What is the Difference Between a Continuous Spectrum and a Bright Line Spectrum

The key difference between a continuous spectrum and a bright line spectrum is that there are no discrete lines in a continuous spectrum whereas there are separate lines in a bright line spectrum.

A continuous spectrum is a series of attainable values of a physical quantity, having no considerable gap between each value. Bright line spectrum is a series of attainable values of a physical quantity having a considerable gap between the values.

CONTENTS

1. Overview and Key Difference
2. What is a Continuous Spectrum 
3. What is a Bright Line Spectrum
4. Continuous Spectrum vs Bright Line Spectrum  in Tabular Form
5. Summary – Continuous Spectrum vs Bright Line Spectrum 

What is a Continuous Spectrum?

A continuous spectrum is a series of attainable values of a physical quantity, having no considerable gap between each value. This value series is the opposite of the discrete spectrum. The values taken to build up a continuous spectrum can be energy, wavelength, etc.

The most common example for a continuous spectrum is the spectrum of light emitted by excited atoms of hydrogen. This spectrum is created due to free electrons, which become bound to a hydrogen ion and emit photons that tend to smoothly spread over a wide range of wavelengths.

The term continuous spectrum is mostly used when the range of values for the physical quantity (mainly energy or wavelength) have both continuous and discrete parts, either at the same time or at different times. This is because the position and momentum of a free particle have a continuous spectrum, and when the particle is confined to limited space, its spectrum becomes a discrete spectrum. Generally, quantum chemical systems are associated with free particles (e.g. atoms in a gas, electrons in an electron beam, conduction band electrons in a metal, etc.).

What is Bright Line Spectrum?

Bright line spectrum is a series of attainable values of a physical quantity having a considerable gap between the values. This type of spectrum is also known as an emission spectrum, where bright lines obtained experimentally are arranged in a specific order.

A bright line spectrum is created when a beam of light passes through an analyte sample where some wavelengths of the light are absorbed by the atoms in the sample; therefore, the electrons in those atoms get to an excited state. Since residing in an excited state is unstable for atoms, the electrons tend to come back to the ground state emitting photons as EMR having an energy that is equal to the energy difference between ground and excited states of those electrons. These emitted photons are detected as a colored light line in a black background, creating a line spectrum.

What is the Difference Between a Continuous Spectrum and a Bright Line Spectrum?

A continuous spectrum is a series of attainable values of a physical quantity, having no considerable gap between each value. On the other hand a bright line spectrum is a series of attainable values of a physical quantity having a considerable gap between the values. Therefore, the key difference between a continuous spectrum and a bright line spectrum is that there are no discrete lines in a continuous spectrum, whereas there are separate lines in a bright line spectrum.

The below infographic lists the differences between a continuous spectrum and a bright line spectrum in tabular form.

Summary –  Continuous Spectrum vs Bright Line Spectrum

A continuous spectrum is a series of attainable values of a physical quantity, having no considerable gap between each value. Bright line spectrum is a series of attainable values of a physical quantity having a considerable gap between the values. Therefore, the key difference between a continuous spectrum and a bright line spectrum is that there are no discrete lines in a continuous spectrum, whereas there are separate lines in a bright line spectrum.

Reference:

1. “Astronomy.” Lumen.

Image Courtesy:

1. “Continuous spectra” By Sharon Bewick (CC BY-SA 3.0) via Commons Wikimedia
2. “Emission spectrum-Fe” By Nilda – Own work (Public Domain) via Commons Wikimedia