![]() But importantly, the winning lamp also happens to be the safest for humans, too. These 222-nanometer systems are almost twice as effective as conventional UV tube lamps, which are often used in ultraviolet disinfecting systems. This translates to needing about 20 seconds to disinfect a space receiving a low intensity of short wavelength UV light, similar to that used in our test. In our experiment, it took a dose of less than 2 millijoules of energy per square centimeter to kill 99.9% of viral particles. While all of the wavelengths we tested can inactivate SARS-CoV-2 at very low doses, the ones that required the lowest dose were the systems that emit UV light at a wavelength of 222 nanometers. We carefully repeated this process for a range of UV doses using the five different UV devices. If the viruses did not cause an infection, the UV source at that dose had successfully killed the pathogen. If the viruses could infect the cells, the dose was not high enough. Finally we examined the viral particles to see if they could still infect human cells in culture. We then shined UV light on the petri dish until we achieved a specific dose. To test each device we spiked a sample of water with millions of SARS-CoV-2 viruses and coated a petri dish with a thin layer of this mixture. There we tested numerous lights across the UV spectrum, including UV LEDs that emit light at 270 and 282 nanometers, traditional UV tube lamps at 254 nanometers and a newer technology called an excited dimer, or excimer, UV source at 222 nanometers. We ran these tests in a biosafety level three facility at the University of Arizona that is built to handle lethal pathogens. Specifically, we tested how large a dose is needed to kill 90% to 99.9% of the viral particles present. My colleagues and I tested five commonly used UV wavelengths to see which work best to inactivate SARS-CoV-2. Karl Linden, CC BY-ND Testing different wavelengths Researchers used this setup to test multiple different UV lights at various doses to see what it took to kill SARS-CoV-2. ![]()
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