Accuracy is a crucial part of the three steps to improved 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.
Improving LED Light 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.
Learn more about SpikeSafe Performance Precision Pulsed Current Sources and Source Measure Units.