How can UV light spread heat

Fight bacteria and viruses with UV light from LEDs

Disinfect with light
Reliable disinfection is essential in medicine, in animal breeding or in drinking water. UVC radiation from lamps containing mercury is often used for this purpose. In the future, mercury-free UVC LEDs will be an alternative.
The laboratories at the HSR investigate which LEDs and in which configuration are best suited for disinfecting food and liquids (symbol image).

UV light, often also called black light, is known from clubs and bowling halls - it makes teeth, light-colored clothing and even some drinks glow. However, UV light can do much more, for example kill bacteria, viruses and fungal spores. Disinfection using UV light is widespread in industry. Drinking water is sterilized by UV light and only then fed into the public water network. In medicine and animal breeding, the food and pharmaceutical industries, it removes dangerous germs, pathogens and mold from surfaces, liquids and air.

The UV light consists of three spectra. UVA and UVB radiation are well known, we protect ourselves against it with sunscreen. UVC radiation is less well known because it does not occur naturally on earth - it is absorbed by the ozone layer in the atmosphere. Exactly this UVC radiation is suitable for disinfection, because it is very rich in energy and, with sufficient radiation, reliably kills bacteria, viruses and other harmful organisms by destroying their DNA. In contrast to chemical disinfectants, the method works without any undesirable physical side effects. For example, chlorine changes the taste of water. The UV light range examined by the IET Institute for Energy Technology, on the other hand, disinfects residue-free and odorless and tasteless.

LEDs instead of mercury vapor lamps

Such UVC light-emitting diodes can rid liquids of bacteria, viruses and other organisms.

So far, UVC radiation in industry has mainly been generated with mercury vapor lamps. However, these have some drawbacks. They contain poisonous mercury which is released into the environment if the lamp breaks. In addition, they usually need a few minutes to warm up before they can deliver their full power, are relatively large, cannot irradiate selectively, require a voltage of more than 50 volts and age faster if they are switched on and off frequently.

For about five years now, it has also been possible to generate UVC radiation with UVC LEDs - without the disadvantages of mercury vapor lamps. UVC LEDs are similar in size to normal LEDs, but are made of different materials, can be operated with only 6 to 9 volts, do not contain any toxins and can be switched on and off as often as desired without affecting the service life. In addition, the major lamp manufacturers are working feverishly on improvements - compared to last year the output of LEDs has doubled. Reason enough for the HSR researchers at the IET Institute for Energy Technology to deal intensively with the applicability of the new technology.

The best LED for the best price

UVC LEDs are so small that they could even be used directly in a tap - an unimaginable application for a mercury vapor lamp. Especially for the disinfection of water, the IET researchers are currently investigating the currently most powerful UVC LEDs with regard to their disinfecting effect against bacteria, viruses, phages and fungal spores. Because the manufacturer's information alone is not sufficient for a reliable assessment of the disinfection performance.

A UVC LED is hardly as big as a match head.

“The combination of irradiance, irradiation time and wavelength is different depending on the target organism - for example, bacteria such as Escherichia coli can be killed more quickly and with less power than Bacillus subtilis spores,” says project engineer Raffael Palazzolo. In the test series, the IET therefore focuses on the effective radiation dose, i.e. the energy that actually acts on the test organisms. For a medically safe disinfection, 99.99 percent of the bacteria in a Petri dish must be killed in the test. “Our goal is to find the LED with the best cost-benefit ratio,” says Palazzolo. Only in this way will mobile applications for private use become conceivable. Palazzolo names, among other things, the use in air conditioning or in the outdoor area, for camping or outdoor sports, as possible areas of application.

A few months will pass in the IET before the best UVC LED is known for mass use. The next generation of UVC LEDs is already available and will also be tested in series of tests.

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University of Applied Sciences Rapperswil HSR

Here the University of Applied Sciences Rapperswil HSR presents stories from research. The articles appeared in advance in HSR magazine.
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