The trick of iridized glass is that at night internal electric light is reflected back from the iridized layer in the back of the glass picking up the color of the stained glass on the way trough the glass. This creates completely different impression from the same panel since the non iridized glass in the panel looks almost black (no passing light from the outside), so it's basically 2 panels in one. In this case the "Spark" and the "Fire" as well as eyelets from the background will demonstrate the reflective property of iridized glass and will be highly visible at night illuminated by internal electric light.