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In this article we aim to answer the basic questions about UV systems. Such as: What are UV lamps used for? How UV lamp or its UV light works? How does UV damage DNA and kill bacteria? Moreover, we want to show you the different types of UV used for water treatment. 

What is UV Light?

UV light is light spectrum invisible to the human eye. The ultraviolet light comes after violet on the light spectrum, hence the name.

There are three different wavelengths of UV light: UV-A, UV-B, and UV-C. Solely UV-C light, which has the lowest wavelength out of the three, can be used to eliminate microorganisms.

How UV disinfection works?

UV systems offer green alternative to traditional chemicals. Chemicals harmful to the environment that are traditionally used for disinfection including chlorine, chlorine dioxide or hypochlorite.

Germicidal lamp is a device that converts electricity into ultraviolet radiation. UV lamps generate energy in the UV spectrum to destroy bacteria, fungi and viruses (microorganisms). Microorganisms include several distinct groups of disease causing germs – bacteria, viruses, fungi, algae and protozoa. Moreover, UV is highly effective in removal of cryptosporidium and giardia – organisms resistant to chlorine that are a major risk to human health. Another advantage of UV is the absence of taste and odour.

As the UV light is emitted it moves through the reactor area and aims at celluar level. The target of UV radiation is the genetic material, nucleic acid – DNA. As the UV penetrates through the cell and is absorbed by the nucleic acids, a rearrangement of the genetic information occurs, interfering with the cell‘s ability to reproduce. A cell that cannot reproduce is considered dead; since it is unable to multiply to infectious numbers within a host. The maximum absorption of UV light by the nucleic acid, DNA, occurs at a wavelength of 260nm.

What types of UV exist?

There are two types of UV lamps used for water treatment – low pressure and medium pressure UV. Low pressure UV lamps are evacuated and then filled with gas to a low pressure. The pressure in the body of the lamp is eventually between 1 – 10 mbar while medium pressure UV lamps are evacuated (a process of making vacuum inside the UV lamp during its production) to 1 – 5 bar and then filled with more gas resulting in a higher pressure in the body of the lamp. A frequent question, no, high pressure UV lamps do not exist.

The body of the discharge UV lamp is usually filled either with pure Argon or with a mix of rare gasses including Argon, Neon and/or others depending on the application. There is also a small amount of mercury in the lamp which necessary to provide the ultraviolet radiation.

As you can see in the picture, low pressure UV (on the left) is long and thin whereas medium pressure UV (on the right) is rather short and thick. That is not their biggest difference, though.

The most important difference between low pressure and medium pressure UV is something you cannot see with human eyes, it is the UV light they emit. Simply put, UV radiation has some wavelengths it consists of and the broader the spectrum of wavelengths is, the more effective the UV disinfection. It is because each organism or substance are destroyed and decomposed by a certain wavelength.

Low pressure UV-C lamps emit a single wavelength at 254 nm whereas medium pressure UVs emit a broad band of wavelengths all over the germicidal UV areas – from 200 to 600 nm. 

From these ranges of wavelengths you can easily see that medium pressure UV lamps have a significantly broader spectrum and radiate broad-band UV-C radiation rather than a single line. Thus can remove more kinds of microorganisms and substances and do that more effectively.  

For more detailed information about the differences between low pressure and medium pressure lamp see our next article: WHAT IS THE DIFFERENCE BETWEEN LOW PRESSURE UV AND MEDIUM PRESSURE UV LAMPS?

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