Maybe you've read the postings on these ...
The reversing lights are wedge base with 16W bulbs (Type 955 £3 each at Halfords).
The front fogs are standard bayonet but with 35W yellow-tinted-glass bulbs.
... and are wondering about making either set brighter and/or losing the yellow tint, as I have just done, two points I'd add for some cheap experimentation are:
1. You can swap the bulbholders between these two positions with the slightest of paring off plastic "pips", plus splicing the wiring of course. Depending what you want to achieve this may open up more options without searching for extra bulbholders.
2. Domestic-type 12v halogen bulbs will fit the wedge base bulbholders (either where they are, or moved to the front "fog" position) the 50W bulbs cost £3 each at B&Q and have pins at the right 6mm spacing, the 21W ones cost £3.76 per pair at B&Q but have thinner pins at 4mm centres. I fitted the 21W one by spreading its pins a bit and inserting a 10mm x 15mm slice of old credit card in the bulbholder first, which padded out the thickness. I fitted the 50W one by squeezing the bulbholder contacts closer to grip the pins - release the catch behind each contact to pull it out.
I emphasise that I'm experimenting here. The vibration and voltage in the car may not suit these bulbs and there are overheating, wiring, fusing and switching considerations. - Dave Mason, 15 March 2002.
P.S. Frequent inspections but no apparent snag using that 50W halogen for reversing - Dave Mason, 24 April 2002.