science

Stack light

Stack light is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Stack light rather than just read about it. In short: Stack lights (also known as signal tower lights, indicator lights, andon lights, warning lights, industrial signal lights, or tower 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. They are a form of andon: a manufacturing syst…

Key takeaways

Stack light belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Stack light to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Stack light from memory before moving on to harder problems.

Reference excerpt

Stack lights (also known as signal tower lights, indicator lights, andon lights, warning lights, industrial signal lights, or tower 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. They are a form of andon: a manufacturing system that identifies errors as they happen.

General Stack lights are used in similar applications to beacon lights/strobes, however the information they typically display encompasses more machine/process conditions. Stack lights typically use incandescent, LED or xenon-type strobes as their illumination source. Stack lights are generally columnar structures in a variety of shapes, placing colour-coded indicator segments on top of one another in a "stacked" orientation. A stack light will typically have up to five differently coloured segments to indicate various conditions on the machine or process. Segments in any combination of (typically) red, yellow, green, blue or clear white are actuated independently and are either off, steadily lit, or flashing. Stack lights are passive devices that may be controlled directly by programmable logic controllers, distributed control systems, PC control systems or hardwired to machine controls such as timers, sensors and latching relays. Discrete signals activate illuminated segments at common industrial control voltages (including 12Vdc, 24Vac/dc, 115Vac, 230Vac). Some units support fieldbus networked control through popular industrial networks such as Modbus, DeviceNet, Profibus, CAN-Open or ASi. Flashing control may be provided by the stack light's internal circuitry or externally controlled with timers or logic controllers. Stack lights are available for all types of industrial environments including washdown (IP65) and explosion proof.

Function

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 AMBER: 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.

Applications

Common applications include, but are not limited to:

Productivity monitoring (often rate-based machine output management with parts-per-hour displays). Uptime & downtime monitoring (overall equipment effectiveness) is a very common use for these devices. Warning indication and machine fault management Lean manufacturing - 5S Initiatives In conjunction with SCADA supervisory control systems and user interface/HMIs: SCADA/HMIs provide more specific machine/process status data; stack lights complement them by providing visual/audible feedback away from the machine operator console. Assembly station workcells Maintenance call stations CNC machining equipment and process monitoring and feedback Broadcast studios (commonly used in broadcast radio studios) to display status of things such as a studio on air, live microphones, phone calls and even as a doorbell in an environment where silent indication is critical. Dispatch centers where the dispatcher frequently uses a headset making it difficult to tell when the dispatcher is on the phone or radio. The light will light one color when the radio is keyed and another when on the phone.

See also Andon (manufacturing) IEC 60073:2002 Basic and safety principles for man-machine interface, marking and identification - Coding principles for indicators and actuators https://webstore.iec.ch/publication/587 http://talk.electricianforum.co.uk/downloads/89021-Light%20colours%20from%2060204-1.pdf Engineering/Installation Reference Guide, https://web.archive.org/web/20160304080801/http://www.onyx-industries.com/downloads/StackLightEngineeringReferenceGuide.pdf Lean Manufacturing "Andon", https://www.workerbase.com/post/the-definitive-guide-to-modern-lean-manufacturing-andon-systems Lean Manufacturing Glossary, http://www.gembutsu.com/articles/leanmanufacturingglossary.html Table 3 related to Pilot & Indicator Light Color Coding: http://wp10625799.vwp6873.webpack.hosteurope.de/rafi.de/index.php?id=841&L=1

References

Illustrations

Stack light: Stack light in automated production for in-line quality inspection — Stack light in automated production for in-line quality inspection

Stack light: Various size stack lights — Various size stack lights

Worked examples

Example 1 — a first encounter with Stack light

Start with the simplest possible case. Write down what Stack light claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Stack light before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Stack light ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Stack light

In research: Stack light appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Stack light in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Stack light is common in secondary-school and first-year university syllabi. It links to neighbouring topics Control devices, Industrial automation, Types of lamp, so understanding it makes those chapters shorter.
In everyday life: Look for Stack light outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Stack light in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Stack light means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Stack light out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Stack light in simple terms?

Why does Stack light matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Stack light?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Stack light.