The White Led Used In The Study In The Automobile Headlamp Illumination

With the advent of LEDs (Light Emitting Diode), the lighting field has experienced another revolutionary period after the invention of tungsten bulb by Edison one hundred years ago. Meanwhile in order to meet the requirements for aerodynamics and styling, the front part of an automobile becomes lower and lower, resulting in less space left for headlamps. The AFS (Adaptive Frontlight System) with automatic beam pattern changing with the traffic situation and weather conditions has become a trend for automotive headlamps. The compact and modularization of LED optical systems can just meet these demands. However as a new kind of light source, LED causes concerns on its photometric and colorimetric performance and poses challenges on traditional optical systems as well. Consequently although the application of LEDs in automobile signal lighting is quite common nowadays, a full package of LED headlamp is still on the way.The potential problems and feasibility of LED's application in automotive headlamps are investigated concerning photometry, colorimetry and optics. In photometry, comparisons are made between LEDs of different CCTs (Correlated Color Temperature) and different spectral compositions, together with traditional light sources such as the incandescent lamp and the HID (High Intensity Discharge) lamp, using two representative mesopic models. It can be concluded that LEDs can have higher visual effective lumen output under mesopic vision. Based on the data calculated a method is proposed to predict the visual effective performance of a light source under the mesopic vision using S/P value of the source. In colorimetry, the color shifts of traffic retroreflective signs illuminated by LEDs are analyzed. The results confirm that phosphor white LEDs won't cause color confusion for traffic signs, if the wavelength of blue peak was no less than 450nm in order to avoid green color shifting towards yellow-green. In optics, discussions on lumen collection efficiency, minimum allowable error of the optical system and filament images are made. Based on complete knowledge of the radiation pattern and intensity distribution from LEDs, a corresponding optical design method is developed. The reflectors based on complex parabolic curves can help reduce the demands for strict mounting positions. The design and test of the freeform reflector and PES(Poly Ellipsoid System) for LED fog lamps verify the design method and simulating results. Further applications are introduced on LED lowbeam modules.Innovations:1. Modifications applied to traditional parabolic reflectors help relaxing the installing precision requirements. With complex parabolic curves and/or complex parabolic surfaces, various beam patterns can be realized. The method is applicable for other types of luminaries as well.2. Using filament imaging and zonal lumen calculating methods and in the knowledge of intensity distribution of LEDs, the lumen output from the LEDs is redistributed into given regions of the freeform and ellipsoid reflectors in a reasonable and effective way, which could be used for LED automotive headlamps.3. Field curvature shield is adopted when designing the PES headlamp, which eliminates the negative effect on the cutoff qualities produced by the decreased dimensions of the PES system.