The least damaging bulbs for Astronomy are the most energy-efficient available. The most damaging are those that emit ultraviolet light, as light at these wavelengths is the most strongly dispersed in the atmosphere and has no value in terms of lighting.
The least polluting lights are low pressure sodium lamps as they emit almost all of their light in a single line of the spectrum, leaving the rest undisturbed. They are also the most energy efficient, consuming 5 times less than incandescent bulbs, 2.2 times less than mercury and 1.5 times less than high pressure sodium and fluorescent bulbs.
Pictures of the most commonly-used bulbs: