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What is ultraviolet (UV) radiation? I’m interested in understanding the basics: What exactly is it, physically? What part of the electromagnetic spectrum does it occupy, relative to visible light, infrared, X-rays, etc.? Where does it originate – is it solely from the sun, or are there other significant natural or artificial sources? And could you also briefly touch upon the different types of UV radiation (UVA, UVB, UVC) and what differentiates them?

Answer

UV radiation, or ultraviolet radiation, is a form of electromagnetic radiation with wavelengths shorter than visible light but longer than X-rays. Its wavelength range is approximately 10 nm to 400 nm. It is invisible to the human eye.

Source of UV Radiation:

The primary source of UV radiation is the Sun. The Sun emits UV radiation across the entire UV spectrum, but the Earth’s atmosphere absorbs a significant portion of it, particularly the shorter wavelengths.

Here’s a breakdown of the UV spectrum and how it interacts with the Earth’s atmosphere:

  • UVA (315-400 nm): UVA radiation is the least energetic form of UV radiation and comprises the majority of UV radiation reaching the Earth’s surface. The atmosphere absorbs relatively little UVA.

  • UVB (280-315 nm): UVB radiation is more energetic than UVA and is significantly absorbed by the ozone layer in the stratosphere. The amount of UVB reaching the surface varies depending on factors such as time of day, season, latitude, and ozone concentration.

  • UVC (100-280 nm): UVC radiation is the most energetic and dangerous form of UV radiation. It is almost entirely absorbed by the Earth’s atmosphere (ozone, oxygen, and water vapor) and does not reach the surface under normal circumstances.

Artificial Sources of UV Radiation:

Besides the sun, UV radiation is also produced by several artificial sources:

  • Tanning beds and sunlamps: These devices emit primarily UVA and some UVB radiation to artificially tan the skin.

  • Welding arcs: Welding produces intense UV radiation, posing a risk to welders who are not properly protected.

  • Mercury vapor lamps: These lamps are used for various applications, including sterilization, disinfection, and industrial processes.

  • Black lights: Black lights emit primarily UVA radiation, which causes certain substances to fluoresce.

  • Germicidal lamps: These lamps emit primarily UVC radiation and are used for sterilization and disinfection purposes, such as in hospitals, water treatment plants, and air purification systems.

  • Lasers: Certain types of lasers can produce UV radiation.

The intensity and spectral distribution of UV radiation from artificial sources vary depending on the specific device.