Recently, I wrote about practical ways to ventilate for COVID-19, and why this is important. The idea from medical facilities and building scientists is that you want to optimize for “ACH” (or “air changes per hour”). This is a good start, because more air movement is better. But it’s really only a measure of how much fresh air you’re bringing in, not how much “bad” air is being produced.

Occupancy matters

There is a difference between a large space with two people in it, and a crowded coffee shop or classroom, or even more seriously, a choir practice. …


Since the pandemic started, lots of people have been infected indoors. Good ventilation helps reduce the number of viruses you breathe in, and it can make spaces a little bit safer during the COVID-19 pandemic.

First, you should read Zeynep Tufekci’s article on the issues associated with “short-range aerosol” transmission. COVID-19 is not measles, but a number of events (a cruise ship, a choir practice, a restaurant) and, relatively speaking, the lack of “super-spreader events” like this outdoors, are making us realize that you can get infected through the air.

If that’s possible, how should we fix it?

TB guidance gets us started

Drug-resistant TB…


Can we use a new kind of UV-C light in occupied spaces?

In 1903, Niels Finsen was awarded the Nobel Prize for using UV-C light for disinfection, originally for lupus. Since then, UV-C has been used in tackling Tuberculosis and MRSA in hospitals.

Recent interest in UV-C for COVID-19 has involved disinfecting air (since there is potential for the virus to transmit via aerosols), and also for fast surface disinfection.

Historically, UV-C sources have mainly been 254nm lamps, a wavelength very good at destroying DNA/RNA. However, 254nm is not safe to use where people can see it, because it can hurt your cornea. …


June 3, 2019

To the Committee on Energy, Utilities, and Communications,

I write to oppose AB-7, and I hope to convince the committee that permanent DST will wake people up too early throughout the winter, restricting how much they sleep. This pattern is associated with increased cancer, heart disease, diabetes, obesity, and depression, and it is especially harmful to night owls and younger people.

I submit that this process has misunderstood recent scientific discoveries in circadian biology. The legislature must consider that “switching” is not the only harm, but instead that persistent disruption to sleep timing (called “social jetlag”) can…


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We have to stop changing the clocks twice a year, but it’s also important to pick the right schedule when we do it.

Thousands of scientists say that Standard Time is better, yet legislators are pushing for permanent DST, anyway. The scientists have shown that seeing light in the morning is essential to health, and without it we get more cancer, diabetes, and obesity.

We need to balance the needs of night owls and early birds to have a good outcome for everyone.

Changing the clocks

Around the world, voters have chosen to end the clock changes twice a year. California, Oregon, Florida…


VR glasses are going to affect sleep like nothing we’ve ever seen

I took my iPhone 6 and popped it into Google Cardboard. Put the spectrometer where my eyes usually go, and pushed the button.

The meter took the reading really fast…

360 lux

f.luxometer says that’s 90% as bright as daylight — meaning it can kick your circadian clock two timezones away, after looking at a device for just a few hours. That’s almost as fast as the sun.

That measurement of Google Cardboard (not a specialized VR device at all) is more than double the 27" Apple Thunderbolt Display cranked up all the way, at a really close distance. …


They’re good for more than the movies

Dolby just announced their Dolby Vision project. To make movies look better, they’re testing incredibly bright screens—20,000 nits—making so much heat they have to use liquid cooling. Normal screens clock in at just 200-400 nits, so it’s quite a jump.

I’m sure the images look splendid, but that’s not why I’m excited.

In the process of evolving our software f.lux, I’ve been reading lots of the academic literature on circadian health.

One idea you’ll find a lot is that our workspaces and homes are too dark during the day and (as we’ve been saying for a few years now) they’re…

Michael Herf

co-founder of f.lux, finding the connections between circadian rhythms, sleep, healthy buildings, and light. (Previously made Picasa.)

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