What is sunlight?

We explain what sunlight is, what is its origin and composition. Also, why its risks and benefits are so important.

  1. What is sunlight?

We call sunlight to the full spectrum of electromagnetic radiation from the central star of our solar system , the sun . Its presence in heaven determines the difference between day and night, and constitutes a vital part of our conception of the world at all levels.

The sun is the most important and constant source of light and heat we know, thanks to which the planet Earth has the ideal conditions for life . The electromagnetic radiations that this star emits penetrate the atmosphere and reach an intensity of 93 lumens of illumination per watt of electromagnetic power, along its three spectra of light: infrared, visible and ultraviolet.

The way in which sunlight reaches the earth’s surface depends largely on the planet’s orbital position, its inclination and rotation movement , as well as the percentage of energy that is dissipated by the atmosphere, especially the ozone layer .

Our planet receives around 4,000 hours of sunlight a year in its equatorial regions, and it is estimated that without these natural filters, its intensity would be such that our planet would be much hotter and much more desert, similar to our neighbor, Mars.

  1. Origin of sunlight

Solar light - sun
The sun produces different levels of heat and electromagnetic radiation.

Sunlight is a product of the nuclear fusion reactions that occur in the heart of the Sun , in which its abundant hydrogen is transformed into helium and other heavier elements, due to the immense gravity of the star (which has more than 99 % of the mass of the Solar System).

This eternal atomic bomb in space produces different levels of heat and electromagnetic radiation, which in its outermost layer, the photosphere, reaches a thermal equilibrium and the highest temperatures, as well as multiple electromagnetic waves, whose visible spectrum is what we call sunlight or natural light.

  1. Sunlight Composition

Solar light - spectrum of light
If sunlight penetrates a prism it will decompose at its various wavelengths.

Sunlight consists in the propagation of energy and not matter through space, that is, in a form of radiation that travels through five different wavelength regions , which are:

  • Ultraviolet C (UVC) light. Light at its highest frequency, in a range between 100 and 280 nm. Most of it is absorbed by the atmosphere, fortunately, since it has an intense impact on life and DNA . Its name comes from the fact that it is in a range far superior to that of violet light, the highest that the human eye can capture, that is, that it is an invisible type of light.
  • Ultraviolet B (UVB) light. With a range between 280 and 315 nm, it produces a strong impact on the atmosphere, where it triggers most of its photochemical reactions, such as the production of the ozone layer. In this way, it also reaches the earth’s surface in very small quantities.
  • Ultraviolet A (UVA) light. With a range between 315 and 400 nm, it is the form of high frequency radiation that most affects the earth’s surface, without being visible by the human eye. To her we owe the tan of our skins, but also the possibility of skin cancers.
  • Visible range light. Extended in a range between 400 and 700 nm, these are the various forms of light that make up the visible spectrum. If sunlight penetrates a prism, such as raindrops from the atmosphere, we can see how it decomposes into its various wavelengths, which in our eyes constitute the different colors : violet (about 400 nm), blue (near 450 nm), green (about 520 nm), yellow (about 600 nm), orange (about 650 nm) and red (about 700 nm).
  • Infrared range light. With a range between 700 nm and 1000 μm, it is the radiation that provides the most heat from the Sun. It is undetectable by the human eye and can in turn be divided into three types: near infrared (800 nm to 2500 nm), medium infrared (2500 nm to 50 μm) and far infrared (50 to 1000 μm).
  1. Importance of sunlight

Sunlight is essential for our planet to be what it is , in various ways. On the one hand, its radiation provides the energy necessary to launch various chemical reactions in the atmosphere and in the primitive lithosphere, whose immediate consequence was the formation of the ozone layer and the modification of the earth’s climate , which eventually led to favorable conditions for the appearance of life.

Without sunlight, photosynthesis would not be possible and life would have had to resort to other methods to produce , massify and evolve. Sunlight provides heat to the atmosphere, allowing the climatic seasons that form the nature cycle . Without sunlight, it is likely that our world was a cold and dead one, as are the outer planets of the Solar System.

  1. Solar light on plants

Photosynthesis consists of a series of chemical reactions driven by solar energy.

The plants survive thanks to the use of inorganic elements such as water , carbon dioxide (CO2) and sunlight, thanks to a process of synthesis of biochemically usable sugars, known as photosynthesis. That is the reason why plants need to be exposed to the sun (in degrees according to the species , of course).

Photosynthesis is carried out by algae, cyanobacteria and all forms of vegetation , and consists of a series of chemical reactions driven by the energy of the Sun, which allows the formation of glucose according to the following formula:

6CO2 + 6H2O + E = C6H12O6 + O2

This process, as will be seen, byproducts oxygen that is released into the atmosphere, making it breathable for animals. Once glucose is obtained through photosynthesis, plants can proceed to oxidize it regularly (cellular respiration), obtaining the ATP necessary to keep their metabolism going , grow, reproduce, etc.

  1. Benefits of sunlight

Sunlight produces cholecalciferol, a natural antidepressant.

Exposure to sunlight has several positive effects on the human body, which go beyond providing us with heat and perceptible light to perceive the world around us. Among its benefits are:

  • The metabolization of vitamin D. Essential for calcium fixation.
  • The release of nitric oxide. Whose effect on the organism includes the regulation of blood pressure.
  • The production of cholecalciferol. A natural antidepressant whose levels fall in populations exposed to dark winters and linked to summer depression.
  1. Risks of sunlight

There is much debate about whether sunlight is entirely beneficial or if it is also a risk factor for certain types of melanoma or skin cancer. It is known that the highest frequency forms of ultraviolet radiation have a dramatic impact on DNA , so much so that they can be exploited as germicidal in laboratories. However, the levels of this light that normally affect the earth’s surface are not high; a situation that could have changed during the years when the ozone layer was weakened by pollution of the atmosphere, at the end of the 20th century.

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