ProprtezAudi

You are incorrect. My owners manual says not to touch, the dealer where I bought the bulbs said not to touch, and it is plain common sense. It is true for even your table lamps at home, just to a lesser degree. But it is particularly true for any lamp that burns exceedingly hot, which these do. They are not halogen, but they are still very sensitive to contaminates on the glass that cause hot spots. Feel free to dirty up your own bulbs, but don't give bad advice to others.

Moviela

My owners manual suggests only a dealer can replace the lamps. That was penned by lawyers because of the danger associated with HID lamp capsules. Europe demands only sanctioned workshops change those lamps. Your post is similar to other old wives tales often spoken by the parts counter man or a misreading of an operators manual. If we follow your line of thinking since all dogs are animals, and all cats are animals, therefore all dogs are cats.

Halogen lamps are made of quartz rather than glass and must avoid sodium and naked fingers because the oils and other residue will cause diversification of the quartz envelope. This can cause early lamp failure. Prior to firing up halogen lamps I clean them with isopropyl alcohol. Any fingerprint must be removed with solvent. The tail of your T-shirt won't do the job.

Quartz is used for two reasons. The halogen cycle prevents the tungsten particles from reaching the inside of the capsule to darken it like conventional incandescent glass envelope bulbs. Quartz also allow transmission of infrared light, while borosilicate glass attenuates it.

Conventional lamps, including automotive lamps, run at much lower temperatures because the enclosure is much larger than halogen lamps. The reason it is larger is to make a larger area for the tungsten atoms to coat inside. This results in a lower density blackening to allow more visible light to escape. The larger envelope also allows a greater surface to radiate heat into the air.

While maximum light output is obtained with a clean glass surface, fingerprints have a de minimus effect on the radiated light, and have no harmful consequence to the lamp.

I have been designing and manufacturing lamps for several decades. I have never seen a glass envelope suffer diversification from a fingerprint.

audi2009

Thanks for post

fpr123

Thanks for posting the follow-up with pics Don

J P A Wasiak

-Great response, idiots that are incorrect and yet call others as misleading stain the forums they participate in.