Now-a-days yellow lamps are frequently used as street lights. Which of the following gases is used in these lamps ?

Answer: Option A

A sodium-vapour lamp is a gas-discharge lamp that uses sodium in an excited state to produce light. There are two varieties of such lamps: low pressure and high pressure. Low-pressure sodium lamps are the most efficient electrical light sources, but their yellow light restricts applications to outdoor lighting such as street lamps. High-pressure sodium lamps have a broader spectrum of light but poorer colour rendering than other types. Because sodium vapour lamps cause less light pollution than mercury-vapour lamps, many cities that have large astronomical observatories employ them.