What Is the Frequency Range of UV Light? | Exact Numbers, No Guesswork

Ultraviolet radiation runs from about 7.5×10^14 Hz up to about 3×10^16 Hz (10–400 nm).

UV light sits just beyond violet light on one side and just before X-rays on the other. Most labels use wavelength (nanometers) because that’s how lamps, filters, and sensors are sold. Frequency (hertz) is the same idea in a different unit, and it’s useful when you’re lining up UV with electronics, spectroscopy settings, or photon energy.

You’ll get the full UV frequency range first, then the ranges for UVA, UVB, and UVC. After that, you’ll see quick conversions, reality checks, and a few common mix-ups that lead to wrong numbers.

What makes UV “UV” on the spectrum

Ultraviolet means “beyond violet.” Visible violet light ends near 400 nm. UV starts there and moves toward shorter wavelengths. A shorter wavelength means a higher frequency, and it also means a higher-energy photon.

A common broad definition places UV between 10 nm and 400 nm. That span includes several named sub-bands used in lighting, safety rules, astronomy, and lab work. Some fields use narrower slices, so it pays to check which cutoff a chart is using.

Why frequency and wavelength tell the same story

Light travels at a fixed speed in vacuum, called c. When you know wavelength (λ), you can find frequency (f) with:

f = c / λ

As λ gets smaller, f rises. That’s why UVC has a higher frequency than UVA.

Two quick conversion anchors

• Speed of light: 3×10⁸ m/s (close enough for most UV work).
• Nanometers to meters: 1 nm = 10^-9 m.

So 400 nm becomes 400×10^-9 m, which is 4×10^-7 m. Plug that into f = c/λ and you’re set.

Taking “What Is the Frequency Range of UV Light?” from wavelength to hertz

If UV runs from 400 nm down to 10 nm, the matching frequency limits are:

• At 400 nm: f = (3×10⁸) / (4×10^-7) = 7.5×10¹⁴ Hz.
• At 10 nm: f = (3×10⁸) / (1×10^-8) = 3×10¹⁶ Hz.

So the frequency range of UV light is about 7.5×10¹⁴ to 3×10¹⁶ hertz. If you see slightly different endpoints in a textbook, the author is usually using a different UV cutoff, not different physics.

Why some sources show a narrower “UV range”

Sometimes “UV” means “UV that reaches the ground,” not the full physics band. A solar overview from NASA notes that UV measured at the surface is in a narrower wavelength window, near 290–400 nm. That doesn’t change what UV is; it changes what you’re likely to measure outdoors. NASA’s ultraviolet radiation overview explains that surface-range framing and why wavelength matters.

Where the 10–400 nm endpoints come from

The 400 nm edge is tied to human vision: it’s where violet light fades into non-visible radiation. The 10 nm edge is a convention that keeps UV separated from X-rays in many charts. In real work, you’ll often see boundaries set by what air, glass, or a sensor can transmit.

That’s why some references start UV at 100 nm, especially in safety guidance, where wavelengths shorter than that may be treated under different hazard models or handled only in specialized setups. The safest move is simple: use the wavelength range given by the standard, spec sheet, or class material you’re working from, then convert those endpoints to frequency.

UV sub-bands and their frequency ranges

Most everyday labels use UVA, UVB, and UVC. Safety standards also reference these bands. ICNIRP’s exposure guidance places UV from at least 100 nm to 400 nm and lists the common UVA/UVB/UVC splits. ICNIRP ultraviolet exposure guidelines is a widely referenced source for that band language.

Below is a practical table that ties named UV bands to both wavelength and frequency. The frequency bounds use f = c/λ with c = 3×10⁸ m/s, rounded to two significant digits. That rounding is fine for planning and learning.

UV band label	Wavelength range (nm)	Frequency range (Hz)
UV (broad)	10–400	3.0×1016 to 7.5×1014
UVA	315–400	9.5×1014 to 7.5×1014
UVB	280–315	1.1×1015 to 9.5×1014
UVC	100–280	3.0×1015 to 1.1×1015
Near-UV (common lab use)	300–400	1.0×1015 to 7.5×1014
Far-UV (common science use)	122–200	2.5×1015 to 1.5×1015
Extreme-UV (EUV)	10–121	3.0×1016 to 2.5×1015
Vacuum-UV (VUV, often noted)	10–200	3.0×1016 to 1.5×1015

How to sanity-check a UV frequency fast

Once you start seeing numbers like 10¹⁵, it’s easy to lose your footing. These checks keep you steady.

Check one: Band label matches wavelength

If someone says “UVA at 250 nm,” that’s a mismatch. 250 nm sits in UVC by common band splits. If the band label and wavelength disagree, the frequency will be off by definition.

Check two: Visible light comparison

Visible light runs around 4×10¹⁴ to 7.5×10¹⁴ Hz. UV begins where violet ends, near 7.5×10¹⁴ Hz, then climbs.

Check three: One-line conversion trick

If you only have wavelength in nm, estimate frequency with:

f (Hz) ≈ 3×10¹⁷ / λ(nm)

It works because 3×10⁸ m/s divided by 10^-9 m per nm becomes 3×10¹⁷.

Photon energy: What the range implies

Frequency links straight to photon energy through Planck’s relation, E = h·f. You don’t need to run that math every time, yet it helps to know why UVC behaves differently than UVA when it hits skin, plastics, inks, or coatings.

As frequency rises, each photon carries more energy. That’s why shorter-wavelength UV shows up in tasks like photolithography and some types of disinfection, while longer-wavelength UVA shows up in curing resins, black lights, and fluorescence work.

Band names shift by field

You might see extra labels like UV-A1, UV-A2, or “deep UV.” These are finer slices of the same 10–400 nm span. When a spec sheet gives a peak wavelength, treat it as your anchor and compute frequency from that number instead of guessing a band.

Common UV sources and where they sit

Real sources rarely emit a whole band evenly. Most have a peak, plus side bands. The table below connects familiar sources to the wavelength you’re likely to see on a label, then to the band you should expect.

Source or device	Typical UV output	What that usually means
Sunlight at ground level	Mostly 290–400 nm	UVA plus part of UVB
“Black light” lamp	Often near 365 nm	UVA used for fluorescence
Nail curing lamp	Often 365–405 nm	Near-UV with an edge into violet
Germicidal mercury lamp	Strong line at 254 nm	UVC peak with higher photon energy
UV LED (germicidal type)	Often 260–280 nm	UVC; the label is usually the peak
UVB phototherapy unit	Often around 311–313 nm	Narrowband UVB
Arc welding emission	Wide UV output	Mix of UVA/UVB; needs shielding
UV curing for inks	Often 365–395 nm	UVA/near-UV used for curing

Measuring UV: Getting a number you can trust

Two people can point “UV meters” at the same lamp and get different readings. That happens when the meter’s sensitivity curve doesn’t match the lamp’s spectrum. If you care about frequency, start from wavelength measurements or a verified peak wavelength on a datasheet.

Use a spectrometer when the exact band matters

A UV spectrometer gives intensity by wavelength. Once you have the spectrum, you can convert any wavelength bin to frequency. This is the cleanest route when you need to know whether output sits at 265 nm, 280 nm, or 310 nm.

Know what your sensor actually sees

Many low-cost sensors respond mostly to UVA and barely react to UVC. That can make a UVC lamp look “weak” even when it isn’t. If a sensor lists its responsivity window, treat that as its real operating band and match your expectations to that window.

Practical conversions worth saving

These anchor points show up a lot, so it’s handy to keep them in notes:

• 400 nm → 7.5×10¹⁴ Hz (UV start near visible violet)
• 365 nm → 8.2×10¹⁴ Hz (common UVA lamp peak)
• 315 nm → 9.5×10¹⁴ Hz (UVA/UVB split)
• 280 nm → 1.1×10¹⁵ Hz (UVB/UVC split)
• 254 nm → 1.18×10¹⁵ Hz (classic mercury line)
• 222 nm → 1.35×10¹⁵ Hz (common excimer line)
• 100 nm → 3.0×10¹⁵ Hz (lower UVC boundary in many charts)
• 10 nm → 3.0×10¹⁶ Hz (broad cutoff near X-rays)

Safety notes tied to band and frequency

Higher frequency UV can injure eyes and skin quickly. Even UVA can do harm with long exposure. A safe mindset is simple: treat any UV source as hazardous until you know its band, intensity, distance, and exposure time.

If you’re working with UVC devices, watch for reflections, unshielded fixtures, and missing interlocks. For consumer gear, a label that hides wavelength is a red flag. You want a clear peak wavelength and a rated irradiance at a stated distance.

Common mix-ups that skew the range

Mix-up one: Confusing UV with blue or violet light

Some “UV” products emit mostly violet or deep blue light near 405 nm. That can still cure some resins, yet it sits at the edge of UV. If your wavelength is longer than 400 nm, your frequency drops below the UV band start.

Mix-up two: Treating band labels as fixed cutoffs

Band splits are conventions. One chart may place UVA at 315–400 nm; another may put the upper edge at 380 nm. When the endpoint moves, the frequency endpoint moves too. Use the chart’s own cutoffs when you’re matching numbers.

A simple checklist before you share a UV frequency

• Write the wavelength in nm and the frequency in Hz on the same line.
• State the cutoff you used (10–400 nm, 100–400 nm, or a surface-only range).
• Round with intent: two significant digits is often enough for learning and planning.
• If the number will drive exposure limits, use a standard and a calibrated instrument.