Light

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

What is light?

What we call light is the part of the electromagnetic spectrum that can be perceived by the human eye. There are, apart from light, various forms of electromagnetic radiation in the universe, which propagate through space and transport energy from one place to another (such as ultraviolet radiation or x-rays), but we cannot perceive any of them naturally.

visible light is composed of photons (from the Greek word phos, “light”), a type of elementary particles that lack mass. Photons behave in a dual way: like waves and like particles. This duality gives light unique physical properties.

Optics is the branch of physics that studies light its properties, behavior, interaction and its effects on matter. However, light is the study of many other disciplines such as chemistry, general relativity or quantum physics, among others.

See also: Dark matter

history of light

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

The ancient Greeks understood light as something close to truth of things. It was studied by philosophers such as Empedocles and Euclid, who had already discovered several of its physical properties. Since the European Renaissance, In the 15th century, its study and application to human life gained great momentum with the development of modern physics and optics.

Subsequently, the management of electricity allowed artificial lighting of homes and cities, ceasing to depend on the Sun or the burning of fuels (diesel or kerosene lamps). This is how the foundations of optical engineering that developed in the 20th century were laid.

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 its physical functioning, in part thanks to quantum theories and the enormous advance in physics and chemistry that took place thanks to them.

Thanks to light and its study, there are technologies as diverse as lasers, cinema, photography, photocopying or photovoltaic panels.

Light characteristics

The light It is a wave and corpuscular emission of photons that is, at the same time it behaves as if it were made of waves and matter.

Always moves in a straight line at a defined and constant speed. The frequency of light waves determines the energy level of light, and is what differentiates visible light from other forms of radiation.

Although light in general (both from the Sun and from a lamp) looks white, it contains waves with wavelengths that correspond to each color of the visible spectrum.

This can be evidenced by pointing it at a prism and decomposing it into the tones of the rainbow. That an object has a particular color is a consequence of the object's pigment absorbing certain wavelengths and reflecting others, reflecting the wavelength of the color we see.

If we see an object as white, it is because the pigment reflects all the light that is emitted on it, all wavelengths. If, on the other hand, we see it black it is because it absorbs all the light and nothing is reflected, we see nothing, that is, we see black. The colors of the spectrum perceptible to our eye range from red (700 nanometers wavelength) to violet (400 nanometers wavelength).

light propagation

Light travels in a straight line and at a speed of 299,792,4458 meters per second in the void. If it has to traverse dense or complex media, it moves at lower 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.

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

Geometry has been an important tool when studying the propagation of light or designing devices to obtain certain effects, for example, the telescope and the microscope.

Light phenomena

The phenomena of light are alterations that it experiences when subjected to certain media or certain physical conditions. Many of them are visible every day, even if we don't know how they operate.

• The reflection When hitting certain surfaces, light is capable of “bounce”, that is, changing its trajectory describing certain and predictable angles. For example, if the object on which it impacts at a certain angle is smooth and has reflective properties (such as the surface of a mirror), the light will be reflected at an angle equal to the incident, but in the opposite direction. This is how mirrors work.
• The refraction When light passes from one transparent medium to another, with different densities, a phenomenon known as “refraction” occurs. The classic example is the passage of light between air (less dense) and water (more dense), which can be evidenced by placing a piece of cutlery in a glass of water and noticing how the image of the cutlery seems to be interrupted and duplicated, as if there was an “error” in the image. This is because water changes the direction of propagation when passing from one medium to the other.
• Diffraction When light rays surround an object or pass through openings in an opaque body, they will experience a change in their path, producing an aperture effect, much like car headlights do at night. This phenomenon is typical of all waves.
• The dispersion This property of light is what allows us to obtain the full color spectrum by dispersing the light beam, that is, it is what happens when we make it pass through a prism, or what happens when light passes through raindrops in the atmosphere and thus generates a rainbow.
• The polarization Light is composed of oscillations of the electric and magnetic field that can have different directions. The polarization of light is a phenomenon that occurs when, for example, by means of a polarizer (such as sunglasses) the directions of oscillation are reduced so that the light propagates with less intensity.

Sunlight and artificial light

Humanity's traditional light source has been that from the Sun, which constantly irradiates us with visible light, heat, ultraviolet light and other types of radiation.

Sunlight is essential for photosynthesis and to maintain the planet's temperature within ranges compatible with life. It is similar to the light that we observe from the other stars in the galaxy, even though they are billions of kilometers away.

From very early times Human beings have tried to imitate that source of natural light. Initially he did it by mastering fire, with torches and bonfires that required combustible materials and were short-lived.

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

Continue with: Color theory

References

• “Light” in Wikipedia.
• “The light” in CITECEA Resources of the Polytechnic University of Catalonia (Spain).
• “What is light?” (video) in Physics Al Límite.
• “What is light?” in Digital Library of the Latin American Institute of Educational Communication (ILCE).
• “What is light?” (video) at Kurzgesagt.
• “What is light – Physics” (video) in The Real Physics.
• “Light (physics)” in The Encyclopaedia Britannica.