On mY C15 I found the something like 35 Watt standard HB12s
were dim and well... crap.
So, I bought a pair of Xenon 60/55w bulbs from Ebay for
About £7.50
A significant improvement
They have a brighter, whiter output as opposed to the warm yellow glow
Remember they're HB12s I saw some incorrectly listed (for my 2001 van )
as H4
This is whaT I bought and use
http://www.ebay.co.uk/itm/Xenon-HIGH-Ma ... 4148e2d33b They also included 2 blue sidelight bulbs which dont fit my C15 but I wasnt that bothered
If you want to throw money at it you could go for HID kits
the various incandescent bulbs Xenon,Kryptonium,unobtainium etc are all much of a muchness
where 90% of the energy is lost in heat
HIDs are brightest and more effiicient
LED headlamps are appearing but aint quite there yet in terms of brightness and will still
be very expensive
Bolting on extra light is a dubious choice as fog lights should only be used in fog
and driving lights should only be used with high beam