There are two main ways to share a Lightbox. You can invite specific people to the Lightbox. You can invite people who are already members of your Mediagraph organization, or invite new people. If you invite someone who is not a member of your Mediagraph organization, they will receive an email inviting them to create a Mediagraph account and will be able to join your organization as a restricted member.
You can also create a share link that allows anyone with the link to access the Lightbox without signing in to the account. This is the easiest way to distribute files to a large group of people. However, anyone accessing the Lightbox without signing in will not be able to make comments in the Lightbox.
The easiest way to describe the permissions is to show you. The following video (6:07-10:20) demonstrates the permission behavior.
You can make a share link for a Lightbox (not a Project or an Organizer).