Introduction to Far-UVC and Air Purifiers

Introduction to Far-UVC and Air Purifiers

Using computational modeling to understand how to best use these technologies in the real world

The Science Behind the Comparison

To understand the differences between Far-UVC and filtration, we need to dive into the physics. Using Computational Fluid Dynamics (CFD) modeling- the same mathematical approach that can model everything from airplane wings to cream swirling in your coffee- we can visualize exactly how air moves through a room and how different technologies affect the pathogens floating within it.

A CFD model is a mathematical representation of a real-life object- in our case, a room. Every detail is calculated: 30 cubic meters (1059.44 cubic feet) of space, the people breathing inside it, and most importantly, how infectious particles move through the air. This isn't an artist's imagination or an illustration- it's pure math rendered visually, like a pie chart for airflow.

We're also using CFD to model the thermal plume. This is the way that the hot air we exhale is pulled up by the heat our bodies naturally generate, lifting the aerosols we produce up to the top of the room.


(Like most of the videos on this page, this model is sped up, the timer on top will give you a better idea of the elapsed time)

Understanding the Playing Field

In our models, we focus on two key areas:

The Breathing Zone: According to ASHRAE standards, this is the air volume from 8 cm (3.14 in) to 180 cm (70.86 in) above the floor, 60 cm (23.62 in) away from each wall. The air the room occupants inhale and exhale tends to mostly come from inside this area. This is represented by the large cube, outlined in green, located in the middle of the room.

The Breathing Box: A 500 cm³ (30.51 cubic inches) volume right below your nose tip. By counting infectious particles inside versus outside this tiny space, we get a pseudo "fit factor"- similar to how we test mask effectiveness. This is also sometimes called "Exposure Reduction Factor". This is represented by a small cube outlined in orange in front of each person's mouth.

The Contestants

For our comparison, we chose:

Why not test the air purifier at maximum power- 141 CFM (239.5 m3/h) CADR? Because the resulting 54.5 dB is genuinely intolerable in a small room. If you won't actually use a device that loud, maximum CADR numbers are meaningless in real life. But don't worry, to keep things honest, we'll also show those results later.

Round One: Single Device Showdown


(You may have to pinch and zoom on mobile or view the video in landscape mode on in the YouTube app. Sorry, there's a lot of data to show and it's hard to fit it in portrait mode)

When we run our first simulation with one device of each type, we can see that both devices performed nearly identically at clearing pathogens from the overall breathing zone. After the simulated people stopped exhaling, both systems gradually cleared the room of infectious particles. 

  • Air purifier- 56.8% inactivation in the breathing zone, and 1.26 fit-factor for the breathing box.
  • Far-UVC- 56% inactivation in the breathing zone, and 1.69 fit-factor for the breathing box.

So it's almost a tie, right? Not quite.

Remember, Far-UVC is specialized- it only works on organic compounds like viruses, bacteria, and mold. It does absolutely nothing for PM2.5 pollution, smoke, dust, or other particles that air purifiers handle easily. So the win goes to filtration as the first thing you should purchase.

The Bathroom Exception

There's one place where Far-UVC excels: bathrooms. Traditional filters often don't work well in humid environments and can become moldy (1, 2, 3, 4,). Plus, bathrooms are often branching points in infection chains due to high traffic, often inadequate ventilation, and the presence of suspended fecal aerosols (1, 2, 3, 4, 5, 6, 7).

If you can only afford one Far-UVC device, put it in the bathroom. It's not as exciting as showing off cool tech in your living room, but it's where you'll get the biggest bang for your buck.

Scaling Up: The Plot Thickens

Here we test four air purifiers running at 88 CFM CADR each against four Lantern devices to see if performance scales linearly.

The four Nukit Lanterns have a total output of 120 milliwatts of filtered, 222-nanometer Far-UVC light. They are mounted in each corner and tilted slightly. If you recall how the warm, exhaled air rose on the thermal plume of the people in the room, you'll understand why they are positioned this way. We want to inactivate those bioaerosols before they cool, fall back into the breathing zone, and get inhaled.


The results:

  • Air purifiers- 91.6% inactivation in the breathing zone, 2.92 fit-factor.
  • Far-UVC- 100% inactivation in the breathing zone, 19.82 fit-factor.

For overall room pathogen inactivation (breathing zone), the results were still pretty close. Based on this, we could reasonably assign each Lantern a very rough "e-CADR" (equivalent CADR, a measurement sometimes used for GUV) of 88 CFM. Four air purifiers performed only slightly worse than four Far-UVC devices in the breathing zone, while costing less money and handling particulates more effectively. Point to team filtration, right?

But if we look at the breathing box data and fit-factor- and that's a very different story.

The Near-Field Advantage

The four air purifiers managed a fit factor of just 2.92 in the breathing box. That's about the same protection as a surgical mask. Meanwhile, the four Far-UVC devices achieved a fit factor of 19.82- reaching KN95 territory.

This is because Far-UVC excels at "near-field protection." It inactivates infectious particles in the air between people before they can be inhaled. Air purifiers, no matter how powerful, struggle with this. 

The Far-UVC devices also accomplished this nearly silently, while the four air purifiers generated 51.7 dB of noise- definitely noticeable.

Throwing More Power (CADR) at the Problem

What if we cranked up the air purification? We tested six air purifiers at maximum power, generating 141 CFM CADR each and a combined 62.3 dB of noise.

The results:

  • Air purifiers- 99.4% inactivation in the breathing zone, 10.34 fit-factor.
  • Far-UVC- 100% inactivation in the breathing zone, 19.82 fit-factor.

The six air purifiers at $960, on the highest setting, equalled the Far-UVC devices at overall room air sanitizing, but their breathing box performance still fell far short, well below the near-field protection from infection that $800 worth of Far-UVC provided.

The amount of pathogens you actually inhale the breathing box fit factor, not the amount that are in the room- the breathing zone, is what determines if you get infected or not. So, for preventing infection, Far-UVC, dollar for dollar, has a significant advantage.

The Real Answer: Why Not Both?

Far-UVC and air purifiers aren't competing technologies- they're complementary ones. They excel at different things:

  • Air purifiers: Great for overall room air quality, handle all types of particles, cost-effective
  • Far-UVC: Excellent for near-field pathogen protection, silent operation, specialized for biological threats

In a future write-up, we'll model both technologies working together and examine how filtration actually enhances the effectiveness of Far-UVC by facilitating air mixing.

Practical Takeaways

Start with filtration: Get the highest CADR air purifier you can afford that operates under 45 dB (preferably under 35 dB for spaces like classrooms and bedrooms). If you won't use it because it's too loud, it won't protect you. The best place to find the right air purifier for your needs is House Fresh.

Add Far-UVC strategically: Place your first unit in the bathroom, then add devices near areas of congregation, like dining tables. Far-UVC in kitchens helps with both airborne pathogens and surface contamination.

Remember the dose-response relationship: You don't need 100% protection to significantly reduce infection risk. Lowering the pathogen load in a room dramatically decreases transmission probability.

Using e-CADR for Far-UVC is not very accurate. e-CADR is an indication of total pathogen inactivation in the entire room. Far-UVC excels at near-field inactivation, which e-CADR does not accurately reflect. 300 CFM CADR from filtration and 300 CFM e-CADR from Far-UVC may have a similar effect on the breathing zone, but a very different impact on the breathing box, so they will have very different infection risks.

Consider alternatives: If your budget is tight, Upper-Room and Egg Crate GUV or DIY air purifiers can help. Opening windows with cross-ventilation is highly effective and free.

The Bottom Line

None of these technologies comes close to a well-fitting N95, FFP2, or KN95 mask, which should remain your first line of defense. But for improving indoor air quality, the choice isn't between Far-UVC and air purifiers- it's about using both strategically.

Filtration gives you broader protection for less money. Far-UVC gives you near-field protection that almost no amount of air purification can match. Together, they create a comprehensive approach to indoor air quality that's greater than the sum of its parts.

All device specifications come from third parties. The Levoit Core 300s measurements come from HouseFresh and the Nukit Lantern measurements come from LightLab International. The CFD modeling can be verified and reproduced using the spectral assay and IES file posted on the Nukit Lantern web page.

The following methods, software, and parameters were used to generate these models. Feel free to iterate, replicate, refine, or correct our work.

Each fluid-particle simulation is completed in 3 stages:

  1. Fluid only stage: Air-flow is allowed to develop completely in the presence of ventilation and any flow-inducing units (-60s to 0s)
  2. Breathing Stage: Mannequins breathe over 60 seconds (0s to 60s) and add (also inhale) particles to the room.
  3. Evolution stage: Breathing is paused. Particle pervasion continues to evolve with air-flow (60s to 300s).

Software: OpenFOAM v2406

  • Eulerian-Lagrangian Solver: reactingParcelFoam with reaction removed.
  • Fluid field solved with k-omega SST turbulence model.
  • Gravitational, aerodynamic and buoyancy forces acting on the particles.
  • One-way coupling.
  • Breathing cycle: 2.8 sin (1.048t).
  • 10 breathing cycles over 60 seconds.
  • Walls modeled as slip boundaries with particle rebound to avoid clumping.
  • 500 particles per second per person injected from the nostrils.

Custom UV Field post-processing:

  • UV Field computed based on Lamp’s Indoor Distribution Radiometry Test Report.
  • UV Field computation accounts for lateral and vertical angle variations.
  • UV Field also accounts for radial Irradiance variation based on Nadir position measurements.
  • UV Dose computation granularity: 0.05 seconds.

Post-processing software: ParaView v5.8.1

ASHRAE relevant parameters:

  • Room ACH: 3
  • Breathing Box dimensions: 4.8cm x 8.0cm x 13.0cm
  • Breathing Zone dimensions: 2.16m x 3.00m x 1.72m
  • Room dimensions: 3.36m x 4.20m x 2.26m
Note: While it is possible to model the particles as liquid aerosols, in the current simulations, the particles have the same density as air. This is done to simulate particles traversing exactly like the flow of air. In more realistic aerosol simulations, we will probably model aerosols with a density closer to water and some Gaussian size distribution (1 micron to 500 micron, perhaps).

All of the above models are provided with the caveat that "all models are flawed, but some models are useful." While they are not perfect, they offer a helpful guide for non-academics looking to protect themselves from airborne pathogens. Obviously, models produced by peer-reviewed sources without a conflict of interest (COI) take precedence, and we defer to those.

All content shown on this page is available under a CC BY-NC-SA 4.0 license: https://creativecommons.org/licenses/by-nc-sa/4.0/deed.en. Kindly inquire, and we will provide additional raw files.

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