Concept
Light
Overview
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. The visible band sits adjacent to the infrared (with longer wavelengths and lower frequencies) and the ultraviolet (with shorter wavelengths and higher frequencies), called collectively optical radiation.
In physics, the term "light" may refer more broadly to electromagnetic radiation of any wavelength, whether visible or not. In this sense, gamma rays, X-rays, microwaves and radio waves are also light. This is why visible radiation is commonly termed visible light.
The primary properties of light are intensity, propagation direction, frequency or wavelength spectrum, and polarization. Its speed in vacuum, 299792458 m/s, is one of the fundamental constants of nature. All electromagnetic radiation exhibits some properties of both particles and waves. Single, massless elementary particles, or quanta, of light called photons can be detected with specialized equipment; phenomena like interference are described by waves. Most everyday interactions with light can be understood using geometrical optics. Quantum optics is an important research area in modern physics.
The main source of natural light on Earth is the Sun. Historically, another important source of light for humans has been fire, from ancient campfires to modern kerosene lamps. With the development of electric lights and power systems, electric lighting has effectively replaced firelight.
Overview adapted from Wikipedia (CC BY-SA 4.0; see the article history for authors).
In the original texts
Passages from public-domain books where Light is discussed.
Lastly, when the light is very bright all lateral movement is lost; and the whole energy of the plant is expended in rendering the circumnutating movement rectilinear and rapid in one direction alone, namely, towards the light.
Charles Darwin, The Power of Movement in Plants
names the idea; a chapter is titled for it; states what it is; opens on it
And that all such reflected Light is of the same Nature with the Sun's Light before its Incidence on the Base of the Prism, no Man ever doubted; it being generally allowed, that Light by such Reflexions suffers no Alteration in its Modifications and Properties. I do not here take Notice of any Refractions made in the sides of the first Prism, because the Light enters it perpendicularly at the first side, and goes…
Isaac Newton, Opticks
names the idea; states what it is; the book is about it; opens on it
Moreover such a ray will not fail of one of two modes: either it will subsist throughout the eye only, in which case Plato’s opinion that it goes forth from the eye is wrong; or else it will subsist throughout a body other than the material of which the eye is composed; for it must inevitably have a vehicle to carry it, seeing that a ray is an accidental quality or mode, and furthermore seeing that that body which…
Avicenna, A Compendium on the Soul
names the idea; states what it is; author linked in the graph; opens on it
Light is considered as one of the first means of extracting colour from substances, and not only the sun-light, but the mere powerless day-light: for as both lights--the direct light of the sun, as well as the derived light of the sky--kindle Bologna phosphorus, so both act on coloured surfaces. Whether the light attacks the colour allied to it, and, as it were, kindles and consumes it, thus reducing the definite…
Johann Wolfgang von Goethe, Goethe's Theory of Colours
names the idea; states what it is; opens on it
All that he saw was the light, and by that light he was blinded. But all that he saw they saw: this same light they saw as well as he. This same light, then, by which he was blinded--were they not blinded likewise by it?
Jeremy Bentham, Not Paul, but Jesus
names the idea; states what it is; opens on it
Philosophers who discussed Light
Related ideas
- Fire
- Aphrodite
- Dignāga
- Hindus
- Isaac Newton
- Johannes Kepler
- Ibn al-Haytham
- Internet Archive
- Luminiferous aether
- Harvard University
- Dharmakirti
- Stephen Hawking
- Aether (classical element)
- Matter
- Pierre Gassendi
- Maxwell's equations
- Quantum
- Visual perception
- Optics
- Physics
- Physical constant
- Physicist
- Photon
- Ptolemy
Opposing perspectives
Place in the tradition
Part of Dualism in cosmology.