Drive faster, okay , no seriously. The faster you go the brighter, I have had the problem of keeping bulbs. the 6v bulbs blow out. I have blown out every bulb from the headlight, and speedometer to the brake light. I have moved to all 12v bulbs.. they seem dim at first but with a bit more rpms they are plenty bright. does your vespa come equipped with a battery? if so get a new 6v battery.. I use the sealed walmart kind.. they are alittle bigger than stock but have more power and don't leak like the stock replacement batteries.