What the evidence actually says

First direct demonstration of far-UVC efficacy against airborne pathogens in an occupied indoor location.

First demonstration of far-UVC pathogen inactivation at full room scale.

Systematic comparison of 222 nm against conventional 254 nm UVC. Full text pending review.

Inactivation is not single-stage. Estimating dose from the first stage alone substantially underestimates what is actually required.

The longest chronic exposure study to date found no skin cancer or other skin abnormality.

Direct human eye exposure up to 75 mJ/cm2 produced no clinically significant photokeratitis, but did produce temporary discomfort.

The tear film is not the protective mechanism it was widely assumed to be.

Animal corneal epithelium is three to four times thicker than human, so animal safety margins are not conservative when applied to people.

The first revision in nearly fifty years raised the 222 nm limits substantially and separated eye from skin for the first time.

Far-UVC does produce ozone. Whether that is acceptable is a risk-management trade-off, not a question with a single answer.

222nm is produced by a four-stage process inside a sealed quartz tube. Nothing about the physics is secret. Building a lamp that runs stably for thousands of hours is the hard part.

A KrCl lamp does not emit 222nm alone. It also emits longer wavelengths above 230nm, and those longer wavelengths are the ones that damage skin. The filter is what makes far-UVC safe, and it is the hardest component to make.

Lamp failure is not a single event but a self-reinforcing loop. Heat reduces efficiency, reduced efficiency means more input power for the same output, more power means more heat.

Rated lifetime rose from 5,000 hours in 2023 to 12,000 hours in 2026, a 2.4-fold increase over three years.

Established the baseline dose figures for far-UVC inactivation of coronaviruses.

Tests three virus families in dried form, which is closer to real contaminated surfaces than liquid suspension.

Tests the hardest organisms to kill, and shows that the surface material itself changes the result.

222 nm and 254 nm cause comparable DNA damage, but 222 nm additionally disables the bacteria's ability to repair it.

Lamp position determines both how well the system works and how much unwanted chemistry it produces.

Under ceiling-mounted fixtures the eye receives far less than the room maximum, because of downward gaze, brow shading and blinking.

A single volunteer exposed to roughly 800 times the ICNIRP limit showed no observable burns or clinically apparent skin damage.

Three years of continuous observation in a working clinical environment found no acute or chronic ocular damage.

Measures subjective comfort rather than clinical damage, and finds none at head doses up to 50 mJ/cm2.

Animal studies place damage thresholds far above occupational limits, but these figures do not transfer directly to humans.

The paper that opened the ozone question in the far-UVC field.

A single lamp used at the manufacturer's recommended coverage produced no significant change in ozone or fine particulate matter.

Ordinary air cleaners can remove far-UVC byproducts, which had not previously been demonstrated.