We explain what sunlight is, what is its origin and composition. Also, why it is so important, its risks and benefits.
What is sunlight?
We call sunlight the full spectrum of electromagnetic radiation from the central star of our Solar System, the Sun. Its presence in the sky determines the difference between day and night, and constitutes a vital part of our conception of the world at every level.
The sun is the most important and constant source of light and heat that we know of, thanks to which the planet Earth has the ideal conditions for life. The electromagnetic radiation emitted by this star penetrates the atmosphere and reaches an intensity of 93 lumens of illumination per watt of electromagnetic power, along its three light spectra: infrared, visible and ultraviolet.
The way in which sunlight reaches the earth’s surface depends to a large extent on the planet’s orbital position, its inclination and rotational movement, as well as the percentage of energy that is dissipated by the atmosphere, especially by the ozone layer.
Our planet receives around 4,000 hours of sunlight per year in its equatorial regions, and it is estimated that without these natural filters, their intensity would be such that our planet would be much hotter and much more desert, similar to our neighbor, Mars.
Origin of sunlight
Sunlight It is the product of 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.
Composition of sunlight
Sunlight consists of the propagation of energy and not matter through space, that is, in a form of radiation that travels along 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, as it has an intense impact on life and DNA. Its name comes from the fact that it is in a range much higher than that of violet light, the highest that the human eye can capture, that is, it is an invisible type of light.
- Ultraviolet B (UVB) light. Ranging between 280 and 315 nm, it has 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 low quantities.
- Ultraviolet Light A (UVA). With a range between 315 and 400 nm, it is the form of high-frequency radiation that most strikes the earth’s surface, without being visible to the human eye. To her we owe the tanning of our skins, but also the possibility of skin cancers.
- Visible range light. Spread over a range between 400 and 700 nm, it is about the various forms of light that make up the visible spectrum. If sunlight penetrates a prism, like raindrops in the atmosphere, we can see how it breaks down 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 contributes the most amount of heat from the Sun. It is undetectable by the human eye and can in turn be divided into three types: near infrared (from 800 nm to 2500 nm), mid infrared (2500 nm to 50 μm) and far infrared (50 to 1000 μm).
Importance of sunlight
Sunlight is essential for our planet to be what it is, in various modes. On the one hand, its radiation provides the necessary energy to start various chemical reactions in the atmosphere and in the primitive lithosphere, the immediate consequence of which was the formation of the ozone layer and the modification of the earth’s climate, which eventually led to conditions conducive to the emergence 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 weather seasons that form the cycle of nature. Without sunlight, our world was likely to be a cold and dead one, as are the outer planets of the Solar System.
Sunlight on plants
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, by-produces 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.
Benefits of sunlight
Exposure to sunlight has a number of positive effects on the human body, which go beyond providing us with perceptible heat and light to perceive the world around us. Among its benefits are:
- The metabolization of vitamin D. Indispensable for the fixation of calcium.
- The release of nitric oxide. Whose effect on the body includes the regulation of blood pressure.
- The production of cholecalciferol. A natural antidepressant whose levels decrease in populations exposed to dark winters and linked to summer depression.
Risks of sunlight
There is much debate as to whether sunlight is entirely beneficial or is also a risk factor for certain types of melanoma or skin cancer. It’s known that higher frequency forms of ultraviolet radiation have a dramatic impact on DNA, so much so that they can be used as a germicide in laboratories. However, the levels of this light that normally fall on the earth’s surface are not high; a situation that could have changed during the years in which the ozone layer was weakened by atmospheric pollution, at the end of the 20th century.