Proposed thermal metric for assessment of cooling systems of LED lighting products

As the operating temperature of a LED lighting product increases, quite a few performance parameters experience a short-term and recoverable shift. With increasing operating temperature of a LED lighting product, forward voltage reduces, luminous flux reduces, and the color characteristics change from the desired characteristics. Furthermore, maximum junction temperature of the LEDs in the lighting product must not be exceeded. Exceeding the maximum temperature, as specified by the manufacturer in the product datasheet, may permanently damage the lighting product and cause irreversible shifts in product performance. In this work the concept of thermal characterization parameter is proposed to assess to quality of the cooling system in a LED lighting product. Currently, internationally there is no well established measurement technique or standard for estimating the junction temperature of LEDs in a market ready luminaire. Also there isn´t any well established method for assessing the quality of the cooling system of a LED luminaire. This work proposes a thermal metric relating the junction and the heat-sink temperatures to estimate the operating junction temperature as well as the quality assessment of the LED luminaire. Findings of the thermal testing on a LED down light are presented in this paper.