When employing specialty lighting on the tower, the Main Observatory often plays an important role. During the second international "White Band Day" on 10 September 2005, the tower was completely unlit except for the Main Observatory, which was lit with a bright white light. The resulting white ring represented the White Band referenced in the day's name. The two floors of windows that make up the exterior of the Main Observatory are utilized to display words or numbers. When the tower employed lighting to commemorate terrestrial digital broadcasting first being available in the Kantō region on 1 December 2005, each side of the Main Observatory displayed the characters ("chi deji", an abbreviation for "chijō dejitaru hōsō" terrestrial digital broadcasting). More recently, the observatory displayed both "TOKYO" and "2016" to stress Tokyo's 2016 Olympic bid. Primitive images, such as hearts, have also been displayed using the observatory's windows.