HIDs are best installed with projector lens housings or the light dispersement goes everywhere including blinding oncoming traffic. From what Ive read, LED headlight bulbs may look bright but dont focus straight forward enough just yet, being that their new for headlights. PIAA bulbs are brighter and clearer than standard bulbs, for what its worth. Yes, I believe h4 and 9003 bulbs are basically the same with one being shorter than the other with the same socket style.