We explain what light is, the history, speed and spread of this phenomenon. Also, its general characteristics, theories and more.

What is the Light?

Light is the part of the electromagnetic spectrum that can be perceived by the human eye . It is one of the forms of electromagnetic radiation that propagates in the universe and carries energy from one place to another.

Like all forms of radiation, light has a dual behavior, according to quantum mechanics. On the one hand, it behaves like an elementary and massless particle called a "photon" and on the other, it has wave properties.

The branch of science in charge of studying the phenomena of light is called optics.

History of light

History of light

Light has been the object of human curiosity and veneration since ancient times . The ancient Greeks considered it a source of life and truth, and it was widely studied by Empedocles and Euclides. Already at that time some of its physical properties were known, although it would be from the Renaissance that its study and application to human life would take a real impulse.

The invention of electricity and the possibility of lighting at will was another of the great drivers of his study, although he was always attentive to the discussion of whether light contained particles or whether it was an energy wave.

As early as the 20th century , optical engineering took over the development, together with electronics, of numerous modern applications for light. Thanks to quantum theories and advances in science, the workings of light were much better understood .

Technologies such as lasers, holograms, film , photography , photocopying or photovoltaic panels emerged from this evolution .

Speed of light

The first successful measurement of the speed of light was made in 1676 by Ole Roemer, a Danish astrologer. Contemporary physics, however, has fine-tuned the measurement mechanisms to the currently accepted magnitude, which is 299,792,458 meters per second, usually around 300,000 kilometers per second.

It should be said that this speed refers to light propagating in a vacuum since, when doing so through matter , its speed decreases according to the nature of the matter passed through.

Propagation of light

Propagation of light

One of the first pointed characteristics of light is its specific way of propagating itself: in a straight line . In fact, the origin of the shadows has to do with this since when crashing against an opaque object, the light projects its silhouette: the background around it is illuminated except for the portion blocked by the body.

The shadow is made up of two regions : the penumbra (the brightest part) and the umbra (the darkest part).

The games of shadows, which depend on the position and angle of the light origin, show that it is possible to foresee the rectilinear movement of light waves . In fact, this is what geometric optics is dedicated to.

Refraction of light

Refraction of light

One of the main observable physical phenomena of light is refraction, which occurs when light changes its propagation medium . As it begins to spread through a new medium, its speed changes and this is evidenced by a sudden change in direction, which can give a false impression of what is observed.

It is the effect that occurs when introducing a teaspoon in a glass of water , for example. Refraction makes the object appear to break when entering the water.

The greater the change in speeds (between one medium and another, for example air and water), the greater the change in direction and the more pronounced the visual effect.

Light diffraction

Light diffraction

The phenomenon of diffraction occurs when a beam of light that has a certain direction passes through a narrow aperture and deflects its course in new directions, using the aperture as a new wave emitter.

The resulting effect is a beam of light that appears to "open up." This is a widely used principle in photography and telescopic design.

Reflection of light

Whenever light hits matter, two phenomena occur : a part of that light is reflected (we can think that it bounces off the material ) and another is transmitted to the material and heats it.

When white light, which has all colors (sunlight for example), falls on an object, only certain frequencies of the light are reflected and reach our eyes . This is how we see the color of the object: it corresponds to the frequency that was reflected, the rest was transmitted to the object.

Smooth or polished optical surfaces, such as mirrors, reflect light at the same angle of incidence.

Light scattering

Light scattering

Scattering is a phenomenon that implies that, when entering a transparent body with non-parallel faces (such as a prism or a drop of water), the light decomposes into its entirety of colors .

This happens because when changing the medium, its speed and wave frequency varies, which allows us to see the entire chromatic spectrum that white light contains.

Polarization of light

Polarization is the ability of certain translucent crystals , once superimposed and turned at a specific angle, to mitigate the passage of light and avoid certain angles of reflection.

Thus they operate, for example, glasses sun or certain filters for cameras , which modulate through this crystal system the amount of light that can enter the appliance or to the human eye .

Theories about the nature of light

Over time many theoretical approaches to the nature of light emerged. Some are:

  • Wave theory . It approaches light by considering it an electromagnetic wave, that is, an electric field that generates a magnetic field (and vice versa) and that propagates itself indefinitely through space. This perspective is useful in describing numerous behaviors of light, but it is not as effective in telling what exactly light is and how it is composed.
  • Corpuscular theory . Think of light as a torrent of chargeless and massless particles called photons. Thus, it is possible to study the interaction of light with matter from the physical considerations between electrons and photons.
  • Quantum theories . They arose due to the need to reconcile the two previous perspectives (the wave theory and the corpuscular theory), but they have not yet managed to reconcile their positions. Great advances in this regard were Einstein's theories regarding relativity and the effect of gravity on the behavior of light, as well as recent approaches to a unified field theory, based on work with elementary particles.

Electromagnetic spectrum

Electromagnetic spectrum

The electromagnetic spectrum is the range of all possible energy levels of light . This spectrum is organized based on the wavelength of the emissions corresponding to each level, of which the visible spectrum is only a delimited portion.

The wavelengths perceptible by humans range from 380 nanometers (where the ultraviolet spectrum begins) to 780 (where the infrared spectrum begins). Colors associated with higher temperatures show lower wavelengths (or higher frequencies), while those associated with lower temperatures correspond to higher wavelengths or lower frequencies.

The above content published at Collaborative Research Group is for informational and educational purposes only and has been developed by referring reliable sources and recommendations from technology experts. We do not have any contact with official entities nor do we intend to replace the information that they emit.


Anas is an editor of a prestigious publishing company in the United States. She studied Mathematics in Arizona. Anas is also a teacher and one of her long-term goals is to build an institution that offers free education to everyone who are financially not stable. .

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