Thank you for the opportunity to help you with your question!
bats are actually very blind and don't see well. They use sonar to pick up on the changes within their environment to help them both hunt and navigate. Its actually the behaviors of the moth that makes it easier for a bat to nab to nab them.
typically the main difference between a mercury lamp and a sodium lamp is what they do. A mercury lamp will actually help insects because insects can see in the uv spectrum. this type of lamp emits that. Where as a sodium lamp emits small strikes of lightning that actually kills insects.
So what happens is the insects are allowed to live near a mecury lamp allowing for a larger population of insects. more opportunities for a bat to nab them. Where as the sodium lamps would kill off the bugs making it harder to hunt.
Please let me know if you need any clarification. I'm always happy to answer your questions.