2001 Vauxhall Vectra headlight issue when damp

hi my drivers side xenon headlight sometimes wont turn on so i flick on/off switch on then off a few times till it decides to work, sometime it flickers like a strobe and there is an arching noise from under the bonnet near the light. once its on its ok but if i turn engine off and restart happens again, same as next time i go to turn lights on. These lights are standard on CDX models. Anyone else had same problems. It seems worse when wet or damp as 90% of the time its fine this mainly happens when its damp or raining.