Feeder lights are useful for getting rid of pests, in this case wild pigs. They used red light and often times are motion sensitive or can recharge via solar energy. You put out some food for bait (which is why they are called feeder lights... they are at the pig's feeder) and since the pig cannot see red light they are not startled when the light turns on. It lets you see the pig without the pig seeing you.
I am interested to know about what kind of stuff people have cannibalized to create their own feeders lights, i.e. taking the motion sensor from motion sensitive flood lights, or how they built their own components.