i know it doesnt affect the brightness but have u tried tinkering with the headlight screw. my headlight used to shine in the air but now ive adjusted screw it goes on the road now.
i think you can get bright white ones form halfords (dont know what they are called lol) yeah that screw ajustes the hight it needs to be at a certain level to pass the M.O.T im sure
This was tested in T&G no 62 http://www.acumen-electronics.co.uk/product/HID_H4,_Large_Ballast_61007# Got a good result in the test.