Originally Posted by jzeiler
I was not attempting to quantify the level of brightness or that it was now some how brighter than it was before but rather state the fact that it got as bright as it does get, rather rapidly. Before it seemed to take much longer on the old ballast to reach that same state.
There is a definite difference in lamp quality between manufacturers. Even the same lamp shop has lamp performance differences based upon which glass blower made the lamp. These lamps are as much art as craft and so, differences do occur. Also, if you inspect the lamp kernel carefully after say, 500 hours of operation, you may observe some darkening around the electrodes inside the bulb. This is contamination that was introduced at time of manufacture. The name brand lamps usually do not suffer from these performance issues due to the additional steps of cleaning the metal electrodes (usually tungsten) purging the bulb before sealing it closed and generally cleaner manufacturing conditions.
Also, the name brand lamps have developed better electrode material (some electrodes are doped with various salts) and sealing techniques to enhance life.
The main factor regarding HID life is hot re-strikes. The more frequently you hot strike an HID lamp, the more likely you are to have a failure due to the extra load placed on the ballast to supply the increased electrical demands of a hot lamp.
The oilhead load shed relay turns on the low beam lamp when the key is turned to the run position. Then, when you operate the starter, the load shed relay extinguishes the lamp while you spin the starter. When the start button is released, the low beam lamp is repowered.
Unless you install some means of eliminating this hot re-strike when starting your BMW oilhead, your going to sacrifice some HID life.
One final comment, when installing HIDs in a plastic headlamp housing, realize that the HID lamp does generate some UV which can cause deterioration in plastics and a good reason to avoid the high Kelvin lamp color which is high in UV. Also, UV is very tiring to the eyes and can cause some vision difficulties so don't look directly at the light source. Check that your headlamp housing uses UV resistant materials.
The name brand HID lamps usually are manufactured with a UV filter layer applied to the lamp for installation in plastic headlamps. The low cost kits from China? Check with the seller although I doubt you'll get an accurate answer.