4. • 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 spreads through space and
transports energy from one place to another, but none of them can
be perceived naturally.
5. 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: as waves
and as particles. This duality endows the light with unique physical properties.
Optics is the branch of physics that studies light, its properties, behavior,
interaction, and its effects on matter.
6. Characteristics of light
• Light 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.
• It 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.
7. Characteristics of light
• That can be evidenced by pointing it at a prism and
breaking it down into the tones of the rainbow. That an
object has a particular color is a consequence of the
pigment of the object 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 the
wavelengths. If, on the other hand, we see it black, it is
because it absorbs all the light and nothing is reflected, we
do not see anything, that is, we see black. The colors of
the spectrum perceptible by our eye range from red (700
nanometers wavelength) to violet (400 nanometers
wavelength).
8. Light propagation
• Light propagates in a straight line and at a speed of 299,792,458
meters per second in a vacuum. If it has to go through dense or
complex media, it moves at lower speeds.
• The phenomenon of shadows also has to do with the propagation of
light: when impacting against an opaque object, the light projects its
silhouette on the background, outlining the portion blocked by the
object.
• Geometry has been an important tool when studying the propagation
of light or designing artifacts to obtain certain effects, for example,
the telescope and the microscope.
9. Light phenomena
• The phenomena of light are alterations that you experience when
subjected to certain means or certain physical conditions. Many of
them are visible on a daily basis, even if we don't quite know how
they operate.
Reflection
Refraction
Diffraction
Dispersion
Polarization
10. Reflection.
• By impacting on certain surfaces, light is able to "bounce", that is, to
change its trajectory by describing determined and predictable
angles. For example, if the object on which it impacts with 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.
11. 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 (denser), which can be evidenced by introducing a cover in a
glass of water and noticing how the image of the cover seems to
interrupt and duplicate, as if there were an "error" in the image. This
is because water changes the direction of propagation as it passes
from one medium to the other.
12. Diffraction.
• When light rays surround an object or pass through openings in an
opaque body, they will experience a change in their trajectory,
producing an opening effect, as happens with car headlights at night.
This phenomenon is typical of all waves.
13. Dispersion (Decomposition of the light).
• This property of light is what allows us to obtain the full color
spectrum by scattering the beam of light, that is, it is what happens
when we make it cross a prism, or what happens when light passes
through the raindrops in the atmosphere and thus generates a
rainbow.
14. 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 decreased so that
the light propagates with less intensity.
15. Sunlight and artificial light
• The traditional light source of humanity has been that from the Sun,
which constantly radiates us with visible light, heat, ultraviolet light
and radiation of other types.
• Sunlight is indispensable for photosynthesis and for keeping the
planet's temperature within ranges compatible with life. It is similar
to the light we observe from the other stars in the galaxy, even
though they are billions of miles away.
16. • From very early times the human being has 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
not very durable.
• Later he used wax candles that burned in a controlled manner, and
much later created lampposts that burned oil or other hydrocarbons,
giving rise to the first urban lighting network, which was later
replaced by natural gas. Eventually it came to the use of electricity,
its safest and most effective version.
17. References
• “Luz” en Wikipedia.
• “La luz” en Recursos CITECEA de la Universidad Politécnica de
Cataluña (España).
• “¿Qué es la luz?” (video) en Física Al Límite.
• “¿Qué es la luz?” en Biblioteca Digital del Instituto Latinoamericano
de Comunicación Educativa (ILCE).
• “¿Qué es la luz?” (video) en Kurzgesagt.
• “What is light – Physics” (video) en The Real Physics.
• “Light (physics)” en The Encyclopaedia Britannica.
