The first atomic absorption spectroscopes, designed by
Bunsen and Kirchhoff and a few others in the second
half of the nineteenth century, used a continuum source
since this was the only reliable light source available at
that time.
This was undoubtedly also one of the main
reasons that optical emission spectroscopy (OES) was
preferred over atomic absorption spectroscopy (AAS)
during the first half of the twentieth century, a period
when atomic spectroscopy was increasingly being used
for quantitative analysis.