Lamp calibration lab speeds up LED characterisation

September 06, 2019 //By Julien Happich
calibration lab
Last June, the National Institute of Standards and Technology (NIST) began offering a faster, more accurate and less labour-intensive calibration service for assessing the brightness of LED lamps and other solid-state lighting products.

Well-calibrated lights ensure that the 60-watt-equivalent LED bulb in your desk lamp truly is equivalent to 60 watts, for example, or that there is proper runway lighting for the pilot in a fighter plane. NIST scientists recently renovated the lab they use for these tests, automating most of the measurements so they can be done in half the time it took prior to the lab’s renovation.

LED manufacturers need to ensure that the lamps they make are really as bright as they designed them to be. To do that, they calibrate those lamps with a photometer, a tool that measures brightness at all wavelengths while taking into account the human eye’s natural sensitivities to different colours. Until recently, the NIST lab has measured lamp brightness with reasonably low uncertainties, ranging from 0.5% to 1.0%, on par with mainstream calibration services.

Now, thanks to the lab revamp, the NIST team has reduced those uncertainties by a factor of three, to 0.2% or less. The scientists have also cut the calibration time significantly. With the old system, it took almost a full day to do a single calibration for a customer.

“Most of that was devoted to setting up each measurement, swapping out a light source or a detector, manually checking distances between the two, and then reconfiguring the equipment for the next measurement”, explained NIST researcher Cameron Miller.

But now, the lab consists of two automated equipment tables, one for the light sources and the other for the detectors. The tables travel on a rail system that positions the detectors anywhere between 0 to 5 meters away from the lamps. The distances can be controlled to within 50 millionths of a meter (micrometers), which is about half the width of a human hair. Zong and Miller can program the tables to move in relation to each other without requiring continuous human intervention. What used to take the better part of a day can now be done in hours.

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