This is the approximate start date when Ibn al-Haytham began writing his most influential work, the Kitāb al-Manāẓir (Book of Optics). The book was written over a period of approximately ten years and covers a wide range of topics related to optics, including vision, light, color, reflection, and refraction. The work is a seven-volume treatise on optics and is considered one of the most important contributions to the field of optics in history.