Thermal Investigation Of Light Emitting Diodes
Free (open access)
159 - 168
K. Domke & K. Wandachowicz
High power light emitting diodes are already a popular alternative to incandescent and fluorescent lamps and it seems that in around a dozen years or so they may become the basic type of lamp used in lighting engineering. In addition to emitting light, LEDs also generate a significant quantity of heat. The assumption is that ca. 75% of total power is released in the form of heat which must be carried into the environment. Heat released in the p-n junction of the semiconductor material markedly increases its temperature and thus indirectly affects the photometric and electric characteristics of LEDs. The paper below presents a test stand designed for measuring such characteristics for a wide range of changes of junction temperatures. Junction temperature adjustment can proceed independently of the thermal power released in the LED. Selected measured characteristics of HP LEDs are also presented. Keywords: light emitting diode, junction temperature, photometric measurement. 1 Introduction Semiconductor LEDs made in the solid state lightning (SSL) technology can be divided into low power (LEDs) and high power (HP LEDs). The latter represent the most advanced group of light sources used in the lighting industry for general and decorative lighting applications and in the automotive industry for marker lights, stop lights, direction indicator lights and car headlights. The LED market is now a major and rapidly developing segment of the electronics market. Forecast growth of the LED technology (published in 2002) is presented in table 1 (supplemented by 2007 data). In the LED markets White High Brightness LEDs will fuel growth to surpass $14 billion by 2017. The present LED market by value is as in table 2: The manufacturing technology of light emitting diodes has been growing exponentially in recent years. Different types and forms of LEDs have varied
light emitting diode, junction temperature, photometric measurement.