A moving light programming term. A User Number is an arbitrary number assigned to a moving light in order to better identify it. Sometimes called a Fixture Number, but this can cause issues with confusion with Instrument Number (Which would be a Location and the number of units one passes before arriving at the proper fixture.). Many programmers set a range of User Numbers to further identity fixtures. All the 200s may be MAC2000s, the 300s may be VL3000s, and so on.