UV Light: How It is Absorbed & Factors the Absorption Depends On?

| Updated on March 28, 2024

Ultraviolet light is a source of electromagnetic radiation that is accountable for suntans and sun damage and making black-light flyers shine. Too much UV radiation contact is rather harmful to live tissues. 

Electromagnetic radiation emerges from the sun and is distributed at varying wavelengths and frequencies by rays or atoms. The electromagnetic spectrum is identified as this large variety of wavelengths. In order to reduce wavelength and increase vibrational frequencies, the spectrum is usually divided into 7 parts. 

Radio waves, microwaves, infrared (IR), visible light, ultraviolet (UV), X-rays, and gamma-rays are the prominent classifications. 

  • UVA, or near UV (315–400 nm)
  • UVB, or middle UV (280–315 nm)
  • UVC, or far UV (180–280 nm)

What Happens When UV Light Falls on an Organic Molecule?

As an atom or molecule absorbs ultraviolet or visible light, an electron is excited. In other words, it is lifted to an orbit of greater energy than the one which normally resides in. For instance, upon light absorption in an atom, an electron passes from an s to a p orbital; in a molecule, an electron travels from one molecular orbital to a more energetic one. 

This excitation is inevitable since light produces a large amount of energy in the ultraviolet or visible portion of the spectrum, i.e., from the magnitude of 50 to 200 kcal/mole, and perhaps more at very short wavelengths. Because all matter comprises electrons, there will be some areas of the visible-ultraviolet spectrum through which every molecule will absorb light. 

For functional considerations, the spectrum’s ultraviolet-visible region is broken into three parts. Vacuum ultraviolet is a light where the wavelength is less than 200 nm (2000 Å); Air and certain solvents are ingested here, and calculations must be carried out in a vacuum, with many difficulties. 

In the ultraviolet portion of the vacuum spectrum, any organic molecule absorbs light very intensely. The range from 200 nm to 360 nm is referred to as the near-ultraviolet region (or merely the ultraviolet region) and the visible region from 360 to around 700 nm. Light has less power in these regions, which can only excite electrons that are relatively loosely attached, like those in pi bonds.

What Factors Affect UV Exposure?

Time of Year and Day Time 

UV levels primarily differ with the sun’s elevation in the atmosphere and are maximum mostly during summer months, especially the 4-hour cycle around noon time in mid-latitudes. 

The Latitude 

Near the equator, UV values are higher. Here, the sunlight has the shortest route to pass through the atmosphere relative to the earth’s surface, meaning less of the damaging UV radiation can be absorbed. 


With increasing elevation, less atmosphere to capture UV radiation is available. UV levels grow by 10 percent every 1000 m in height.

Haze and Clouds 

UV radiation is reflected by several materials and contributes to the average UV rate you encounter. Although grass, soil, or water represent less than 10 percent of incident UV radiation, around 15 percent incorporates sand, and about 25 percent illustrates sea foam.

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