The IDA (International Dark-Sky Association) advocates that outdoor lighting be utilized sensibly to minimize the detrimental effects of light pollution.  Outdoor lighting typically makes use of different industrial sources of light.  They are as follows:

abcs of lighting “LPS” – Low-pressure sodium is considered very efficient and is usually utilized in environmentally sensitive areas (e.g., astronomical observatories). However, LPS lighting is considered limited in the spectrum of light it emits and is considered undesirable.
abcs of lighting “HPS” – High-pressured sodium is frequently used for street lighting in cities and towns. Its orange coloring is preferred to the brighter orange band of LPS.
c White Light – Metal halides or “LEDs” (light emitting diodes) are two predominant choices in areas where it is necessary to use white light with LED lighting having an advantage since it can be dimmed accordingly when full brightness is not required. Consequently, this feature saves energy and reduces light pollution at night.  LEDs lighting is considered the most efficient (longer life and energy), thus becoming more widespread.  Click here to IDA’s practical guide to LED Practical Guide
WARNING: The careless utilization of artificial lighting detailed above results in Light Pollution!