Of course the first consideration is electrical safety. Make sure you use appropriate wiring means and methods, and ground everything really well. The next main design consideration is heat, heat, heat. Stay away from high wattage line voltage incandescent or quartz. Some of the display lighting I've seen really scares me, cheap made, heat bombs, poor designs. A lot of them are cheap made-overseas that have questionable UL listings. Probably the source of some mystery fires. Stick with reputable American manufacturers where possible and install per manufacturers recommendations and instructions. I would recommend LED, T5 (NOT T5HO high output) fluorescent or low voltage (12 volt) lighting because of lowered heat considerations, plus the ability to remote mount the drivers, ballasts or transformers on top of the display case. On T5 and LED, most of the heat is released through the ballast and driver. Particularly the T5 fluorescent lamps themselves are not big heat producers. I'm currently building a lighted display case that I've been designing and thinking about for a couple of years. I have (2) low profile showcase T5 fluorescent fixtures with remote ballasts made by Legion Lighting Co. Inc, I will mount the two fixtures in the top of the cabinet behind a decorative wooden valance and drill a few vent holes in the top for heat venting, this will be the primary general lighting in the case. The remote ballasts will be located in the open on top for efficient heat dissipation. This project also has a top "pediment" or enclosure that will have the main display signage that will also need illumination front and back for visibility. The sign will be lit with low voltage lowered candela LED specialty strip fixtures located concealed in front of the sign with remote drivers located on top of the case. The backlighting will be done with 2 low voltage 12 volt track heads with 15 watt MR11 lamps, again with the remote low voltage transformer located on top of the case. I will drill some vent holes at the top back of the pediment for heat convection.
I you want more concentrated "cones of light" inside the case, there are some good quality small low voltage downlights available that will be safe and do a good job. You can "piggy-back" all of the low voltage downlight fixtures off one larger remote transformer located on top of the cabinet. Sorry for the windiness of this post, just try to share some the thought and work I've put into this.
