[Alan Anderson]

Your code has two problems.

The name you assign to the refnum is case-sensitive. You have lowercase "light" where you get the refnum, but you used uppercase "Light" when you set it. Fix them to match exactly.

The other problem is something I can't pin down exactly right now, as I don't have access to LabVIEW. Notice those little red dots on your DIO Open? They're telling you that what you have connected to the function doesn't match the kind of thing it's expecting. It's possible that you accidentally wired up the DIO number constant to the module number input.