Durably transparent: PLEXIGLAS® and PLEXIMID® for headlamp lenses

• PLEXIGLAS® and PLEXIMID® molding compounds are especially suited for lenses in LED headlamps
• Product benefits: no optical birefringence effects with PLEXIGLAS®, highest possible transparency and negligible drop in light transmission even after years of service
• PLEXIMID® remains clear-transparent even after prolonged use at temperatures up to 150°C

LEDs are very popular in many different sectors, including automotive construction. Whereas LED headlamps have so far been mainly used in high-end vehicles, more and more automobile manufacturers are now following this trend in mid-range cars too.

One aim is always to stand out from the crowd by choosing an eye-catching design or adding special functions. These include variable functions that are only possible with LEDs, such as adaptive lights for variable headlamp range control depending on driving speed and environmental conditions.

Applications range from large main headlamps to edge-lit lenses and light guides for daytime running lights up to lenses for dynamic indicator lights.

The innovative headlamp designs with a clear brand signature of the car manufacturing company often place high demands on the lenses. Depending on their construction and the LED grades used, the lenses have to withstand very high temperatures and also over longer periods of operation.

No birefringence: clear view in incident light
A number of features make PLEXIGLAS® especially suited for headlamp lenses. The material can be formed at will and is therefore the perfect choice for attractive designs. In addition, PLEXIGLAS® offers high transparency and durability. These are properties that are particularly advantageous for use in headlamp lenses, and offer benefits over other transparent plastics. PLEXIGLAS® also suppresses the disturbing colored light halos around the edge of the lenses. This is because of the material's low birefringence combined with its high Abbé number that guarantees low dispersion effects.

Constantly high luminous efficiency
PLEXIGLAS® also comes up trumps in other optical respects. It is clear-transparent, which means there is no clouding. Light shines through with complete clarity. Better still, because of its stability, PLEXIGLAS® loses none of its high transmission even after several years, and provides constantly high luminous efficiency.

High temperature requirements-no problem for PLEXIMID®
The chosen headlamp construction creates temperatures over 150 degrees Celsius inside the headlamp? No problem for PLEXIMID®. PLEXIMID® is a polymethyl methacrylimide (PMMI) that offers an extremely high heat deflection temperature in addition to the properties of PMMA. It remains completely stable under permanent thermal load. This means that even in a 40-day long-term exposure test at 150 degrees Celsius, the light transmission remains almost as high as before and no noticeable yellowing or clouding occurs.

This makes it particularly suitable for all types of headlamps in which the illuminant is meant to offer extremely high performance and brightness, or LEDs are installed very close to the lens.

That applies both to main headlamps and light guides for daytime running lights that have to guarantee uniformly strong illumination of long distances. Here too, PLEXIMID® remains clear in permanent use.

 
PLEXIGLAS® and headlamp lenses: applications with a future
One thing is clear: LED technology is one of the elements that will be used even more frequently and diversely in the future, and will put other technologies in the shade. The possibilities for developing modern headlamps, edge-lit lenses or designer lighting have not been exhausted by a long shot. And the requirements to be met by the relevant materials are just as varied as the applications themselves. For this purpose, Evonik offers a broad product portfolio of PLEXIGLAS® and PLEXIMID® molding compounds with different heat deflection temperatures and customized optical properties.

Evonik is a worldwide manufacturer of PMMA products sold under the PLEXIGLAS® and PLEXIMID® trademarks on the European, Asian, African and Australian continents and under the ACRYLITE® and ACRYMID® trademarks in the Americas.