A brand name for a single
dimmer, autotransformer, often used to provide regulated
voltage on a test bench,

Picture from
Variacs - Staco Variable Transformers.
or as a single manually operated
dimmer, very commonly found dimming the
index strip lights on a
counterweight fly system's
lockrail.
Luxtrol WBD.jpg
http://www.superiorelectric.com/LUXTROL.htm