With the current Corona virus issues, we get many questions about using LEDs with an ultraviolet (UV-C) wavelength for killing bacteria, and more specifically viruses like Covid 19.
While UV-C light is very effective at eradicating pathogens, there are huge technical issues related to producing low-cost short-wavelength UV-C LEDs with a high enough power conversion efficiency necessary to have a good germicidal efficacy.
Why? Blue and ultraviolet LEDs use a Gallium Nitride (GaN) base. The trouble is that GaN is is not transparent to UV-C light. The result is that even in the best examples of UV-C LEDs, the photon extraction efficiency is less than 5%, so the power conversion efficiency is horrible. Other coatings and silicones used in LED manufacturing to protect the LED die also absorb UV-C wavelengths, compounding the issues and the price.
UV-C LEDs are very expensive, and still very inefficient, but many companies and labs around the world are working on this problem. Currently, low-pressure mercury vapor lamps provide a more effective solution than LEDs.
The bottom line is that you aren't going to purchase a cheap and effective UV-C LED germicidal lamp or wand from Amazon, or any of the Chinese internet sites. Chances are you will receive a nice purple blacklight, which will work great on your old psychedelic glow-in-the-dark posters, but be pretty useless against Covid 19.