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visible light

In astronomy, the word light is often used to denote any kind of electromagnetic radiation, from infrared radiation to X-rays and beyond. If, in contrast, an astronomer is talking about the ordinary light to which our eyes are susceptible – electromagnetic radiation with wavelengths between about 400 and 700 nanometers (400 to 700 billionths of a metre) – he or she will use the expression “visible light”.

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visible light

In astronomy, the word light is often used to denote any kind of electromagnetic radiation, from infrared radiation to X-rays and beyond. If, in contrast, an astronomer is talking about the ordinary light to which our eyes are susceptible - electromagnetic radiation with wavelengths between about 400 and 700 nanometers (400 to 700 billionths of a metre) - he or she will use the expression "visible light".

light

Light in the strict sense of the word is electromagnetic radiation the human eye can detect, with wave-lengths between 400 and 700 nano metres. In relativity theory and in astronomy, the word is often used in a more general sense, encompassing all kinds of electromagnetic radiation. For instance, astronomers might talk about "infrared light" or "gamma light"; in this context, light in the stricter sense is referred to as "visible light". Within classical physics, the properties of light are governed by Maxwell's equations; in quantum physics, it turns out that light is a stream of energy packets called light quanta or photons. In the context of relativistic physics, light is of great interest, and for a number of reasons. First of all, the speed of light plays a central role in both special and general relativity. Also, there are a number of interesting effects in general relativity which are associated with the propagation of light, namely deflection, the Shapiro effect and the gravitational redshift.

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visible light

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