Tom Melly Ph.D.
Feasa Enterprises Ltd.
In today's world it is important that a product has sufficient accreditation that it can be enter many different market places. While accreditation can be a costly process, it is prudent to know that your product is fit for purpose before going for accreditation. We propose a novel cost effective system for testing 100% of the LEDs (Light Emitting Diode) on a lighting product. This system will not only monitor the intensity and colour changes of a product while it is running but alert the engineer of early failures allowing the test to terminate, and faults to be examined.
We propose this system as a rapid prototype tester. This system also allows unique LED changes to be monitored such as one LED to noticeably change while not changing the macro properties of the lighting unit. While a small change in individual LEDs or a small group of LEDs in a lighting product might not affect the accreditation process, it could have warrantee effects when the product is in the market place. We will introduce the system, and show the results of five different LED based products being tested simultaneously over the course of three months.
Each product consists of twenty LEDs, so we will monitor 100 LEDs simultaneously. The results will show unexpected behaviour of the LEDs, over the period of three months as a case study. We will show how such a system could be adapted for Standards such as IESNA LM-80  and TM-21 . Lastly we will show the advantage of pre-aging LED products to allow for improved lifetime estimation. While not a replacement for standards such as IESNA LM-80  and TM-21 , the technique outlined above would allow smaller companies increased confidence in their product when getting a product range accredited. The system allow shorter prototype development times and hence a cost
saving to end-users.
A technique that uses a spectrometer and sensor combination has been developed to achieve continuous absolute intensity monitoring of each individual LED of an LED based product.
This continuous monitoring has highlighted unusual behaviour, which would be undetected if using only an individual spectrometer. In this case, the LEDs required a certain burn-in time before they approximately stabilised. At the end of the first month, in the case of this LED based board, the variation between the brightest LED and dimmest LED was 15%. This met the requirements of the TM-21  standard. The LEDs variation would need to be much less than 30% at the end of the 6 month measurement period.
The technique is adaptable for the TM-21 approach, as these measurement products are designed to operate up to 100 degrees Celsius, and so can meet the 55 degree Celsius and 85 degree Celsius conditions.
Initially Published in the IPC Proceedings