Fully functional LED headlamps debut on the new Cadillac Escalade Platinum, making the upscale SUV one of the first vehicles in the world to use this lighting technology. Hella's LED headlamps handle high beam, low beam, parking lamp, side marker, and daytime running lamp, which uses the same LEDs and lenses as the low beam but reduces input power to the required level via pulse-width-modulation. "Each LED illuminates a specific area in the beam pattern, but the LED module generates the entire light pattern," said Siegfried Hetz, Product Engineering Specialist for Hella North America. The only non-LED part of the headlamp is a side reflex reflector.
The headlamp comprises seven lenses, but six different types of lenses provide the entire light pattern. "The lenses differ in two ways. The outside geometry is different—some lenses have a more circular shape and some lenses have a more rectangular shape—and the other difference is the geometry of the front surface is free form. Each geometry is calculated to project light to a certain area within the beam pattern," Hetz said.
For the low beam, each Escalade Platinum headlamp uses five LEDs, with each LED containing five chips. The high beam consists of two LEDs per headlamp. "However, if the high beam is on, the low-beam LEDs stay lit. So in reality a total of seven LEDs per headlamp are lit when the high beam is switched on. This means a total of 14 LEDs are lit to realize the high beam function on the vehicle," said Hetz. The parking lamp uses two LEDs per headlamp.
In designing and developing fully functional LED headlamps, engineers addressed photometric issues. "Several iterations and optic concepts were necessary to achieve the final light pattern design. The unique challenge was finding a way to achieve equal or better photometric performance compared to the current Cadillac Escalade headlamp, which uses a high intensity discharge system," said Hetz.
That issue was resolved "by the individual design—free-form geometry—of the lenses. State-of-the-art software was used to generate the free-form surfaces based on the required light distribution. During the final assembly process of the headlamp, all seven LED multi-chip light sources are individually adjusted in order to form the final light pattern," Hetz said.
Other problematic engineering issues overcome were packaging constraints and thermo-management of the headlamp. "The electrical fan is needed to create the necessary airflow inside the headlamp to dissipate the heat from the LEDs. In addition, the generated airflow prevents condensation on the inside of the lens and deices the headlamps' outer lens," said Hetz.