A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a
continuum. The word was first used scientifically in
optics
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. Optics usually describes the behaviour of visible, ultrav ...
to describe the
rainbow
A rainbow is a meteorological phenomenon that is caused by reflection, refraction and dispersion of light in water droplets resulting in a spectrum of light appearing in the sky. It takes the form of a multicoloured circular arc. Rainbows c ...
of colors in
visible light
Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 te ...
after passing through a
prism
Prism usually refers to:
* Prism (optics), a transparent optical component with flat surfaces that refract light
* Prism (geometry), a kind of polyhedron
Prism may also refer to:
Science and mathematics
* Prism (geology), a type of sedimentary ...
. As scientific understanding of light advanced, it came to apply to the entire
electromagnetic spectrum
The electromagnetic spectrum is the range of frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energies.
The electromagnetic spectrum covers electromagnetic waves with frequencies ranging fro ...
. It thereby became a mapping of a range of magnitudes (wavelengths) to a range of qualities, which are the perceived "colors of the rainbow" and other properties which correspond to wavelengths that lie outside of the visible light spectrum.
Spectrum has since been applied by analogy to topics outside optics. Thus, one might talk about the "
spectrum of political opinion", or the "spectrum of activity" of a drug, or the "
autism spectrum
The autism spectrum, often referred to as just autism or in the context of a professional diagnosis autism spectrum disorder (ASD) or autism spectrum condition (ASC), is a neurodevelopmental condition (or conditions) characterized by difficulti ...
". 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 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.
Etymology
In
Latin
Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
, ''spectrum'' means "image" or "
apparition", including the meaning "
spectre
Spectre, specter or the spectre may refer to:
Religion and spirituality
* Vision (spirituality)
* Apparitional experience
* Ghost
Arts and entertainment Film and television
* ''Spectre'' (1977 film), a made-for-television film produced and writ ...
".
Spectral evidence Spectral evidence is a form of legal evidence based upon the testimony of those who claim to have experienced visions.
Such testimony was frequently given during the witch trials of the 16th and 17th centuries. The alleged victims of witchcraft w ...
is testimony about what was done by spectres of persons not present physically, or
hearsay
Hearsay evidence, in a legal forum, is testimony from an under-oath witness who is reciting an out-of-court statement, the content of which is being offered to prove the truth of the matter asserted. In most courts, hearsay evidence is inadmiss ...
evidence about what ghosts or apparitions of
Satan said. It was used to convict a number of persons of
witchcraft
Witchcraft traditionally means the use of magic or supernatural powers to harm others. A practitioner is a witch. In medieval and early modern Europe, where the term originated, accused witches were usually women who were believed to have ...
at
Salem, Massachusetts
Salem ( ) is a historic coastal city in Essex County, Massachusetts, located on the North Shore of Greater Boston. Continuous settlement by Europeans began in 1626 with English colonists. Salem would become one of the most significant seaports tr ...
in the late 17th century. The word "spectrum"
pektrumwas strictly used to designate a ghostly optical
afterimage
AfterImage is a Filipino rock band formed in 1986, best known for their songs "Habang May Buhay", "Next in Line", and "Mangarap Ka". They disbanded in 1997 and became active again in 2008 after they reunited and released their fourth studio alb ...
by
Goethe
Johann Wolfgang von Goethe (28 August 1749 – 22 March 1832) was a German poet, playwright, novelist, scientist, statesman, theatre director, and critic. His works include plays, poetry, literature, and aesthetic criticism, as well as tr ...
in his ''
Theory of Colors'' and
Schopenhauer
Arthur Schopenhauer ( , ; 22 February 1788 – 21 September 1860) was a German philosopher. He is best known for his 1818 work '' The World as Will and Representation'' (expanded in 1844), which characterizes the phenomenal world as the pr ...
in ''
On Vision and Colors
''On Vision and Colors'' (originally translated as ''On Vision and Colours''; german: Ueber das Sehn und die Farben) is a treatise by Arthur Schopenhauer that was published in May 1816 when the author was 28 years old. Schopenhauer had extensive d ...
''.
The prefix "spectro-" is used to form words relating to spectra. For example, a
spectrometer
A spectrometer () is a scientific instrument used to separate and measure spectral components of a physical phenomenon. Spectrometer is a broad term often used to describe instruments that measure a continuous variable of a phenomenon where the ...
is a device used to record spectra and
spectroscopy is the use of a spectrometer for
chemical analysis
Analytical chemistry studies and uses instruments and methods to separate, identify, and quantify matter. In practice, separation, identification or quantification may constitute the entire analysis or be combined with another method. Separati ...
.
Physical sciences
Biological science
Antibiotic spectrum of activity is a component of
antibiotic classification. A
broad-spectrum antibiotic
A broad-spectrum antibiotic is an antibiotic that acts on the two major bacterial groups, Gram-positive and Gram-negative, or any antibiotic that acts against a wide range of disease-causing bacteria. These medications are used when a bacterial ...
is active against a wide range of bacteria,
[Clayton L. Thomas Editor, Taber's Cyclopedic Medical Dictionary 17th ed., 1993 ()] whereas a
narrow-spectrum antibiotic
A narrow-spectrum antibiotic is an antibiotic that is only able to kill or inhibit limited species of bacteria. Examples of narrow-spectrum antibiotics include fidaxomicin and sarecycline.
Advantages
* Narrow-spectrum antibiotic allow to kill or ...
is effective against specific families of bacteria.
[S.J. Hopkins, Drugs and Pharmacology for Nurses 12th ed., 1997 ()] An example of a commonly used broad-spectrum antibiotic is
ampicillin
Ampicillin is an antibiotic used to prevent and treat a number of bacterial infections, such as respiratory tract infections, urinary tract infections, meningitis, salmonellosis, and endocarditis. It may also be used to prevent group B stre ...
.
An example of a narrow spectrum antibiotic is
Dicloxacillin
Dicloxacillin is a narrow-spectrum β-lactam antibiotic of the penicillin class. It is used to treat infections caused by susceptible (non-resistant) Gram-positive bacteria.Product Information: DICLOXACILLIN SODIUM-dicloxacillin sodium capsule. T ...
, which acts on
beta-lactamase
Beta-lactamases, (β-lactamases) are enzymes () produced by bacteria that provide multi-resistance to beta-lactam antibiotics such as penicillins, cephalosporins, cephamycins, monobactams and carbapenems ( ertapenem), although carbap ...
-producing
Gram-positive
In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall.
Gram-positive bact ...
bacteria such as ''
Staphylococcus aureus''.
In psychiatry, the
spectrum approach
A spectrum disorder is a mental disorder that includes a range of linked conditions, sometimes also extending to include singular symptoms and traits. The different elements of a spectrum either have a similar appearance or are thought to be cause ...
uses the term spectrum to describe a range of linked conditions, sometimes also extending to include singular symptoms and
traits. For example, the
autism spectrum
The autism spectrum, often referred to as just autism or in the context of a professional diagnosis autism spectrum disorder (ASD) or autism spectrum condition (ASC), is a neurodevelopmental condition (or conditions) characterized by difficulti ...
describes a range of conditions classified as
neurodevelopmental disorders.
Mathematics
In
mathematics, the
spectrum of a matrix is the
multiset
In mathematics, a multiset (or bag, or mset) is a modification of the concept of a set that, unlike a set, allows for multiple instances for each of its elements. The number of instances given for each element is called the multiplicity of that e ...
of the
eigenvalue
In linear algebra, an eigenvector () or characteristic vector of a linear transformation is a nonzero vector that changes at most by a scalar factor when that linear transformation is applied to it. The corresponding eigenvalue, often denoted ...
s of the matrix.
In functional analysis, the concept of the
spectrum of a bounded operator is a generalization of the eigenvalue concept for matrices.
In
algebraic topology
Algebraic topology is a branch of mathematics that uses tools from abstract algebra to study topological spaces. The basic goal is to find algebraic invariants that classify topological spaces up to homeomorphism, though usually most classify ...
, a
spectrum
A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors ...
is an object representing a
generalized cohomology theory.
Social science
![Political-spectrum-multiaxis](https://upload.wikimedia.org/wikipedia/commons/b/b0/Political-spectrum-multiaxis.png)
In
social science
Social science is one of the branches of science, devoted to the study of societies and the relationships among individuals within those societies. The term was formerly used to refer to the field of sociology, the original "science of so ...
,
economic spectrum is used to indicate the range of social class along some indicator of wealth or income. In
political science
Political science is the scientific study of politics. It is a social science dealing with systems of governance and power, and the analysis of political activities, political thought, political behavior, and associated constitutions and la ...
, the term
political spectrum
A political spectrum is a system to characterize and classify different political positions in relation to one another. These positions sit upon one or more geometric axes that represent independent political dimensions. The expressions politi ...
refers to a system of classifying political positions in one or more dimensions, for example in a range including right wing and left wing.
References
{{Authority control
Concepts in physics
Light
Broad-concept articles