Quick answer: This is a dive light from BigBlue.
A good light brings back the color water filters out and adds a safety margin on every dive. It's essential for night dives, wrecks and caverns, and handy for signaling your buddy on any dive.
Check the battery type, charging and burn time, and inspect the O-rings before each dive. Read How Smart Accessories Improve Every Dive Trip. More options: Dive Lights.