educate me on headlights

Noticed one of my headlights is pretty dim...

From what I gather, you can buy a 6054 replacement unit and bob's your uncle.
Are any of the ones available actually brighter than stock? I saw sylvania and GE's that claimed to be X% brighter/better than something else.

What's the deal with H4's?

Any recommendations?

search and you shall find

http://www.naxja.org/forum/showthread.php?t=60812

How dim is dim? Before you go too far make sure you check the condition of the headlight sockets and their wiring. It's marginal at best. The sockets can corrode, and on my 99 the prongs of the headlights themselves corroded off. If you have a pre-97 XJ, also check the front harness connector that is near the bulkhead, just beneath the air cleaner, for corrosion. Even if everything is all right now, a good clean and lube of those connectors will help with whatever bulbs you decide on.