Don’t worry that strong lighting in supermarkets is bad for fresh vegetables. In fact, it can actually increase their nutrient levels.
In a United States Department of Agriculture (USDA) study, spinach was stored in clear plastic containers under fluorescent lights for three to nine days, which caused the leaves to synthesize more vitamin C, K, E and folate, as well as carotenoids such as lutein. After nine days, for instance, levels of folate and vitamin K rose by as much as 100 percent. In contrast, nutrients in spinach that had been stored in the dark declined or were unchanged.
These findings should also apply to many other fresh leafy vegetables, as long as they are kept cool and moist.