I built several over the years after being pretty unimpressed with what was available early on..
I ended up just using loose LED's of various intensity, mounted in whatever I had handy, running them off the feeder battery on a timer.
What I've learned;
1. Timers work better than motion detectors; if it's on from, say, dusk until midnight, the hogs accept that and don't care. That as opposed to it turning on every time they show up; they're walking into a dark feeder and then all of a sudden the light pops on? That spooks them if anything does.
2. We've used as many as 30 or so led's on a light; how many really didn't matter to the hogs, just makes it easier to see. We never got to the point where it would drain the battery more than the solar panel would recover during the day. I would certainly imagine this is dependent on battery condition, of course.
3. Color didn't matter; we started with green since that was the prevailing "industry standard", and went through trying every color available at the time. We finally settled on white; we could never tell a bit of difference as far as the hogs were concerned no matter what color was out there, but we could certainly see better with the white lights.
We were doing feeder lights, and the "prevailing wisdom" at the time was a little anemic unit with a half dozen green led's on the feeder; we started there and just evolved it with every new light. If I had to do it all over again, I'd just head to Home Depot and get the solar-powered led landscape dusk to dawn light and just throw it out there, as has been suggested here.