Based on the analysis and hardware test results, it is understood that the limitations of using an LED light source to design headlamp are based on two principles of non-imaging optical system: (A) the system cannot change (increase) the luminance of the light source used. (B) Etendue value of the output from the system is always equal or larger than the input value. Because of these principles, for the photometry requirements of the headlamp beam pattern and the design restriction for the system aperture, the luminance of LEDs must be comparable to or higher than the existing tungsten halogen light sources. Comparing to filament-like light sources, some disadvantages exist when using multiple discrete (non-elongated as a filament) light sources such as LEDs to design automotive headlamps. First, when the lamp aperture is divided into several sub-structures, each sub-structure may require smaller focal length. As the consequence, the associated optical accuracy or tolerances is increased. This may lead to addition reduction for the system efficiency. Second, because the headlamp beam patterns are highly non-isotropic, the vertical spread angle is very narrow; the horizontal spread angle is rather large. This asymmetric beam pattern can be rather easily achieved with tungsten halogen filament with axial orientation in an Free-Form Reflector (FFR) system. However because the current LED emitters are square shape, the associated optical system must introduce a horizontal spread to form a hot spot or other parts of the beam pattern, which leads to less overall light concentration. Therefore, comparing to the elongate light source with higher aspect ratio, square shape emitter LEDs may be less spread of hot spots to be used in the FFR type headlamp. To achieve tungsten halogen or high intensity discharge source equivalent headlamp performance without increase lamp aperture or package size, LED source must provide luminance comparable to these sources. In addition, the geometry of LED chip should be optimized so that it can be more efficiently used.
Studies for headlamp optical design using leds
Studien zum optischen Entwurf von Autoscheinwerfern mit LEDs
2004
9 Seiten, 14 Bilder, 2 Tabellen, 7 Quellen
Aufsatz (Konferenz)
Englisch
Studies for Headlamp Optical Design Using LEDs
British Library Conference Proceedings | 2004
|Studies for Headlamp Optical Design Using LEDs
SAE Technical Papers | 2004
|Studies for headlamp optical design using LEDs
Kraftfahrwesen | 2004
|Studies for Headlamp Optical Design Using LEDs
British Library Conference Proceedings | 2004
|Design of automotive headlamp with high-power LEDS
Online Contents | 2014
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