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in tri-stimulus colourimeter, which is used to perform flicker measurements.’ Flicker is an issue that has


existed in lighting since the 1980s, and is observable to the human eye at frequencies of approximately 50 to 70Hz at large enough modulation depths. ‘Above these frequencies, we can’t see it, but can still sense it, which can prove dangerous for people with certain medical conditions, such as epilepsy,’ commented Lemmens. ‘In workshops, if a saw is rotating at a certain frequency that happens to match the frequency of a flickering light, then it may look like the saw is stationary when really it’s rotating.’ Manufacturers therefore use spectrometers to ensure that LEDs comply to


“Accurate and traceable spectrometers become more and more affordable for the smaller manufacturers”


standards such as IEEE 1789, a recommendation introduced at the end of 2015 for modulating current in high-brightness LEDs to mitigate health risks. According to Lemmens,


the quick checks that are performed on production lines are made at one or two luminance levels, whereas the measurements made in research and development labs are very precise and are taken over a range of values. Admesy offers its Rhea spectrometer for these lab inspections – a more accurate, CCD sensor-equipped system with a larger dynamic range due to an integrated filter wheel. ‘The Rhea spectrometer is used when entirely new luminaires are being developed, for example if a manufacturer is about to make a new LED lamp and they need to check the spectral behaviour very accurately at both very low and high luminance levels,’ explained Lemmens. ‘If they


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are working with a sample of a WRGBW lamp – an RGB lamp with additional warm and cool white LEDs – they might want to tune it in a certain direction to cover certain colour points. These measurements have to be done with a very high precision, as this is an application where high-end spectral data is required.


‘We are definitely seeing


a growth in the number of spectrometers that are sold for the purpose of LED inspection, especially as accurate and traceable spectrometers become more and more affordable for the smaller manufacturers and research and development labs who occasionally use


a spectrometer,’ concluded Lemmens. ‘That’s a completely different shift from years and years ago, where spectrometers were very expensive and needed a lot of attention, in terms of calibration. Now these systems are offered at a lower price and are easier to use, while ensuring both the standard and quality.’ EO


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