Originally Posted by TheOtherDave™
And there's another issue to consider with aftermarket headlights... heat dissipation.
Usually, these aftermarket headlghts are made as cheaply as possible, with low-grade plastics being the norm. IMO, you run the risk of melting the headlamp housing due to the increase in temperature with either an HID retrofit or the "9006 conversion".
HID burns cooler than halogen, so melting wouldn't be an issue. But the suckyness of the output definatly would be.