Why does plasma emit light

The energy can be of various forms — heat, electrical or light ultraviolet light or intense visible light from a laser.

With insufficient sustaining power, plasmas recombine into neutral gas. Further out into space, all gas is ionised, and it is the highly energetic electromagnetic radiation from the Sun, itself made of plasma, that is responsible for this ionising process.

Space is therefore dominated by plasma. Plasmas occur naturally but can also be artificially made. Naturally occurring plasmas can be Earth-based terrestrial or space-based astrophysical. Artificial plasmas have been developed to service the needs of a wide range of fabricating, manufacturing and specialised coatings industries. Plasma is the highest energy state of matter. It consists of a collection of free-moving electrons, positive ions and neutral particles.

Although it is closely related to the gas phase in that it has no definite shape or volume, it does differ in a number of ways:. To produce and maintain the highly energetic state that exists within plasma, there must be a continual supply of energy.

Hot or thermal plasma is produced in atmospheric arcs, sparks and flames. The highly ionised plasma consists of large numbers of electrons and positive ions, with the temperature of both being extremely high.

Cold or non-thermal plasma is less well ionised, and although the electrons are high temperature, the positive ions and neutral particles are at a lower temperature. By plotting the few, distinct colors present in the light given off by a single molecule, a "line spectrum" is formed, which looks like a collection of thin lines.

In addition to electrons getting excited, the whole molecule itself can get excited by spinning more or vibrating more. There are therefore three ways a molecule can emit light: an electron falls to a lower state electron transition , the molecule spins less rotational transition , and the molecule vibrates less vibrational transition.

Now something interesting happens if you have more than one molecule involved. If you have a collection of molecules, they tend to bump into each other. When they collide, some of the energy in the excited electrons, excited spinning states, and excited vibrating states is converted simply to movement kinetic energy. As a result, there is less energy present for the photon that is emitted when the molecule transitions, leading to a photon with a color that is different from if there had been no collision.

Because the collisions are random, the color changes of the light given off are random. Where there was just one color a line in a certain portion of the spectrum of the light emitted, there are now many colors. Collisions between molecules therefore tend to smear the nice crisp lines of the light's color spectrum into bands with many colors. The more collisions there are and the harder they are, the more colors there are in the light given off. If there is a very high amount of strong collisions between molecules, all of the light given off by molecular transitions gets smeared into one continuous band of colors.

In such a case, all colors of the rainbow are present in the light and the light is therefore white. The light is typically not pure white, but is whitish red, whitish orange, etc.

Light with this broad arrangement of colors is called "thermal radiation" or "blackbody radiation" and the process that creates this light is called "incandescence". In every day life, we refer to incandescence as "glowing hot".

A material with zero collisions therefore emits a line spectrum, which is a collection of a few perfectly defined, unsmeared colors. On the other extreme, a material with an infinite number of collisions emits a blackbody spectrum, which is a perfectly smooth collection of all colors in a very distinct distributional shape called a "blackbody curve". The two opposite extremes; the line spectrum and the blackbody spectrum; are idealizations. In the real world, each spectrum is somewhere between the two extremes.

When we say that the color distribution of light is a line spectrum, we mean that it is close to a line spectrum, and not that it is exactly a line spectrum. There are two things that determines how fast molecules collide with each other. The first is the density of the molecules. The closer the molecules are together, the more chance they have to collide.

Solids have their molecules very close together and therefore collide enough to emit all colors of light. Solids typically emit a spectrum that is close to a blackbody spectrum. On the other hand, a dilute gas has its molecules much farther apart, so the color distribution of its emitted light looks more like a line spectrum. Some types of electrical lights contain plasmas.

Electricity in fluorescent lights creates a plasma. Colorful neon lights, often used in signs, also use electricity to convert a gas into glowing plasma. Certain types of flat-screen televisions make use of plasma as well. Plasmas are also common in nature. In fact, plasma is the most common state of "ordinary" matter that is, all matter other than the mysterious "dark matter" that astronomers have been puzzling over in recent years in the universe.

Far more matter is in the plasma state than in the liquid, solid, or gaseous states. Lightning strikes create plasma via a very strong jolt of electricity. Most of the Sun , and other stars, is in a plasma state. Certain regions of Earth's atmosphere contain some plasma created primarily by ultraviolet radiation from the Sun.

Collectively, these regions are called the ionosphere. The extreme upper layers of Earth's atmosphere, the thermosphere and exosphere and to a lesser extent the mesosphere , also contain a fair amount of plasma mixed in with gas atoms and molecules.