In automotive lighting, LED technology is not only applied for signaling function, but also for lighting function thanks to the development of semiconductor technology.Especially nowadays, LED lamp becomes a main stream for premium, and compact vehicle since first full LED headlamp was introduced in the worldwide market in 2008.The main advantages for LED lamp include CO2 reduction, new styling concept, more compact product, high security with quicker response time, long life time product etc.In contrast, the well known disadvantages are LED performance and LED life time strongly which depends on the junction temperature of LED.A systematic thermal method to design led product at the required flux output is presented.After providing a theoretical thermal analysis of a LED system, the impact of PCB layout, interface and heatsink shape on the junction temperature is presented.The optimization of the copper layout, interface and heatsink shape enable to decrease the junction temperature by 4 to 10 ℃ for each modification within less than 2 days of simulation.Once the optimization of the LED module is achieved the impact the headlamp integration on the performance is analyzed.The simulation can help providing solutions to decrease confinement of the LED module by analyzing internal air flow.The performance of the full product with all functions on can be predicted as function of the ambiance temperature.Thermal simulation accuracy is demonstrated within 5℃ by correlation with tests on representative parts.The verification of the flux prediction is also performed by correlating flux performance of real parts with the expected one based on junction temperature of module alone and module in product.This confirms also that the LED flux expectation from the data sheets are on line with the final usage of the LED in the product.