I would have to recommend against HID lights for freediving, for the following reason.
When freediving in dark water or at night, it is only usually necessary to turn on your light when you are on the bottom, or at least right before you start the dive. At the end of each dive, at the surface, it is beneficial to turn off your light to conserve battery power.
Now, with an HID light, you cannot turn it on and off during your surface interval. This is because HID bulbs will die in one day if you do that, and further they take forever to ramp up to full power, so even if you turned it on right before your dive, then it wouldn't reach full power until maybe near the end of the dive.
Sure, you could leave the HID light on during your entire session, but this wouldn't make sense either, for one main reason. If you are diving an HID light and having it on all the time, you are wasting tons of battery power. You could use a halogen or LED light, of the same size, and three to four times the power, getting much more light out of the same package. This is, of course, because with an LED or halogen light, you can turn it off during the surface interval.
As an example, if you dove a 2 hour session, with 20 freedives, then you would need either:
1. HID light with 2 hour battery life
OR
2. LED or halogen light with 20 minute battery life
Now, suppose you chose a light with a battery of 50 W-h (watt hours).
Such a light would give you:
25W for 2 hours
50W for 1 hour
100W for 30 minutes
150W for 20 minutes
So, with an HID light, you would be limited to 25W of HID power, however with a halogen light you could use a 150W light and it would be the same size.
Just my opinion!!