What are some examples of light sources

Propagation of light

The sun
The light of the sun is created in the approximately 300km thick layer of the photosphere. Its temperature is around 5500 ° C and its density is very low at around 0.000 001g / cm³ (density air 0.001g / cm³).

Stars
Stars are very distant "suns" with surface temperatures between 3000 ° C (red glowing stars) and 25000 ° C (blue glowing stars). At night you can see many of them in the sky.

Meteors (shooting stars)
Meteors are small celestial bodies (stones, chunks of ice, etc.) that have entered the earth's closest area of ​​attraction and are slowed down by the air when they penetrate the earth's atmosphere. They get so hot that they glow and sometimes become liquid and gaseous. Only a part of very large meteors therefore reaches the earth's surface as a solid, the liquefied and gasified part practically sinks to the ground atom by atom.

lightning
In the case of lightning, the luminous phenomena come about through electrical discharges that stimulate the air gas to glow in various ways in the lightning channel.

Northern lights
The northern lights are created when particles (mainly electrons and protons) coming from the sun, deflected by the earth's magnetic field, reach the earth's atmosphere near the poles and stimulate the air gas atoms to glow.

Embers / lava
All strongly heated bodies emit a "light" that is characteristic of the body's temperature. Less hot bodies radiate red, very hot bodies white.

Fire / flames
The heat that is released during a chemical combustion reaction creates light in the flame.

Lightbulb
In the incandescent lamp, a wire is heated so much by electricity that it emits the light radiation characteristic of the heated body. The hotter the filament, the "whiter" the light.
More about incandescent lamps from Christoph Wallner

Fluorescent tube
In fluorescent tubes, electrons that have been accelerated by the applied electrical voltage hit gas atoms in the tube and stimulate them to glow.

Glow lamp
The glow lamp is the smallest form of the fluorescent tube.

Light emitting diode (LEDs)
In the case of light-emitting diodes, structures of the semiconductor are stimulated to glow directly at a semiconductor boundary layer.

Luminescent material
Luminescent material absorbs light, electron beams or UV radiation and emits them again as light of a different color either immediately (fluorescent) or with a delay (phosphorescent). This is used, among other things, for fluorescent tubes, television screens, nocturnal clock faces, etc.

Firefly
Female fireflies (approx. 2 mm long) and some other animals stimulate chemical reactions by emitting nitrogen, which make phosphorescent materials glow in order to attract the attention of males.