line spectrum

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line spectrum

physics

Also known as: atomic spectrum

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June 30, 2026

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In physics, a line spectrum is observed when incandescent gases emit only specific wavelengths of light, appearing as a series of parallel lines. These lines are characteristic of the elements emitting the radiation and are also known as atomic spectra because they represent wavelengths radiated when electrons change energy levels within atoms.1

A spectral line is a bright or dark feature in a spectrum caused by a photon changing the energy state of an ion, atom, or molecule. Emission lines occur when an atom moves from a high-energy state to a low-energy state, releasing energy as a photon. Conversely, absorption lines appear when a substance absorbs specific wavelengths of light, causing them to be missing from a continuous spectrum. The unique pattern of these lines acts as a "fingerprint" for identifying specific atoms or molecules.23415

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spectroscopy
Basic atomic structure
The emission and absorption spectra of the elements depend on the electronic structure of the atom. An atom consists of a number of negatively charged electrons bound to a nucleus containing an equal number of positively charged protons. The nucleus
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The emission and absorption spectra of the elements depend on the electronic structure of the atom. An atom consists of a number of negatively charged electrons bound to a nucleus containing an equal number of positively charged protons. The nucleus
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spectrum
…other hand, is called a line spectrum because only a few wavelengths are emitted. These wavelengths appear to be a series of parallel lines because a slit is used as the light-imaging device. Line spectra are characteristic of the elements that emit the radiation. Line spectra are also called atomic…
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…other hand, is called a line spectrum because only a few wavelengths are emitted. These wavelengths appear to be a series of parallel lines because a slit is used as the light-imaging device. Line spectra are characteristic of the elements that emit the radiation. Line spectra are also called atomic…
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spectroscopy
Line sources
Light sources that are capable of primarily emitting radiation with discrete, well-defined frequencies are also widely used in spectroscopy. The early sources of spectral emission lines were simply arc lamps or some other form of electrical discharge in a sealed tube of gas…
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Light sources that are capable of primarily emitting radiation with discrete, well-defined frequencies are also widely used in spectroscopy. The early sources of spectral emission lines were simply arc lamps or some other form of electrical discharge in a sealed tube of gas…
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quantum mechanics
Bohr’s theory of the atom
…atoms is known as a line spectrum, because the radiation (light) emitted consists of a series of sharp lines. The wavelengths of the lines are characteristic of the element and may form extremely complex patterns. The simplest spectra are those of atomic hydrogen and the alkali atoms (e.g., lithium, sodium,…
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…atoms is known as a line spectrum, because the radiation (light) emitted consists of a series of sharp lines. The wavelengths of the lines are characteristic of the element and may form extremely complex patterns. The simplest spectra are those of atomic hydrogen and the alkali atoms (e.g., lithium, sodium,…
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X-ray
Production of X-rays
…spectrum of discrete X-ray emission lines that is characteristic of the target material. This “characteristic radiation” results from the excitation of the target atoms by collisions with the fast-moving electrons. Most commonly, a collision first causes a tightly bound inner-shell electron to be ejected from the atom; a loosely bound…
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…spectrum of discrete X-ray emission lines that is characteristic of the target material. This “characteristic radiation” results from the excitation of the target atoms by collisions with the fast-moving electrons. Most commonly, a collision first causes a tightly bound inner-shell electron to be ejected from the atom; a loosely bound…
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