I finally received the Phillips H9 bulbs today.
Phillips are the most recommended H9 bulbs as they are the highest quality, rated at 450 hours. Sylvanias are much easier to come by--all the Advanced O'Reilly Zones carry them--but are rated at under 300 hours. Bringing up the rear are the GE bulbs, which are only rated at 150 hours. If you order the "Hella" H9 bulbs off Amazon like I did, they send you the GE bulbs. No thanks.
I had read online that some vehicles have H11 housings that do not require the "rotary"-style tab to be trimmed, so I test fitted the H9 bulb into the LR4's H11 housing. It's a little more difficult than installing an H11, but the H9 bulb does positively "click" all the way in without having to trim the tab.
So, for purposes of installing an H9 bulb in a LR4, the only modification needed is to trim the guide-tab in the electrical connection. Here's a picture of that modification I pulled from the internet:
After sitting and pondering easy, clean ways to go about doing this, I had to settle for the rather inelegant method of using a Dremel to "drill" the guide-tab out, similar to this video:
https://youtu.be/_mrbdQmck7E?t=4m10s
I must admit, however, that my finished product looked better than his.
With that, I installed the H9's and went for a drive. The filament on the H9 bulbs is located in the exact same position as the H11 bulbs, so the light has the exact same pattern as the Land Rover engineers intended, only brighter. The road immediately in front of the LR4 is brighter. The road is brighter at a distance. The periphery is brighter as well--I could see details in the trees much clearer as I drove down my block.
An H9 bulb measures at about 2200 lumens. The stock H11 bulb measures at around 1300 lumens. This more or less corresponds with what I saw as I drove around.
Be warned, however. The light from a standard H9 bulb still resides in the warm side of the spectrum, so if you don't like the stock bulbs because they aren't blue enough, you probably won't like these either. If blue is what you want, there are blue-tinted H9 bulbs available (
link). But again, these are just standard halogen bulbs that push the light through a blue filter, and therefore have degraded performance over a standard, clear-glass bulb.
So, in my mind, a standard Philips H9 bulb is the best upgrade you can do to the halogen projector on an LR4.
What of the other options, such as the H11 LED bulbs or the HID retrofits?
Halogen headlights in every vehicle, including the LR4's projectors, are designed around a specific model of halogen bulb that puts out a radial light at a single, specific point. An LED bulb is not a radial light, and therefore would not work in a halogen housing as intended by the engineers that designed it. An HID bulb puts out an arc as a light, and the same thing happens: putting an HID retrofit in a housing designed around a halogen bulb puts out a sub-optimal light pattern.
Daniel Stern, one of the preeminent automotive lighting experts, explains this in detail
here (link).
You ever read other people installing HID or LED lights in their vehicles brag about how their lights are so bright that they keep getting flashed by oncoming traffic? This isn't because their lights are so bright, per se. It's because their modification has sent stray light directly into the eyes of oncoming traffic, whereas the stock bulbs projected a nice, sharp cutoff that did not.
Even if an HID retrofit or LED bulb yields a cutoff (which it might, depending on how the halogen housing was designed), they will not output light in the correct spots. Often time they shine a ton of light right in front of the vehicle, convincing the driver that they are excellent, bright bulbs, but won't shine nearly enough light further up the road where it is needed.
To paraphrase the way Daniel Stern puts it, attempting to get better night vision by installing HID lights in a halogen housing is like trying to help someone else see better by given them your prescription eyeglasses.
The LED bulbs have the exact same problem. This is why the Philips LED bulbs state that they are for fog lamps only. This is because factory fog lamps are, for the most part, merely an aesthetic add-on with little or no actual utility, and therefore throwing a bulb in them that produces a completely different light-source doesn't muck things up much.
So, back to my point. If you have an LR4 with halogen headlamps, I believe the only modifications you can make are (1) install H9 bulbs, or (2) install Land Rover factory HID headlight housings.
See also:
http://www.candlepowerforums.com/vb/showthread.php?393807-H11-projector-bulbs-35w-HID-vs-LED