This report describes the process and results of a demonstration of solid-state lighting (SSL) technology combined with occupancy sensors in a set of upright grocery store freezer cases. The project was supported by the U.S. Department of Energy (DOE). A retrofit of freezer cases at a Eugene, OR Albertsons grocery store indicates a potentially successful application of light-emitting diode (LED) technology with additional energy savings from the use of occupancy sensors.
The test location is an aisle of freezer cases storing a variety of frozen food items at or just below 0 degrees F. The retrofit side of the aisle includes four five-door cases and two three-door cases facing into the aisle capped by similar cases on each end. The opposite side of the aisle contains a similar case setup. Each case is lighted with vertically mounted linear fluorescent lamps between doors. The store aisles were lighted with standard overhead strip fluorescent luminaires aligned parallel with the aisles, which are typically on 24 hours a day due to cleaning and stocking activities. The replacement LED lighting strips and LED drivers were supplied by LED Power.
The uniformity of light distributed within the case was evaluated and found to be generally comparable to the fluorescent system. It is commonly believed that the directional nature of LED light emission means that much higher uniformity can be achieved compared with the omnidirectional light emission of a fluorescent system. However, in product cases where widely varying package graphics and colors are the norm, the limited personal observation from this study revealed little noticeable difference due to varying distribution uniformity.
The logistics of arranging this comparison test did not allow for relamping of the existing fluorescent case lighting prior to the test and therefore a small portion of the apparent savings may be attributable to fluorescent lumen depreciation. It is more important to note that while the power consumed by the LED system showed a 61% reduction from that of the fluorescent system, a significant portion of the savings has resulted from a 36% reduction in illuminance as determined by relative measured levels before and after the retrofit. This 36% light level reduction accounts for more than half of the savings, which may have been alternatively accomplished with a retrofit of different fluorescent technology in the form of a lower output lamp and/or lower driving ballast. However, the complete retrofit demonstrated here that incorporates step dimming based on occupancy would be difficult with fluorescent technology, given the limited market offerings of specific dimming ballast technology.