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[[Image:lighterstill.jpg]] [[Image:PrismAndLight.jpg|right|frame]].  

[[Image:lighterstill.jpg]] [[Image:200PrismAndLight_2.jpg|right|frame]].  

 

'''Light''', or '''visible light''', is [[electromagnetic radiation]] of a [[wavelength]] that is visible to the human [[eye]] (about 400–700 [[nanometre|nm]]).  In a [[Science|scientific]] context, the word ''light'' is sometimes used to refer to the entire [[electromagnetic spectrum]].[http://www.lightsources.org/cms/?pid=1000166] (What Is a Light Source?) Light is composed of an [[elementary particle]] called a [[photon]].

'''Light''', or '''visible light''', is [[electromagnetic radiation]] of a [[wavelength]] that is visible to the human [[eye]] (about 400–700 [[nanometre|nm]]).  In a [[Science|scientific]] context, the word ''light'' is sometimes used to refer to the entire [[electromagnetic spectrum]].[http://www.lightsources.org/cms/?pid=1000166] (What Is a Light Source?) Light is composed of an [[elementary particle]] called a [[photon]].

Light can exhibit properties of both [[wave]]s and [[Particle physics|particles]].  This property is referred to as [[wave-particle duality]].  The study of light, known as [[optics]], is an important research area in modern [[physics]].

Light can exhibit properties of both [[wave]]s and [[Particle physics|particles]].  This property is referred to as [[wave-particle duality]].  The study of light, known as [[optics]], is an important research area in modern [[physics]].

==Speed of light==  

==Speed of light==  

The speed of light in a [[vacuum]] is exactly 299,792,458 [[Metre per second|m/s]] (about 186,282.397 miles per second). The speed of light depends upon the medium in which it is traveling, and the speed will be lower in a transparent medium. Although commonly called the "velocity of light", technically the word ''[[velocity]]'' is a [[vector (spatial)|vector]] quantity, having both magnitude and direction.  ''Speed'' refers only to the magnitude of the velocity vector.  This fixed definition of the speed of light is a result of the modern attempt, in physics, to define the basic unit of length in terms of the speed of light, rather than defining the speed of light in terms of a length.  

The speed of light in a [[vacuum]] is exactly 299,792,458 [[Metre per second|m/s]] (about 186,282.397 miles per second). The speed of light depends upon the medium in which it is traveling, and the speed will be lower in a transparent medium. Although commonly called the "velocity of light", technically the word ''[[velocity]]'' is a [[vector (spatial)|vector]] quantity, having both magnitude and direction.  ''Speed'' refers only to the magnitude of the velocity vector.  This fixed definition of the speed of light is a result of the modern attempt, in physics, to define the basic unit of length in terms of the speed of light, rather than defining the speed of light in terms of a length.