Junction Temperature and Thermal Resistance Restrict the Developing of High-power LED

The junction temperature of LED has directly influence upon light output efficiency,device life time,reliability,emitting wavelength of LED.With the invention of high-power LEDs,the requirement for drive current has increased significantly,thereby increasing power dissipation.But only approximately 5%-to-10% of the input electrical power in LEDs is dissipated optically while the other portion produces heat energy based on the current technology.Specially,the heat inside high-power LEDs rely mainly on natural cooling,but no active cooling was used because the active cooling will increase the cost,decrease the reliability,and shorten life time of the whole LED lighting system.Only if the cost of each lumen(for example,USD/lm) in the semiconductor lighting is lower than other lighting source,the semiconductor lighting could replace the conventional lighting sources.So,effective thermal management of high-power LEDs must be dealt with by way of low cost and natural cooling.Keeping the junction temperature of LED in the given range is a main research goal of chip fabricating,device packaging and application.Specially,it's also a key issue being dealt with during packaging and application of high-power LED.The influences of pn junction temperature on capabilities of LEDs are described in this paper,firstly.And then the relations of junction temperature and thermal resistance of high-power LEDs are analyzed.The conclusion that junction temperature and thermal resistance restrict farther developments of high-power LEDs has been deduced based on the thermal resistance analyses of high-power LEDs.Meanwhile,the following viewpoints is put forward:(a) How to increase light output efficiency is a basic sticking point in process of raising the power of LED devices.(b)There is no point in developing high-power LEDs which go beyond 5 W for engineering applications if the light output efficiency of LEDs has no improvement.