(3) Light: Natural crystal vertically placed in the sun, no matter from which Angle it can release beautiful brilliance. Fake crystals don't.
In addition to the multiple panes of glass, insulated window units also feature low-emissivity (low-E) coatings on the glass surfaces. These coatings help to reflect heat back into the room, further reducing heat transfer through the windows. Low-E coatings also help to block harmful ultraviolet (UV) rays, which can fade furniture and flooring over time.
Crystal is a crystal of silicon dioxide, and glass is just a molten mixture containing silicon dioxide.