Final answer:
Vapor lamps operate by exciting gases or vapors with an electrical current to emit light, with common types being sodium-vapor and mercury-vapor lamps. They are known for their efficiency and the quality of light suitable for applications like street lighting.
Step-by-step explanation:
Vapor lamps, also known as gas-discharge lamps, operate by passing an electrical current through a gas or vapor, causing it to emit light. The most common types of vapor lamps are sodium-vapor and mercury-vapor lamps, which are often used in street lighting and industrial applications. Sodium-vapor lamps produce a characteristic bright yellow color known for its ability to penetrate fog, due to the yellow light's low scatter compared to white light. This is a result of the emission spectrum of sodium. Similarly, mercury-vapor lamps use a mixture of argon and mercury vapor that, when excited by an electrical current, emits ultraviolet (UV) light. This UV light then stimulates a fluorescent coating inside the lamp, resulting in the emission of visible light.
Fluorescent lamps, including compact fluorescent lamps (CFLs), also use a gas discharge principle but with a different operation mechanism. CFLs contain a ballast that increases the voltage to excite argon and mercury vapor mixture, producing UV light which stimulates the fluorescent coating inside the tube to emit visible light. These lamps are more energy-efficient compared to older incandescent bulbs, which use a tungsten filament in a partially evacuated glass envelope that glows when heated by an electric current.
In summary, vapor lamps rely on the excitation of gases or vapors to produce light, and are appreciated for their high efficiency and the unique quality of light they provide, which is suitable for a variety of applications, including street and industrial lighting.