OK....I'm going to chime in here as I know a fair amount about this topic.
I put some HIDs into my Xterra using the OEM headlight housing with no modifications. Doing that was a disaster. So I speak from experience.
Things you should know about doing this.
- the reflectors and housings of the OEM headlights that came with halogen bulbs are designed for just that. Halogen bulbs.
- HID bulbs are of a different design and size thus defeating the effectiveness of the OEM reflectors and housings.
- The "gain" you see is light being spread out omnidirectional (see glare) regardless of having them "aimed". You can't "aim" an OEM headlight with HID bulbs.
- You become "That Guy" everyone hates on the road.
The only thing you can do in this situation is to do a complete retrofit with projectors.
Why waste so much light up into the sky and other drivers eyes??
They are easy to do, if you have some mechanical knowledge. You can find some mod shop around town where you could pay someone to do it.
Check out this company for kits.
I did the projector mod myself over a weekend. Took my time. Painted the housings and shrouds chrome black, baked the housings and did all the wiring. I wasn't in any rush.
Bottom line- If you just put in P&P HIDs into OEM housings, you are just wasting your money and being "that guy". Do it right and use projectors.