Ibn al-Haytham, alongside Galileo, in polish astronomer Johannes Hevelius’s work on the Moon, Selenographia, published in 1647. Image from book’s title page (Source Houghton Library, Harvard University)
Abu Ali al-Hasan Ibn al-Haytham, ابن الهیثم (Latinized name: Alhazen), was born in Basra (in current Iraq) in 965 AD, but details of his ancestry remain uncertain. He made important discoveries in astronomy, mathematics, and optics. He died in Cairo in 1040.
Caliph al-Hakim of Cairo, impressed by Ibn al-Haytham’s claim that he could regulate the flow of the Nile, persuaded him to come to Egypt. However, Ibn al-Haytham soon found out that he was not up to the task. He fell in disgrace and was placed under house arrest for many years. This proved to be beneficent for continuing his studies in mathematics, astronomy, and optics.
According to Aristotle, the light was a manifestation of a change of the state of the medium from opaque to transparent. Ptolemy had considered vision to be the result of visual rays, spreading out from the eye, that were reflected or refracted by surfaces of objects. Ibn al-Haytham (as well as Ibn Rushd) proposed an alternative view that light has a much more active role in color vision. It is light which is seen, according to Ibn al-Haytham [1]. Moreover, light is directed toward the eye instead of spreading from it. Ibn al-Haytham was the first to consider light as an entity by itself, traveling from visible objects to the eye, according to mathematical laws originally proposed by Euclid [2]. Regarding the role of the medium for color vision, Ibn al-Haytham adopted the view from al-Kindi, الکندی (d. 873), that the medium plays a passive role in color vision in the sense that it should not block vision.
In Ibn al-Haytham’s theory, color is a distinct property of material bodies. He stated that color and light are distinct, but that colors behave exactly as light does in transmission, reflectance, and refraction. Therefore, Ibn al-Haytham’s theory of light is at the same time a theory of color [3]. However, apart from formulating these theories, Ibn al-Haytham went further and designed many experiments by which he verified the proposal step-by-step and afterward subjected the results to thorough mathematical analysis [4, 5]. Nevertheless, Ibn al-Haytham also explored some more philosophical treatments of color and light [4].
7.1 Alhazen’s Optics
His Kitab al-Manazir, کتاب المناظر (Book on Optics), made the works from Aristotle, Ptolemy, and Euclid obsolete. He merged their classical theories, combining the mathematical, physical, and physiological aspects into one unified optical theory. The Kitab al-Manazir also introduced the distinction between optics and physiology/psychology that is a cornerstone of modern optics and colorimetry.
In his work, Ibn al-Haytham attempted to show how illumination, hue, and saturation combine together into color perception. Although he was not able to establish a complete system of color attributes, his account is largely consistent.
In terms of scope, details and comprehensiveness of treatment, Ibn al-Haytham’s observations on the subject of color perception are unequalled in any single writer before him. Vol. 2, p.43 of Ref. [5].
The Kitab al-Manazir would be the dominant text on optics for several centuries to come, both in the East and West. Latin translations appeared from 1200 until 1572 (Perspectiva, De aspectibus, Opticae Thesaurus), and in Italian around 1350 (Prospettiva). Basing themselves on what they read in this book, Kamal al-Din al-Farisi and Theodoric of Freiberg around 1300 discovered the correct explanation for the colors of the rainbow. Kepler also formulated the theory of the retinal image in 1604 using this book, and Willebrord Snellius discovered a few years later what is now known as Snellius’ law of refraction. In the East, Ibn al-Haytham’s work survived through its thorough treatment and further elaboration by Kamal al-Din al-Farisi (d. 1318).
This behavior indicates that the eye observes the colors of colored objects only according to the colors that fall on them [6, 7].
Ibn al-Haytham was one of the first to use the word saturation as describing an aspect of color in his Kitab al-Manazir. Generally, it refers to the sensation one feels after a copious meal, indeed analogous to the modern English word saturation. In modern Arabic, the same word is still used for color saturation [8]. About this and other words related to color that appear in the Kitab al-Manazir, see Vol. 2, p. 43 in Ref. [5].
In other aspects, Ibn al-Haytham followed classical traditions. He supported the Aristotelian view that the colors of the rainbow are the result of mixing light and darkness, and the Ptolemaic interpretation that color mixing in the spinning top is a visual illusion.
Al-Hazen’s image in a 10 Dinar National Bank of Iraq note. (Wikimedia, this work was first published in Iraq and is now in the public domain because its copyright protection has expired by virtue of the Law No. 3 of 1971 on copyright, amended 2004 by Order No. 83, amendment to the copyright law)