Supermarket freezers may soon look a lot brighter while demanding less energy, thanks to LED lighting. A recent study from the Lighting Research Center at Rensselaer Polytechnic Institute found that shoppers overwhelmingly prefer LED lighting inside supermarket freezer cases when it comes to merchandise appeal and the brightness, comfort, and evenness of the freezer lighting. And now, some freezer case manufacturers are planning to include LED lighting in their products.

Freezer cases installed in supermarket in Albany, NY area. The LED Freezer on the right shows better lighting uniformity than the identical freezer with fluorescent lighting on the left.

A 2002 laboratory study conducted by LRC researchers had concluded that white LEDs would be ideal for lighting freezer and refrigerated display cases because they can improve the merchandize lighting and lower the energy cost. To further validate the findings, the LRC evaluated a prototype four-door, LED-lighted freezer case installed at an Albany, N.Y., area Price Chopper supermarket. The two-year field study was sponsored by the New York State Energy Research and Development Authority (NYSERDA). The freezer, built by Tyler Refrigeration, was outfitted with several 1-watt high-power white LEDs in a lighting system designed by GELcore, GE Consumer & Industrial’s Cleveland-based LED business.

Over the course of the study, the LRC investigated shoppers’ preferences for an LED-lighted freezer case compared to a matching freezer with conventional fluorescent lighting. LRC researchers also analyzed sales data and measured the energy usage of the two test freezers, which were installed side by side next to the existing freezer cases in the frozen-food aisle.

Shoppers give high ratings to LEDs
Overall, shoppers stated that products were more appealing and the lighting was brighter, more comfortable to look at, and more even inside the LED freezer.

More than 300 shoppers were asked their opinions about the lighting of the two test freezers. In the first part of the study, the average illumination on the face of the merchandise was kept at similar levels in both the LED and the fluorescent-lighted freezers. More than 86% of shoppers selected the LED freezer as the one they liked the most. Then the average light level inside the LED freezer was dimmed and the survey was repeated. Even after dimming, 68% of shoppers preferred the lighting in the LED freezer.

LRC Director of Research N. Narendran, Ph.D., believes that the LED freezer got high marks because of the more uniform light distribution and the sparkle the LED lighting created within the lighted space.

“Even though the average illuminance level of the fluorescent-lighted freezer was slightly higher, the uneven distribution of the fluorescent lighting led to areas at the center of each glass door that had roughly half of the average LED light level,” Dr. Narendran said. The light levels were more uniform all the way across in the LED freezer, while the fluorescent freezer had dark areas at the center of the case. “This likely led to the perception that the LED case was brighter,” he said.

Chris Bohler, Ph.D., director of technology systems at GELcore, added, “At GELcore, we are not at all surprised by this overwhelmingly positive reaction from consumers. It’s consistent with the response we received from the marketplace when we debuted our GE LED refrigerated display lighting solution.”

Narendran also noted that studies have shown that higher (“bluer”) color temperatures can also bring a perception of greater brightness. The LEDs had a correlated color temperature (CCT) of 5500 kelvin (K), while the fluorescent lamps had a lower CCT of 3500 K.

No effect on sales
A statistical analysis of sales in the test freezers compared with sales of the same products at a control store located nearby showed no significant difference in sales due to the change in lighting. Narendran says this finding is consistent with previous lighting-and-sales studies conducted by the LRC and by other researchers.

Energy usage at ‘threshold’ level
Narendran says that while this particular test freezer was not built with the intention of showing immediate energy savings, a real potential exists now for LEDs to save energy in freezers illuminated at an acceptable light level. “Because white LEDs have evolved since this study began, they now have more than two times the efficiency of the LEDs used in the test freezers.” LEDs available today can match the energy usage of fluorescent lamps in supermarket freezer display cases. And as LEDs become more efficacious, they will eventually provide greater energy savings over fluorescent, he says. They are also expected to compete cost-effectively with fluorescents for freezer illumination. Some retailers are already taking notice of LED lighting. “Wal–Mart expects to net up to 66 percent energy savings and $2.6 million in energy-cost savings, compared with fluorescent technology, when it finishes installing the latest LED refrigerated display case lighting from GELcore in 500 U.S. stores,” says Chris Bohler.

Problems with fluorescent
Fluorescent lamps are an efficient source of lighting for many types of applications. But within refrigerators and freezers, their quality can be poor. Cold temperatures cause the mercury vapor pressure inside fluorescent lamps to drop, leading to reductions in light output of up to 25% under typical conditions found inside a beverage cooler display case. In contrast, LEDs do not suffer the same fate. In some situations, their light output improves in colder environments. Poor mounting location and a lack of optics also can hinder light output and the uniformity of fluorescent lamps.

Future opportunities for LEDs in freezers
LEDs can not only save energy, but they also last much longer than fluorescent lamps in freezer environments, providing a much lower lifecycle cost for owners. The flexibility of LEDs allows them to be mounted in various locations (e.g., along mullions, along the length of shelves, etc.) and illuminate products evenly by using several distributions to throw light throughout the case. Their flexibility also means that the interior shape of freezers could be redesigned for more efficient cool-air flow, decreasing the power needed by compressors and other cooling equipment. “The maximum potential of LED technology in this application will be reaped if the whole freezer is redesigned and shaped for styling and optimizing cooling within the cases,” Narendran advises.

Several manufacturers now offer commercial LED systems for lighting freezers and refrigerated display cases.

Rick Waldron, senior product manager for Tyler Refrigeration, a unit of Carrier, says Tyler Refrigeration was pleased to participate in this study and agrees that LEDs offer an appealing, more even light wash at reduced energy consumption as compared to fluorescents. “Our customers also like the fact that the maintenance has been significantly reduced by eliminating the need for regular lamp and ballast replacements,” he says.

Waldron says that because LED technology has been changing rapidly over the last 12 months, customers are now evaluating the trade-off between sufficient LED light illumination and energy savings. He added, “We have also been testing various LED versions in our lab and plan to have LED lights in our door case production in the second quarter of 2007.”