A disco ball (also known as a mirror ball or glitter ball) is a roughly spherical object that reflects light directed at it in many directions, producing a complex display. Its surface consists of hundreds or thousands of facets, nearly all of approximately the same shape and size, and each having a mirrored surface. Usually it is mounted well above the heads of the people present, suspended from a device that causes it to rotate steadily on a vertical axis, and illuminated by spotlights, so that stationary viewers experience beams of light flashing over them, and see myriad spots of light spinning around the walls of the room.
What are now sometimes called "disco balls" were first widely used in nightclubs in the 1920s. They were already in existence and use before then, appearing in a description of a ballroom dance in 1897 in Boston. An example from 30 years later can be seen in the nightclub sequence of Berlin: Die Sinfonie der Großstadt, a German silent film from 1927. In the 1960s, 1970s and 1980s, these devices were a standard piece of equipment in discothèques, and by the end of the 20th century, the name "disco ball" had grown quite popular.
Miniature glitter balls are sold as novelties and used for a number of decorative purposes, including dangling from the rear-view mirror of an automobile or Christmas tree ornaments. Glitter balls may have inspired a homemade version in the sparkleball, the American outsider craft of building decorative light balls out of Christmas lights and plastic cups. The UK television series Strictly Come Dancing and US counterpart Dancing with the Stars award competition winners a "Glitter Ball Trophy".
With the appearance of infrared networks, glitter balls have found a new application, as a method of dispersing the infrared signals.
Pink Floyd used a glitter ball on their 1987 and 1994 world tours. The glitter ball used on the 1987 tour was somewhat larger than normal but nowhere near as large as the glitter ball used on the 1994 tour. This particular glitter ball is one of the largest in the world. 4.9 metres in diameter, it rises to a height of 21.3 metres before opening to a width of 7.3 metres, revealing a 12 kilowatt Phoebus HMI lamp. Both can be seen on the video of each tour: "Delicate Sound of Thunder" and "Pulse" during the song "Comfortably Numb".
U2 also featured a lemon-shaped disco ball on their 1997-1998 PopMart Tour. The band entered the lemon disco ball at the end of the main set and emerged from the lemon disco ball at the start of their encore. The band also released promotional disco balls to promote the band's album Pop, the single "Discothèque", and lead singer Bono also sported the alter-ego of "Mirror Ball Man" during their 1992 tour Zoo TV Tour.
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