What is the light?

We explain everything about light, the history of its study, how it spreads and other characteristics. In addition, natural and artificial light.

  1. What is the light?

What we call light is the part of the electromagnetic spectrum that can be perceived by the human eye . There are, apart from it, various forms of electromagnetic radiation in the universe , spreading through space and transporting energy from one place to another, such as ultraviolet radiation or x-rays, but none of them can be perceived naturally.

Like those other forms of radiation, visible light is made up of photons (from the Greek word phos, “light”) , a type of elementary particles that lack mass . Photons have a double behavior: as waves and as particles . They are responsible for the particular physical properties of light.

The optic is the branch of the physical charge of study , both in their light emitting properties and their effects on materials . However, there are many other disciplines that are interested in light, such as chemistry , theoretical physics or quantum physics .

  1. Light story

The nature of light has intrigued the human race since ancient times, when it was considered a property of matter, something that emanated from things themselves. It was also linked to the Sun , the star king in most religions and worldviews of primitive humanity, and therefore also with heat and life.

The ancient Greeks understood light as something close to the truth of things. It was studied by philosophers such as Empédocles and Euclides, who had already discovered several of its physical properties. From the European Renaissance , in the fifteenth century, its study and application to human life took a big boost , with the development of modern physics and optics.

Subsequently, the management of electricity brought with it the possibility of artificially illuminating our homes and cities, ceasing to depend on the Sun or the burning of fuels (oil lamps or kerosene). Thus the foundations of optical engineering that developed in the twentieth century were sown.

Thanks to electronics and optics it was possible to develop applications for light that centuries ago would have been unthinkable. It increased our understanding of their physical functioning, in part thanks to quantum theories and the enormous advance in physics and chemistry that took place thanks to them.

To this route we owe such disparate technologies as laser, film , photography , photocopying or photovoltaic panels .

  1. Light characteristics

light characteristic properties dispersion colors prism
All colors are contained in the light.

Light is an emission of photons in a wave and corpuscular form, that is, at the same time it behaves as if it were made of waves and matter, respectively.

It always travels in a straight line , at a defined speed and pace. In fact, the frequency of light waves determines the level of light energy, while the wavelength is what differentiates visible light from other forms of radiation.

The colors are contained in the light , although the light looks white, ordinarily. That can be evidenced by pointing it to a prism and breaking it down into rainbow tones . However, matter absorbs much of the spectrum from it and reflects only one color , which is why things have the color they have.

The exception is white, which reflects all colors (that is, returns light completely) and black, which does not return any color, but absorbs them all. The colors of the spectrum noticeable by our eye range from red (700 nanometers) to violet (400 nanometers).

  1. Light propagation

The light propagates in a straight line and at a speed of 299,792.4458 meters per second in a vacuum. If you have to go through dense or complex media, it moves at different speeds.

Danish astronomer Ole Roemer made the first approximate measurement of the speed of light in 1676 . Since then, physics has greatly refined measurement mechanisms and has come up with the exact figure.

The phenomenon of the shadows also has to do with the propagation of the light: when hitting an opaque object, the light projects its silhouette on the background, delineating the portion blocked by the object. The shadow is composed of two stages: a brighter one, called penumbra; and a darker one, called umbra.

Geometry has been an important tool when studying the propagation of light or designing artifacts that, knowing their behavior, take advantage of it to obtain certain effects. This is how the telescope and the microscope were born , for example.

  1. Phenomena of light

light phenomena refraction
Refraction occurs because the speed of light decreases as it passes through water.

The phenomena of light are alterations, variations and visual effects that you experience when you undergo certain means or certain physical conditions. Many of them are visible daily, even if we don’t know how they operate.

  • Reflection . Upon impact on certain surfaces, the light is able to “bounce”, that is, to change its trajectory by describing certain and predictable angles. For example, if the object on which it hits is smooth and has reflex properties, such as the surface of a mirror, the light will be reflected in the same identical angle it brought, but in the opposite direction. That is precisely how mirrors work.
  • Refraction . On the other hand, when light passes from one transparent medium to another, with a noticeable difference in densities , a phenomenon known as refraction can occur. The classic example of this is the passage of light between air (less dense) and water (more dense), which can be evidenced by introducing a cover in a glass of water and notice how the image of the cover seems to be interrupted and duplicate, as if there was an “error” in the image. This is because the water changes its travel speed, generating an optical illusion by refraction.
  • Diffraction . Similarly, when the rays of light surround an object or pass through openings in an opaque body, they will experience a change in their trajectory, producing an opening effect, as occurs with the headlights of a car during the night. This is a property that light shares with other types of waves.
  • The dispersion . This property of light is what allows us to obtain the full color spectrum by dispersing the beam of light, that is, what happens when we pass it through a prism, or what happens when the light passes through the raindrops in the atmosphere and thus generates a rainbow.
  • The polarization . This phenomenon occurs when the light oscillates in more than one orientation, that is, when the light, due to some means or some alteration of its origin, propagates in a weaker or controlled way. This is what happens, for example, when we wear sunglasses: crystals polarize the light our eyes receive, decreasing their intensity and often changing color slightly.
  1. Sunlight and artificial light

The traditional light source of humanity has been that coming from the Sun, that gigantic atomic explosion in space that constantly radiates us with visible light, heat , ultraviolet light and other types of radiation.

The sunlight is essential for photosynthesis and to maintain the temperature of the planet within ranges compatible with life. It is similar to the light we observe from the other stars in the galaxy, although these are thousands of millions of kilometers away.

However, since very early times the human being has tried to imitate that source of natural light . Initially he did so by dominating the fire, with torches and fires, which required combustible materials and were not very durable.

Subsequently, he used wax candles that burned in a controlled manner, and much later lamps that burned oil or other hydrocarbons, thus emerging the first urban lighting network. This was later replaced by natural gas. Eventually it came to the use of electricity , its safest and most effective version.

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