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Automotive Headlamps Disclosure Number: IPCOM000129410D
Publication Date: 2005-Oct-06
Document File: 4 page(s) / 10K

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Automotive Headlamps

Discharge lamps, especially high intensity discharge (HID) lamps like Xenon lamps, have found an increasing use especially as head lamps for vehicles ("Xenon lights").

When producing such lamps, care has to be taken that the desired quality of the lamps, especially lamp properties, lamp specifications, lamp parameters or other lamp data are obtained. In order to ensure this, the manufactured lamps of a related production line have to be monitored and controlled thoroughly. The control of the present output of the production line is an important part of the whole production process.

Before testing the manufactured lamps and measuring their parameters, the lamps (especially automotive HID headlamps or Xenon lights) are usually burned for a special time after production at nominal wattage power (e.g. 35W). The effect of this first step is a stabilisation in the main lamp parameters, like e.g. colour point, lamp voltage, luminous flux, in order to prepare the lamp for a second, subsequent, separate measurement step of these lamp parameters.

During such burning, the lamps reach elevated temperatures (the maximum temperature inside the burner at the top is e.g. about 1100°C). The effect of this first step is twofold:

First, reactions of the filling salt constituents with each other, but also with the electrode material, with the surrounding glass and impurities in the lamp take place, leading to a stabilisation in the main lamp parameters mentioned above.

Second, the lamp is thus prepared for a measurement step of these lamp parameters, to control the present output of the production line.

However, the first step takes a remarkable time (e.g. up to about 90 minutes) leading to significant power consumption.

Experiments have shown that a significantly shorter burn in time can be realised by operating the lamps inside of a magnetic field which is especially homogeneous and which causes a

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significant up bending or up shifting of the discharge arc. As a result, the lamp top temperature is increased with respect to normal operation, resulting in a decreased process time. This procedure leads to the same stabilisation result, without any detrimental effects on the lamp quality. Thus, process time and energy consumption can be reduced.

The burn in process inside a homogeneous magnetic field has to be performed such, that the elevated temperatures are reached for a defined time:

On the one hand, the process time must not be too long, because otherwise the lamps - which are thermally designed for the standard top temperature of about 1100°C - might be damaged and might even fail at the customer.

On the other hand, the process time has to be long enough to allow the necessary reaction processes to take place to obtain a stabilised condition. But due to the elevated temperature, this needed time is significantly reduced, because the process time scale of the thermally activated reactions, which underlie the lamp...