@Tamara-IT: you can display gallery images in a lightbox easily using File Gallery.
WordPress comes with Thickbox included - it is a bit dated by today's standards, but works just fine.
When inserting a gallery, just set the link class to 'thickbox' (without quotes) and, if it's not already there, also add 'thickbox' under 'Auto enqueue lightbox scripts for which link classes (separate with commas)?' option on the media settings screen - and that's it :)
I'll add a section about it in the help file, but here's how lightbox support is implemented in File Gallery:
1) register your lightbox script in WordPress (or install a plugin of it)
2) that same script name you used to register lightbox with WP, add it to the 'Auto enqueue lightbox scripts for which link classes (separate with commas)?' option field
3) use that same script name as link class in your gallery
4) File Gallery will try to enqueue that script automatically
I'll still have to implement support for a variety of lightbox scripts, but the basic support is there for most of them.
Hope this helps :)