A lot depends on the depth of the shelves, obviously, plus the size of the miniatures.
Earlier this year I splurged on a row of display cabinets, and they are only 15cm deep. The height between two shelves is roughly the same, and this works out pretty well. But I reckon, if they were 30cm deep, the 15cm height would not suffice.
Also, I have several larger miniatures/models that are over 15cm tall, so I had to leave the bottom shelf off in each one, to accomodate those. So; if your collection is mainly infantry and mounted miniatures, I'd say 20cm would be workable, but ideally, you'd work with 30cm; as high as they are deep.
But obviously this severely limits the amount of shelf space you'll have available, so the 20cm compromise would be your best bet then...
Oh, and I had wanted to put in LED strips under the front of each shelf, at an angle, to light the shelf below. But because of costs, I had to postpone those. However, now that the cabinets have been in use for nearly half a year, I'm in doubt whether or not I actually should put in lighting at all.
The lighting in the room is pretty sufficient already, and all miniatures are perfectly visible as is.
Now, of course I'm working with 15cm deep shelves, so I have little to no issues with the back rows not being visible, something that 30cm shelves (or deeper) obviously would struggle with.
If you decide to light up the thing, be sure to either do strips on each side, just inside of the doors, or under each shelf. because my previous setup had just the one light in the top, and that was woefully inadequate for the job of lighting anything displayed deeper than 3 shelves down from it. (also, it was halogen and got extremely hot. So, fearing for the integrity of my miniatures and paint jobs, I very, very rarely switched it on, and even then only for a few minutes).
The solution I was thinking of for the new cabinets involved clear poster rails, that could be slided onto the front of the glass shelves. Those have one angled side to them, which would be on the bottom. On that angled side, I would then stick the LED strips. I was planning to string them from the side, with one power wire/cable running top to bottom in one front corner.
I had given no thought to the switching though (which would have been another interesting thing, considering I wanted to switch them all on and off with the room's light switch).
I though the poster rail was rather clever myself, so hopefully it's of help to you...
