How do UV Light Air Purifiers Work and Can They Kill Viruses?

Air purifiers with UV lights have sprung up as potential saviors for fighting the coronavirus. These ‘sterilization lamps’ are being lauded a reliable way to kill 99.9% of viruses. But are they as good as people say, or are UV light air purifiers just another way for companies to jack up the cost of air purifiers and profit from the COVID-19 pandemic?

UV Light Air Purifiers on the Market Today

Often you’ll see terms like ‘UV-C sanitizers’ or ‘UV Light Germ Killers’ used to refer to UV light air purifiers. The idea is simple: they use a UV light to kill viruses and disinfect or ‘sanitize’ the air. That’s it.

Taobao and Amazon household UV light air purifier comparison review


What is UV light and how does it kill viruses? Read our explainer article here →.


But are UV light purifiers available on the market right now powerful enough to kill viruses? We found  data on 3 UV light sanitizers from China’s biggest e-commerce platform – Taobao. These included one purifier from Samsung:

UV light air purifier comparison power and airflow

The average UV bulb power for these 3 purifiers is 6W. Using a simple rule of thumb, this means the purifiers give out on average 6mW/cm2 of UV light, at a distance of 10cm.

6W UV light from common household UV light sanitizer kills virus at 10cm distance

Scientists have shown a dose of 75mJ/cm2 is needed to kill >99.9% of COVID-19. So for these UV air purifiers, they’d need to shine on a surface or in the air for 12.5s to kill >99.9% of COVID-19.

That doesn’t sound so long. However, in these air purifiers, air is passing in one side and out the other in around 0.35s. If these purifiers wanted to kill 99.9% of COVID-19, air would need to flow through the purifiers 36 times!

Result: Typical UV light air purifiers aren’t effective at killing COVID-19


What about really strong UV light air purifiers?

In response to the COVID-19 pandemic, new companies have popped up claiming to offer “incredibly strong UV light air purifiers”. Here’s one:

New powerful UV light air purifier to kill and disinfect COVID-19 coronavirus

This company claims that its UV light air purifier is specifically suited for killing viruses. They’re able to achieve a UV light intensity of 16.8mW/cm2 due to a ‘special coating’ inside the purifier which increases UV light intensity (the ‘standard’ ones above have an intensity of 6mW/cm2).

Intensity of UV light in an air purifier to kill COVID-19

At 16.8mW/cm2, viruses would need to be exposed to the UV light for 4.46s to kill >99.9% of the virus. That’s a little better than ordinary UV light purifiers, but still not great. Air would still need to pass through this purifier 15 times before it killed >99.9% of COVID-19.

Result: even more powerful ‘COVID-19 ready’ UV light purifiers don’t give enough time to kill the coronavirus.


What All UV light Air Purifiers Have in Common: a HEPA Filter

At this point, let’s backtrack. There’s one thing all the UV light air purifiers above have in common: they all have a HEPA filter. If UV light is so great at killing viruses, why do these companies include a HEPA filter in their air purifier? The reason’s simple: UV light can only kill a small amount of viruses in the air during one pass. HEPA filters, however are great at capturing viruses. Data shows they can capture over 99.9% of viruses in a single pass.


Maybe the UV light is to Kill Viruses Stuck in the HEPA Filter?

This seems like a smarter way to use UV light: the HEPA filter captures the viruses, and the UV light disinfects the viruses stuck in the HEPA filter over a longer period of time.

Using UV light to disinfect HEPA filter from viruses and COVID-19


However, that’s got its own problems. HEPA filters are a complex mat of pleated fibers. It’s unlikely that a UV lamp shining on HEPA filter surfaces can actually disinfect the entire surface.

UV Light Ineffective Disinfect Clean HEPA Filter Virus

What’s more, UV light can also damage materials like masks and HEPA filters. And there’s more:

Are UV Light Air Purifiers Really That Bad? #1

If UV lights get dusty, it has a huge impact the UV light bulb’s irradiation. That means UV light purifiers will either lose their efficiency quickly, or they’ll need cleaning regularly.

Are UV Light Air Purifiers Really That Bad? #2

UV lights will cost you more. Adding a UV light to a purifier will not just make the purifier more expensive, but will also run up higher electricity bills. A typical UV 50W UV-C light will cost you $4.32 a month if running 24 hours per day in the US. That’s wasted money for something that gives you little in return.

Are UV Light Air Purifiers Really That Bad? #3

UV-C light is really dangerous stuff. In fact, it’s the most damaging type of UV light out there. Why put something near you that could potentially do more harm to your body? Even if the UV light is sealed inside the air purifier, it can still leak out. The guys selling the fancy COVID-19 purifier mentioned above admitted that UV-C light leaks out.

Use a HEPA Filter Air Purifier to Purify the Air, not UV-C Light Sanitizers

HEPA filters do an incredible job of capturing viruses. Data shows that they can capture more than 99.9% of nanoparticles (many times smaller than the COVID-19 coronavirus) in just one pass.

UV lights aren’t a replacement for HEPA filters. HEPA filters have been used by hospitals and in other medical environments for a long time, and have proven the test of time.

dust really affect the efficiency of UV light


Bottom Line: How Effective Are UV Light Air Purifiers at Killing Viruses

UV light air purifiers are too weak to kill viruses quick enough. What’s more, most UV light purifiers contain HEPAs – the real key in removing 99.9% of viruses from the air. UV lights add extra cost, are difficult to maintain, and can damage HEPA filters. All with little benefit for removing COVID-19 from the air.

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