UV FAQs - especially for the use of UV sensors and UV light sources

These FAQs answer recurring questions on the use of UV sensors and UV light sources – for UV curing, disinfection, materials testing and occupational safety alike. This page covers calculating the photon flux density PPFD and the dose quantities SED and MED.

The remaining answers sit with their topic:

Measuring UV – choosing the spectral and measuring range, how the sensors work, calibration intervals, measurement system analysis, spectral mismatch
UV knowledge – radiometric and photometric quantities, spectral ranges and standards
UV sources & lifetime – UV LEDs and lamps, lamp cooling, ageing, a broken UV lamp, irradiance from the spectrum
UV as a tool – curing, printing, cleaning, UV resistance of the materials used
Safety, Standards & Regulation – UV erythema in the workplace, RoHS, PFAS

Molecular models splitting into radicals under UV irradiation, absorption curves over wavelength on the left – photoinitiators and UV absorbers

Photoinitiators & UV absorbers

Measurand: absorption spectrum versus the source's emission spectrum

Photoinitiators use UV to cure coatings, inks and adhesives in fractions of a second; UV absorbers keep the same radiation away from plastics and skin. The article compares spectra, applications and approvals of both groups.

Tensile specimens of PLA, PETG, TPU and ASA each next to their UV-aged counterpart, UV-C, UV-B and UV-A spectra on the left – UV ageing of 3D printing materials

UV aging of 3D printing materials

Short answer: ASA outdoors, PETG and PLA indoors only

Of four 3D printing materials compared, only ASA is designed for lasting UV and weathering exposure outdoors; PLA and standard PETG are not. The article shows the measurement results from the irradiation chamber.

Dispensing needle applying potting compound to an assembled circuit board, a coated part with a glossy surface alongside – UV-curable adhesives, coatings and potting compounds

UV-curing adhesives, coatings and compounds

Measurand: irradiance and dose within the photoinitiator's absorption band

UV-curing adhesives, coatings and potting compounds cross-link within seconds once the photoinitiator absorbs matching radiation. The report classifies free-radical and cationic systems and names the process quantities that decide through-cure.

Material samples – PTFE, aluminium, stainless steel, white paint and black lacquer – under UV light with reflectance curves on a monitor

UV reflectance

Over 70 verified UV reflectance values – aluminium, stainless steel, PTFE, paints, building materials – with wavelength, measurement method and source.

LED module above seedlings with photons shown as arrows onto a leaf and the emission spectrum on the left – calculating the photon flux density PPFD

Calculation of the photon flux density PPFD

Short answer: PPFD in µmol/(m²·s) from the spectrum, not from lux

Photosynthetic photon flux density (PPFD) counts photosynthetically active photons between 400 and 700 nm per area and time. The article shows the conversion from the spectrum and why watts alone say nothing for plants.

UV LED emitter above a shoulder with a reddened irradiated area, on the left a skin layer model with penetration depths and a wavelength scale – standard erythema dose and minimal erythema dose

Standard Erythema Dose (SED) and Minimal Erythema Dose (MED)

Short answer: SED is a unit, MED is a skin reaction

SED and MED do not measure the same thing: the Standard Erythema Dose is a standardised physical unit (1 SED = 100 J/m² erythemally weighted), the Minimal Erythema Dose an individual reaction threshold. The article explains both and how they relate.

Contact

Dr. Mark Paravia
Tel.: +49 (0)7243 / 94 783 - 50