Far-UVC (222nm) in 30 Seconds
- Germicidal like 254nm — but safe for human exposure
- Cannot penetrate past dead skin or tear film
- Enables continuous disinfection in occupied rooms
- Source: KrCl excimer lamps (222nm peak emission)
Practical Guide
When to Use Far-UVC
Occupied spaces where continuous air/surface disinfection is needed: hospitals, schools, offices, public transit. Not a replacement for conventional UVC in water treatment or closed chambers.
Why It's Safe
222nm photons are absorbed within the first few micrometers of tissue — the dead cell layer (stratum corneum) on skin and the tear film on eyes. They cannot reach living cells.
Light Sources
KrCl excimer lamps emit at 222nm with a narrow bandwidth. Optical filters remove residual wavelengths above 230nm. No LED equivalent exists yet — excimer technology only.
Exposure Limits
ACGIH 2022 TLV for 222nm: 479 mJ/cm² (8h) — that's 27× higher than the 254nm limit of 6 mJ/cm². IEC 62471 risk group assessment still required for installed systems.
Current Limitations
Lower output power than mercury lamps. Higher cost per watt. Ozone generation possible without proper filtering. Regulatory frameworks still evolving in many countries.
Next Step
Evaluate whether your application requires occupied-room disinfection. If yes, Far-UVC may be the only viable UV option — contact us for a feasibility assessment.
The ACGIH threshold limit value for 222nm is 479 mJ/cm² over 8 hours — compared to just 6 mJ/cm² for conventional 254nm UV-C. This 27× higher limit enables practical continuous room disinfection.[7]
Far-UVC vs. Conventional UV-C
| Criteria | Far-UVC (222nm) | Conventional (254nm) |
|---|---|---|
| Primary Wavelength | 222nm | 254nm |
| Human Safety | Safe for continuous exposure | Requires empty room / shielding |
| ACGIH TLV (8h) | 479 mJ/cm² | 6 mJ/cm² |
| Germicidal Efficacy | Effective (slightly lower per mW) | Gold standard |
| Light Source | KrCl Excimer only | Mercury lamp or LED |
| Cost per Watt | High (emerging tech) | Low (mature tech) |
| Best Use Case | Occupied rooms, continuous | Closed chambers, water, air ducts |
Welch et al. exposed human skin to 222nm for 66 weeks with no adverse effects. Sugihara et al. studied eyes for 36 months — also no damage. These are the longest Far-UVC safety studies to date.[7]
Far-UVC Adoption Timeline
KrCl excimer lamps emit a small amount of radiation above 230nm. Without proper optical bandpass filtering, these residual wavelengths can damage skin and eyes. Always verify that installed systems include certified optical filters.
Deep Dive
How can 222nm kill pathogens but not harm humans?
It comes down to penetration depth. At 222nm, photons have higher energy than at 254nm, but they are absorbed much more readily by proteins and other biomolecules in the outermost tissue layers.
On skin, the stratum corneum (dead cell layer, ~5-20µm thick) absorbs virtually all 222nm radiation before it can reach the living epidermis below. On eyes, the tear film (~5µm) provides similar protection.
Microorganisms on surfaces or in aerosols have no such protective layer — they are fully exposed to the germicidal radiation. This asymmetry is what makes Far-UVC uniquely suited for occupied-space disinfection.[7]
Why can't we use Far-UVC LEDs?
UV LEDs are based on AlGaN (aluminum gallium nitride) semiconductor technology. As the target wavelength gets shorter, the aluminum content must increase, which creates severe material challenges:
At 265nm, LEDs achieve 3-10% wall-plug efficiency. At 222nm, the required Al content is so high that crystal defects multiply, internal quantum efficiency plummets, and light extraction becomes extremely difficult. No commercial 222nm LED exists as of 2026.
KrCl excimer lamps remain the only practical 222nm source. They work by exciting krypton chloride gas to produce a narrow emission centered at 222nm. Research into alternative approaches (laser-driven, quantum dots) is ongoing but years from commercialization.
What about ozone generation?
Photons below 240nm can dissociate oxygen molecules (O₂ → 2O), leading to ozone formation (O + O₂ → O₃). KrCl excimer lamps have a small emission tail below 200nm that can generate ozone.
Proper optical bandpass filters eliminate this issue by blocking sub-200nm radiation. Well-designed commercial systems produce no measurable ozone increase in room air. Always verify that any Far-UVC installation includes certified optical filtering and has been tested for ozone generation under operating conditions.
Need Expert Guidance?
Our team helps you select the right UV technology for your application — vendor-neutral, data-driven.
- [7] Welch et al.: 66-Week Far-UVC Skin Safety Study; Sugihara et al.: 36-Month Eye Study
- [9] IEC 62471: Photobiological Safety of Lamps and Lamp Systems