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The use of vented automotive lamps while reducing cost can also result in moisture intrusion through the vent openings into the lamp. If the lamp internal air humidity approaches 100% water vapor may condense on the lens inner surfaces which detracts from the lamp appearance and quality of the light output. Headlamps are required to pass a humidity clearing test which is specified by the FMVSS108 procedure[1]. Prior to the use of CFD predictive tools, lamp venting design was basically a trial and error process which could sometimes require several different prototypes before passing the test. Now by using CFD the venting design can be optimized without the need for prototypes which results in reduced design cost and faster time to market. By utilizing a combined external/internal flow CFD model with coupled heat and mass transfer, lamp vents can be placed in regions that will maximize the removal rate of humidity from the lamp interior.

An advanced high intensity discharge (HID) light source thermal model has been developed and used to analyze heating problems in a HID fog lamp. The HID thermal model incorporates coupled specular radiation and natural convection to accurately predict the HID capsule surface temperatures. The HID light source model was used to predict fog lamp lens and housing temperatures and to provide critical information regarding material specifications. The development of a HID light source model is a major step forward in the use of predictive tools for the thermal analysis of automotive exterior lighting.

The headlamp designs of today and the future will be increasingly complex to match the increasingly dramatic vehicle designs. These complex shapes require lamps that are vented to relieve pressure and thermal stresses. Specifying headlamp vent locations to optimize humidity clearing while minimizing dust intrusion is often a trial and error process requiring several iterations using prototypes. Computational Fluid Dynamics external flow simulations can provide an accurate view of the lamp external air flow and pressure gradients which allows the designer to specify vent locations for maximum air exchange. CFD can thus reduce the need for prototyping and testing while reducing cost.

The need to perform thermal analysis for automotive lamps has increased in recent years, due to the use of plastics for the lens and housing materials. Tremendous advances have been made in finite element analysis methods for solving coupled specular surface radiation and natural convection with an unstructured mesh. Headlamp temperature rise predictions were made using the ADINA-F CFD code. The results showed very close agreement between the predicted and measured lens and housing temperatures with an accuracy of +/-10 percent. The successful benchmarking of the lamp thermal model has allowed the analysis method to be applied to a wide variety of lamp designs and operating conditions which has reduced the cost of products and development.