Blaker,
As stated directed, read the articles attached by JGK.
Just ask me... . the idiot. I read the article a year ago and still went out and wasted money on overpriced blue "zenon" bulbs.
Worse still, I knew they were illegal in my area... DUH!!!
What a waste of money. Don't get me wrong, they look pretty cool, but the light output is less than the same size halogen.
OK, let me refraise that... . the light output is less in the spectrum HUMANS eyes use. Sorta like having a 200W infra-red lamp... Lotta good it will do ya in the truck... .
Additionally, some have been fooled into thinking they are brighter because they swapped a halogen 55W bulb for a blue 85W or 100W. .

Ahhhh..... self explanatory.
Or, some must think because they spend a bunch of money... . its gotta be better... . Trust me... I tried that the night I installed them.
The glare of the blue bulb is only seen by on-coming traffic. Ever notice the high beam flashes from on-coming traffic??
True HID and Zenon are excellent lights. Unfortunately neither allow you to simply pull out a $4. 00 halogen bulb and replace it with a blue bulb containing 4% zenon gas. . and charging $50.
Both cost MEGA money for the gain.
Best light upgrade is to install "slightly" higher wattage halogen lamps. Or better still. Add a good set of driving lights.
My PIAA 1200's and stock headlight bulbs outshine the heck out of a set of 100W headlamps. And I can turn them off.