What are the requirements for the use of stained glass in a green environment?
The practice of putting stained or leaded glass inside insulated glass inserts is potentially damaging to the leaded glass. There seems to be a probability of 1 that the seals will eventually fail and draw moisture into the interior of the IG unit. Moisture, along with the heat entrapment caused by the unventilated space of the IG's interior, is highly destructive for the leaded glass. The National Park Service's "Preservation Brief 33" outlines in detail the potential damage to historic stained glass with so-called protective glazing. Common sense says that the same principles apply to contemporary stained glass. What do you suggest as an alternative?
Instead of trying to put the stained glass in a sealed IG unit, consider using the stained glass as part of a double-pane window assembly which is built up, similar to applying a storm window to the outside of an old single pane window and leaving the single-pane window in place.
The effect of the storm window essentially improves the performance to that of an IG unit, without the issues associated with the thermal seals of an IG unit.
You can also consider installing the stained glass in front of or behind a separate IG unit.