Andon & Stack Light Colors: Map Machine Status Before Choosing Colors

1. Define the Status Before You Choose the Color

List the states people actually need to recognize.

For example:

• running
• waiting
• fault
• maintenance
• material shortage
• assistance request

Do not assign colors yet.

First decide what role each state has:

If the application truly has a fourth state that needs its own visual indication, check whether a 4-layer red-yellow-green-blue LED Andon signal tower matches the status structure.

The decision should not start with:

Start with:

Does the site actually have a fourth state that people need to distinguish?

“Waiting” is a good example.

Waiting for the next normal process step may still be a normal state.

Waiting because of missing material, a blockage, or required operator action may be an abnormal or action-required state.

The state name does not choose the color. Its meaning on the site does.

2. What Red, Yellow, Green, Blue, and White Commonly Mean

IEC 60073 provides general coding directions for indicator colors.

For signal-tower selection, these are the useful points:

Red does not always mean one specific fault.

Green does not always mean “machine running.”

Green can represent normal operation, ready status, or another satisfactory condition.

Blue also does not automatically mean “help.”

It is better used for a condition where:

Someone is expected to carry out a clearly defined action.

White depends even more on local definition. Cycle complete, inspection, setup, or another informational state may use white, but the meaning should be documented.

3. Keep the Status Map Simple and Clear

Being able to show more states does not mean more colors and combinations should be used.

More visual combinations ≠ clearer status information.

A state deserves its own visual signal when it changes what people need to understand or do.

If two states do not change the operator’s response, they may not need separate colors.

Once the mapping is defined, document it and keep it as consistent as practical across related equipment.

For example:

This is only a site-specific example, not a universal color table.

A color is useful only when people know what it tells them.

4. Match the Status Map to the Signal Tower

Once the states are defined, move to product selection.

Use the multi-layer Signal Tower / Stack Light range to narrow the options by layer count, color structure, and sound configuration.

Confirm four things:

• how many visual states need separate indication
• which colors are required
• whether the color order matters
• whether any state also needs an audible warning

For three states that fit a red / yellow / green mapping, a 3-layer red-yellow-green Stack Tower Light can be checked against the application.

If more states or a custom color arrangement are needed, use a configurable structure.

Not:

If one state also needs sound, evaluate the buzzer requirement separately.

Color meaning and buzzer control are separate decisions.

5. What to Confirm Before Ordering

Do not stop at:

How many colors does this signal tower have?

Ask:

What does each color need to tell the operator?

Frequently Asked Questions

What do red, yellow, and green stack lights usually mean?

Common industrial directions are:

• Red: danger, emergency, fault
• Yellow / Amber: warning, abnormal condition
• Green: normal, satisfactory condition

These are general directions, not fixed machine-state names that every application must use.

Is there a universal Andon color code?

No single fixed color table applies to every factory and machine.

IEC 60073 provides general color-coding directions, while the actual machine or process states still need to be defined for the site.

What does blue mean on a signal tower?

Blue is generally associated with a condition that requires a defined action.

The actual action may be assistance, material replenishment, inspection, or another site-defined task.

What does white mean on a signal tower?

White has no fixed universal machine-status meaning.

If white is used, its meaning should be clearly defined and documented for the site.

Can a company define its own signal-tower color meanings?

Yes. The specific mapping can be defined around the site process, while still taking established industrial color directions into account and keeping the mapping consistent across related equipment where practical.