I'm surprised no one has suggested this. Your dog is perfectly capable of finding an unlit ball in the dark. You just have to show him how. Teach him to use his nose. It's really easy to teach "find it," and if there's a usual place where you always play ball, your dog should know the general area. We have some woods across the street from my house and my dogs will search for balls I've buried under several inches of leaves until they find them. They ain't usin' their eyes. Teach your dog what the game is and you'll not only never lose a ball again, you may find the ones you've already lost.