Question

Why are street lamps yellow?

Answer 1

This is because orange or yellow light are much cheaper to produce since it is formed from high pressured sodium lamps which on coming from excited to lower state imparts yellow colour rather orangish colour 

Answer 2

many street lights are orange because of the type of bulb used.  The two main types of street lighting used in the United States are sodium-vapor bulbs and mercury-vapor bulbs.  Both types work by applying electricity to a sealed container of gas in order to create light.  The color of the light comes from the spectral output of the gas....
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