The Live Lighting Filter allows you to import an image to use as a bump map.
I would also like the option to use an existing layer within the open document as the bump map (Much like the way the Displacement Map filter allows you to use another layer as the source. However I think entering or selecting the layer name in the Lighting filter panel would be preferred over the "Use layers below" approach in the DM filter)
With an imported bump map, you can't make any edits to the bump map without opening it as a separate document. That makes it very difficult to edit the bump map in context of the image you are applying it to.
By allowing an existing layer within the open document to be used as the bump map, you could easily modify it and quickly see the results. Examples: erase a portion of the bump map where you want no texture, alter the contrast of the bump map, rotate, re-size the bump map, etc. all without the trial & error of editing a separate image.
Thank you for your consideration. Love Affinity!