They operate differently then normal bulbs:

"HID headlamp burners produce between 2,800 and 3,500 lumens from between 35 and 38 watts of electrical power, while halogen filament headlamp bulbs produce between 700 and 2,100 lumens from between 40 and 72 watts at 12.8 V."

 

Just swapped out my 8k HID bulbs back to the OEM stock 4.3k bulbs, and what a big difference it made in overall in illuminating the streets for me. The 8k bulbs looked nice, but the bad thing about them was that it didn't light up a huge radius of the road when driving. Changing the bulbs back to 4.3k was so much better at lighting up the road at night and overall visability. Contemplating on purchasing 6k bulbs..

 

6k bulbs are a good medium.