Ultraviolet radiation covers the 100–400nm range and splits into three bands — UVA, UVB and UVC — that serve completely different industries. UVA cures adhesives, inks and coatings. UVB drives phototherapy and narrow-line material treatment. UVC disinfects air, water and surfaces. The bands share no specification language, and confusing them fails the process regardless of cost. This guide defines each band, explains how each one works, and separates the four datasheet numbers most often mixed up.
The Three UV Bands at a Glance
| Band | Wavelength Range | Baseline Wavelength | Main Applications |
|---|---|---|---|
| UVA | 315–400nm | 365nm | Curing of adhesives, inks and coatings; 3D printing; inspection |
| UVB | 280–315nm | 311nm | Phototherapy; specialized material treatment |
| UVC | 100–280nm | 254nm | Disinfection of air, water and surfaces |
UVA is the workhorse band for industrial curing, and 365nm is the classic reference wavelength; LED systems also emit at 385nm, 395nm and 405nm depending on the chemistry. UVB occupies a narrow window where spectral lines matter more than raw power — narrowband 311nm sources dominate medical phototherapy. UVC carries the germicidal role: 254nm, the output of low-pressure mercury lamps, remains the reference line for disinfection dose calculations, while UVC LEDs commonly emit at 260–285nm.
How Each Band Does Its Work
The photochemistry differs by band. In UVA curing, photoinitiator molecules inside the material absorb photons and start the polymerization chain. The activation wavelength of the chemistry — not the raw power of the source — decides whether the cure completes. That is why peak wavelength sits at the top of every curing datasheet. LEDs replaced mercury lamps in most curing lines because they switch on and off instantly, contain no mercury vapor, and fit compact optical heads for robotics and inline production.
In UVC disinfection, photons damage the nucleic acids of microorganisms so the cells can no longer replicate. Two numbers make or break a disinfection claim: wavelength and dose. Dose combines irradiance at the target plane, measured in mW/cm², with exposure time in seconds, and the result in mJ/cm² predicts the log reduction achieved. Each additional log step multiplies the required dose roughly tenfold, which is why a dose budget belongs in every disinfection specification.
Four Numbers, Four Different Conversations
| Parameter | Unit | What It Actually Tells You |
|---|---|---|
| Electrical wattage | W | What the driver consumes, not what the target receives |
| Dose | mJ/cm² | Irradiance × time; the quantity tied to cure quality and kill rate |
| Peak wavelength | nm | Which photochemistry or which microbial response is engaged |
| Safety class | IEC 62471 | Photobiological risk to eyes and skin; drives labeling and interlocks |
The most common specification error is treating wattage as performance. Radiant output at the working plane can differ from electrical consumption by a wide margin, and it falls further with heat. Thermal management matters because UV output drops as junction temperature rises; a datasheet that quotes radiant power at 25°C says little about a 60°C installation.
Specifying in the Right Order
A disciplined sequence prevents wrong-band errors:
- Define the application: curing, phototherapy support or disinfection.
- Fix the band: UVA for curing, UVC for disinfection.
- Set the wavelength and the dose budget at the target plane.
- Only then compare electrical, thermal and mechanical parameters.
Check that the datasheet publishes radiometric data — peak wavelength, spectral half width, radiant power at operating current, and thermal behavior — rather than electrical ratings alone. For safety, IEC 62471 classifies photobiological hazard into risk groups from Exempt to Risk Group 3. UVC sources generally land in the moderate or high groups because actinic UV limits are strict, and the class determines labeling, interlocks and operator protection.
Key Takeaways
- UVA (315–400nm) cures, UVB (280–315nm) treats, UVC (100–280nm) disinfects; the application sets the band, and the band sets the vocabulary.
- Dose in mJ/cm² — irradiance × time — predicts curing quality and log reduction, not wattage.
- 254nm remains the disinfection reference line; UVC LEDs typically operate at 260–285nm and lose output as temperature rises.
- IEC 62471 risk classification governs labeling and protection; it is a specification item, not fine print.
