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- Dictionarylight/lʌɪt/
noun
- 1. the natural agent that stimulates sight and makes things visible: "the light of the sun" Similar Opposite
- 2. an expression in someone's eyes indicating a particular emotion or mood: "a shrewd light entered his eyes"
verb
- 1. provide with light or lighting; illuminate: "the room was lit by a number of small lamps"
- 2. make (something) start burning; ignite: "Allen gathered sticks and lit a fire"
adjective
- 1. having a considerable or sufficient amount of natural light; not dark: "the bedrooms are light and airy" Similar Opposite
- 2. (of a colour) pale: "her eyes were light blue" Similar Opposite
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Learn the meaning of light as a noun, adjective, and verb in English. Find out how to use light to describe brightness, flame, lungs, colour, mood, and more.
- Overview
- Ray theories in the ancient world
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Light is electromagnetic radiation that can be detected by the human eye. Electromagnetic radiation occurs over an extremely wide range of wavelengths, from gamma rays with wavelengths less than about 1 × 10−11 metres to radio waves measured in metres.
What is the speed of light?
The speed of light in a vacuum is a fundamental physical constant, and the currently accepted value is 299,792,458 metres per second, or about 186,282 miles per second.
What is a rainbow?
A rainbow is formed when sunlight is refracted by spherical water droplets in the atmosphere; two refractions and one reflection, combined with the chromatic dispersion of water, produce the primary arcs of colour.
Why is light important for life on Earth?
While there is clear evidence that simple optical instruments such as plane and curved mirrors and convex lenses were used by a number of early civilizations, ancient Greek philosophers are generally credited with the first formal speculations about the nature of light. The conceptual hurdle of distinguishing the human perception of visual effects from the physical nature of light hampered the development of theories of light. Contemplation of the mechanism of vision dominated these early studies. Pythagoras (c. 500 bce) proposed that sight is caused by visual rays emanating from the eye and striking objects, whereas Empedocles (c. 450 bce) seems to have developed a model of vision in which light was emitted both by objects and the eye. Epicurus (c. 300 bce) believed that light is emitted by sources other than the eye and that vision is produced when light reflects off objects and enters the eye. Euclid (c. 300 bce), in his Optics, presented a law of reflection and discussed the propagation of light rays in straight lines. Ptolemy (c. 100 ce) undertook one of the first quantitative studies of the refraction of light as it passes from one transparent medium to another, tabulating pairs of angles of incidence and transmission for combinations of several media.
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With the decline of the Greco-Roman realm, scientific progress shifted to the Islamic world. In particular, al-Maʾmūn, the seventh ʿAbbāsid caliph of Baghdad, founded the House of Wisdom (Bayt al-Hikma) in 830 ce to translate, study, and improve upon Hellenistic works of science and philosophy. Among the initial scholars were al-Khwārizmī and al-Kindī. Known as the “philosopher of the Arabs,” al-Kindī extended the concept of rectilinearly propagating light rays and discussed the mechanism of vision. By 1000, the Pythagorean model of light had been abandoned, and a ray model, containing the basic conceptual elements of what is now known as geometrical optics, had emerged. In particular, Ibn al-Haytham (Latinized as Alhazen), in Kitab al-manazir (c. 1038; “Optics”), correctly attributed vision to the passive reception of light rays reflected from objects rather than an active emanation of light rays from the eyes. He also studied the mathematical properties of the reflection of light from spherical and parabolic mirrors and drew detailed pictures of the optical components of the human eye. Ibn al-Haytham’s work was translated into Latin in the 13th century and was a motivating influence on the Franciscan friar and natural philosopher Roger Bacon. Bacon studied the propagation of light through simple lenses and is credited as one of the first to have described the use of lenses to correct vision.
Learn about the nature, characteristics, and applications of light, the electromagnetic radiation that can be detected by the human eye. Explore the history, theories, and experiments of light from ancient times to modern physics.
Learn the meaning of light as a noun, adjective, and verb, with examples and synonyms. Explore the different senses and uses of light in physics, art, architecture, and more.
Learn the various meanings and uses of the word light as a noun, verb, adjective, and adverb. Find synonyms, examples, and related phrases for light.
Light, visible light, or visible radiation is electromagnetic radiation that can be perceived by the human eye. Visible light spans the visible spectrum and is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 terahertz.
Learn the meaning, pronunciation, and examples of the word light as a noun, verb, and adjective. Compare and contrast the different senses and idioms of light in physics, perception, illumination, and more.
