Tank cover or not

[Aquattro]

I think you risk the chance of cracking the glass if your lights are that close. I also think you'll get tired of cleaning the glass after the first week. No point spending a ton of money on bright lights and then blocking them out with glass. You'll need to evaporate water to cool the tank, and a lid will prevent that. Air exchange isn't an issue really unless you have a rubber gasket on the lid.
Overall, my opinion is a lid has no place on a reef tank. You're just fighting yourself and making things more difficult than need be. I really can't think of a reasn to have a lid at all. JMO