Purpose: Show the spectrum of sodium, but does not resolve the yellow doublet.
Description: The low-pressure sodium lamp produces a line spectrum containing a bright yellow line (the unresolved doublet) as well as several other faint red and green lines. Light from the source passes through a condenser lens and iris onto a slit. A 20 cm focal length spherical convex lens focuses the slit onto a distant screen, with the flint glass prism placed in the light just after the spherical lens.
