Traceability validation of a high speed short-pulse testing method used in LED production

Elena Revtova,Jacques Brenkman,Dongsheng Zhao,Edgar Moreno Vuelban,Henk Ulden

doi:10.1051/ijmqe/2017024

Abstract

Industrial processes of LED (light-emitting diode) production include LED light output performance testing. Most of them are monitored and controlled by optically, electrically and thermally measuring LEDs by high speed short-pulse measurement methods. However, these are not standardized and a lot of information is proprietary that it is impossible for third parties, such as NMIs, to trace and validate. It is known, that these techniques have traceability issue and metrological inadequacies. Often due to these, the claimed performance specifications of LEDs are overstated, which consequently results to manufacturers experiencing customers' dissatisfaction and a large percentage of failures in daily use of LEDs. In this research a traceable setup is developed to validate one of the high speed testing techniques, investigate inadequacies and work out the traceability issues. A well-characterised short square pulse of 25 ms is applied to chip-on-board (CoB) LED modules to investigate the light output and colour content. We conclude that the short-pulse method is very efficient in case a well-defined electrical current pulse is applied and the stabilization time of the device is “a priori” accurately determined. No colour shift is observed. The largest contributors to the measurement uncertainty include badly-defined current pulse and inaccurate calibration factor.

Highlights

A measurement gap is identified between the way LED manufacturers test single LEDs and LED packages/modules during production and the way lighting calibration and testing laboratories calibrate/test SSL products.In industry, the so-called single-pulse method [1,2] limits LED power by powering the LED with a single current pulse or series of multiple pulses, usually in the length of 50–300 ms
We focused on the determination of the absolute power distribution P(l) of the direct current (DC) and short-pulse driven sources for the purpose of traceability validation
The short-pulse testing method used in industry to evaluate light output performance of the LEDs during production has been validated in this study

Summary

Introduction

The so-called single-pulse method [1,2] limits LED power by powering the LED with a single current pulse or series of multiple pulses, usually in the length of 50–300 ms. Such pulses are short enough to limit LED package heating but not short enough to limit junction heating [2]. The main objectives of this research are threefold: (1) to validate the high speed short-pulse testing method of LEDs for its applicability by pointing out any inadequacies (e.g. inaccurate characteristics of driving pulse, synchronization problem between driving and measuring equipment, and discrepant and fluctuating temperature setting), (2) to provide traceability to the measurands through the.

Objectives

Methods

Findings

Discussion

Conclusion