Due to their compact lateral size and their stylish look ellipsoid headlamp systems (PES - polyellipsoid system) experience an increased application in vehicle lighting systems. PES systems are available now for many application functions and variants: for low beam, high beam and fog beam and using halogen or HID light sources. Unfortunately the small lateral size of these projectors is mostly opposed by a rather large length along the optical axis and an often critical temperature concentration in the optical path near the plastic outer lens which may cause degradation or even melting of the lens. These drawbacks can be overcome by a coated element in the beam path which selectively reflects a fraction of the invisible heat radiation. This paper reports about the reduction of the thermal load in front of the PES-lens by use of thin optical coatings and the consequential possible reduction of the system length. Such a high tech element consisting of very thin layers of material has to be selected and tested properly to perform well under harsh automotive conditions. It has been shown that optical coatings which have enhanced infrared reflection while transmitting visible light almost unchanged can protect cover lenses of automotive headlamps and consequently they can be used in conjunction with ellipsoid headlamp modules to build even more compact headlamps The projected headlamp geometry, for example the cover lens position and inclination, must be carefully analysed to select the right coating at affordable costs and to solve heat critical situation by early design adaptation The application principle is presented along with design considerations and evaluation test results. As an additional benefit an optical coating can enhance the headlamp styling by a proper selection of the visual spectral transmission.
How ellipsoid headlamps can profit from thin optical coatings
Wie ellipsoidförmige Scheinwerfer von dünnen optischen Beschichtungen profitieren können
2007
8 Seiten, 5 Bilder
Aufsatz (Konferenz)
Englisch
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