I was kind of surprised too when I heard that LED are using heat sink, not the type of LED display people used to see. Are we going to have useful LED dive lights? It depends on how the semiconductor technology is moving e.g. different kinds of dopants etc. When we heard that heat, UV are being generated instead of visible light, it means that part of the energy is lost already with respect to dive light application. Although the high output LED's are not "as realiable as" the old ones, we can still see that the auto industry is trying to use the LED for signal lights, plus, as a matter of fact, we are having LED traffic lights already, at least I can see that in CA. That means the reliability is somewhat under control, depends on how we use it; another question to ask maybe is this: do we see more luxeon burned out than HID? This should give us an idea at least for now.
About HID light, I was actually surprised about the reliability for many of them, as some experts here reminded, we are not having bulbs which are dedicated for dive lights application, I think this is a significant point. It reflects how much we have done already in building our dive lights today, and where we can go tomorrow; factors like, the cost of replacing light bulbs, having the light burn out at the middle of a dive etc. These are all major concerns for HID light users, and people who are considering using HID to be their next. When I observe that HID being used in automobile is not having the same issue, I start to think that there must be something the manufacturers can do about it. This issue is very very important, because as we push from 18W to 35W or 50W, the heat dissipation would only be worse. This is a common problem for HID and high output LED.
Let me branch off for a bit, for the semiconductor industry, the most common type of heat sink is what we can see on the back of a chip package over a pc board, for example -- a metal piece sicked on the back of a chip package. Besides that, there is another type: fluid cooled heat sink, it's one step further than the pure metal heat sink -- more effective, but the manufacturing cost is much higher, therefore people would not use it unless they have to. Now, our application is dive light and sea water is all around, so there is a very high chance that we can change the structure of the light or the material used to facilitate.