Can these be used with a 4x4 vinyl deck post, that is hollow? Thanks

yes they can be used with any 4x4 or 6x6 wood post. The light fits over the post. We also include screws if needed to make sure the lights would never come off. Note however, if your wood post has a 4x4 vinyl sleeve, there are severall options to make the product fit: cut down the sleeve and put the light over the wood post, add a piece of wood between the adapter and the post (also helpful if you have non-4x4 or 6x6 posts) or have the light go inside the vinyl sleeve. Skip West

No, they DO NOT fit over vinyl post sleeve. I just got mine and tried them out and they do not fit. They do fit over the wood post but not the vinyl