I read that a hollow cathode lamp is preferable to a continuum light source since it emits a sharp atomic spectrum and hence the noise is lower. Could someone please explain how the noise is affected by the sharpness of the atomic lines? Also would you expect only the colours corresponding to the element to be emitted from the lamp or do the fill gas atoms emit light too? So the only wavelengths emitted are from these atoms, am I right? Thank you for your time.