To evaluate its efficiency, a prototype switchable-mirror glass with the size of 0.8 m x 1.2 m was fabricated using DC magnetron sputtering. By introducing 4% hydrogen gas in At, it can be switched from the mirror state to the transparent state within 15 s. We installed the prototype switchable-mirror window in our testing facility and monitored energy consumption of the air conditioner in the room. Preliminary results show that the switchable-mirror window can save about 34% of cooling load compared with a transparent double-glazing window in sunny climate. (C) 2009 Elsevier B.V. All rights reserved.