they have a sharp wavelength peak,
but they'll have a continuous spectrum superimposed on that as well. I think.
Any light coming from them will no doubt have been affected by other things by the time it hits your retina anyway.
( Moon Girl Technologies horrendous beanbag, Sun 14 Jun 2009, 22:05, archived)

the spectrum of a sodium street lamp apparently looks like this:
www.chemistryland.com/CHM107Lab/Exp7/Spectroscope/SodiumLamp500.jpg
( Moon Girl Technologies horrendous beanbag, Sun 14 Jun 2009, 22:13, archived)