Sodium vapor lamp
A sodium vapor lamp is a kind of gas discharge lamp. It produces a yellow or orange light. There are two types; the high pressure lamp and the low pressure lamp. The high pressure one is very energy-efficient and is the orange light in streetlights. The low pressure one is yellow. These lights contain sodium metal in them. They operate by a spark through a tube that contains the sodium. The sodium emits a yellow color, which produces the light.