Life time comparison of LED package and the self-ballasted LED lamps by simple linear regression analysis

Highlights

• We try to find out new approach for LED Lamp's life based on single LED life.

• We use slop compare with single LDE package and LED lamp life

• We show at each thermal stress for increasing number of LED

Abstract

The energy efficient long-life self-ballasted LED lamps are designed considering the reliability test result of LED package. We also try to predict the lumen maintenance life for the self-ballasted LED lamps because there were a lot of failure mechanisms for a various environment stress. Many studies have investigated the environmental stress effects on LED packages [2], [3],4, and 5]. However, comparing to LED package, there is not enough data to study the lumen maintenance life for the self-ballasted LED lamps. IES LM-80-08 is the approved method for measuring lumen maintenance of LED light sources [1]. It suggests using the Arrhenius Equation to calculate the interpolated lumen maintenance life. We followed this method and obtained lumen degradation patterns from three different thermal stresses as indicated in the IEC 62621 standard. Under the three different thermal stresses, the on-off test (30 on and 30 s off) was conducted on the self-ballasted LED lamps which were made of the same selected LED package (3 V, 64 mA). The intent of the research isn't to set up a new curve-fit for non-linear lumen degradation pattern. Our research goals are to find methods to compare the lumen degradation pattern of LED package and the self-ballasted LED lamp using simple linear regression analysis. As simple straight linear line is assumed for lumen degradation after ALT testing We found the slope of the mathematical model is easily comparable for three different temperatures and for different number of LED whether it is single or consists of forty or eighty LED. By comparing each values of the slope the effect of increase in number of LED can be shown at each thermal stress. This study is the first step towards the presentation on the lumen maintenance life of the self-ballasted LED lamp on three different temperatures. Additional information must be accumulated in the future to further study on the LED lighting product reliability.

Introduction

After the development of blue LED package in 1994 and the commercialization of white LED package, the lighting industry became more environmentally friendly with longer lifetime products. In Korea, the safety certification standards have been steadily established from 2009 with current 37 standards by various product types. However, there have been concerns on the method for evaluating the reliability of the LED package and also of the self-ballasted LED lamps which includes the power source. This paper will discuss the accelerated factors which were driven by many preceding studies and integrate the accelerated factors (temperature and electric stress) which have the biggest effects on the self-ballasted LED lamps lumen degradation. First, to verify the influence of temperature on the degradation of the self-ballasted LED lamps, accelerated stress tests at several temperature levels were performed. The lumen degradation test at the normal temperature condition was also performed to compare its result to that obtained at the accelerated conditions. Before we discuss the accelerated conditions, we first need a lumen degradation data of single LED package's temperature for long term test. Normal life test (25 °C) and thermal accelerated life test (70 °C, 90 °C) were first conducted on the low power LED package (3 V, 64 mA). Then the normal temperature (25 °C) plus 30 s on and 30 s off test and thermal accelerated life test plus 30 s on and 30 s off test were conducted on the self-ballasted LED lamps (8 W, 16 W) made with the same low power LED (3 V, 63 mA) installed on the Metal PCB. Input power was from 100 to 240 V of working Voltage and total lumen flux was 480 lm. Fig. 1 shows the test sample of a single LED package and the self-ballasted LED lamps (8 W, 16 W). In IEC 62621 (Self-ballasted LED Lamps for general Lighting services with supply voltages > 50 V — Performance requirements) the criteria of failure is below the minimum 70% of the initial lumen. In this research this criteria is used as a base for determining the failure data using Weibull analysis. Chan et al. recommended LED's activation energy to be 0.33 eV when using Weibull analysis [5]. Therefore, we adopted this Weibull analysis for HAST testing results. The total test condition for the research are designed following the below Table 1. The normal life test have been conducted following the test condition with temperature of 25 °C, tolerance of ± 1 °C and a relative humidity of 65% maximum as indicated in IEC 62612 for minimum of 4000 h to maximum of 10,000 h (one and a half year).