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What Is Solar Radiation? Definition, Types, and Characteristics

What is solar radiation? Definition, types, and characteristics

Solar radiation definition: it is the energy emitted by the Sun in interplanetary space. 

When we speak about the amount of solar energy reaching the surface of our planet, we use irradiance and irradiation concepts. Solar irradiation is the energy received per unit area (J/m2), the power received in a given time. Likewise, solar irradiance is the power received in an instant - it is expressed in watts per square meter (W/m2)

Nuclear fusion reactions take place in the solar nucleus and are the source of the Sun's energy. Nuclear radiation produces electromagnetic radiation at various frequencies or wavelengths. Electromagnetic radiation propagates in space at the speed of light (299,792 km / s).

A singular value is the solar constant; the solar constant is the amount of radiation received instantly per unit area in the outer part of the earth's atmosphere in a plane perpendicular to the solar rays. On average, the value of the solar constant is 1.366 W / m2.

Types of Solar Radiation

Solar radiation is made up of the following types of radiation:

  • Infrared rays (IR): Infrared radiation provides heat and represents 49% of solar radiation.

  • Visible rays (VI): represent 43% of radiation and provide light.

  • Ultraviolet rays (UV radiation): represent 7%.

  • Other types of rays: represent about 1% of the total.

Types of Ultraviolet Rays

In turn, ultraviolet (UV) rays are subdivided into three types:

  • Ultraviolet A or UVA: They easily pass through the atmosphere, reaching the entire earth's surface.

  • Ultraviolet B or UVB: Short-wavelength. Has greater difficulty passing through the atmosphere. As a result, they reach the equatorial zone more quickly than at high latitudes.

  • Ultraviolet C or UVC: Short-wavelength. They do not pass through the atmosphere. Instead, the ozone layer absorbs them.

Characteristics of Solar Radiation

The total solar radiation is distributed in a broad spectrum of non-uniform amplitude with the typical shape of a bell, as is typical of the spectrum of a black body with which the solar source is modeled. Therefore, it does not focus on a single frequency.

The radiation maximum is centered in the band of radiation or visible light with a peak at 500 nm outside the Earth's atmosphere, which corresponds to the color cyan green.

According to Wien's law, the photosynthetically active radiation band oscillates between 400 and 700 nm, corresponds to visible radiation, and is equivalent to 41% of the total radiation. Within photosynthetically active radiation, there are subbands with radiation:

  • blue-violet (400-490 nm)

  • green (490-560 nm)

  • yellow (560-590 nm)

  • orange-red (590-700 nm)

When crossing the atmosphere, solar radiation is subjected to reflection, refraction, absorption, and diffusion by the various atmospheric gases to a variable degree as a function of frequency.

Earth's atmosphere acts as a filter. The outer part of the atmosphere absorbs part of the radiation, reflecting the rest directly into outer space. Other elements that act as a filter are carbon dioxide, clouds, and water vapor, which sometimes convert into diffuse radiation.

We have to bear in mind that solar radiation is not the same everywhere. For example, tropical areas receive the most solar radiation because the Sun's rays are nearly perpendicular to the Earth's surface.

Why Is Solar Radiation Necessary?

Solar energy is the primary energy source and, therefore, the engine that drives our environment. The solar energy that we receive through solar radiation is directly or indirectly responsible for aspects vital to biological processes such as photosynthesis, the maintenance of a planet's air temperature compatible with life, or the wind.

The global solar energy that reaches the earth's surface is 10,000 times greater than the energy currently consumed by all of humanity.

How Does Solar Radiation Affect Health?

Ultraviolet radiation can have various effects on human skin depending on its intensity and the length of its waves.

UVA radiation can cause premature skin aging and skin cancer. It can also cause eye and immune system problems. 

UVB radiation causes sunburn, darkening, thickening of the outer layer of the skin, melanoma, and other types of skin cancer. It can also cause eye and immune system problems.

The ozone layer prevents most of the UVC radiation from reaching Earth. In the medical field, UVC radiation can also come from certain lamps or a laser beam and is used to kill germs or help heal wounds. It is also used to treat certain skin conditions such as psoriasis, vitiligo, and nodules on the skin that cause cutaneous T-cell lymphoma.


    Published: May 13, 2015
    Last review: July 8, 2021