Why sodium vapour lamp is a monochromatic light and why not a 1000w bulb?
Atoms emit specific wavelengths of light when excited (energized) due to the discrete nature of their internal electronic energy levels. A sodium light works by electronically exciting a specific pair of closely related emission lines of sodium atoms in a *transparent gas* which are extremely close in wavelength. An incandescent bulb works on the principle that when you heat an *opaque solid* (in this case by Ohmic heating), myriad emission lines add and smear together into a broad spectrum called a Planck or Black Body spectrum.
