Gracilaria cornea was exposed to different irradiance intensities (low, moderate, and high) and light qualities (white and white + blue) in experimental cultures. Photosynthetic physiology was measured through daily growth rate, maximum photosynthesis, maximum photochemical efficiency, pigment content (chlorophyll a, phycobiliproteins, carotenoids), and elemental content of carbon and nitrogen. Gracilaria cornea effectively acclimated to low irradiance conditions and displayed tolerance to moderate irradiance, whereas high irradiance resulted in the deterioration of thalli. A decrease in maximum photochemical efficiency and maximum photosynthesis rate under high irradiance conditions was observed. Pigment content decreased during the acclimation period at high irradiance levels but increased when blue light was added under moderate irradiance conditions. The antioxidant capacity decreased in thalli exposed to high irradiance conditions, whereas the addition of blue light increased antioxidant capacity. Overall, the combination of white and blue light stimulated the accumulation of all evaluated compounds in G. cornea. Interestingly, higher values for photosynthesis, pigments, and certain antioxidants were observed under low irradiance conditions. These findings enhance our understanding of the adaptation strategies employed by G. cornea, potentially leading to improvements in indoor cultivation and the control of chemical compound production for nutraceutical applications.