Well, it's not really a fair comparison because they are very different lights.
I loved my Light Cannon while it lasted. But frankly, I disliked the expensive and fragile bulb. HID's are definitely brighter, whiter, more focused, but I can't deal with the lack of what I call the "klutz factor" and the costs involved. If the bulbs were only $20 a pop, I could probably deal with that, but not $100! Mine broke the first time with just normal usage (well, what I was used to as normal usage). Ok, I'll replace it once, I told myself. I handled it with TLC after that and even got a little padded case for it. But when it broke again from an 18" drop to a carpeted floor just a short time later, I laid it to rest. For the price of a bulb, I went with the Shockwave II LED and am fairly content with it, particularly the high "klutz factor". I believe LED technology will eventually be par with HID. There was an article in Science News about a month or two ago that they've already developed an LED that is 7 times brighter than the ones on the market today. But it's not there yet.
If available funds are high, your "klutz factor" is low, then go with an HID (if you're considering Green Force, then I assume you have a healthy budget). If you dive mostly in 70ft+ vis waters, HID is an overkill.
I have seen an HID dropped from table height onto a concrete floor and be none the worse for wear. I have seen one literally hurled against a drywall building wall, WHILE lit, and didn't hiccup. I've seen them literally banged on a podium while lit and be fine. The demo for the GreenForce 21w head has the present drive nails into 2x4s with the lighthead while it's on.
It all depends on the HID, as they are clearly not all the same.
