The use of skylights in supermarkets can result in substantial energy savings as photocontrols automatically adjust the electric lighting when adequate daylight is present. In stores such as Puget Consumer Cooperative Natural Markets, skylights are an integral part of the lighting design and offer an ambient environment.
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Challenge While roaming the supermarket aisles for bread, milk, eggs, and the like, many shoppers likely do not think twice about their surroundings. At stores across the country, however, customers might be noticing something different about their grocery trip, even if they cannot put their finger on the reason: daylighting. But how can grocery retailers successfully incorporate daylight into their stores—and, perhaps more importantly, why should they? Research over the past several years by the Fair Oaks, California–based Heschong Mahone Group studied the benefits of retail skylighting, and retailers currently employing these strategies are reaping the benefits.

Solution “People don't think a lot about lighting in general,” says Lisa Heschong, principal of Heschong Mahone Group, which provided the content and graphics for the knowhow series lighting design guide on retail skylighting, available at www.designlights.org/guides.html. However, while most customers might not realize that daylight is behind their improved shopping experience, Heschong adds, “They do make positive comments about increased visibility, how they're able to read fine print, and that they feel the stores are cleaner and more spacious. There's some sense of ambient conditions that they like.” That also goes for the employees working in daylit stores. “The most significant benefit [of daylighting] is certainly in customer and staff satisfaction,” says Lori Ross, director of store development for Seattle-based Puget Consumer Cooperative (PCC) Natural Markets. “Bringing the light inside is a great boost to the shopping and working environment. Daylighting creates a warmer, more intimate ambience.”

Aside from the ambient environment it creates, daylighting in single-story retail stores (including smaller retailers such as PCC and big-box retailers such as Wal-Mart) can provide other benefits as well, the most popular likely being energy savings, particularly as building owners begin to fully understand the impact and benefits of sustainable design approaches. “In the push for low-energy, zero-energy buildings, we have to do daylighting to get there,” Heschong says. “It's a fundamental component of any low-energy sustainable green design.”

Depending on factors such as economics and climate, Heschong says that supermarkets generally can see an attractive payback from daylight harvesting, which uses photocontrols to measure daylight levels to automatically adjust the output of electric light levels. “Because grocery stores tend to have high light-levels and operate seven days a week during all daylit hours, that improves the equation for energy savings,” she explains. Joel Loveland, director of the BetterBricks Integrated Design Lab in Seattle, started working in 1999 with the supermarket chain Albertsons, headquartered in Boise, Idaho. “They were concerned about the cost of skylights,” he recalls. “They wanted to see the paybacks.” By redesigning the roof systems, the amount saved on the cost of the steel structure was more than the cost of the skylights. “It's a great integrated design story,” Loveland says. “When you look at things more holistically, really great high-performance ideas oftentimes have no cost premium.”

It is not uncommon to have to make adjustments to energy-saving approaches to get the most out of them—it is part of the process of trial and error. Energy performance at one PCC store, Ross says, showed smaller savings than the company had expected. However, modifications regarding the electric lighting are being implemented at a store currently under construction, where Ross anticipates higher savings, with up to 40 percent wattage reduction.

Jim Blomberg, president of Sacramento, California-based Sunoptics Prismatic Skylights, says a skylight “is nothing more than a light bulb.” Skylights generally are seen as the primary way to bring daylight into a retail space, which means good things for Blomberg's company as it is involved with companies such as Kroger, Wal-Mart, and Food4Less. “If used properly, [skylights] will do great things for saving energy,” he adds. Many architects will try to provide daylight through clerestories, sawtooth roofs, or other architectural forms, but Heschong says skylights are the most successful way to introduce daylight and make the most sense. One benefit she points out is that a horizontal skylight in a roof will let in more daylight than any other type of aperture. “On a cloudy day, you can have a skylight that's one-third the size of a window and letting in the same amount of light,” Heschong says. “On a sunny day, you are able to take advantage of the sun, from sunrise to sunset, all year long. Whereas with a vertical window, clerestory, or sawtooth it has a distinct orientation. It will receive sun some hours of the day and exclude it other hours of the day.”

Christopher Meek, daylighting specialist at the Seattle Integrated Design Lab, agrees with Heschong, pointing out that when conditions are overcast, the brightest part of the sky is directly overhead, making skylights a smart choice for supermarkets. “With the distance from one side of a store to the other, it's really impractical to bring in light from traditional windows,” he explains. “It's important to deliver that light from above.” Meek generally tries to design daylighting systems to provide about 60 percent of ambient lighting requirements during daylight hours. However, he notes that lighting power itself tends to be a small part of the energy-savings picture, which typically is the result of a combination of efforts. Jihad Rizkallah, vice president of design and engineering for Massachusetts-based Stop & Shop Supermarket Co., has discovered this over the years since first introducing daylight into Stop & Shop stores in 1999. “Daylighting was part of a holistic approach that included other energy-saving features such as more efficient refrigeration systems and more efficient HVAC systems,” he says. “It wasn't just one thing [contributing to energy savings], it was all three.”

When Stop & Shop installed skylights in the stores, Rizkallah recalls, the interior atmosphere became warmer. “Our older stores were lit using 400W metal halide fixtures, which were kind of harsh on your eyes,” he explains. “Daylighting provides you with a comfortable environment, and the combination of daylighting and fluorescent provides you with that.” About 80 to 90 Stop & Shop stores have skylights in them, featuring a daylight harvesting system that is used in conjunction with T5HO fluorescent lighting fixtures that can be dimmed down to 20 percent, Rizkallah says.

The Redmond, Washington, PCC store, which has achieved Leadership in Energy and Environmental Design (LEED) Gold certification, uses a three-step ambient light process that is triggered by light sensors on the skylights, Ross explains. The electric lights are either all on, half on, or all off based on the available daylight.

Electric lighting can be considered a cultural issue when it comes to retail, as Heschong points out that “in the past 50 or 60 years, we have come to expect that having the lights on means the store is open.” For stores with visible luminaires, such as direct systems, she says that expectation is even greater. With cove lighting or indirect lighting systems, however, people cannot see the light source, so they do not have the expectation for the light to be on. According to Heschong, lighting designers need to think about what, other than the electric lights, could be the signal that says stores are open and operating.