Three red lettuce (Lactuca sativa L.) varieties, Red Rapids, Lollo Rosa and Falbala, were grown in greenhouse and subjected to varying levels of light using shade nets two weeks before harvest to determine the effect of these conditions on the antioxidant profile of the plants. When lettuce was exposed to increasing light intensities, i.e. very low light (VLL), low light (LL), medium light (ML) and high light (HL) conditions, leaf growth was enhanced specifically in Red Rapids and an increasing trend in total phenols (TP) and total anthocyanins (TA) was observed. These findings were associated with the enhanced radical scavenging activity in these varieties. The activities of the enzymatic antioxidants superoxide dismutase (SOD) and catalase (CAT) were also increased at ML and HL as compared to plants under VLL and LL. Ascorbate peroxidase (APX) activity, on the other hand, only increased at HL in Red Rapids and Lollo Rosa. Varietal differences were observed with the non-enzymatic antioxidants evidently higher in the deep red varieties while the antioxidant enzymes were higher in Red Rapids at higher light conditions. This research demonstrated that growing red lettuce at ML and HL two weeks prior to harvest increases the synthesis of health-promoting antioxidants in the fresh produce. This method offers a feasible strategy to increase the market value of the crop.