In industrial automation and machine-status signaling, stack light and signal tower usually refer to the same general type of industrial signaling device.
An Andon light may use the same type of hardware, but “Andon” can also describe a broader production-status communication or visual-management function.
When selecting this type of product, the practical requirements include:
- how many states need to be displayed;
- which colors are required;
- whether flashing or an audible signal is needed;
- what power supply is available;
- what signal will control the device;
- how the device will be mounted;
- what environmental conditions apply.
| Term | Usually Refers To | What to Keep in Mind |
|---|---|---|
| Stack light | An industrial machine or process status light | A common product name |
| Signal tower | An industrial visual or visual/audible signaling device | Overlaps heavily with stack light |
| Andon light | A visual signaling device used for production status or Andon applications | The hardware may be similar, but Andon can have a broader meaning |
1. Stack Lights and Signal Towers Usually Belong to the Same Product Category
In industrial product catalogs, stack light and signal tower are often used interchangeably.
WERMA, for example, describes modular signal towers as stack lights.[1]
One supplier may describe a product as:
3-color stack light
while another uses:
3-color signal tower
The name alone does not mean they belong to different product categories.
“Stack light” naturally suggests a vertically stacked arrangement of light segments, while “signal tower” more directly describes the device's industrial signaling role.
That distinction can help explain why the names exist, but it should not be treated as a strict product-classification rule.
For purchasing purposes:
The same name does not guarantee the same specifications, and different names do not necessarily mean different products.
2. An Andon Light May Use the Same Hardware, but Andon Can Mean More Than the Light Itself
In the industrial market, Andon light can refer directly to a stack light or signal tower used for production-status indication.
The meaning of Andon can also be broader.
The Lean Enterprise Institute describes Andon as a visual management tool used to communicate production status, abnormalities, and actions that need to be taken.[2]
An Andon signal may be triggered automatically by a machine or initiated by an operator through a button, pull cord, or another input.
Typical applications may include:
- machine status;
- production status;
- operator call;
- material request;
- fault condition;
- maintenance request;
- process assistance.
Colored status lights mounted on a machine or in a work area can provide the visual output for this information. In factory and work-area signaling applications, the same physical signaling hardware may be used for machine-generated status or operator-requested signals.
The Toyota Production System also includes Andon applications for machine abnormalities and operator calls. When a problem is identified, an Andon board can be used to communicate the condition and request a response.[3]
A practical way to understand the relationship is:
A stack light or signal tower can provide the physical signaling hardware. When that signal is used for production status, abnormalities, or operator-response processes, it can also serve an Andon function.
Whether a device is part of an Andon application depends on how the signal is used in the production process, not simply on the shape of the light.
3. Different Manufacturers May Use Different Names for Similar Products
Industrial signaling devices do not always have a single market name.
Product catalogs may use terms such as:
- stack light;
- signal tower;
- tower light;
- signal column;
- Andon light.
These terms overlap to different degrees.
If one manufacturer uses stack light and another uses signal tower, that alone does not mean the products belong to different equipment categories.
The product name helps identify the general direction. The actual specifications still need to be checked.
What About “Tower Light”?
In industrial automation, tower light may also be used for a signal tower or stack light.
The term is broader, however.
Outside machine-status signaling, “tower light” can also refer to mobile lighting towers used on construction sites, road projects, and other outdoor work areas.
For a project involving machine-status indication, using stack light or signal tower usually makes the required product category clearer to a supplier.
4. Move From Product Names to Actual Selection Requirements
Once the requirement is clearly within this type of industrial status-signaling device, the next step is to move from terminology to the actual configuration.
At minimum, confirm:
| Selection Input | What to Confirm |
|---|---|
| Signal states | How many machine or process states need to be distinguished |
| Colors | Which colors are required and in what arrangement |
| Light behavior | Steady, flashing, or other required behavior |
| Audible signal | Whether a buzzer is required |
| Power supply | What AC or DC supply is available at the installation point |
| Control method | Machine wiring, PLC, relay, manual control, or another method |
| Mounting | Installation position, base, and available space |
| Environment | Dust, water, temperature, and other site conditions |
When comparing industrial signal towers and stack lights , define these conditions first, then compare the available layers, colors, control methods, electrical requirements, and mounting configurations.
Two suppliers may use the same product name without offering interchangeable products.
A different name is also not a reason to reject a product if its electrical, control, mounting, and environmental requirements match the project.
5. Use the Term That Matches the Actual Requirement
If the requirement is:
A multi-state visual indicator mounted on a machine or piece of equipment.
stack light or signal tower will usually communicate the requirement clearly.
If the project is centered on:
- production status;
- operator calls;
- material requests;
- abnormal-condition response;
- maintenance requests;
Andon light or Andon system may better match the application context.
Regardless of the term used, a quotation request should not stop at:
I need an Andon light.
That only identifies the general product or application direction.
A more useful requirement would be:
Packaging equipment requiring three machine-status indications; machine-controlled; 24V DC supply; mounting method and environmental protection to be confirmed.
Even if the exact product name is not yet clear, these site conditions can already help a manufacturer narrow the product range.
If a requirement is still unknown, mark it as To be confirmed rather than filling the specification with an estimate.
Frequently Asked Questions
Is a Stack Light the Same as a Signal Tower?
In normal industrial automation usage, the two terms often refer to the same general type of industrial signaling device. Manufacturer terminology may vary, so the actual product specifications still need to be compared.
Is an Andon Light the Same as a Stack Light?
The physical hardware may be the same. A stack light or signal tower can be used in an Andon application, while Andon can also describe a broader production-status communication or visual-management function.
Can a Stack Light Be Used in an Andon System?
Yes. Status lights mounted on machines or in work areas can provide the visual output in an Andon application. Whether the signal is triggered automatically by a machine or manually by an operator depends on the system design.[2]
Why Do Some Manufacturers Call Them Stack Lights While Others Use Signal Tower?
Industrial product terminology varies by manufacturer, product family, and application context. Different names do not necessarily mean the devices belong to different product categories.
References
- WERMA Signaltechnik. Signal Towers and Stack Lights — Modular and Fully Configured. Current WERMA product-category and terminology information. WERMA — Signal Towers and Stack Lights
- Lean Enterprise Institute. Andon — Lean Lexicon. Definition and application of Andon as a visual management tool. Lean Enterprise Institute — Andon
- Toyota Motor Corporation. Toyota Production System. Official Toyota overview of Jidoka, operator calls, and Andon board use. Toyota — Toyota Production System