A friend asked me today how I attach my lights to my shelves where I grow my seedlings.
The shelves themselves aren't solid - they're a grid. So I bought some s-biners and chain. S-biners are similar to a s-hook, except that they have a closure that you can open by pushing, just like a carabiner. This means I don't have to worry about bumping a light or chain and the hook slipping, causing the light to fall.
I hook the s-biner to the shelf above and then attach the chain to the other end of the s-biner. This makes it easy to raise and lower the lights as necessary. Them a second s-biner connects the chain to the light.
I just bought a pack of s-biners at Home Depot that were the perfect size to go in the holes that are already in the shop lights. They come with a s-hook, but I knocked the hook off a half dozen times before I even got them set up. The s-biners work much better and fit in the same hole.
The lights come with a chain and I think on some of the lights I just went ahead and use that chain. But mostly I've gone and bought 2' or so sections of chain from the bulk area at Home Depot. You don't need a heavy duty chain since the lights aren't that heavy and you're going to be using two for each light. So it's pretty cheap to buy and they cut it for you.
Hope this helps. :)