sentence: Streetlights are normally either orange or blue.
sentences_before: A 'streetlight' is a light bulb on a pole used for lighting streets. Streets can be lit for safety or visibility reasons, so people can see where they are walking at night.
sentences_after: The blue ones are mercury-vapor lamps. They are older and last longer. The orange ones are sodium vapor lamps. They are newer and more efficient.
concept_name: streetlight
headings: Streetlight
categories: Light sources