Light and nutrients are among the most important factors for sustained plant production in agriculture. As one of the goals of the European Green Deal strategy is to reduce energy consumption, greenhouse growers focus on high-value crop cultivation with less-energy-demanding growing systems. This study aimed to evaluate the effect of fertilization at different light intensities on the growth of lettuce and basil and the activity of the antioxidant system. Sweet basil (Ocimum basilicum, ‘Opal’) and lettuce (Lactuca sativa, ‘Nikolaj’) were grown in a greenhouse supplementing natural light (~80 µmol m−2 s−1) with lighting at two photon flux densities (150 and 250 µmol m−2 s−1), 16 h photoperiod, and 20/16 °C day/night temperature in May (Lithuania, 55°60′ N, 23°48′ E). In each light regime treatment, half of the plants were grown without additional fertilization; the other half were fertilized twice a week with a complex fertilizer (NPK 3-1-3). The results showed that the antioxidant activity of basil was most affected by 150 µmol m−2 s−1 PPFD lighting and the absence of fertilization. Altered antioxidant activity in lettuce in the presence of 250 µmol m−2 s−1 PPFD additional light intensity and fertilization resulted in higher morphological parameters.