1. The range of colors presented when white light is resolved into its constituent colors by being passed through a prism or through a diffraction grating : red, orange, yellow, green, blue, indigo, and violet, arranged in increasing frequency of vibration or decreasing wavelength. 2. Figuratively, the range of pathogenic microorganisms against which an antibiotic or other antibacterial agent is active. 3. The plot of intensity vs. wavelength of light emitted or absorbed by a substance, usually characteristic of the substance and used in qualitative and quantitative analysis. 4. The range of wavelengths presented when a beam of radiant energy is subjected to dispersion and focused. [L. an image, fr. specio, to look at]
- absorption s. the s. observed after light has passed through, and been partially absorbed by, a solution or translucent substance; many molecular groupings have characteristic light absorption patterns, which can be used for detection and quantitative assay.
- antimicrobial s. s. (2).
- broad s. a term indicating a broad range of activity of an antibiotic against a wide variety of microorganisms.
- chromatic s. the continuum of colors that white light forms on passing through a prism or diffraction grating. SYN: color s..
- color s. SYN: chromatic s..
- continuous s. a s. in which there are no absorption bands or lines.
- excitation s. fluorescence produced over a range of wavelengths of the exciting light.
- fluorescence s. fluorescence evoked over a range of wavelengths when the excitation wavelength is at a maximum.
- fortification s. the zigzag banding of light, resembling the walls of fortified medieval towns, that marks the margin of the scintillating scotoma of migraine. SYN: fortification figures, telehopsias.
- frequency s. the range of frequencies in a signal, used to describe the resolving power of an imaging system in radiology.
- infrared s. the part of the invisible s. of wavelengths just longer than that of visible red light. SYN: thermal s..
- invisible s. the radiation lying on either side of visible light, i.e., infrared and ultraviolet light.
- Raman s. the characteristic array of light produced by the Raman effect.
- thermal s. SYN: infrared s..
- ultraviolet s. the electromagnetic s. at wavelengths shorter than the violet end of the visible s..
- visible s. that part of electromagnetic radiation that is visible to the human eye; it extends from extreme red, 7606 Å (760.6 nm), to extreme violet, 3934 Å (393.4 nm).
- vocal s. the frequency and intensity ranges of the voice.
- wide s. s. (3).

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spec·trum 'spek-trəm n, pl spec·tra -trə or spectrums
1 a) a continuum of color formed when a beam of white light is dispersed (as by passage through a prism) so that its component wavelengths are arranged in order
b) any of various continua that resemble a spectrum in consisting of an ordered arrangement by a particular characteristic (as frequency or energy): as (1) ELECTROMAGNETIC SPECTRUM (2) MASS SPECTRUM
c) the representation (as a plot) of a spectrum
2) a continuous sequence or range specif a range of effectiveness against pathogenic organisms <an antibiotic with a broad \spectrum>

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spec·trum (spekґtrəm) pl. specґtra [L. “image”] 1. a charted band of wavelengths of electromagnetic vibrations obtained by refraction and diffraction. See invisible s. and visible s. 2. by extension, any measurable range of activity, such as an antibacterial spectrum or the range of manifestations of a disease.

Medical dictionary. 2011.

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