this has been debated endlessly, the use of jQuery is not an issue. An abstraction layer like jQuery buffers the code from browser differences and since it's almost always already in the user's cache and nearly always used for anything non trivial, it's overhead is minimal both from a networking point of view and code path.
Well, I have actually been going through many lightbox clones lately and almost all have a dependency on jQuery. The problem lies in when you are trying to inject a lightbox into a page you are not the creator of and they are using a very old outdated jQuery, causing conflicts. (When used for making browser extensions etc). This would be perfect for me if it was not dependent on jQuery and loaded iFrames and inline html (other options out there are bloated and outdated), but regardless, awesome job and thank you for the contribution :)