SSC JE Electrical Engineering 2011 Paper

Low pressure sodium vapour discharge lamp have a gas discharge tube containing sodium solid sodium, a small amount of neon, and argon gas in a penning mixture to start the gas discharge the discharge tube may be linear or ‘U-shaped when lamp is first started, it emits a dim red/ pink light to warm the sodium metal, within a few minutes as sodium vatal vaporizes, the emission become the common bright yellow .