Hi, Alan of cpe1991land! 🙂 If I type really quickly, maybe I will be the first to respond.
In most CCI members' homes, I have observed numerous wall units (glass fronts) and stand alone glass (and metal?) shelving units.
When Floyd and Bernice (of Lichess) visited my home (and collection) a few years ago, one of Bernice's comments was that she observed that none of my sets were in any (glass) cabinets, and who and how often did the sets get dusted... At that time, most of my sets were displayed on open wood shelving - and as I recall - in a basement back room.
So, I took Bernice's comments as a piece of inadvertent advice, and I have been appreciative and glad since then. I have placed many of my sets behind glass door cabinets. Little if any dusting!
Alternative ways to display under glass could be (and I have done this in the past!) under rectangular glass aquariums!
I do not spread the sets around the house because my wife is not crazy about that. In fact, she barely tolerates the sets I have in two room: one in the basement, and one on the first floor.
I have all of my ivory sets in glass cabinets. In the winter (in Vermont), I place at least one or more glasses or bowls of water inside of each cabinet (depending on the size of the cabinet). I try to keep the R.H. at between 30-40 percent. Supposedly, ideal is about 50 percent, but that is difficult to do, and as the weather gets warmer (and is able to hold more moisture), one generally does NOT want to keep glasses of water in the cabinet. It will act as a catalyst / contributing ingredient for fungal growth.
In the winter, limit the use of mechanical humidifiers. Even though 50 percent R.H. is ideal for humans, too much humidity in winter (e.g. N.E. USA) tends to be harmful to interior building components, and of course to some types of chess sets....
If you keep ivory sets in the basement during warm / damp weather, then I suggest either an air conditioner or a dehumidifier. (Do NOT open the basement windows to "air it out" and "ventilate" it during humid daytime weather or damp nighttime weather. Keep the windows closed during those times and run a dehumidifier. Try to keep the humidity below 60 percent (max). 50 percent would be better.
I am not all that knowledgeable about bone sets and wood sets. However, I suspect that too dry or too moist is also harmful. Don't display them near heaters, radiators, wood stoves, etc.
It is difficult to understand why someone would NOT want to display the sets even if the 150 year old sets are currently perfectly protected (at least from light or handling)... that is, unless one is looking at it primarily or only as investment.
I don't know much at all about effects of light on sets. So I will leave that to someone else...
Overall, I would say that sets displayed behind glass, rather than on open shelving is better (less dusting, and better able to control humidity.)
Hope the above is somehow helpful.
John, Vermont.