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.