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After a collection is built only the items that you have checked enabled to display in the LUNA Viewer will be available to your audience. This can be done automatically in the LUNA Uploader or manually in the Record Editor. To see all items in a collection which are available in the LUNA Viewer simply click on the "In LUNA Viewer" filter. You'll also know an item is being displayed in the LUNA Viewer when you see the little green indicator on the media item thumbnail:
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