Headlight bulbs for PX150E (year 2000)

Greetings from South Africa

I fitted a new headlight unit (bought from SIP) on my PX150E recently. The headlight requires an H4 globe. I have now fitted two of these globes in succession, both Hella HS1 35/35W, and both of them lasted for roughly two weeks before the dipped beam filament blew. Traffic regulations here make it compulsory to keep the headlight on at all times, so I can't even use the scooter in day time now.

My questions: * Why do the globes have such a short life ?

                       * Am I right in saying that the headlight is run on (unrectified) A/C voltage ? If correct, might this be a factor in the short lifespan ? Might it help to install a bridge rectifier in the headlight circuit ?

                       * My own theory is that it's the vibration which destroys the globes. If this is correct, would it help to mount the headlight on rubber shims ?

Any suggestions how to overcome this problem will be highly appreciated.

GB in ZA