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U.S. Department of Energy Energy Efficiency and Renewable Energy

CBEA Light-Emitting Diode Refrigerated Display Case Lighting Specification

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Light-emitting diode (LED) technology is advancing into new categories of white light applications, including refrigerated display case lighting. In September 2009, a Commercial Building Energy Alliances (CBEA) working group formed to investigate the use of LED refrigerated display case lighting for retail buildings.

Although LED technology is progressing, some barriers exist to mass adoption of LEDs. At present, tested products are available from a limited number of suppliers, performance in the later years of the product's lifetime can only be estimated, and LED luminaires are relatively expensive on a first-cost basis.

To address these issues, members of a CBEA working group investigated the use of LED refrigerated display case lighting, in coordination with the U.S. Department of Energy and the Pacific Northwest National Laboratory (PNNL), and have:

  • Surveyed candidate products and compiled available performance data
  • Developed product performance specifications and evaluation procedures based on CBEA member needs.

Performance Specification

The following points detail information about the specification:

  • Efficacy is evaluated in terms of the actual luminaire(s) load imposed on a given power supply. Power supply efficiency is negatively affected by under-loading, which occurs when the total wattage of luminaire(s) fed by a power supply is significantly lower than the power supply's rated wattage. This effect is captured via the power supply schedule, which lists the efficacy of every configuration installed on a given project.
  • Useful life is evaluated in terms of warranty period, not on manufacturer projections. Without IES TM-21, which is still in development, there is no standard means of extrapolating rated lifetimes from LM-80 data. Specific warranty requirements allow for objective comparisons of manufacturer claims.
  • LED device manufacturers are required to perform industry-standard reliability testing
  • Rather than relying on field measurements, luminaires are tested in a controlled independent lab environment per LM-79 for consistency and slightly understated output
  • Since many luminaire designs preclude the use of standard far-field photometry in these applications, near-field photometry is mandated to accurately assess uniformity
  • To ensure acceptable rendition of saturated colors in product packaging, requirements for special indices R9 through R12 are included as a supplement to the color rendering index (CRI)
  • While a recommendation for minimum light levels is offered, criteria are structured to allow for flexibility in the selection of appropriate light levels on a project-by-project basis.

Several luminaire types and corresponding case geometries are addressed, as indicated in the figure below:

This graphic consists of three separate images. Left Image: Cut out of enclosed case with luminaires installed vertically on mullions. Caption reads: 1. Symmetric (middle) 2.Asymmetric (case ends). Below the image it reads: LED luminaire typically replaces a fluorescent luminaire with one-lamp cross-section. Middle Image: Cut out of open case with asymmetric luminaires installed horizontally. Caption reads: 3. Down (under canopy) 4.Up (floor of case, like #2). Below the image it reads: LED luminaire typically replaces a fluorescent luminaire with two-lamp cross-section. High-end retailers will sometimes have a third lamp in the canopy or add another lamp at bottom of case. Right Image: Cut out of open case with luminaires installed horizontally. Caption reads: 5. Under-shelf (like #1) 6. Under-canopy (like #3). Below the image it reads: LED luminaires typically replace fluorescent luminaires with single-lamp cross-section under shelves and two-lamp cross-section under canopy.

The following table shows some of the benefits of using LEDs in refrigerated cases, as compiled by PNNL:

Product Feature

LED Benefits

Uniformity

Smaller sources allow for improved beam control and even illumination

Visual Comfort & Focus

Stray light and glare are reduced, allowing focus on merchandise

System Efficacy
  • Inherent directionality of LEDs reduces internal losses
  • More light is able to exit the luminaire
  • LED efficacy improves at lower temperatures
  • Fluorescent efficacy worsens at lower temperatures
  • No light is wasted in non-uniform "hot spots"

Dimmability
  • Wide dimming range allows for increased energy savings
  • Light output can be smoothly controlled by occupancy sensors for minimal customer distraction
  • Light levels can be fine-tuned to balance appearance and energy savings

Maintenance

Very low maintenance expected due to long life and durability

Disposal

Contains no mercury