Evolution of Luminaires in the Automotive Lighting Industry towards LEDs requires Revolution of Thermal Management

Boris Marovic; Andras Poppe; Gabor Molnar

doi:10.4271/2012-01-0259

With the change of luminaires from incandescent bulbs to Light Emitting Diodes (LED), we all know that the concept of thermal management for this application is now redundant and new ways of thinking need to be established. While incandescent bulbs mostly radiate (~83%) and dissipate (~12%) heat loss and do not face thermal challenges related to the light source, LEDs mostly transfer their heat loss (~60-85%) by conduction and are sensitive to the thermal management. Therefore the efficiency of a 100W incandescent bulb is ~5% while the efficiency of LEDs is ~15-40%.

The main thermal challenges with LEDs are to maintain a high color stability and life expectancy. LEDs in the automotive industry need to have lifelong durability. With LEDs being not only more efficient, but also valuable in terms of higher visibility and therefore higher safety, the Economic Commission for Europe (ECE) set the Day-time running lamp (DRL) as mandatory from 2011 for all new models of cars.

Since exterior lights such as headlights and tail lights are almost completely sealed systems, except for the very small airflow inlet, outlet and the small opening for regular incandescent bulbs, it is not realistic to allow a change of LEDs in case of a defect. Therefore high reliability and quality not only of the LED but also of the overall lamp design is compulsory since the change of a whole headlight is expensive and if it falls under warranty it can be very expensive for the OEM and supplier of the system.

This paper will address methods to achieve the best in class thermal management for the lighting industry. Starting from selecting and measuring the thermal characteristics of LEDs to being able to choose the most suitable LED and conduct accelerated ageing tests, to thermal simulation of complex-shaped lighting systems such as headlights, with concurrent Computational Fluid Dynamics (CFD) technology for higher quality products and a faster, more efficient and cost-effective development of lighting systems.

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Evolution of Luminaires in the Automotive Lighting Industry towards LEDs requires Revolution of Thermal Management 2012-01-0259

SAE MOBILUS