Ultraviolet germicidal irradiation

Ultraviolet germicidal irradiation (UVGI) is a special way to clean things using ultraviolet (UV) light, especially a type called UV-C. This UV light can kill or stop tiny living things like bacteria, viruses, fungi, molds, and other pathogens by hurting their genetic material. Because of this, UVGI is useful for cleaning food, surfaces, air, and water.

Scientists have found that UV-C light can stop the SARS-CoV-2 virus, which causes COVID-19. Many germicidal lamps give off UV light that can be unsafe for people, so UVGI is usually used where people are not present, such as in hospitals and in water treatment.

Recently, a newer type of UV light called far-UVC has become popular because it is safer for human skin and eyes. This type of UV light is very good at killing germs. UV-C light does not come from the sun because Earth’s ozone layer in the atmosphere blocks it.

History

The use of ultraviolet (UV) light to stop tiny living things from growing started in 1878. Arthur Downes and Thomas Blunt found that sunlight, especially its shorter wavelengths, slowed the growth of these tiny living things. Later, in 1885, Émile Duclaux noticed that different kinds of bacteria reacted differently to sunlight. Robert Koch showed in 1890 that sunlight could kill a type of bacteria that causes tuberculosis.

In the 1930s, scientists began using UV light to clean the air. William F. Wells showed in 1935 that UV light could quickly stop bacteria in the air from growing. This idea was tested in a hospital operating room at Duke University in 1936, where it helped reduce infections after surgeries. The method was also used in schools to help stop the spread of diseases like measles.

UV light has also been used to clean drinking water. The first attempt was in Marseille, France, in 1910, but it did not work well. By 1955, UV water treatment systems were used in Austria and Switzerland. Later, it was found that UV light could effectively stop tiny water creatures like cryptosporidium and giardia, leading to more use of UV water treatment in North America. Today, many countries have rules about using UV light to keep drinking water safe.

Method of operation

UV light is a kind of energy we cannot see with our eyes. It has wavelengths shorter than the light we see but longer than X-rays. One type of UV light, called UV-C, is very good at stopping tiny living things from growing.

When UV-C light touches the parts inside these tiny living things, it changes them so they cannot make more copies of themselves or do what they need to survive. This helps keep things clean and safe.

UV light can come from special lamps, like mercury lamps that shine at just the right wavelength, or from newer LED lamps that can choose their wavelength. Some lamps, like pulsed-xenon lamps, shine UV light across many wavelengths.

UVGI systems use these special lamps to clean places like water tanks, rooms, and air systems. The air or water moves through the area with the lamps, so it gets cleaned as it passes by.

Effectiveness

Ultraviolet germicidal light can help kill tiny living things by harming their genetic material. This makes it hard for them to stay alive or grow.

The success of this method depends on how much UV light reaches the tiny living things and how sensitive they are to the light.

The amount of UV light used is called the UV dose. It depends on how strong the light is and how long the tiny living things are exposed to it. Factors like how far the light is from the tiny living things, how clear the water or air is, and whether there are objects blocking the light can affect how well it works. Special guidelines help make sure the UV dose is strong enough to work well.

Safety

See also: Ultraviolet § Human health-related effects

Ultraviolet germicidal irradiation (UVGI) uses special light that can be harmful to humans if not handled properly. This light can hurt the eyes and skin.

To keep people safe, many UVGI systems have special features. These include warning labels, safety switches that turn off the lights when the system is opened, and protective eyewear that blocks harmful rays.

UV light can also affect indoor air. Using proper ventilation and filtration helps keep the air clean. Additionally, UV light can damage certain materials like plastics, so protective measures are needed in those cases.

Applications

UVGI can clean air with long exposure times. In the 1930s and 40s, a test in schools in Philadelphia showed that special lights could lower the spread of measles among students.

UV light can also stop SARS-CoV-2, the virus that causes COVID-19. Levels of UV light like those from the sun can stop the virus found in sputum from COVID-19 patients. This suggests that fewer cases in summer might be because of the sun’s UV light.

UV light is used to clean water without chemicals. Even tough germs are stopped by UV light. The world’s largest water cleaning plant, in New York City, uses UV light to clean billions of gallons of drinking water every day.

UV light is also used to clean water in homes and labs, and it helps keep fish and plants healthy in aquariums and ponds by stopping harmful germs. It is also used to clean food and drinks, like fruit and vegetable juices, to make sure they are safe to eat.

UV Sources

Main article: Germicidal lamp

Mercury vapor lamps

Ultraviolet light used to clean and disinfect comes from a special lamp called a mercury-vapor lamp. These lamps give off a strong beam of light that can kill tiny living things. The best light for cleaning is close to 260 nm.

There are two main types of these lamps: low-pressure and medium-pressure. Low-pressure lamps are very good at creating the right kind of light, but they don’t produce much power. Amalgam lamps are a special kind of low-pressure lamp that can work at higher temperatures and last a long time. Medium-pressure lamps get much hotter and give off a broader range of light colors, but they are not as good at creating the cleaning light.

Depending on the glass used for the lamp, low-pressure and amalgam lamps also give off light that can create a gas called ozone.

For cleaning water, special lamps are used. The lamp never touches the water. The water flows past the lamp, and the light kills tiny living things in the water.

LEDs

New technology using LEDs (light-emitting diodes) can now create the cleaning ultraviolet light. These LEDs can give off light by changing the materials used. As of 2019, LEDs were not as efficient as mercury lamps for turning electricity into the cleaning light. However, LEDs are smaller, which makes them useful for small cleaning systems or for use in medical tools. Because they use less power, these LED systems can even run on solar power in places far from electricity.

LEDs may not last longer in total hours of use than traditional lamps, but they can be used in ways that make them last longer when used only for short periods. Heat can make LEDs wear out faster, but engineers can design them to give more light for a shorter time or less light for a longer time.