Helium lamps work by passing an electric current through helium gas, causing it to emit light. Here's a breakdown of the process:
1. Gas-Discharge Principle: Helium lamps are a type of gas-discharge lamp. Gas-discharge lamps produce light by ionizing a gas inside a tube or bulb.
2. Electrical Excitation: An electric voltage is applied across two electrodes within the lamp, which contains helium gas (often with small amounts of other gases like neon or nitrogen).
3. Ionization and Excitation: The electric field accelerates electrons. These electrons collide with helium atoms. These collisions excite the helium atoms, raising their electrons to higher energy levels. In some cases, the collisions are energetic enough to ionize the helium atoms, creating positively charged helium ions and more free electrons.
4. Light Emission: The excited helium atoms are unstable and quickly return to their lower energy levels. As the electrons transition back down, they release energy in the form of photons – light. The specific wavelengths (colors) of light emitted are characteristic of helium, resulting in a distinct spectrum of light.
5. Color Variation: While a pure helium discharge produces a specific color, manufacturers often add other gases (like neon or nitrogen) to the helium to create a wider range of colors, as seen in some novelty lamps. The exact gas mixture determines the color produced.
Example:
Consider a "flicker flame" light bulb. While often described as using helium mixed with neon and nitrogen, its light production follows the same principle. The electric current ionizes the gas mixture, and the various gases emit light as their electrons return to lower energy states. The barium azide coating on the electrodes helps to initiate and sustain the gas discharge, particularly the flickering effect.
In summary, helium lamps use electricity to excite helium atoms, which then release light as they return to their normal state. The color of the light is determined by the specific energy transitions within the helium atom (and the presence of any other gases in the lamp).
