It’s likely that you’re familiar with the concept of UV light. Commonly mentioned on sunscreen packaging or seen glowing through black-light posters, UV is present in many forms of light, including fluorescent strips, LEDs, and the sun itself. But what is UV exactly?

UV is short for ultraviolet light, which is a type of electromagnetic radiation. This radiation is naturally emitted from the sun, transmitted in waves or particles that travel at different frequencies or wavelengths. This range of wavelengths is known as the electromagnetic spectrum, which is divided into seven categories. These categories are organised according to decreasing wavelength and increasing energy, or frequency. The different groups of electromagnetic rays are as follows: microwaves, radio waves, infrared (IR), ultraviolet (UV), visible light, X-rays and gamma-rays.

Ultraviolet light falls between the range of visible light and X-rays in the electromagnetic spectrum. This means it should be handled with care, although in some forms, isn’t explicitly dangerous. Ultraviolet light oscillates between 800 and 30,000 THz with wavelengths of between 100-400 nanometres, which is, of course, quite broad. To further define the nature of UV rays, they are divided into three main categories: UVA, UVB, and UVC. Their wavelengths are as follows:

– UVA, or near UV: 315–400 nm

– UVB, or middle UV: 280–315 nm

– UVC, (including far UV): 180–280 nm

Although you might have noticed only UVA and UVB labelling on sunscreen, the sun actually emits three types of UV light. UVA comprises the majority of sunlight, which although less intense than UVB, penetrates deeper into the skin. UVB is generally responsible for the superficial burns, and subsequently, skin cancer. UVC is even more harmful, but thankfully, these rays are largely blocked by the ozone layer.

As a result, humans and other organisms have not evolved to cope with UVC exposure. Although this may sound dangerous, this makes UVC light a powerful tool for disinfection.

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