The light sources are those that emit electromagnetic radiation in wavelengths between 380 nm and 750 nm (nanometers), the band known as the visible spectrum, because it is detectable by the sense of sight.
The main source of light for Earth is the Sun, followed by the Moon, the planets, and the stars. When artificial lights did not exist, if the nights were clear enough, the Milky Way would dimly illuminate the night, casting shadows on the ground.
At some point, it is estimated that it was about 200,000 years ago, humanity discovered fire and with it the possibility of lighting the night, obtaining heat, warding off predators and carrying out activities.
In addition to the celestial bodies, there are other sources of natural light, among which we can mention rays or lightning, which are of short duration, incandescent lava, and even animals and plants that are capable of emitting their own light..
Light is linked to high temperatures, electric shocks, and chemical reactions where combustion occurs. All these phenomena can be used to obtain a stable, durable and transportable light source, adjustable at will to illuminate interior spaces and facilitate nighttime activities..
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Light sources are classified in several ways. They can basically be:
-Primary: they emit the light they produce.
-Secondary: reflect the light produced by primary sources.
The Sun is the most familiar primary light source of all. The sun king, like all stars, produces large amounts of light and energy due to the reactions that occur in its nucleus..
Other primary sources are candles, torches, and lamps..
Instead, bodies that do not produce light by themselves must be illuminated to be seen. They reflect the light coming from the primary sources and are therefore called secondary light sources.
The Moon and planets like Venus, Mars and Jupiter, for example, are secondary sources, since they reflect sunlight.
However, it must be noted that materials that do not produce light by themselves under normal circumstances, can become luminous under certain conditions, for example if they are heated: a metal heated to red hot emits light.
The Sun is the most important star for the Earth and the most studied of all. Thanks to the light and heat of the Sun life develops on the planet, hence the star king aroused the interest of humanity from the beginning of history.
The Sun is a huge ball of gas, at the center of which high temperatures are reached to allow the fusion or conversion of hydrogen into helium, a process that generates a large amount of energy in the form of radiation.
To obtain a helium atom, four hydrogen atoms are required, but a small fraction of the present mass is converted into energy, according to Einstein's famous formula E = m.ctwo, where AND represents energy, m the mass and c the speed of light in a vacuum.
This energy travels as an electromagnetic wave in a vacuum and contains various wavelengths, mainly in the range of visible light. But it also contains other lengths not perceptible to the human eye, such as infrared and ultraviolet.
The lamps made it possible to extend people's working hours and contributed to safety on roads and cities. In the beginning, the first lamps made use of combustion, such as torches and candles.
The combustion materials used in different times depended on the resources that people had on hand: oil and wax, for example. This form of lighting lasted for a very long time, until in the 19th century the design of lamps improved significantly, producing more intense light. By then, gas lamps were in common use in public lighting in major European cities..
The advent of electric light brought with it the development of lighting systems based on electricity and various light-emitting devices..
The fundamental principle is, as indicated at the beginning, to convert some kind of energy into light. For example, when the atoms or molecules of certain substances go from the energy state of lower energy to a higher one and then back to the base state, they are emitted photons, which are tiny bundles of light energy.
There are several ways to get atoms to do this. The most convenient is to pass an electric current through the material, be it solid or gas..
Some of the most widely used lamps today, based on electricity, are described below. The two ways in which light is emitted through the passage of current are incandescence and luminescence..
In the process of glow the atoms of the material are excited by the increase in temperature caused by the current. Instead, in the luminescence the energy is absorbed by the material and emitted again accompanied by photons.
They consist of a transparent or colored glass bulb or capsule, and resistant to temperature, with a metal filament inside, usually tungsten, a very appropriate element thanks to its high melting point. Additionally the bulb is filled with an inert gas, such as argon, for example.
When the electric current passes through the filament it heats it and it emits energy, most of it in the form of heat, but a small percentage is transformed into light.
Although they are easy to produce and their cost is affordable, they have low performance and for this reason they have been replaced for some time by other types of lamps that are more efficient and durable..
The principle of operation of halogen lamps is the same as that of the common incandescent bulb, only the interior is filled with a halogen gas, usually bromine. The addition of halogen gas greatly improves the performance of the lamp and prolongs the life of the filament.
They consist of a gas enclosed in a tube, whose particles are excited (change to a higher energy state) when current passes. When the electrons in the gas return to their original state, they emit light, the color of which depends on the gas used in the lamp..
Originally the current came from the discharge of a capacitor, that is why the name given to this type of lamp.
They consist of a tube, which in addition to a mercury gas inside, contains a layer of material that also emits light by fluorescence, when its atoms are excited by the current..
The radiation emitted by mercury atoms when they return to the original state is almost all ultraviolet, however the coating of fluorescent material increases the emission in the visible light range, but its efficiency is greater than that of incandescent lamps..
They are built using light-emitting diodes, whose electrons are temporarily excited by the passage of current. When they return to their fundamental state, they emit intense light and of very good performance, which is why they are replacing traditional types of lamp.
It is a monochromatic light source, that is, of a single wavelength, unlike the sources previously described, which contain a variety of wavelengths.
The word "laser" is an acronym, formed by the initials of the name in English: Light Amplification by Stimulated Emission of Radiation. The translation is "light amplification by emission by stimulated radiation".
Laser light is high-powered and can be handled to produce a variety of effects on matter, not just lighting. They are used in CD devices, for the transmission of information and in the field of health.
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