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Light exerts physical pressure on objects in its path, a phenomenon which can be deduced by Maxwell's equations, but can be more easily explained by the particle nature of light: photons strike and transfer their momentum. Light pressure is equal to the power of the light beam divided by c, the speed of light.
Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. [1] Optics usually describes the behaviour of visible , ultraviolet , and infrared light.
Brightness is a subjective sensation of an object being observed and one of the color appearance parameters of many color appearance models, typically denoted as . Brightness refers to how much light appears to shine from something.
The luminance of a specified point of a light source, in a specified direction, is defined by the mixed partial derivative = where L v is the luminance ( cd / m 2 ); d 2 Φ v is the luminous flux ( lm ) leaving the area dΣ in any direction contained inside the solid angle dΩ Σ ;
A basic distinction is between isotropic materials, which exhibit the same properties regardless of the direction of the light, and anisotropic ones, which exhibit different properties when light passes through them in different directions. The optical properties of matter can lead to a variety of interesting optical phenomena.
Newton then suggested in Qu. 18 and Qu. 19 that light propagates through vacuum via a very subtle "Aethereal Medium", just like heat was thought to spread. Although the previous hypotheses describe wave-like aspects of light, Newton still believed in particle-like properties.
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It is based on subjective judgements of which of a pair of different-colored lights is brighter, to describe relative sensitivity to light of different wavelengths. It is not an absolute reference to any particular individual, but is a standard observer representation of visual sensitivity of a theoretical human eye .