The Arabs and the Enlightenment of Optics


Optics and vision theories were attractive topics of study for ancient scientists. Famous mathematicians as Euclid and Ptolemy adopted the theory of extramission; they interpreted vision as light emitted from the human eyes on the object, where the reflected rays help the individual perceive the color, shape, and size of the object. Another opposing theory was adopted by Aristotle and Galen; the intromission theory, where they thought that light was transmitted to the eye from the object or its surroundings.

In the 11th century, an Arab physician, mathematician, and astronomer Al-Hassan ibn al-Haytham—Latinized as Alhazen—wrote a seven–volume book about optics entitled The Book of Optics. The book explained theories on light and its properties and the vision phenomena. Moreover, he described his own theories of vision supported by experimental evidences, introducing the scientific research methodology. Ibn al-Haytham presented a pioneering model of the eye anatomy with an explanation of how perception works and how light is transmitted inside the human eye.

The book discussed the intromission theory; Ibn al-Haytham stated that light coming from an external source and emitted (reflected or refracted) from the object hits the human eye causing the perception. He divided light into two types: primary light that originates from self-luminous objects such as a fire, a candle, a star, or the sun; and secondary light that arises from objects that emit the light they obtained from self-luminous objects.

Ibn al-Haytham explored the nature of light through constructing a device known as camera obscura—also known as the pinhole camera—or Albeit Almuzlim. The device was a dark obscure room that has a tiny hole to pass the light; images were projected reversed on the opposite wall. This device resembles the camera invention and it was the base of photography.

Moreover, Ibn al-Haytham studied the light and color theory, and how light passes beneath colored material; transparent objects can transmit light through them, such as air and water, but opaque objects cannot pass light through them. He also explained that objects vary in transparency and opaqueness leading to different degree of light passage. Besides, he mentioned theories of light properties like the refraction when it passes through partially transparent mediums or vice versa, and the reflection when it hits smooth surfaces like mirrors.

Most of Ibn al-Haytham works, including his Book of Optics, have been translated into Latin; they had a massive impact on the European development. Famous European scholars during the Middle Ages and Renaissance were influenced by his writings: Roger Bacon, Johannes Kepler, and even Leonardo da Vinci.

His works have all been studied and they were references for many years. European scientists studied his theories and built his devices; based on these studies, modern tools such as eyeglasses, magnifying glasses, telescopes, and cameras were invented. These indispensable tools are actual evidence that Arabs were pioneers in their era and they offered the world precious gifts of science.


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