The content here can be crawled and read properly by search engines. The problem in the normal implementation is that the contents of this popup can get indexed and when visited is a very plain page with no other site elements.
All bots and all types of cralwers will see this page. This page detects the referring URL and if this content is accessed from within the page calling this Lightbox, it will appear as is. But when clicked from a different source, this will redirect to a page with the same content but with the complete site elements.
The referring URL of this page is:
See how this page looks like when accessed diretly or from a search engine result link.
If ever you got to this page by accident and has no idea what this page is all about, please visit the complete example on doing SEO for Greybox (Lightbox JS-like content).