I don’t know about the actual manufacturing, but I can address the durability question. If you are looking for lights on a smaller scale, the low voltage industry is quickly moving to LED’s. The underwater LED’s are usually completely sealed–no removable portions/gaskets in the casing or wiring– which is where water usually leaked in the older fixtures. They do this because the bulb is the major expense and it lasts much longer, so it makes sense to simply replace the entire fixture when it goes bad. LED’s also don’t have a heat problem like the old incandescent/halogens had which caused a lot of wear and tear on everything rubber…
I don’t know about larger commercial applications, but I would not be surprised if LED’s are showing up there too. It is a new application, and sometimes they don’t get the quality of the light right–they can sometimes be too harsh and concentrated. But they usually work this out in the next generation or two.
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