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General information from regulator and public-health documents; not medical, safety-engineering or purchasing advice.
Short answer
UV-C is the shortest-wavelength band of ultraviolet light used for germicidal devices. The FDA describes it as 200-280 nm; CDC/NIOSH gives 100-280 nm. NIOSH names 254 nm, the main output of a low-pressure mercury lamp, as typically the optimal wavelength for germicidal radiation.
Definition and scope
Ultraviolet (UV) radiation lies between visible light and X-rays. Documents split it into three bands, and the edges are conventions. NIOSH calls the band designations “approximate spectral regions” that “may vary between sources.” The table shows where two primary documents place the edges (documents checked 2026-10-30).
| Band | FDA GUV panel summary (Dec 2025) | CDC/NIOSH Publication 2009-105 |
|---|---|---|
| UV-A | 315-400 nm | 315-400 nm |
| UV-B | 280-315 nm | 280-315 nm |
| UV-C | 200-280 nm | 100-280 nm |
The only disagreement is the lower edge of UV-C, which sits well below the 254 nm output discussed below. The FDA summary also states that germicidal devices “typically generate ultraviolet radiation over a light band range of 200-400 nm” and that most operate in the UV-C range because those wavelengths have been demonstrated to be highly effective at microbial inactivation. For the biology of the damage itself, see how UV damages DNA.
Why 254 nm: how the wavelength works in practice
NIOSH describes the mechanism at 254 nm: when a photon strikes a cell, covalent bonds can form between adjacent thymine bases in DNA, which may lead to cell death or an inability to replicate. NIOSH adds that UV germicidal radiation has a significant effect because many biological polymers absorb energy in this band. In its guideline a “UVGI lamp” means a low-pressure mercury lamp that emits germicidal radiation predominantly at 254 nm, and NIOSH notes that only low-pressure mercury lamps had been evaluated in upper-room systems.
Lamp wavelengths: a checklist from NIOSH
NIOSH distinguishes lamps that look similar but emit differently. These points come directly from its guideline for choosing a lamp for upper-room systems in healthcare settings:
- Germicidal lamp: low-pressure mercury, predominantly 254 nm, UV-C.
- Tanning-type lamps: radiate in the UV-A and/or UV-B range; NIOSH says they may have a negligible effect on airborne microorganisms and, over extended periods, adverse health consequences for exposed people.
- 184.9 nm lamps: designed to emit at 184.9 nm and produce ozone, which NIOSH calls hazardous to humans even at low concentrations. Low-pressure mercury lamps “should be rated for low or no ozone generation.”
- Mercury content: because all lamps are eventually discarded, NIOSH says each lamp should contain a relatively small quantity of mercury (5 mg or less).
The FDA summary lists ozone and reactive oxygen species among the safety risks of germicidal UV and says testing of devices covers photobiological safety and ozone generation within the limit in 21 CFR 801.415. The related guide on ozone disinfection covers ozone as a disinfectant in its own right.
Where it matters for labs, clinics and supply decisions
Exposure limits are written at a wavelength
NIOSH states its recommended exposure limit as 6 mJ/cm² at 254 nm for a daily 8-hour work shift, matching the ACGIH threshold limit value at 254 nm, and says this corresponds to a maximum irradiance of 0.2 μW/cm² for 8 hours at 254 nm. These are 2009 figures for 254 nm; NIOSH points to its criteria document for calculating the limit at other wavelengths. A number quoted for UV-C in general is not the same as the 254 nm value.
Wavelength does not change line of sight
The FDA summary states that germicidal UV treats only directly illuminated surfaces and, unlike liquid disinfectants, does not penetrate lumens or porous materials. It names shadowing, distance and surface angle, soiling and microbial resistance as limits, and notes that dirt and biological residues can shield microbes. The guide on ultraviolet sterilization of medical devices covers device categories and FDA terminology; the related guide on terminal cleaning covers cleaning as a separate topic.
Regulatory status
Per the FDA summary, UV products are medical devices when their intended use meets the Federal Food, Drug, and Cosmetic Act definition of a device.
Common misunderstandings
- “UV-C is exactly 254 nm.” 254 nm is a typical lamp output; the band spans a range, and sources disagree on its lower edge.
- “Any UV lamp disinfects.” NIOSH says some lamps, such as tanning lamps, radiate in UV-A or UV-B and may have negligible effect on airborne microorganisms.
- “A shorter wavelength is safer or stronger.” NIOSH notes that 184.9 nm output produces ozone.
Common questions
What is the UV-C wavelength range?
The FDA summary gives 200-280 nm and the NIOSH guideline gives 100-280 nm; both place UV-B at 280-315 nm and UV-A at 315-400 nm. NIOSH notes that band designations are approximate and may vary between sources.
What is UV disinfection?
UV disinfection, or ultraviolet germicidal irradiation (UVGI), uses UV radiation, mostly UV-C, to inactivate microorganisms; NIOSH describes the effect as cellular or genetic damage that can prevent a cell from replicating. The FDA summary notes it acts on directly illuminated surfaces only.
What is a UV-C lamp or germicidal lamp?
In the NIOSH guideline it is a low-pressure mercury lamp emitting predominantly at 254 nm. Lamps that emit at 184.9 nm produce ozone, and tanning lamps emit UV-A or UV-B.
What wavelength is UV-C disinfection done at?
NIOSH calls 254 nm typically optimal. The FDA summary says the majority of germicidal devices operate in the UV-C range (200-280 nm).
Sources
- U.S. FDA, Executive Summary, General Issues Panel Meeting on Germicidal Ultraviolet (GUV) Devices, December 10, 2025. Checked 2026-10-30.
- CDC/NIOSH, Environmental Control for Tuberculosis: Basic Upper-Room Ultraviolet Germicidal Irradiation Guidelines for Healthcare Settings, DHHS (NIOSH) Publication No. 2009-105, March 2009. Checked 2026-10-30.
