A significant consideration used in street lighting is cost and efficiency.

"Low-pressure sodium vapor" lighting is almost entirely one (actually two very close together) wavelength of yellow light, and that it gives the most illumination for the amount of electricity.

A big problem with this light, though, is that it throws off color perception, a very poor CRI (~5). Under sodium vapor light, most colors look gray. This makes it hard to recognize your car in a parking lot.