Preparation of a standard light-emitting diode (LED) for photometric measurements by functional seasoning

Abstract

We propose an alternative scheme for preparing a standard light-emitting diode (LED) for luminous intensity or total luminous flux measurements, which differs from the conventional approach by an advanced seasoning method. Our method for seasoning, referred to as ‘functional seasoning’, gives quantitative information on the temperature dependence and the ageing effect of the LED emission by simultaneously recording the photometric quantity to be specified and the junction voltage. Based on a theoretical model, we demonstrate experimentally the method by using a fully automated LED seasoning system to measure the luminous intensity and the junction voltage of 12 LEDs simultaneously. By independent measurements of the temperature dependence, we confirm the discrepancy of the theoretical model to be less than 0.5% and evaluate the total uncertainty contribution of the functional seasoning to be less than 0.5% for all the tested samples. As a result, the standard LEDs of four different colours (white, red, green and blue) could be prepared for a seasoning time of only 70 h, which can be applied in specified conditions: for example, for a temperature of (25 ± 5) °C and for a burning time of 20 h without any active temperature control.