Jeff KaufmanModify

2026-04-30 21:00:00

When I pitch people on far-UVC they often ask about in-duct UV. How about putting UV inside your HVAC ducts, where you can safely blast the air with cheap toxic wavelengths. Unfortunately, it's rarely a good approach.

The biggest issue is that most people don't have ducts. They're common in the US, though less so in older construction (radiators) or newer (mini-splits). Outside the US (and Canada, and Australia), however, ducted systems are mostly limited to large modern office buildings. Worldwide, maybe one in ten indoor hours are spent in ducted spaces. [1]

Even in spaces that do have ducts, in-duct UV only works when air is flowing. Most HVAC systems only run the blower when they're calling for heat or cooling: a small fraction of the time. To get useful pathogen reduction you need ~constant recirculation, which isn't great. Blower motors draw a lot of power, so running them continuously gets expensive. Plus, during cooling season in a humid climate it will pick up humidity from the coil and have to work harder later.

If you do set your system to blow constantly, you don't get much additional benefit from in-duct UV. You can typically use a MERV-13 filter, and this removes the majority of particles, even tiny viral droplets and bacteria. In-duct UV helps some, getting you from >50% to nearly 100%, but at best this doubles your CADR.

Another risk with in-duct UV is that it fails invisibly and fails open. If the bulb dies you won't notice, everything will work identically, you'll just stop having cleaned air.

In-duct UV is just not that widely applicable, and even if you do have a compatible system you still generally do much better with stand-alone air purifiers (good default choice), far-UVC (especially for larger spaces or where you need minimum noise), or upper-room UVC (especially for high-ceiling spaces).

[1] I asked Claude Opus 4.7, ChatGPT 5.5 Thinking, and Gemini 3.1 Pro "Approximately what fraction of indoor hours spent by humans around the world are in spaces with a ducted HVAC system? Can you give me your 50% confidence interval?", and got 9-13%, 10-20%, and 6-11% respectively.

Comment via: facebook, lesswrong, mastodon, bluesky

2026-04-29 21:00:00

While I was traveling Julia asked me: why is Anna saying her fiddle practice is only two minutes? In this case, two minutes was the right amount of time!

Anna (10y) and I had been fighting a lot about practice. She'd complain, slump, stop repeatedly to make adjustments, and generally be miserable. I'd often have to pull out "if you want to keep taking fiddle lessons you have to practice": she loves her teacher and is very motivated by the prospect of being good at fiddle. Still, it would take us ages and we'd barely get through anything.

One evening when she seemed like she might be open to it I explained that we were spending twenty painful minutes on two minutes of material. I challenged her: if she focused, and went through with no fussing, we'd be done in two minutes. It did turn out to be the right time for this message, she gave it a good try, and (with a little fussing in the middle) we were done in three minutes.

Over the next few days I continued to remind her that if she buckled down it would go quickly, and we got into a pattern of efficient and pleasant 2min practices. We probably continued this a bit longer than ideal, and then I went on a trip without handing this off well. Julia's question was a good reminder that we weren't done with the progression.

When I came back I started gradually increasing how long we practiced. Now that we had a good non-complainy dynamic this went well, and Anna started learning much faster. She wanted to be able to participate in jamming at NEFFA, worked hard at that goal, and last weekend she got to play Coleman's March at the annual Kids Jam:

Part of why I took a long time to start lengthening lessons, beyond just forgetting, was that I don't want to apply too high a marginal tax rate. If I had said "you still have to practice the full time, even though you're getting 10x done now", that would have been super demotivating. Instead, she got to enjoy a few weeks of the full profits (2min practice) before gradually working back up.

(This is just me writing about a thing that happened to work with one of my kids. No reproducibility claims here, your fiddleage may vary!)

Comment via: facebook, lesswrong, mastodon, bluesky

2026-04-27 21:00:00

Damon Binder recently wrote up an argument for prioritizing air filtration over far-UVC for pathogen control:

UVC and filtration are close substitutes—both deliver effective air changes per hour, both reduce airborne pathogen concentrations by the same amount per eACH—and on current pricing, filtration is cheaper.

There's a lot of good stuff in his analysis, but I see [1] three considerations that really change the bottom line:

1. Cost is actually much lower.
2. Noise is a serious issue.
3. Performance is dramatically higher in larger rooms.

Cost is straightforward. Binder priced far-UVC based on the high-quality Care222 lamp with the Krypton-11 at $2,500, but there's a much cheaper option, the Aerolamp at $500. It's also moderately higher output.

Binder analyzes a 30m2 room with a 2.5m ceiling. I'll assume this means 6x5x2.5. If I configure Illuminate with an Aerolamp in one corner pointed 0.5m above the far corner the installation is within TLVs and I get a median effective number of hourly air changes (eACH) of 11.6. The lamp degrades approximately linearly over Binder's 11,000 hour evaluation period down to 70% capacity, so we're averaging an eACH of 9.8. Over that time you're paying $500 for the lamp and $16.50 for the electricity (0.01kW * 11,000hr * 0.15 $/kWh) for a 5-year $/eACH of $53. Adding this to the best-performers from Binder's table, the Aerolamp is now the same cost as the cheapest filter:

Now let's consider noise. I have an AirFanta 3Pro, and it absolutely works. On high, it clears cooking smoke from my kitchen very quickly. But, like all commercial air purifiers that clean significant amounts of air, when you put it on high it's very noisy. As in, "hard to have a conversation in the same room" noisy. Binder describes this as "audible fans", but that's a huge understatement when you're talking about running them on high. When filters are too noisy, people unplug them. Here's one I saw this weekend, just before I took the initiative to plug it back in:

So lets say we we model running these filters at half speed, which cuts filtration by about half and noise by a lot more:

Now the filters are significantly more expensive per ACH than the Aerolamp. And they're still moderately noisy while far-UVC is silent.

The advantage grows for larger rooms. Consider one that's 20m by 12m, with the same 2.5m ceiling. This room has 8x the volume, and how much air you need to clean to "change out" the whole room is proportional to volume, so an eACH now represents 8x more cleaning. Modeling filters is simple, since they clean air at a constant rate, so their $/eACH values are now 8x higher. For UVC, however, the lamp cleans more air because it's light: it can go further in a larger room. Modeling with Illuminate and pointing the lamp from a ceiling corner to a spot in the middle of the floor I get a median eACH of 2.2 (1.9 with degradation), compared to the 1.4 you'd expect if it was linear with volume. Here's the same table for this 8x bigger room:

Getting to somewhat uncommon room shapes, if the room is also taller, say 6m (20ft), as large gathering places can be, we've added another factor of 2.4 to the room's volume. The filter costs go up by 2.4x, but modeling with Illuminate I get a median eACH of 1.6 (1.4 with degradation). Costs are now:

In this large room, for a given level of filtration the Aerolamp is 1/6th the cost of the next cheapest option. Far-UVC really shines here. This is why I've advocated for it in dance halls, and why the dance I helped organize until very recently decided to deploy far-UVC:

youtube; see the stand with four lights on stage

In the other direction, while Binder is right that fans are commodity items, fans that move large volumes of air extremely quietly are not. No one makes a commercial air purifier that approaches the limits of what's possible if you design for maximum air cleaning at minimum noise. So while the best far-UVC options outperform the best filter options in medium to large rooms today, future improvements in air purifier design might change that.

Despite the critical tone, I'm very happy Binder shared this, and there's a lot of good thinking in the piece. The point that filters are useful for a lot more scenarios, including pollen and smoke (I couldn't replace my kitchen AirFanta with an Aerolamp!) is an important one, especially as we push for everyday clean air. But I do hope he'll reconsider the potential for far-UVC to produce much more clean air for a given budget in dollars and noise.

[1] After drafting this I asked Opus 4.7 "What are the errors Jeff Kaufman would point out on https://defensesindepth.bio/on-far-uvc-and-air-filtration-2/ ?" It found (1) and (2) but not (3).

Comment via: facebook, lesswrong, the EA Forum, mastodon, bluesky

2026-04-24 21:00:00

A friend observed a pattern where contra dance events seem to be pairing older and younger callers. I looked over my notes for two-caller events in 2025 and saw [1]:

• Two older callers: 33 events
• One of each: 30 events
• Two younger callers: 4 events

Seems pretty clear evidence of pairing, no? But this actually turns out to be what you'd expect to see if organizers ignored age.

With 67 two-caller events there are 134 slots. Of these, 96 (72%) went to older callers and 38 (28%) went to younger ones. So there are four possibilities:

This gives us:

• Two older callers: 34 events (72% * 72%), vs 33 observed
• One of each: 27 events (72% * 28% + 28% * 72%), vs 30 observed
• Two younger callers: 5 events (28% * 28%), vs 4 observed

While this is very slightly in the direction you'd expect if organizers preferred to match different-age callers, it's well within what you could get by chance. It looks to me like this is just "two moderately rare events both happening is very rare."

We can compare this to the situation with gender, where you consistently get male-female pairs more often than you'd expect by chance:

The biggest caveat, though, is that this is based on a count of just one year's bookings. If I had more time, I'd like to go back over all the past data and count, but I really don't.

[1] Age is continuous, so this bucketing is somewhat arbitrary. Since most callers are either baby boomers or millennials, though, I do think there are two meaningful groups. I also don't know how old almost anyone actually is, so am just guessing from appearance.

Comment via: facebook, lesswrong, mastodon, bluesky

2026-04-22 21:00:00

When I write about things like storing food or medication in case of disaster, one common response I get is that it doesn't matter: society will break down, and people who are stronger than you will take your stuff. This seemed plausible at first, but it's actually way off.

Looking at past disasters, people mostly fall somewhere on a "kind and supportive" to "keep to themselves" spectrum. When there is looting it's typically directed at stores, not homes, and violence is mostly in the streets. Having supplies at home lets you stay out of the way.

One distinction it's worth making is between short (hurricane, earthquake) and long (siege, economic collapse, famine) disasters. Having what you need at home is really helpful in both cases, but differently so.

In short disasters (1917 Halifax explosion, London Blitz, 1985 Mexico City earthquake, 2011 Japanese earthquake and tsunami) you typically see sharing and mutual aid. Stored supplies mean you're not competing for scarce resources, have slack to help others, and make you more comfortable.

Stories of looting in situations like this are often exaggerated or cherry-picked. I had heard post-Katrina New Orleans had a lot of looting, but this was actually rumor. There's a really good article, "Katrina Takes a Toll on Truth, News Accuracy" on how rumors got reported as fact, and how the truth was nowhere near this bad. But the rumors had real effect at the time, including contributing to police and vigilante overreaction. Future disasters will also have rumors and reckless people with guns trying to be the 'good guys'; more reason to stock what you need so you can stay home.

Long disasters are uglier. Here I think having supplies matters even more, but so does caution. The siege of Leningrad is a pretty extreme example, where survival mostly came down to things outside people's control (ex: ration categories). When people did have stored food, however, it was very helpful as long as they were discreet. As people became increasingly desperate over the prolonged siege-induced starvation there are stories of people cooking at night or eating food raw to avoid alerting their neighbors (and, in the case of raw food, also because of lack of fuel).

Argentina and Venezuela are less extreme examples, but still informative. Because these were not nearly as severe as Leningrad there was much less societal breakdown. When there was violence and theft, it was concentrated around stores and transit; while there were home robberies this was uncommon. People who had more at home needed to shop less, which meant less exposure.

Similarly, in the siege of Sarajevo the risk was different (snipers and shelling, not robbers) but the takeaway is the same: people who had supplies and were able to stay home were less exposed to the risk.

Across both short and long disasters the pattern is similar: risk is mostly external, homes are rarely targeted, and having supplies that let you stay home is protective. The "people who are stronger than you will take your stuff" still happens, and in long disasters it's worth putting thought into how to avoid being a visible target, but it's not a major factor and it's not nearly enough to outweigh the value of having food and other resources on hand.

Comment via: facebook, lesswrong, mastodon, bluesky, substack

2026-04-21 21:00:00

Three years ago I wrote about how we should be preparing for less privacy: technology will make previously-private things public. I applied this by showing how I could deanonymize people on the EA Forum. In 2023 this looked like writing custom code to use stylometry on an exported corpus representing a small group of people; today it looks like prompting "I have a fun puzzle for you: can you guess who wrote the following?"

Kelsey Piper writes about how Opus 4.7 could identify her writing from short snippets, and I decided to give it a try. Here's a paragraph from an unpublished blog post:

Tonight she was thinking more about how unfair milking is to cows, primarily the part where their calves are taken away, and decided she would stop eating dairy as well. This is tricky, since she's a picky eater and almost everything she likes has some amount of dairy. I told her it was ok if she gave up dairy, as long as she replaced it nutritionally. The main tricky thing here is the protein (lysine). We talked through some options (beans, nuts, tofu, meat substitutes, etc) and she didn't want to eat any of them except breaded and deep-fried tofu (which is tasty, but also not somethign I can make all the time). We decided to go to the grocery store.

Correctly identified as me. Perhaps a shorter one?

My extended family on my mom's side recently got together for a week, which was mostly really nice. Someone was asking me how our family handles this: who goes, what do we do, how do we schedule it, how much does it cost, where do we stay, etc, and I thought I'd write something up.

Also correctly identified as me, with "Julia Wise" as a second guess.

And an email to the BIDA Board:

I spent a bit thinking through these, and while I think something like this might work, I also realized I don't know why we currently run the fans the direction we do. Could they blow in from the parking lot, and out to the back? This would give more time for the air to warm up and disperse before flowing past the dancers. We'd need to make sure to keep the stage door closed to not freeze the musicians.

Also correctly identified as me.

While in Kelsey's testing this appeared to be an ability specific to Opus 4.7, when I gave these three paragraphs to ChatGPT Thinking 5.4 and Gemini 3.1 Pro, however, they also got all three.

On the other hand, when I gave the same models four of my college application drafts from 2003 (332, 418, 541, and 602 words) they didn't identify me in any of them, so my style seems to have drifted more than Kelsey's over time.

Now, like Kelsey, being prolific means the models have a lot to go on. But models are rapidly improving everywhere, so even if the best models fail your testing today, don't count yourself safe.

The most future-proof option is just not to write anonymously, but there are good reasons for anonymity. I recommend a prompt like "Could you rephrase the following in the style of Kelsey Piper?" Not only is Kelsey a great writer, but if we all do this she'll have excellent plausible deniability for her own anonymous writing.

Comment via: facebook, lesswrong, mastodon, bluesky