answer seems to be this: You can enjoy and benefit from more natural light by taking advantage of selective daylighting principles and materials, but comprehensive daylighting systems don't make sense in most homes.
For one thing, the potential energy savings are not the same as for commercial and institutional buildings. Though houses do use plenty of electricity for lighting, high-wattage electric appliances and heating gobble up a healthy share of a home's power needs.
And there's the issue of occupancy. Unlike an office or library, many homes are relatively unoccupied during daylight hours, which shifts a larger percentage of electrical usage to the evenings.
Control is different too. At home, it's easy to flip off the lights when they're not needed. Sophisticated controls that automatically raise and lower indoor artificial light levels according to daylight are not necessary.
Providing natural light in houses is often fundamental to their design. As Russell Leslie and Kathryn Conway point out in The Lighting Pattern Book For Homes, published by Rensselaer's Lighting Research Center, "Homes often have generous amounts of daylight, and residential building codes require that most rooms have windows. Typical residential rooms are small enough so that daylight can reach deep into the room, particularly if windows are located high on the wall."
LET THERE BE LIGHT
But what are some ways to effectively improve the quality and quantity of natural light in a house? Small skylights can be very helpful at bringing natural light into a dark hallway or room, but be careful. As Architect Kristine Anstead points out, "During the summer, when you don't want heat and you have the sun directly overhead, they allow an abundance of heat. In the winter, when the sun is at a low angle, you get the least amount of available sun." As an alternative to skylights, she suggests investigating clerestory windows or roof monitors.
Regarding windows, she adds, "Glazing technologies have begun to catch up with the energy efficiency movement. Now you can use more glazing to get more light in but not have the heat loss or gain problems."
Indeed, the trick with glazing is usually to admit as much light as possible without causing excessive winter heat loss or summer heat gain or glare--the factors that, in the past, have limited window numbers and sizes. Heat moving through windows destroys a building's energy efficiency and wastes our natural resources. In fact, according to the Rocky Mountain Institute, more energy is lost through American windows every year than flows through the Trans-Alaska oil pipeline.
The good news is that many new types of high-performance glazing have been developed in recent years that make it possible to use a lot more glass while minimizing heat loss, heat gain and glare. If you're building a house, remodeling or replacing windows, you can choose from a wide range of options, selecting glazing best suited to a particular window.
Talk with a window dealer about the specific properties and values available. Generally speaking, if you want to minimize heat transfer, pick high-performance glazing that has a high R-value. For maximum light, choose a type with a high visual light transmittance value or, to cut glare, with a lower light transmittance value. To cut heat gain, select glazing with a high shading coefficient. Glazing with a high UV value will block nearly all furniture-fading ultraviolet rays.
RELATED MEASURES
But what if you're not building or remodeling? Of course, there are a number of ways to cut electricity used for lighting. Turning off lights that aren't being used is a big one. Another is converting standard incandescent light bulbs to highly efficient compact fluorescents. Compact fluorescents use from about one quarter to one third as much energy to produce the same amount of light as a standard incandescent bulb (a 20-watt compact fluorescent will give you about the same light as a 60-watt incandescent). Though most cost considerably more than conventional bulbs, they last up to thirteen times longer which, combined with the energy savings, makes them a long-term good buy.
If you want to get more natural light into areas that are away from windows, clerestories, atria or skylights, there are a few daylighting techniques that can help. First, try to bounce natural light off the ceiling. To do this, a window located close to the ceiling works well. Louvers or operable blinds can direct light, too.
You can also install a "light shelf" horizontally across a window to ricochet light off the ceiling and back into the room.. This shelf, normally located about 12 inches from the top of the window for a standard 8-foot ceiling (lower for a high ceiling), may be mounted inside, outside or in both locations. It's usually painted with high-reflectance, glossy paint. Actually, any light-toned surfaces, including walls, ceilings and floors, will reflect light. If you want more light in rooms and glare isn't a problem, look for wall paints that have high reflectance values (ask your paint dealer for them) and floor coverings that are light in color.
The bottom line is this: If you'd like to get more natural light into your home, consider some of the basic daylighting materials and techniques available. Thoughtful, controlled use of glazing combined with a few simple light-enhancing techniques can make nearly any home sparkle with natural light.
WINDOW PLACEMENT
Of course, daylight originates at the sun. But more specifically, the daylight that enters a building may shine directly from the sun, bounce off of bodies of water, streets, buildings, or other surfaces, or come from the diffuse, day-lit sky.
Placing and sizing windows and figuring control measures, such as roof overhangs, requires a clear understanding of the sun's path. The sun's daily east-to-west arc changes throughout the year. At the summer solstice, June 21, the sun rises and sets farthest to the north, which means that it is higher during the day. At the winter solstice, December 21, the sun's arc is at its southern-most position, with a much lower mid-day elevation. The sun's angle at any given time of the day depends on your latitude. The further north you live, the lower the winter sun will be in the southern sky.
Whether a window faces north, east, south or west makes a big difference in the type of light it receives.
If you want morning sunlight to spray across your breakfast table, your breakfast room window should face east.
Light from the south is bright and direct; solar houses are oriented to the south for maximum heat gain. South-facing windows are often located beneath eaves or roof overhangs that block the high, intense summer sun but allow the warmth of the lower winter sun.
Western sun can be intense and glaring. Controlling it is more difficult because, as the sun sets, its low angle dips beneath eaves and overhangs. Shades, blinds or glare-resistant glazing are generally required. It's also helpful if deciduous trees are planted on the west side of a house--their spring-and-summer leaves block unwanted heat, then when the leaves drop in the fall, the trees allow the sun's warmth and light.
North light, never direct from the sun, has cool, bluish hues because it comes from the sky. Because it's constant, north light is favored for artists' studios and the like.
Be sure any architect or builder you hire will take all of this into account when planning your house's window placement; ask for references and call previous clients.
--Don Vandervort
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