Here's the code used by the widget page:
To use this example, copy the above code to an HTML file and replace the <body> section with your own widget content. Add a call to the openLB() function somewhere as a clickable object, as demonstrated with the <span> in our example. Then, host the HTML online and point to it using your HTML5 widget.
The only other requirement is to have a standard light box link somewhere else in the publication, because without this your viewer won't know to load the light box code. If you do not have any light box links elsewhere, you can "fake it" by simply creating a small link outside of one of the pages of the publication.