Some products sold now that claim to be germicidal are actually the wrong wavelength, says Andrea Armani, a chemical engineering and materials scientist at the University of Southern California. In order to disinfect, the wavelength “should be 260 nanometers, but you can’t really tell, so that is one challenge,” she says.
Scientists can measure UV light electronically with
optical sensors or chemically with UV-C cards that changes colors with dose. Consumers can also purchase versions of these cards online, but Shen and Armani caution against false readouts; some companies don’t provide a specific sensitivity range that would trigger a chemical reaction strong enough to kill viruses. “There is no way to gauge how useful it is in practice,” says Armani.
You can’t tell by looking, either. Some wands give off a blue glow. That’s the LEDs, not the UV light itself; we can’t see light in the ultraviolet range. “I can’t say this enough: Don’t look at the bulb, just don’t look at the bulb,” adds Armani.
But consumers do have a few ways to spot fakes. Read the product specifications and make sure the wand is in the 260 nanometers range. If specifications aren’t provided, contact the seller. Read online instructions, too. If a product lacks a specific time frame — or lists a duration that's more than seconds — that's a red flag.
The price gives you a clue, too. High-powered UV-C LEDs cost around $15 each, says Armani, and you need an array of them. If the company sells a light for under $20 and the instructions say it works in minutes, it’s probably fake.