I had the opportunity to compare and contrast my 3 favourite canister lights this weekend, all by Diverite, the 10w HID, the LED500 and the new LED700. LED technology is receiving a lot of focus and the light they emit in diving use is clean, bright and white, as is that of the HID units. There was not a lot in it between the 3 lights, tested in the pitch dark at a depth of 140'. The 10w HID is a narrower beam than the LEDs and the LED700 was, it seemed, every bit its equal in terms of brightness, whiteness, intensity and penetration and is a broader beam. The LED500 was a shade behind these two in terms of brightness but in fairness the batteries were not new and had been on several dives- testament to the long lived delivery from this light (13 hours from 8 AA batteries!)
My preference is for LED. I am hard on my equipment, am not as diligent as I could be in looking after it and still expect it to perform flawlessly. I have had several HID systems and sooner or later the bulb goes and these are not at all inexpensive to replace. I have all 3 of the above systems and my HID will be sent in for an LED retrofit once this bulb blows.
The LED500 is, I find, an excellent primary in its own right and extraordinarily good for travel. Weighing in at only a few ounces it uses widely available AA batteries (8) and lasts an age on them.
We have yet to touch on backup lights. More about lights etc on the course.