Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. The ETC (Electronic Theatre Controls) Source Four (also known unofficially as Source 4 or S4) is an ellipsoidal reflector spotlight (ERS) or Profile (in Europe) , a type of spotlight used in stage lighting. In 1992, the Source Four came out with an improved lamp and reflector design, invented by David Cunningham. The Source Four implements tool-free lamp adjustment, and a rotating, interchangeable shutter barrel. The Source Four is a widely used ellipsoidal reflector spotlight among professional theaters in the United States. Source Four is a registered trademark of ETC (Electronic Theatre Controls).

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