Understanding what you are going to be lighting is the first step in designing a joinery lighting scheme. In shelving you might be lighting specific objects, you might be lighting an array of objects such as books, or you might simply be looking for ambient lighting for a space. A solid block of books can't be lit from behind or directly above where individual items might be better lit with a single spot from above.
How is the joinery constructed?
Looking at shelves again, are the shelves fixed or adjustable? What are the shelves made of? How thick are they. The nature of the joinery is going to have a huge impact on how you light it. An 18mm shelf might not give you enough depth to recess even the shallowest of linear LED fittings. Glass shelves don't allow linear LED to be used directly in the shelves themselves but offer other opportunties.