Yeah, Scott, tough one to answer. Lighting is in the eye of the beholder. It all depends on what you deem enough. So here's my subjective answer with as many caveats as necessary:
Two is enough to give you good light. Four is a bit of overkill, but that's me. I have the "inners and outers" on separate lines so I can control them separately.
These are the flood-type, so the spread on them is rated at 120 degrees. At spreader height, they light the deck bow to stern, plus they put plenty of light out amidships to light the water or deck along side the boat. My thought at first was that I might have to "tilt" one set fore and one set aft--but the spread of light on these is sufficient that that was not necessary. They are $17-$20 a pop, very reasonable compared to typical spreader lights and especially LED-type. Plus, the profile is great on our smaller boats/spreaders.
Now, this isn't daylight, but I can read by them and I'm at the age where my eyes are "dimmer" than they once were.
I put spot lights up on top of the mast to shine down on the foredeck and the cockpit. Those have a much tighter spread that puts a nice 8-10 foot diameter spot from that height. Overkill here? Maybe, but I figure it good to get some "task" lighting at the ends of the boat as well. Again, not daylight, but nice. Figure the worse case, they'll work great to light up your sails to make you VERY noticeable at night.
Best thing, they are VERY lean on the energy usage! Here's a shot with them all lit.
And here's a shot of the fixture at the top of my mast. The spot are mounted at the ends underneath the "deck".
