Luminous flux modeling for high power LED automotive headlamp module

The development of automotive lighting systems with high illumination quality and high reliability is essential for driving safe and comfort. LEDs have many superiorities over the traditional light sources, such as high reliability, good color quality, long lifetime, energy and space saving, environment friendly and so on, when they are operated under an effective health management (such as thermal, electrical and optical managements). In the recent decades, LEDs have been widely applied in automotive as dashboard lightings, interior and exterior signal lightings. However, when they are introduced as a light source into automotive headlight system, LEDs must be required to have both high luminous flux (>1000 lm for low beam) and high thermal stability, because automotive headlamps are always installed near engine and their typical ambient temperature is about 80°C. The luminous flux model has often been used to describe the light output behavior of a LED as function of the driven current (I_f) and junction temperature (T_j), which can be used to represent LED's state of performance. This paper introduces the luminous flux model for a high power LED automotive headlamp module. Firstly, the junction temperatures of LED modules are estimated and verified under the conditions of different driven currents and case temperatures (T_c). The characterization data with the measured luminous flux (Φ), the estimated T_j and I_f are then used to estimate the coefficients in the luminous flux models with the Goodness-of-Fit method. The result shows that the modified luminous flux model can describe the actual nonlinearity of LED's luminous flux when it is operated at the condition of high temperature and high driven current.