What are Stack Lights?

Stack lights, also known as signal tower lights, warning lights, indicator lights, etc., are columnar constructions of various shapes that stack colour-coded signal elements on top of the other in a “stacked” pattern. A stack light will often contain up to five different coloured segments to signify different machines or process conditions. Independently operated segments in any combination of usually red, yellow, green, blue, or clear white are either off, continuously on, or flashing. Internal circuitry in the stack light can govern flashing, timers or logic controllers.

In industrial manufacturing and process control operations, stack lights are often implemented on equipment to offer visual and aural indicators of a machine’s status for the workers. It is a type of andon, which are production systems that detect problems as they happen. Stack lights are similar to beacon lights/strobes in that they display additional machine/process statuses, but the information they display is often more extensive. The illumination source for stack lights is usually incandescent, LED, or xenon-type strobes. LED produces brighter light while using less energy, therefore, it is also used for patlite revolving light and stack lights.

Patlite Revolving Light


Stack lights are utilised in different equipment and process environments, with the system designer assigning unique colour coding according to it.  The following are some of the most widely used colour codes depending on the machine state conditions: Faulty conditions such as an emergency shutdown or a machine fault are indicated in RED; YELLOW shows warnings like high pressure or high temperature; GREEN means that the machine or process is running normally; BLUE refers to the operator requesting for external support like raw materials or maintenance personnel assistance; WHITE is user-defined circumstances applied to a particular machine, frequently in the context of productivity tracking. A loud alarm buzzer, often in the 70–105dB range, can be provided as an option to alert machine workers to major priority situations.

IEC60073 specifies machine status colour-coding and audio alerting for devices such as panel pilot lights and stack lights. In red and yellow machine states, which are usually errors or warnings, machine operator involvement is usually needed. In blue and white circumstances, manual intervention may be required.


What places use the stack lights?

  1. Monitoring Productivity: It is usually rate-based machine output administration with parts-per-hour displays. Stack Lights are frequently used for measuring equipment effectiveness.
  2. Machine fault management and warning indication
  3. Workcells in assembly stations
  4. Stations for maintenance alerts
  5. Broadcast studios: It is used in the studios to show the status of items. For instance, on-air studio, live microphones, phone conversations, and even a doorbell in an atmosphere where silence is crucial.
  6. Monitoring and feedback on CNC machining equipment and processes.
  7. In cooperation with SCADA supervisory control systems and graphical user interfaces/Human Machine Interfaces (HMIs): More detailed information on the status of machines and processes are given by SCADA/HMIs. They are supplemented by stack lights, which provide visual and aural input from the manufacturing engineer console.

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