The microoptic lenses behind BMW's Welcome Light Carpet
For the late-night reveler, the BMW 7 Series has a feature that makes the walk through the carpark a bit less frustrating. At the press of a key fob, the Welcome Light Carpet lighting system shines a striped pattern of light on the ground to guide motorists back to their car thanks to a system of specially developed microoptic lenses.
Now standard equipment on the new BMW 7 Series, the Welcome Light Carpet uses microoptics developed by the Fraunhofer Institute for Applied Optics and Precision Engineering IOF in Jena. On command, it projects a striped light pattern over about 4m2 on both sides of the car by means of a lighting module installed on the vehicle underbody under the driver’s door.
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From the module, microlenses aim the light where it's wanted using a honeycomb array of microprojectors. Fraunhofer says that these tiny projectors should produce less light, but this is overcome by packing many of them in a small area. These lenses can be arranged individually, so the images from them can be made to precisely overlap for a high-intensity image even at low angles of illumination.
"We can alter the intensity of the light by altering the number of microprojectors used," says Andreas Bräuer, Microoptic Systems department head. "Regardless of whether we use 150 projectors, as with the BMW Welcome Light Carpet, or we use 3,000 of them, the thickness of the array still remains within a range that is measurable in millimeters."
For the BMW Series 7, the Welcome Light Carpet was configured into a 10 x 10 mm² microoptic assembly fitted with a glass cover. This is fitted to the underbody of the car and faced away from the direction of travel to minimize damage from stones thrown from the road surface. According to Fraunhofer, road dirt isn't a large problem because the multiple projectors can continue to operate with reduced brightness without being completely obscured.
"This marks the first time our technology has been applied in a volume market," says Bräuer. "There is an extremely wide range of possible uses for this type of array lighting, extending from safety technologies and medical applications to mechanical engineering and traditional signal lighting."