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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.
An important property of light fixtures is the luminous efficacy or wall-plug efficiency, meaning the amount of usable light emanating from the fixture per used energy, usually measured in lumen per watt. A fixture using replaceable light sources can also have its efficiency quoted as the percentage of light passed from the "bulb" to the ...
Helen is a feminine name of Greek origin that means "torch" or "light." It can also mean "shining" or "warming." Helen was originally the name of a solar deity. Helen is associated with the phrase "the face that launched a thousand ships." Helen, worshipped as a goddess in Laconia and Rhodes, is a major character in Greek mythology.
While luminance is a linear measurement of light, lightness is a linear prediction of the human perception of that light. This distinction is meaningful because human vision's lightness perception is non-linear relative to light. Doubling the quantity of light does not result in a doubling in perceived lightness, only a modest increase.
[12] [13] The reason for this is the Purkinje effect, i.e., the cones do not function as efficiently in dim light, so red objects appear to be black. In Australia, this form of chartreuse yellow is also known as "ACT yellow" as this is the color of the fire engines in the Australian Capital Territory .
This is an accepted version of this page This is the latest accepted revision, reviewed on 27 January 2025. Color of tan commonly found in arid-region military uniforms This article is about khaki as a color. For other uses, see Khaki (disambiguation). Khaki is a common color in military uniforms and equipment, particularly those intended for use in desert or arid regions, as seen on these ...
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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 ;