Ibn al-Haytham was the first to explain that vision occurs when light reflects from an object and then passes to one's eyes.^[27] He was also the first to demonstrate that vision occurs in the brain, rather than in the eyes.^[28] Building upon a naturalistic, empirical method pioneered by Aristotle in ancient Greece, Ibn al-Haytham was an early proponent of the concept that a hypothesis must be supported by experiments based on confirmable procedures or mathematical evidence—an early pioneer in the scientific method five centuries before Renaissance scientists.^{[29][30][31][32][33][34]}

Born in Basra, he spent most of his productive period in the Fatimid capital of Cairo and earned his living authoring various treatises and tutoring members of the nobilities.^[35] Ibn al-Haytham is sometimes given the byname al-Baṣrī after his birthplace,^[36] or al-Miṣrī ("of Egypt").^[37][38] Al-Haytham was dubbed the "Second Ptolemy" by Abu'l-Hasan Bayhaqi^[39][40] and "The Physicist" by John Peckham.^[41] Ibn al-Haytham paved the way for the modern science of physical optics.