Standard bulbs are rather poor yellow light and litronics are a significant improvement, HID kits were as good and despite what many said about needing self leveling and washers to comply with the law - that was not true - after market were exempt from needing those two aspects, I fitted them and no problems come MOT time, however, the MOT was beefed up significantly in 2012 and im not sure what the current legislation is regarding after market fitment.
But, be carefull and sceptical about bulbs being offered that deliver a brighter light as many are simply higher wattage bulbs, ignore all the hype about "Zenons" as all those bulbs are standard bulbs just filled with Zenon gas instead of Halogen, and that does not make them brighter.
Construction and use limit bulb wattage to 55 watts so the 100 watt bulbs will fail MOTs, but, the main problem with higher wattage is heat, 100watt bulbs will melt the outer lens if they are left on whilst you are in either very slow moving traffic or stationary as there is no airflow to cool them down - first sign of this is discolouration of the lens.
