LED technology saves energy, attracts shoppers to retail windows

Emerging lighting technology for retail
Retailers use lighting in display windows to illuminate merchandise, attract attention, and even send a message about the quality of their store. To get the most impact, Dan Frering of the LRC says stores often use plenty of high-wattage accent lights to highlight mannequins and merchandise. "This creates visual interest and makes the merchandise stand out from the background," he says. This technique is effective but when used 12 or more hours every day, the energy consumption and costs can climb. The United States Department of Energy says lighting is the biggest energy expense for retailers, accounting for 37 percent of total energy use in U.S. retail buildings.

This energy problem could be eased with new types of efficient lighting now taking off. The LED, a tiny semiconductor that emits light in a range of vivid colors, is commonly found in traffic signals, exit signs, and electronic displays, but recent improvements have prompted lighting specialists to look at new ways to use LEDs for illumination. The potential benefits, including better efficiency and longer life (up to 50,000 hours, or 40 times longer than conventional incandescent lamps), have catalyzed global research efforts in LED and solid-state lighting technology. Colored LEDs, in particular, have become popular as an architectural and display lighting option because they offer flexibility to designers and consume half the energy of traditional incandescent sources with color filters.

Experiments show potential for LED lighting
The Los Angeles Department of Water and Power (LADWP) sponsored the LRC field study to determine whether energy-efficient, colored window lighting could draw the interest of shoppers, reduce energy consumption in store windows, and maintain or improve retail sales. LRC researchers installed custom, slim-profile LED fixtures in the windows of three stores owned by a popular clothing retailer found in Los Angeles area shopping malls. To cut energy consumption by 30 to 50 percent in each window, they eliminated all general fluorescent lighting, reduced the number and wattage of halogen accent lights, and added LED systems to create colored backgrounds for interest. The researchers tested different window display and lighting scenarios over an eight-week period and surveyed shoppers about the attractiveness, visibility, and eye-catching ability of the windows. (Lighting inside the stores remained unchanged.)

Frering says, "We designed the window lighting to create impact and contrast with color, instead of high light levels. This allowed us to reduce the amount of accent lighting and cut energy use."

Shoppers approve
After eight weeks and more than 700 surveys, the results were in: The colored LED lighting was a hit with shoppers. They preferred the colored LED window with a 30 percent reduction in power over the typical high-energy lighting design. The survey results also showed:

• 74 percent of shoppers found the new lighting design to be eye-catching.
• 84 percent agreed that the LED display windows were visually appealing.
• 91 percent confirmed that the reduced accent lighting did not diminish the visibility of the window mannequins and merchandise.

Cutting the lighting power consumption further to 50 percent in each window resulted in no significant difference in shoppers' opinions compared with the typical lighting, and a lower opinion compared with the 30 percent reduction.

Sales data gathered by the retailer showed no significant change in sales at the three test stores during the study period, even with a 50 percent reduction in power consumption. Sales were compared with the same weeks for the previous year and with comparable stores owned by the retailer.

Savings and payback offer incentive
The potential savings and payback that can come from using alternative LED lighting designs may lead retailers to consider these new concepts. The LRC estimates that the average store can reduce power demand from lighting store windows by up to 1 kilowatt, saving 5,500 kilowatt-hours per year.* Given current LED lighting system costs and estimated energy and maintenance savings, the typical system payback is less than two years.

"Helping our commercial customers save energy while increasing the effectiveness of their retail display lighting is a good thing," said Lillian Kawasaki, assistant general manager of environmental affairs and economic development for LADWP. "As more lighting designers become familiar with the value of LED color enhanced display lighting, we can expect to see significant energy savings in Los Angeles and across the nation."

However, a successful switch to LED lighting is not as simple as replacing one type of lamp for another in the same socket. LRC Director of Research Nadarajah Narendran, Ph.D., says that many lighting applications can benefit from LEDs if the implementation is appropriate and takes advantage of the LED's characteristics and performance. This often means finding creative design solutions. "Instead of trying to replace conventional technology with the new in a given application, it is better to identify alternate lighting solutions that exploit the strengths of the new technology, even if it breaks tradition," he says. "That was one of our goals with this field study."

The Lighting Research Center conducts numerous projects in the emerging field of solid-state lighting. For more information about LEDs, solid-state lighting and their applications, visit www.lrc.rpi.edu/programs/solidstate.

The LEDs and drivers used in the field study were donated by Lumileds Lighting and Advanced Transformer Co.

* Based on 2,000 watts of window lighting and 14 hours of use per day.

About Los Angeles Department of Water and Power
The Los Angeles Department of Water and Power (LADWP), the largest municipal utility in the nation, was established more than 100 years ago to deliver reliable, safe water and electricity supplies to some 3.8 million residents and businesses in Los Angeles. The Department provides its 640,000 water customers and 1.4 million electric customers with the best service and lowest cost resources available. Visit www.ladwp.com.

About Rensselaer Polytechnic Institute
Rensselaer Polytechnic Institute, founded in 1824, is the nation's oldest technological university. The university offers bachelor's, master's, and doctoral degrees in engineering, the sciences, information technology, architecture, management, and the humanities and social sciences. Institute programs serve undergraduates, graduate students, and working professionals around the world. Rensselaer faculty are known for pre-eminence in research conducted in a wide range of fields, with particular emphasis in biotechnology, nanotechnology, information technology, and the media arts and technology. The Institute is well known for its success in the transfer of technology from the laboratory to the marketplace so that new discoveries and inventions benefit human life, protect the environment, and strengthen economic development.