Node Gallery Lightbox
It can be done quite easily. I'm assuming that you are using Drupal 7 and using the Node Gallery as well as the Node Gallery API.


Install Colorbox for Drupal (including the library - follow the instructions on that page).
Now you have to some editing of the site structure (exact paths may vary but the provided paths will work if you are using the default Node Gallery installation settings):
go to admin/structure/file-types/manage/image/file-display (or browse: Admin->Structure->FileTypes->Image [Manage File Display]). Select Node Gallery File Thumbnail and put a check before Colorbox. Scroll down to Display Settings and under Content Image Style select node_gallery_thumbnail and select Per page gallery in the Gallery (image grouping) dropdown. Then Save Configuration.


Slightly complicated but not horribly so.