Sodium vapor is a type of gas that is created when sodium metal is heated. This gas emits a bright yellow light, which is why it is commonly used in streetlights and other outdoor lighting. The light produced by sodium vapor is very efficient, making it popular for illuminating large areas. When sodium vapor is energized, it produces a characteristic spectrum of light. This spectrum is primarily made up of two wavelengths, which correspond to the bright yellow color. Sodium vapor lamps are known for their long lifespan and low energy consumption, contributing to their widespread use in urban environments.