UV LED Measurements – Radiometric vs. Spectroradiometric Methods
Mark Paravia | Opsytec Dr. Gröbel GmbH, Germany
Recent advances in the development of UV LEDs enable new and larger UV LED-based systems for tap-water treatment or municipal water treatment. For the actinic evaluation, e.g. the disinfection efficiency, the microbicide function of an organism must be known. This can be found in publications and standards .
The emission wavelength and the radiation flux of the UV LEDs are of special importance. Both are challenging to measure. However, as the tolerances of the emission spectra of the UV-LEDs are still very large, the disinfection efficiency can vary by approx. +/- 20%. The variation can be found if the emission of the UV-LED is shifted due to a different production lot.
The presentation will give an inside view of current measurement methods, requirements and possible accuracies for UV LED measurements. Therefore the classical filtered radiometry and spectroradiometric methods are compared.
Filtered radiometers are broad-band radiometers and available for commonly divided spectral ranges UVA, UVB and UVC . The filtered radiometers sensitivity functions are made to match the UV spectral ranges. As UV-LEDs with nominal emission at 275 nm emit next to the filter edge the measured signal is overlapped from filter tolerances. E.g. a small wavelength shift due to reduced cooling or higher LED power may result in an increase drop of the measurement signal. This may give results in efficiency drops of about 30% as the real efficiency drops only by some percentage.
Spectroradiometers may be used to overcome this problem. Spectroradiometers are available in a wide range of size and performance starting from laboratory double- monochromators and going to small array-spectrometers. Note that standards like  recommend array-spectrometer only for measurements above 300 nm. When they are used at shorter wavelengths special care must be taken for stray light and calibration.
The presentation will show measurement results of different filtered radiometers and spectrometers and give practical tips for UV LED measurements.
 DIN 5031-10:2018-03, Optical radiation physics and illuminating engineering - Part 10: Photobiologically effective radiation, quantities, symbols and action spectra
 Online database of the International Lighting Vocabulary ILV (CIE S 017/E:2011), 17-1367; available at eilv.cie.co.at
 ASTM G130-12, Standard Test Method for Calibration of Narrow- and Broad-Band Ultraviolet Radiometers Using a Spectroradiometer