Mankind has been making use of artificial light for thousands of years. But it was only towards the end of the last century that the role played by sodium in both daylight and artificial light was discovered. In 1860, Kirchhoff showed that the reversed D-lines in the spectrum of the sun observed by Wollaston and Fraunhofer are identical to the yellow sodium D-lines in the light emitted by flames.
Unable to display preview. Download preview PDF.