I'm not sure a headlamp is your better illumination option? I don't know where you are located and what your crabbing technique is but I can tell you mine for simple reference. I crab using waders and along the shoreline. So I'm never is water deeper than 3 to 4 feet and typically when its pretty calm. Normally from late August to the end of October. Maybe into November if the season is rocking. I like to use a Coleman lantern myself. I own just about every make and type of headlamp there is and not one of them would be suited to the task. Wouldnt matter if they were spot or floody. Beam profile would be dependent on where my head was turned. That's not well suited to finding crab using my catching method. One needs to be looking left and right with a uniform amount of lumens, sweeping the area to look for changes in bottom color. That's how you detect crabs here. A spot type would only light up the immediate area in front of you and movement out of your peripheral would suffer. A flood might work but once again it would be dependent on ones head movement and where you were looking at.
I have my coleman tucked into the baggy front upper section of my waders between the suspenders. The backside of the globe has a section of aluminum foil to block light from blinding me and the best part of using a propane lantern is the byproduct. Heat. Water around here even in August is still in the upper 50's and in October it's down in the 40's. Don't know about you but my hands are almost always wet, even with neoprene gloves, and they get chilly. The warmth coming off the lantern is just what the doctor ordered for staying out a tad bit longer than I had planned. In case you were wondering I use a large cooler tied to me, floating like a barge behind me, for my welcome dinner hosts. Best of all? It's that season again right now. Hmmmmm,........Dungies. It's whats for dinner!