[Background] Marigold (Tagetes erecta L.) is the main source of the natural pigment lutein. [Methods] In this study, Marigold served as the experimental material for systematic observation of floral organ development. Based on floral morphology and lutein content, the full-flowering stage was identified as the optimal harvesting period. [Results] Under different light intensity gradients (30–1500 μmol·m⁻²·s⁻¹), the highest lutein content in petals occurred at ≈500 μmol·m⁻²·s⁻¹. Increased light intensities promoted flowering and enlarged flower diameter while significantly shortening the growth cycle. Transcriptome analysis revealed that light intensity variation markedly influenced the expression of genes related to metabolic pathways, plant hormone signal transduction, and carotenoid biosynthesis, and enriched transcription factor families including bHLH, MYB, NAC, and WRKY. Metabolomic profiling identified lutein esters, such as lutein dimyristate and lutein dipalmitate, as the dominant accumulated forms, with their contents positively correlated with light intensity; under high light, intermediate metabolites, including α-cryptoxanthin and zeaxanthin, were significantly up-regulated. [Conclusions] This study clarifies the molecular mechanism by which light intensity precisely regulates lutein accumulation through coordinated synthesis, esterification, and degradation pathways, offering a theoretical foundation for light-regulated cultivation of T. erecta L. and efficient lutein production.