Ultraviolet LEDs are specified by wavelength and by radiant output, not by lumens. There is no photopic response above about 380 nm, so a UV emitter has no luminous output to quote and no efficacy figure to compare. Every number on a UV datasheet — irradiance at a working distance, dose per exposure, radiant power in milliwatts — is a radiometric quantity, and the units must not be mixed with the photometric ones used for visible parts.
The practical consequence is that a UV design is a radiometric calculation. Working distance, beam angle and exposure time all enter the dose, and the same emitter at two working distances delivers two different doses. This is why the three pages here are ordered by application rather than by wavelength.
1. What is in this section
- UVA Curing and Sensing
365 to 405 nm. Ink curing, photochemical processes and fluorescence sensing, where the dose is set by the process rather than by a photometric target. - UVB Phototherapy Dosimetry
Therapeutic band. Dosimetry, treatment geometry and the difference between a cure and a dose, with the irradiance figures the therapy depends on. - UVC 275 nm Dosage Design
Germicidal band. Dose design for disinfection applications at 275 nm, and why the dose figure and the irradiance figure are not interchangeable.
2. Where to start
Start from the application rather than from the wavelength, because the wavelength is usually a consequence of the process. If you know the process — curing, therapy, disinfection — go straight to that page. If you only know you need UV, read the three in order of decreasing wavelength: UVA is the widest and most benign band, UVB is therapeutic, UVC is germicidal and requires the most conservative handling.
3. Three things that are commonly misunderstood
- Wavelength is not interchangeable across bands. UVA, UVB and UVC do not substitute for each other in a process, a dose calculation or a safety assessment. The band is a specification, not a preference.
- Dose and irradiance are different quantities. Dose is irradiance multiplied by exposure time. Quoting one when the other is meant is the most common specification error on UV designs.
- Working distance changes the answer. Every irradiance figure is stated at a distance. A fixture that moves the emitter changes the dose unless the geometry is recalculated.
4. Why this class is separate
Ultraviolet is separated from the visible range not because the engineering is different but because the measurement system is. Visible parts are measured with a photometric system that weights the spectrum by the eye response, and above about 380 nm that weighting falls to zero. There is therefore no photometric quantity to quote for a UV emitter, and no luminous efficacy to compare against a white part.
That single fact changes how a UV design is specified and how it is verified. A visible design is usually closed by checking a lumens figure against a target; a UV design is closed by checking an irradiance at a stated distance against an exposure time, and the two numbers are not interchangeable. The three pages here are separated by application because the dose requirement, the working distance and the acceptable exposure all differ between curing, therapy and disinfection, even where the emitter is the same part.