Editing Spectrum (section)

{{Use mdy dates|date=August 2017}}
{{About|variation within extremes}}
{{Short description|Continuous range of values, such as wavelengths in physics}}
[[File:Rainbow above Kaviskis Lake, Lithuania.jpg|thumb|The spectrum in a [[rainbow]]]]

A '''spectrum''' ({{plural form}}: '''spectra''' or '''spectrums''') is a set of related ideas, objects, or properties whose features overlap such that they blend to form a [[Continuum (measurement)|continuum]].<ref>{{cite web |url=http://dictionary.reference.com/browse/spectrum |title=Spectrum  |archive-url=https://web.archive.org/web/20080223153840/http://dictionary.reference.com/browse/spectrum |archive-date=February 23, 2008 |work=The American Heritage Dictionary of the English Language |edition=4th |publisher=Houghton Mifflin Company |year=2004 |access-date= January 25, 2008}}</ref> The word ''spectrum'' was first used scientifically in [[optics]] to describe the [[rainbow]] of colors in [[visible light]] after passing through a [[dispersive prism|prism]]. In the optical spectrum, light [[wavelength]] is viewed as continuous, and spectral colors are seen to blend into one another smoothly when organized in order of their corresponding wavelengths. As scientific understanding of light advanced, the term came to apply to the entire [[electromagnetic spectrum]], including radiation not visible to the human eye. 

''Spectrum'' has since been applied by analogy to topics outside optics. Thus, one might talk about the "[[political spectrum|spectrum of political opinion]]", or the "spectrum of activity" of a drug, or the "[[autism spectrum]]". In these uses, values within a spectrum may not be associated with precisely quantifiable numbers or definitions. Such uses imply a broad range of conditions or behaviors grouped together and studied under a single title for ease of discussion. Nonscientific uses of the term ''spectrum'' are sometimes misleading. For instance, a single [[left–right political spectrum|left–right spectrum]] of political opinion does not capture the full range of people's political beliefs. Political scientists use a variety of biaxial and multiaxial systems to more accurately characterize political opinion.

In most modern usages of ''spectrum'' there is a unifying theme between the extremes at either end. This was not always true in older usage.