How about a light that complements your GoPro Hero 3 or 3+ and is waterproof up to 40m? Check out the GoPro In The Dark – Knog qudos Action from Knog.

GoPro In The Dark - Knog qudos Action

Knog (bike lights) have produced the qudos action for exactly this purpose.

[qudos] action from knog on Vimeo.

Spec:

150g
Waterproof up to 40m depth (IP68)
3 mode settings
Rechargeable battery
Built for GoPro but conversion mounts available to use with other cameras.

GoPro In The Dark - Knog qudos Action

RRP is $119.95 (US Dollars)

GoPro In The Dark - Knog qudos Action