Rising up over the spinning and clacking machines in the Prince Street Technologies factory is a 60- x 20-foot picture window. Placed in the south wall, the window commands a view of the "Georgia prairie" natural landscaping that surrounds the carpet manufacturer’s mill in Cartersville, GA, and together with 32 skylights fixed into the roof provides daylight for the workers on the open 160,000-square-foot mill floor. The use of daylight as supplemental lighting, say the owners, has made a world of difference to the employees. Meanwhile, in the hallways, offices, and showrooms of the facility, daylight streams in onto richly colored carpet samples.

"The workers love it," said Frank P. Boardman, manager of creative services for Prince Street. "They love the light, and they love to see what’s going on outside. It’s made an immense difference in attitude." In fact, before the company moved to the new facility it averaged 20 worker’s compensation cases per year. In the three years since Prince Street relocated to the new, more spacious and daylit facility designed by Atlanta-based Thompson, Ventulett, Stainback & Associates, the company has had only two cases — a decrease Boardman feels is very much due to the presence of daylight.

Stories such as this indicate the immense promise of daylighting, and are circulating in the architectural community like modern day cries of gold in the hills: A post office in Reno, NV, whose employees sorted more mail under natural light; a Walmart in Kansas where a daylit area of the store had a spike in sales and happier employees; companies that won’t release information on their daylighting-borne productivity because of the "competitive advantage" it provides.

The stories are true, however, and the use of daylight as both an energy-efficient lighting source and an agent of increased occupant happiness and productivity has been documented in numerous case studies around the country. In fact, according to the U.S. Green Building Council’s Sustainable Building Technical Manual, well designed daylighting can reduce lighting energy use by 50% to 80% and increase worker productivity up to 15%.

The question remains, then, why daylighting has not become a standard practice by architects and lighting designers. The answer is, of course, not an easy one.

What Good the Sun?

There is still hesitance in the building industry to embrace daylighting as a lighting source, and some question whether daylight can ever light office space as effectively as the old standby, the electric lamp. Dr. Mark Rea, director of the Lighting Research Center at Rensselaer Polytechnic Institute and a professor of architecture, is one expert who feels that although daylighting has productivity benefits, its role in providing reliable, inexpensive general lighting is limited at best. "An exterior view is important for a species that likes to know what’s going on outside. But daylighting is lousy for functional lighting, unless you do something extremely expensive," said Rea, who added that today’s office buildings do not allow for ceiling heights much past 10 to 12 feet, which, in turn, limits the amount of floor space that can be lit to around 10 feet from the windows. Light shelves, roof monitors and other measures "are just too expensive" for the average building owner, he observes.

Others are just as adamant about daylighting’s potential, such as Alexander E. Othmer, manager of Florida’s Energy Conservation Assistance Program (ECAP) and a certified energy auditor. As manager of ECAP, Othmer has helped small businesses in Florida become more efficient and save money by providing loans and assistance for energy efficiency upgrades. According to Othmer, 29 Florida businesses that installed daylighting systems with his organization’s help reduced daytime electric lighting consumption by an average of 93% while still achieving an average of 160 foot candles of light with a color rendering index (CRI) of 98 at work surfaces. In one 8,000-square-foot printing press facility, a passive solar daylighting system that consisted of "light tubes" (see above) supplemented an existing array of fluorescent lights that produced 7 to 10 foot candles. After the installation of the passive solar lighting, light levels increased an average of 225% with an effective lighting and air-conditioning savings of $2,500 per year.

And both sides are passionate and even secretive at times over a topic that is continually debated and discussed in conferences and meetings around the country. One lighting design firm in Colorado was adverse to being interviewed about the subject, even though it had repeatedly used daylighting to increase building and occupant performance at no increased first cost to building owners. The hesitance resulted from the designer’s fear that an ill-conceived story article on the subject would damage any clout daylighting might gain among an intensely skeptical design community. "When you discuss daylighting, if you don’t address all the things that go into it — what it does to the exterior envelope, what it does to lifetime maintenance, and at least a dozen other topics — then [the architectural community] will think you didn’t think of them and shoot holes through it," said the designer.

The Evidence Looks Good

It’s hard, however, to shoot holes in some of the case studies that have shown daylighting to be not only economically feasible but highly desirable due to it’s affect on energy savings and occupancy health.

In a report issued in May 1996, researchers from Berkeley, CA-based Lawrence Berkeley National Laboratory documented the successful use of daylighting techniques in the retrofit of the single story Palm Springs Chamber of Commerce in Palm Springs, CA. The entire retrofit — which included T8 lamps with dimmable ballasts and accompanying photosensors, an innovative skylighting system, and heat gain-reducing mechanical measures like glazing and spectrally selective windows — reduced annual electricity consumption by an estimated 47% and achieved favorable comments from occupants, who were often able to work with no electrical lighting at all. Although the project was not cost effective due to the use of custom-made materials, the main purpose of the demonstration was to prove the effectiveness and energy efficiency of daylighting.

Using daylight, however, does not mean extravagant first costs. The Utah Department of Natural Resources office building in Salt Lake City, for instance, utilizes daylighting as an integral part of an energy-efficient design that saves $50,000 dollars a year over a reference-case building. Designed by Salt Lake City-based Gillies Stransky Brems Smith Architects and completed in the summer of 1996, the building cost only 3% more than a baseline building and has a payback period of six years. Daylighting features include a long east-west axis, low-e windows, an open floor plan, interior clerestory windows, dimming ballasts, and exterior and interior light shelves on the south facade. These measures helped reduce the lighting load by 51%.

One of the more famous examples of the benefits of daylighting is a series of schools built in Johnston County by the Raleigh, N.C.-based architecture firm Innovative Design, Inc. By replacing much of the electric light demand with natural light from roof monitors and view glass, the architects provided between 22% and 64% energy savings over typical neighboring schools. And according to a study by the architects, students who attended these schools out-performed students in comparable non-daylit schools by 5% to 14%. "It’s proven that full spectrum lighting is best for creative, good learning," said Gary B. Bailey, principal and co-partner at Innovative Design. "Every architect should be doing this if they’re going to build good learning spaces." (In fact, according to a study conducted in Alberta, Canada, students in full spectrum light not only did better but actually grew taller and had less dental decay.) The daylighting measures did not mean inflated budgets, either. In the Raleigh-based Durant Road Middle School project, completed in June of 1995, the total cost of the daylighting features was $230,000. But after subtracting the first cost savings due to downsized mechanical systems and chiller, the net cost was only $115,000 — less than 1% of the construction budget. All of Innovative Design’s schools achieved a payback in under three years’ time.

Proper daylighting design can make a big difference in residential homes too, even though some might assume that because of small footprints and numerous windows most houses do not need special attention. For instance, many times a client who is building in a scenic area will want large windows on one wall for a wide view. Although this brings in lots of daylight, it can cause an uncomfortable brightness in a room. By using clerestory windows — smaller, operable windows placed high on a wall — on the opposite side of the room, an architect can not only balance light in the room and reduce further the need for electric lamps but also promote a "thermal siphon" by allowing hot air to escape through the high windows during the summer months.

But much of the potential for energy savings from daylight harvesting remains in the commercial sector, and it is there where designers are confronted with numerous design challenges and technological limitations.

Addressing the problems

George Loisos, the architectural program coordinator for the Pacific Gas and Electric (PG&E) Center in San Francisco, teaches a course on daylighting for architects and has been involved in numerous daylighting research projects. According to him, "we are at a peculiar point where the technology for predicting and controlling daylight is quite advanced," he said, adding that the potential for energy savings due to daylighting is "phenomenal." But a few crucial problems hold back the industry at large from utilizing daylight. The first is the lack of readily accessible tools for architects who want to design daylit spaces quickly and easily. The second is the status of a new generation of daylighting controls, which are extremely efficient in simple installations but are only now becoming adept at fine-tuning daylight and drawing it deeper into a building, "a process that is more complicated by several scales of magnitude," he explained. The third, and perhaps most difficult, is inertia from building developers — "who still value buildings according to standards made in the seventies" — and architects who are hesitant to take on the challenge of using anything other than an electric lighting source.

As for the complexity of computer-based tools, Loisos sees this as changing relatively soon as programs that simulate daylighting and provide valuable data on a building design are becoming more numerous and easier to use. PG&E will soon release a new version of Radiance — one the most powerful modeling programs for daylighting applications available. The complex program once required a user who was part computer hacker and part physicist, but the new program will have a user-friendly interface that makes the modeling process easier and quicker. And the easier the software, the more plausible daylighting design becomes, explained Loisos, because for large projects, "the only practical way to design these is through computer simulation."

One recent project that went through an extensive modeling process for it’s daylighting design was a corporate campus for The Gap Inc. in San Bruno, CA. Designed by Charlottesville, VA-based William McDonough + Partners and completed just this past fall, the building is a mix of energy efficiency and sustainable design. Composed of three modules, each with a 30- x 90-foot roof monitor enclosing an interior courtyard, the entire complex is designed so that any office area is at most 22 feet from a source of light.

The design process of The Gap Building involved computer simulations and extensive analysis of physical models in diffuse daylight and heliodon labs. And although The Gap paid more for a finished building that featured daylighting and other green features, the company did an extensive cost-benefit analysis to measure the amount of savings those features would provide. "They definitely took into account the payback period on the investment," said McDonough’s Kevin Burke, project architect for The Gap Building. "They were interested in a payback of under 10 years, and the building came out a lot better than that."

Another major concern for any architect who would like to bring in more daylight is the heat gain and glare problems that arise. More sophisticated products that mitigate the effects of sunlight on a building’s envelope are on their way to mass use. According to a report by LBNL, many labs are producing "exciting new optical materials" that can dynamically change a window’s thermal conductivity, optical properties (such as light transmission and reflection according to wavelength), and the direction and appearance of the light. Linking this and other kinds of dynamic systems such as automated blinds and photosensor-linked dimmers into an "integrated" system controlled by computers could generate large energy savings and increase employee comfort and health.

A test at the Federal Office Building in Oakland, CA, by an LBNL team used a prototype automated venetian blind system in conjunction with daylight dimming controls to achieve a 22% to 86% lighting energy savings and a daily cooling load reduction of 22% to 24% — with high worker satisfaction and few complaints. Stephen Selkowitz, head of Building Technologies Program at LBNL, explained that this particular system demonstrates the effectiveness of an integrated daylight control system. "Many times control systems are installed as pieces: someone puts in the shading system, someone puts in the lighting system and someone else puts in the window system, and they don’t think of it as a complete system," he said. LBNL is now looking for a manufacturer to supply their system as a whole, "and offer with it a simple design tool or guidelines so when someone specs and installs the system they do it right," said Selkowitz.

Using even the common photosensor, however, is still less than a simple and quick affair, and architects and researchers have mixed opinions whether dimming controls are worth the investment. According to Dr. Rea, not only can installing the equipment drive up initial construction costs, but building owners who are continually called to adjust the sensors often simply fudge the settings so the lights are continually on at full power — thereby avoiding further complaints (and negating any possible benefits). And in new buildings where an architect does attempt to use devices like dimmable ballasts and sensors, the systems are often value-engineered right out of a building when the squeeze is on to bring a project in on budget. A similar case happened at Prince Street Technologies, where the architects proposed a lighting system that would dim according to outside light levels — saving the company an estimated $15,000 a year in electricity costs — but because the system wasn’t in the original budget, it was left out in the end due to financial constraints. (The owners have since decided to install a dimming system, and expect to save 910,000 kilowatt-hours per year once the system is in place.)

Others have found success with photosensors, and are convinced of their usefulness. For architects like Bailey, who counts on the sensor to bring lighting heat loads down and achieve energy savings, the initial adjustment of sensors is negligible. "Initially we have to do a series of adjustments, but after that we usually don’t have any problems," he explains.

New York-based lighting designer Hayden McKay, meanwhile, feels that occupancy sensors are superior to dimming controls in some situations: "In perimeter individual offices, it’s actually much cheaper to automatically turn the lights off when nobody is there instead of dimming them whether the room is occupied or not," said McKay. "In that situation a cost-benefit analysis shows the occupancy sensors preferable to dimming."

Another snag to the proper use of daylight, says Nancy Clanton, lighting engineer and president of Boulder, CO-based Clanton Engineering Inc., is that many times engineers "duplicate daylight," not only neglecting its use but actually overlighting an area with electrical light as a quick hedge against future demand. This over-engineering is possible because inhabitants can work under lighting conditions that are far in excess of what’s needed. "If you overheat, people complain. If you overlight, nobody really cares."

Clanton’s complaint hints at a deeper problem, which has been addressed by the work of LBNL’s Dr. Sam Berman. According to Berman, the common unit used to measure light levels, the lumen, is inadequate because it does not properly take into account the physiology of the human eye. The eye perceives "scotopically enhanced" light — light with a substantial blue-green spectral content — as being brighter than light with lower spectral content but of the same intensity. Not only do higher temperature, higher CRI lights provide better light at fewer lumens, but daylight, being high in the "scotopic" range, becomes an effective lighting source unrecognized by engineers relying on light meters and the inaccurate lumen. "Architects and engineers continually muddy the waters by trying to compare the new technologies [of daylighting] to old prescribed formulas that are used to calculate standard light levels," said Othmer, who used Berman’s work in his own tests on daylighting.

Helping Others See the Light

Despite the problems with controls and measurement and the lack of easy-to-use tools, the biggest hurdle for those who wish to implement daylighting is the lack of knowledge by building owners and architects of the benefits it provides. In the end, it will be buildings themselves that prove daylighting’s worth. "We know an awful lot, we have a lot of equipment, but we’ve implemented extraordinarily little. It’s the projects around the country that are going to make the difference," said Loisos. To help these projects along, many organizations are providing information and tools to assist daylighting design.

One organization helping to demonstrate daylighting’s potential is the Golden, CO-based National Renewable Energy Laboratory (NREL). Through its Exemplary Buildings program, NREL helps architects and builders design efficient buildings and to test those buildings once completed. To qualify as an exemplary building, a building must (among other requirements) use solar technologies to satisfy at least 75% or more of the building’s energy demand. Much of this savings comes in the form of daylighting.

NREL’s Thermal Test Facility (TTF) is one of the programs’ star buildings. The TTF building has numerous clerestory windows that light the entire open-space facility, while simultaneously protecting interiors from strong, summer light. Motion control and light sensors control electric lighting to supplement daylight. In total, daylighting and other integrated energy efficiency features in the TTF reduce energy use by 70%. Other buildings in the Exemplary Building program include the St. Benedict’s Child Care Center in Louisville, KY, the Grand Canyon House in Grand Canyon, AZ, and the Emergency Services Building in Valmeyer, IL.

Other organizations are assisting daylighting design as well. In Berkeley, CA, LBNL houses a 24-foot-diameter sky simulator to test scale-models for daylighting performance. In Seattle, The Lighting Design Lab assists designers by supplying a mock-up room and a daylighting lab, as well as experience and lighting expertise. For example, the Lighting Design Lab helped local manufacturer Northwestern Industries design and model a 60,000-square-foot addition to a production facility. The addition included diffusing skylights to improve lighting levels and insure a safe workplace, as well as cut lighting costs. (In a report on the project, the lab quoted a worker saying "coming into the new building was like moving out of dungeon into daylight.")

New Products

The last few years have seen an increase in the popularity of "light pipes," although many would be surprised to know that the design was patented in the late 1800s. Basically, a light pipe consists of a long pipe with a reflective inner surface that channels light from a rooftop light-collecting dome through an attic (or other building areas) to an insulated diffuser lens. The lens, mounted in a ceiling fixture, then disperses light throughout a room. The system is meant to offer a cheaper and easier alternative to skylights, and as a supplement, or even replacement, to electrical lighting.

So why the 100-year wait? It seems that manufacturers only recently began to increase the performance of the basic design by utilizing reflective material initially developed for parabolic reflectors. According to the president of one light pipe company, most producers have only gotten their marketing machines rolling in the last three years. There are four large-scale manufactures of the product, with one manufacture, Solatube, claiming a quarter million units installed worldwide.

And interest is growing. "For every unit we sell off of advertising, we get at least three referrals," said Lou Ann Powell, CEO of Sarasota, FL-based Tubular Skylight, one of the first manufacturers of modern light pipes. Powell’s product has been installed in the Webster Elementary School in Webster, FL, and in NASA’s John F. Kennedy Space Center. The product was tested by NASA and found to have an R-22 insulation rating and a CRI of 98.7.

Some architects prefer the pipes to skylights, and not only because of cost. "They don’t have the problems that skylights do," said Mike O’Brien, Principal of O’Brien and Associates, an architecture firm in Portland, OR. "They don’t have the leak problems or lack of insulation. Many times, it’s impossible to get workers to insulate skylight wells when they blow insulation into ceilings, so then the skylight ends up with condensation and mold on the inside." At a cost of around $500, he adds, the light pipes are an economical solution to daylighting needs. He warned, however, that the units are not an adequate source of light in rooms like bathrooms or kitchens where high-contrast, bright lighting is needed.

Other daylight-distributing products have mechanical additions that attempt to increase the amount of light collected from the sun through mirrors and lenses. Companies like Los Angeles-based So-Luminaire Daylighting Systems Corp. and Hampton Bays, NY-based DayStar Sunlighting Systems LLC, produce moveable mirror systems that are placed on a roof and actively track the sun to increase the amount of light that is collected and sent down through an insulated light shaft into a building space. Products from both companies have been used successfully in a range of applications, including grocery stores, offices and factory workspace.

On the skylight front, Andersen Windows Inc. of Bayport, MN, is planning to introduce a new commercial skylight that combines the best qualities of skylights and light bubbles. Set for release sometime next year, the skylight incorporates a Fresnel lens that collects more light for illumination than a standard skylight and at the same time distributes it more evenly into an interior. The light is also of higher quality than a plastic bubble skylight. "It gives you a view to the sky, a good color rendition and good distribution of light" says Dawn De Keyser, project manager at Andersen. The skylights have been tested at Walmarts in Lawrence, KS, and The City of Industry, CA, and just recently in July of last year at a Target store in Vadnais Heights, MN. Two more Target stores plan to install them this year on a test basis.