Answer: When negative and positive charges meet, producing streaks of bright light and sound. This process is called an electric discharge. When the accumulation of charges between lower part of clouds and earth becomes large, it is sufficient to break the insulation of air.

Examples of electric discharge phenomena include: Brush discharge. Dielectric barrier discharge. Corona discharge.

Electric discharge denotes the excitation of atomic states in a gaseous medium on passing an electric current through the medium. An ordinary household fluorescent lamp is an example of an electric-discharge source.

Electric discharge lamp, also called Vapour Lamp, lighting device consisting of a transparent container within which a gas is energized by an applied voltage and thereby made to glow. Mercury vapour in a neon lamp gives a bluish light; mercury is used also in fluorescent lamps and some ultraviolet lamps.

High-pressure sodium lighting—a type of high-intensity discharge lighting—is becoming the most common type of outdoor lighting. High-pressure sodium lamps have an efficacy of 50–140 lumens per watt—an efficiency exceeded only by low-pressure sodium lamps. They produce a warm white light.

This process is known as electric discharge, or gaseous discharge. It is the process used to produce light in fluorescent and high intensity discharge lamps. In many of these lamps a second process is used to change the color of the light produced. The process is called fluorescence.

Sources of Light – Incandescence, Fluorescence, Bioluminescence, Chemiluminescence, Phosphorescence, Electric Discharge. Incandescence is light emitted from material because of the high temperature of the material. In a conventional incandescent light bulb, the excited atoms in the tungsten wire give off light.

Fluorescent light bulbs

the helium is used instead of a light bulb because a certain element only emits certain wavelengths of light while the bulb would emit all wavelengths, and even if you were to split this with a prism you would still see all the colors and not specific ones.

: an electron tube which contains gas or vapor at low pressure and through which conduction takes place when a high voltage is applied.

CAUTION: BE CAREFUL NEAR THE DISCHARGE TUBES. THEY ARE VERY FRAGILE, EXTREMELY HOT AND MAY GIVE AN ELECTRIC SHOCK IF MISHANDLED.

A gas- discharge tube is usually a glass tube with two electrodes sealed through its walls. When a voltage is applied to the two electrodes and the pressure of the gas in the tube is reduced, eventually a pressure is reached at which a current flows, and the gas begins to glow.

In discharge tube experiment, at low pressure and at very high voltage, an electric current is passed. Due to passage of electric current, a stream of rays is passed in the tube originating from cathode. These rays are called “CATHODE RAYS”.

If an electric current flows through a gas, it is known as electrical conduction or discharge in the gas. A tube used to study the electrical conduction through gases at low pressure known as discharge tube.

(1) Discharge-tube experiment: In J. J. Thomson’s experiment, the stream of cathode rays in the gas-discharge tube shows the presence of negatively charged subatomic particles called electrons.

Low pressure means that less number of gas molecules is present in the discharge tube. If the number of molecules is very less, the collisionws between the electrons which move towards the anode with a high velocity and the gas molecules and formation of cathode rays takes place.

William Crookes

So a low pressure ensures that the distance between collision is sufficiently large to enable the electron to cause excitation/ionisation of the gas molecules. This means that the gas pressure must not to be too low thus decreasing the distance the electrons travel between collisions with the gas molecules.