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 LEDlighting 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.