Three Steps to Improved LED Light Measurements: Accuracy

Improving LED Light Measurements

Jeff Hulett, Vektrex CTO, narrates this three part webinar series on how to improve LED light measurements. Instrumentation and the selected measurement method are key factors to improving your measurements.

In the last webinar (Power), Hulett talked about finding a current source that provides enough sustained power and the importance of having a current source that can use the three key measurement methods: DC, single pulse, and continuous pulse. Once you have the capability to use all three methods, the question becomes: which method will yield the most accurate measurements? Vektrex engineers conducted an L-I sweep with the Osram LY W5SM-GZJX-46-0-400-R18-Z Yellow LED using each of the three methods. Comparing the luminous flux output across each of the methods shows that there is a significant drop in output when using single pulse or DC as compared to continuous pulse.

What Causes Luminous Flux Loss?

LED output drops due to junction heating. By using continuous pulse, you can minimize your junction heating and thereby improve the quality and accuracy of your LED light measurements. In the L-I sweep conducted with the Osram Yellow LED, it was determined that single pulse measurements yield a 25% drop in luminous flux output and DC measurements yield a striking 70% drop.

How to Effectively Use Continuous Pulse

Unlike single pulse and DC measurements, the spectrometer integration time in continuous pulse incorporates entire pulses. This means that the sloped sides of the pulse are part of the measurement. Since LED output is not linear, at 50% current you get a luminous flux output greater than 50% which introduces error. It’s critical to have fast rise and fall times to avoid these errors. The industry recognizes this error and TC2-63 specifies that your current source must be able to produce microsecond-level rise times.

This webinar will help you learn the sources of measurement errors and how to best minimize them to improve your overall accuracy.

Click here to watch part three of this webinar series.

Click here to learn more about SpikeSafe Performance Series Precision Pulsed Current Sources.

led light measurements icons: power, accuracy, repeatability

Jeff Hulett

Jeff Hulett is the Founder and CTO of Vektrex Electronic Systems, Inc. Because of his vision and leadership, the company grew from a start-up to the market leader. Currently, Hulett is the Chief Architect for Vektrex products placing the highest emphasis on technology and quality. Hulett holds a BSEE from the Illinois Institute of Electronics, and has been awarded four U.S.patents. He is a member of the Illumination Engineering Society of North America (IESNA), and chairs the IESNA LM-80 working group that is focused on LED flux maintenance testing. He has been active in the LED testing and reliability field since 2004.

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