Spectra of Gas Discharges

Note by J.K.: the intensities of the lines in these spectra appear to be different from what is seen in ordinary street lamps. Whether this is because the excitation is different in the street lamp from the laboratory setup with which these data were obtained, and what is the exact reason, I do not know at the present time.
I plan to overhaul these pages ...

Colour spectra of elements undergoing electrical discharge excitation.

Note by J.K.: the colours on your screen may not closely correspond to the colours which you would observe with your eyes. Also, the relative intensities of the lines shown here may be quite different in the lamp you observe, as they depend on the excitation conditions in the discharge. The region shown is the wavelength interval from 400 nm (left edge) to 700 nm (right edge), with wavelength going linearly with position on the screen.

This is how my eyes perceive the colours of the solar continuum

and this is how my eyes perceive the solar spectrum


















JPEG screen grabs of an applet which computes and plots the spectra in a web browser window. The above images aren't dithered. They may appear so if your display doesn't have enough colors to represent the entire color range. Displays limited to 256 colors or less don't produce acceptable spectra. Try increasing your color resolution to 16 or 24 bits (16 million colors).

This Java program reads a file containing a list of emission line wavelengths and their corresponding strengths then simulates the appearance of the spectrum in a good visual spectroscope.

Note: This program generates deep 24 bit color plots, therefore you may need to increase the color depth of your system to view subtle details in these spectra.

Warning: There may be a small delay as the Applet loads it's element emission line file and computes the spectra...

Note by J.K. Some of the line intensities do not agree with what one would expect from discharge lamps we encounter in everyday life. I have not traced under what excitation conditions the intensities in the data files were obtained. Since one was primarily interested in determining the wavelengths of the lines of each element, the excitation may have been much different from say a street lamp! As Paolo Sirtoli told me, the NIST Atomic Spectra Database also provides data with line intensities.

Most common elements in solar spectrum.
(listed in order of decreasing abundance)
Element Symbol Data File Emission Lines
4000-7000 Å
1 Hydrogen H hydrogen.txt 5 JPEG hydrogen.dat.gz
2 Helium He helium.txt 23 JPEG helium.dat.gz
8 Oxygen O oxygen.txt 73 JPEG oxygen.dat.gz
6 Carbon C carbon.txt 27 JPEG carbon.dat.gz
7 Nitrogen N nitrogen.txt 84 JPEG nitrogen.dat.gz
10 Neon Ne neon.txt 75 JPEG neon.dat.gz
12 Magnesium Mg magnesium.txt 54 JPEG magnesium.dat.gz
14 Silicon Si silicon.txt 109 JPEG silicon.dat.gz
16 Sulfur S sulfur.txt 39 JPEG sulfur.dat.gz
26 Iron Fe iron.txt 235 JPEG iron.dat.gz
11 Aluminum Al aluminum.txt 38 JPEG aluminum.dat.gz
20 Calcium Ca calcium.txt 78 JPEG calcium.dat.gz
18 Argon Ar argon.txt 159 JPEG argon.dat.gz
11 Sodium Na sodium.txt 90 JPEG sodium.dat.gz
36 Krypton Kr krypton.txt 75 JPEG krypton.dat.gz
54 Xenon Xe xenon.txt 139 JPEG xenon.dat.gz
80 Mercury Hg mercury.txt 40 JPEG mercury.dat.gz
All Spectra High Resolution 784 X 64 JPEG catalog.dat.gz
306 KBytes

Atomic Number The number of protons in the nucleus of the element.
Element Click on the name in this column to launch the Applet which displays an emission line spectrum of the corresponding element
Symbol Symbol from the table of the elements
Data File Click on the name to download a text file containing an a list of emission lines in Ångstroms and their associated strengths for the corresponding element
Emission Lines
4000-7000 Å
Number of tabulated emission lines in the visible wavelength range
Jpeg Image JPEG screen grab (784 X 8). The narrow height is to reduce transmission time, it expands to 64 pixels using HEIGHT=64 option in IMG tag of HTML file. To use images outside the context of a web browser, you should expand them vertically with image processor.
Original Data Spectra of neutral and singly ionized elements from the Astronomical Data Center (ADC) catalog A6016, by Reader J., Corliss Ch.H. :1981, 'Line Spectra of the Elements', CRC Handbook of Chemistry and Physics; NSRDS-NBS 68

The element, wavelength range and line width are all controlled by applet parameter (PARAM) tags in the HTML source for this page. There are other options such as width and height of spectra in pixels and contrast which can also be controlled. There are also options to overlay a continuous blackbody spectrum of varying strength and to limit the wavelength range.
For example here are the parameters for Neon :

<APPLET CODE=discharge.class WIDTH=784 HEIGHT=64>
<PARAM NAME=element VALUE=neon.txt>
<PARAM NAME=startWavelength VALUE=4000>
<PARAM NAME=endWavelength VALUE=7000>
<PARAM NAME=lineWidth VALUE=2.5>
<PARAM NAME=contrast VALUE=10>
<PARAM NAME=continuum VALUE=0.3>
The simulated gas discharge spectrum is synthesized by assigning each emission line to a gaussian and each point in the spectra is computed as a mathematical sum of all the emission lines. This applet was successfully run under the following browsers : An upcoming version of this Applet will include a more graphical user interface for controlling these parameters.

This Applet was created by John Talbot. Source code is available : discharge.java (Currently limited to 200 emission lines, however this limit can easily be removed by changing the source code and recompiling. There are more details on the color encoding subroutine)

You can also download the source file, class file, these HTML pages and all the element data as :
discharge.zip (43 kBytes)

Physics Background

There are two basic line broadening mechanisms; instrumental and intrinsic : In most thin plasmas one sees a combination of Doppler and Lorentzian broadening called Voigt profiles. The Lorentzian component affects mostly the low intensity 'wings' of the emission lines so line profiles can be approximated as gaussians, especially considering the dynamic range limitations of computer screens. Most of the time spectra taken by researchers do not fully resolve the intrinsic line profile so the lines are broadened mainly by instrumental imperfection.

The data for these spectra is courtesy of the Astronomical Data Center, and the National Space Science Data Center through the World Data Center A for Rockets and Satellites.


slightly modified by: J.Köppen, 13 Feb. 2003