Here's a little bit of headlight bulbs 101:
"White" light has a temp rating of about 5000K. Lights that are significantly lower than this produce yellowish light and lights that are significantly higher than this produce blueish to purpleish light. Halogen light bulbs don't put out "white" light in their native state. They produce light at about 3000-3200K typically. It is possible to put a filter on a halogen bulb, and cause them to produce white light. This is why "white" halogens have a blue looking filter on the end of them.
Doing this ALWAYS cuts down the actual light output. Filters never increase light output, they always reduce light output. Bulb manufacturers deal with this limitation in a few ways, all of which have significant tradeoffs.
1) They can increase the wattage, but this causes the bulbs to not be street legal. This is why some bulbs are labeled for off-road use only (PIAA labels all their bulbs this way even though some of them don't have increased wattage). Increasing wattage also carries the risk of damaging the lamp and/or damaging the vehicles wiring.
2) They can overdrive the filament. This causes the filament to burn hotter which increases light output at the expense of greatly reducing the life of the bulb. For instance, 9006 Sylvania Silverstars have a rated life of just 150 hours. Sylvania 9006LL bulbs have a rated life which is 10 times greater.
3) They keep the same wattage and filament. This overcomes the tradeoffs in 1 and 2, but the light output is greatly reduced because there is no compensation for the filter.
Anyone who tries to claim their bulbs run at the street legal wattage, burn white, produce more light, and last as long as standard bulbs is full of crap. There is no free ride with halogen bulbs. Many white halogens (including Silverstars) don't increase actual light intensity. They adversize their bulbs are "brighter" but this is highly subjective and impossible to prove. They do not advertise thier bulbs are more intense because this would be false and fraudulent.
Personally I run the Sylvania XtraVision bulbs. They burn the same color as standard bulbs, however they overdrive the filament slightly to produce more light. This reduces the rated life to 850 hours, but this is not bad if you consider the standard Sylvania 9006 bulb is rated at 1,000 hours. OSRAM doesn't make the European Silverstars (which don't have a filter) in the 9006s, however the XtraVision bulbs are almost as good.
HID upgrades are the only way to significantly increase light output in a way that doesn't sacrifice bulb life or risk damaging your vehicle. HID bulbs produce light by arcing electricity between two points. They have no filaments. This is why they need balasts so the voltage can be kicked up to very high levels capable of producing arcs. However HID upgrade kits are not worth doing on some vehicles. The reason is because the focal point for HID bulbs is not the same as halogen bulbs. Due to the optics in some lamps, HID bulbs can actually degrade lamp performance vs halogen. IMO the only worthwhile HIDs are those which have projector lamps such as the ones in BMWs vehicles as well as many others. The bulbs are only part of the picture. The optics of the lamp is the rest of it, and can ultimately make the most difference when paired with a good HID bulb.
:angry :grrr These smilies say it all for me. I remember the day when all you had to do was remember high beams or low beams, and which screws to unscrew when changing headlight bulbs. They were of one shape and one shape only: round! Sigh...