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 first webinar of the series (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. In the second webinar (Accuracy), Hulett talked about which measurement method should be used to achieve the most accurate LED light measurements. The final segment of this webinar series discusses which factors must be controlled for optimal repeatability and gives examples of what to look for and what to avoid in your measurement equipment.
Single Pulse and DC Measurements Require a Consistent Delay
Unlike incandescent light measurement repeatability (which is primarily affected by current stability and spectrometer stability), LED light measurement repeatability is reliant on timing stability. When taking measurements with DC or single pulse, light measurement is started after a delay. If that delay is not consistent, your light measurements will not be repeatable due to a variation in junction heating from one measurement to the next. Precise triggering is key to improving repeatability with DC and single pulse.
At the End of the Day, Jitter will Drive You Crazy.
Repeatability with continuous pulse can be improved by minimizing pulse width jitter. Each current source has a jitter specification, which is the amount that their pulse width can vary. Several popular current sources specify a pulse width jitter of 1 or 2µs, which results in over a 2% lumen error as you begin using narrow pulse widths (in the 100µs range or below). These jitter errors will drive you crazy, especially if you are working on long term trend measurements such as those you might take for LM-80.
The SpikeSafe Performance Precision Pulsed current source specifies just 0.03µs pulse width jitter which means that you can use narrow pulse widths (down to 10µs) without large lumen errors. At 10µs pulses, Performance Precision Pulsed current sources have only a 0.3% lumen error.
This webinar will teach you how to recognize equipment that will best allow you to improve your overall repeatability.
Click here to learn more about SpikeSafe Performance Precision Pulsed current sources.