Refrigerator and freezer grocery case lighting was one of the first lighting applications in which the LED alternative to fluorescent tubes gained a foothold. LEDs have several distinct advantages when used in grocery display case lighting. LEDs offer reliable operation and long-life in the cold environment. Unlike the traditional fluorescent tube case lights they replace, LEDs generate little heat which decreases refrigeration electrical costs. LEDs also provide directional light which can be better focused on the merchandise to give the best visual appearance for the retail customer. Given these advantages, grocers were quick to adopt LED lighting for their cold display cases.
A three-year study conducted by the US Department of Agriculture in partnership with Sensor Electronic Technology Inc. has concluded that LED lighting in the ultraviolet-B spectrum can double the shelf-life of refrigerated produce. The study was conducted on strawberries in a tightly controlled refrigerated environment. The strawberries were held at 42˚F with a humidity level maintained between 94-98% under several different lighting conditions to test the effect of the lighting on the rate at which the strawberries decayed.
In the study, strawberries which were kept in total darkness exhibited both mold and decay after four days. Strawberries which were continuously under LEDs generating ultraviolet-C spectrum light were mold free after nine days but still showed visible signs of decay. Strawberries which were continuously under LEDs generating ultraviolet-B spectrum light were free from both mold and visible decay after nine days. The researchers also measured characteristics of the fruit such as weight, soluble solids, titratable acidity, and anthocyanin levels throughout the course of the experiment. The research team found “no significant change in the strawberry composition” in the UV-B lit berries, even after nine days. In comments about the study, Steven Britz, research plant physiologist with the Agricultural Research Service of the USDA, said, “We are exploring the possibility that the UV effect involves the induction of defense mechanisms in the fruit itself in addition to inhibition of mold growth, since evidence indicates parts of the UV spectrum retard decay.”
Further research into the effects of ultraviolet spectrum emitting LEDs on other produce items such as lettuce and leafy vegetables is currently being conducted. However, expectations are high that this same preservation effect will be demonstrated again with other types of produce. This study has found that LED lighting can actually have a positive physical effect on the lit merchandise, in addition to the usual positive economic effects which are typically discussed when talking about display lighting applications. The ability to significantly extend the salability window of a very delicate and perishable produce commodity such as strawberries is one more great advantage of LED lighting for grocers.