page_title: Stack light
section_title: Function
hierarchical_section_title: Stack light / Function
caption_attribution_description: English: "Command Tower" 251 Series of Indicating Stack Lights, Onyx Industries
context_page_description: Stack lights are commonly used on equipment in industrial manufacturing and process control environments to provide visual and audible indicators of a machine's status to machine operators, technicians, production managers and factory personnel. It is a form of andon - systems in manufacturing which identify errors as they happen.
context_section_description: Stack lights are used in a variety of machines and process environments; specific colour-coding is assigned by the system designer.
  Commonly used colour codes for machine state conditions include:
  RED: Failure conditions such as an emergency stop or machine fault
  YELLOW: Warnings such as over-temperature or over-pressure conditions
  GREEN: Normal machine or process operation
  BLUE: External help request, where an operator might be requesting raw materials, scheduling or maintenance personnel assistance
  WHITE: User-defined conditions to a specific machine, often related to productivity monitoring
  Optionally an audible alarm buzzer, typically in the range of 70–105dB, may be added to alert machine operators to high priority conditions.
  IEC60073 addresses machine state colour-coding & acoustic alerting, which can be applied to devices including panel pilot lights & stack lights. Machine operator intervention is typically required in red and yellow machine states, as these are normally errors or warnings. Manual intervention is possibly necessary in blue and white conditions.
caption: Various size stack lights
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