The curved HELLA taillights dominate the sporty yet elegant design of Opel's Crossland X. Responsible for the intense, evenly distributed red light is a customized PLEXIGLAS® molding compound from Evonik.

The days when the family car was notable for its unimaginative design are long gone. The brand-new Crossland X from Opel, for example, aims to combine “the properties of a cool SUV with the elegance and functionality of a sedan,” notes Mark Adams, the European vice president for design for the Rüsselheim, Germany, automaker. As he goes on to explain, “Our new Crossover unites these two strengths in a way that is unsurpassed, while still offering a great deal of interior space despite its compact size.” The result is a “cool family car, perfect for young families.”

According to Adams, the automaker draws upon a combination of sculptural styling, German precision, and a high-tech look: “The new Crossland X is unmistakably Opel”—a brand, he notes, that embraces the essence of a design philosophy best described as ‘sculptural design meets German engineering.’ For Opel, one aspect of this philosophy is about perfectly uniting form and function in every detail of the vehicle, which means constantly redeveloping their model designs. The Crossland X, for instance, is the first model to sport a newly developed LED taillight made by the innovative lighting specialists at HELLA. The taillights act as an interface between the trunk lid and roof lines, making the brand's signature double-curve motif clearly visible along both components.

PLEXIGLAS® light guides

The double-curve motif is the dominant design element of the LED taillight recently developed by HELLA: when lit, its arrow-like shape is a uniform red, but even when the lights are off, the curved lines are still easy to see. The effect is the result of light guides made from a newly modified PLEXIGLAS® molding compound—poly(methyl methacrylate) (PMMA) from Evonik, which has long been established for taillights.

“This application was the first time that we combined light-diffusing additives with the signal color red,” says Jörg Stricker, head of Global Key Accounts Automotive at Evonik. “PLEXIGLAS® 8N 3V219 disperses light more evenly than other molding compounds, making it even better for use with LEDs.” Light-emitting diodes, while popular in the automotive industry for their energy efficiency, place considerable demands on light-diffusing taillight covers: “LEDs emit a powerful point light, and that quickly leads to undesired differences in brightness known as hotspots,” Stricker points out. “So the material used for covering them has to do a good job of diffusing light.

Thanks to this customized PLEXIGLAS® specialty molding compound, taillight covers can now be positioned more closely to the LEDs without resulting in hotspots.

“This means the taillight as a whole can be much flatter and, as a result, take up less space in the body of the car,” explains Ludger Rembeck, who heads up taillight development at HELLA. “That provides a really practical benefit for the driver: bigger trunks.”

Long-lasting signal color’

Plus, the newly modified molding compound makes the red of the light guide look even more intense. “It makes the signature double-curve motif even easier to see during the day,” Rembeck observes. The red shade itself likewise places unique demands on the material used, however: since the colors used in taillights are standardized all over the world, manufacturers have to be able to adjust the color of the material with tremendous precision. “PLEXIGLAS® starts out completely colorless, so it can be colored to any signal color you need,” says Martin Mohrmann, senior technical marketing manager at Evonik for automotive products. “It doesn’t alter optical properties like excellent light transmission or diffusion either.” And that benefit is permanent: PLEXIGLAS® molding compounds are stable in the presence of UV light and heat, which means the precise color of the taillight covers remains unchanged for the life of the car.