There are basically two schools of thought on this.
The old traditional way is to have it light up and be seen from as far away as possible [
at night]. The newer ideas seem to be..... a reverse.
While a reverse is certainly a worthwhile thought, it seems silly to me in this instance. Why, if you have a backlit cabinet
sign face, would you blacken out the
sign entirely except for the letters ?? If your lettering were to end up being the size of normal channel letters, then yes, this would work, but the size of most
sign cabinets is smaller and won't do the proper job, so I think keeping the background light in color and go with powerful graphics and/or lettering. The
sign cannot be read from a great distance, but at least you can see a lit up box on the horizon. As you get closer, you'll be able to read it. As for a reverse, you won't be able to read it, until the last moment, so why even bother. However, there will be exceptions and mostly due to location. If the
sign is located at a busy intersection, then maybe, but if it's a well lit intersection, then again it probably won't, again.
Now, if you cover the entire background with a digitally printed graphic, you're probably doing your customer a disservice for any distant or closeup readership. It will look great on a
computer screen, but not in real life at night.