Coleman North Star will give the best results when they aren't showing well. If the clams are showing...any old headlamp will work. The problem with headlamps that I've seen, is sometimes you need that little bit of side-light, or shadow to see them well...especially in the surf.
If you are using one of the newer propane lanterns, make sure you drill a few holes in the flange of the base. If you don't, you will set it down, dig your clam, pick it back up, and the base will suction to the wet sand, and pull off. Next wave comes, and now you need a new base for your new Northstar lantern. Or worse yet, you catch a glimpse of the base, go splashing after it, and a little bit of water hits the globe of your lantern...now you need one of those too!
I saw a guy a few years ago that had THE best lighting setup I've seen. It was a handtruck with pneumatic tires, a full sized battery, and at least a dozen led flood lights mounted all around it. We stayed about 30-50 yards away from him, and dug our limits without turning on a light. It was an amazing sight. If I had the money he had wrapped up it that set-up...I'd just go buy clams!