This study investigated the effects of different light intensities (40, 100, 200, and 300 μmol·m⁻²·s⁻¹) on the growth, nutritional quality, and flavonoid accumulation of celery under hydroponic and full LED light conditions. The experiment was conducted over three harvest periods (S1, S2, and S3) at 15, 30, and 45 days after treatment, respectively. The results showed that light intensity significantly influenced the growth parameters of celery, with plant height and aboveground biomass increasing at 200 μmol·m⁻²·s⁻¹. This intensity also promoted the accumulation of chlorophyll, carotenoids, total phenols, vitamin C, cellulose, total flavones, and apigenin. Enzyme activities (PAL, CHS, CHI, and ANS) and gene expression (Ag3GT and AgFNS) were highest at 200 μmol·m⁻²·s⁻¹, leading to the highest anthocyanin content at this intensity. However, the highest apigenin content was observed at 300 μmol·m⁻²·s⁻¹. Overall, the study concluded that a light intensity of 200 μmol·m⁻²·s⁻¹ was most favorable for celery growth and nutrient synthesis.This study investigated the effects of different light intensities (40, 100, 200, and 300 μmol·m⁻²·s⁻¹) on the growth, nutritional quality, and flavonoid accumulation of celery under hydroponic and full LED light conditions. The experiment was conducted over three harvest periods (S1, S2, and S3) at 15, 30, and 45 days after treatment, respectively. The results showed that light intensity significantly influenced the growth parameters of celery, with plant height and aboveground biomass increasing at 200 μmol·m⁻²·s⁻¹. This intensity also promoted the accumulation of chlorophyll, carotenoids, total phenols, vitamin C, cellulose, total flavones, and apigenin. Enzyme activities (PAL, CHS, CHI, and ANS) and gene expression (Ag3GT and AgFNS) were highest at 200 μmol·m⁻²·s⁻¹, leading to the highest anthocyanin content at this intensity. However, the highest apigenin content was observed at 300 μmol·m⁻²·s⁻¹. Overall, the study concluded that a light intensity of 200 μmol·m⁻²·s⁻¹ was most favorable for celery growth and nutrient synthesis.