This report investigates the use of single and multi-layer coatings on replaceable headlamp bulbs and how such coatings can affect the performance of bulbs in terms of light scattering, which can contribute to glare, and spectral separation in headlamps. Tests were developed to investigate the effects of absorptive and interference (multi-layer) coatings on bulbs, and on bulbs in headlamp systems. These tests provide validation for a proposed bulb color separation test, which establishes limits for spectral separation within the boundaries of SAE J578 white color requirements. The chromaticity spread in the bulb color separation test and the filament ghost images observed in the data from the goniometer scans show a correlation with the bulb coating type and the projected headlamp glare for axial filament bulb designs with mostly axially positioned internal components, e.g. the 9006, H4, H7 bulb types. For an ANSI 9007 design dual filament lamp, the internal components create more 'uncontrolled light' than a typical coating. However well-designed 9007 systems compensate for the presence of this internal component related uncontrolled light. For the 9007 design a correlation between the color test and glare due to uncontrolled light has not been confirmed yet. In the measurements with ECE type bulbs and ECE beam distributions the test results indicate a clear correlation between the beam pattern produced with a color-coated bulb and the spread of color coordinates for different spatial measurements across the bulb surface: Well-defined, intense beam patterns with a clear cutoff, low fluxes in the glare region and low glare/hot-spot ratios fulfilling the legal beam requirements can be achieved with bulbs that exhibit a very little color separation, while bulbs that show a wide spread in color coordinates also show bad-quality beam patterns and can cause glare and/or insufficient road illumination when used in the same headlamps, and vice versa. For U.S. and ECE bulb types, the bulb color separation test is the most sensitive method for isolating and quantizing coating-related uncontrolled light from a coated bulb. The test places one and the same requirement on all bulb types, is straightforward to carry out and can be performed on a widely available measurement system with low cost additional equipment. The color separation test is now prescribed for the ECE region by the supplement 22 of the 03 series of amendments to the ECE regulation R37, which came into force on 7 December 2002.
Investigation into the effects of absorptive and interference coatings applied on replaceable headlamp bulbs
Untersuchung des Einflusses von Absorptions- und Interferenzschichten in der Anwednung von austauschbaren Schweinwerferglühbirnen
2004
22 Seiten, 25 Bilder, 10 Tabellen, 8 Quellen
Conference paper
English
Absorptive and Interference Coatings Applied on Replaceable Headlamp Bulbs
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