What do the colours of machine indicator lights and push-buttons mean?

At a glance

Machine electrics

IEC 60204-1:2016 with Amendment 1 (2021)

Coding principles

IEC 60073:2002

Status colours

Red emergency/fault · yellow abnormal · green normal · blue action needed · white general

Emergency stop

Red actuator (also required by US OSHA on hazardous machines)

State, not command

Machine colour coding answers 'what state is the process in, and does someone need to act?' Red means something has gone wrong or an emergency function has operated; yellow means conditions are drifting towards a problem, such as rising temperature or pressure; green means everything is normal. Blue is the odd one out: it does not describe a hazard level but asks for a specific operator action, such as a reset, a material top-up or a maintenance visit. White, and in practice clear lenses, are left for designers to use for conditions specific to that machine. Stack lights on production lines apply the same palette vertically so a supervisor can read a whole hall at a glance.

Why green is not always 'go'

People carry the traffic-light association into control panels, and that is sometimes dangerous. On a machine, a green lamp usually means 'normal', not 'safe to approach'; a machine can be running normally and still be lethal to reach into. Similarly, green on a push-button customarily marks a start or on function, but pressing it is only appropriate when the operator has checked the machine is ready. The coding standard deliberately ties colour to meaning, not to the physical action of pressing, and adds other cues — position, shape, marking, and whether a lamp is steady or flashing — so the colour is never the only signal.

Flashing matters: IEC 60073 uses flashing to draw attention or show that a state is changing, so a flashing green is not the same message as a steady one.

Emergency stop: the one colour everyone agrees on

Emergency-stop actuators are red in every major system — IEC machinery standards, the separate ISO 13850 on emergency-stop design, and US OSHA's colour rule, which requires red for emergency stop bars, buttons and switches on hazardous machines. The shared convention exists because an emergency stop is the one control an untrained bystander may need to find and use. That is also why red should not be used casually for ordinary stop or reset functions on the same panel: every extra red control makes the real emergency stop harder to find in a hurry.

Designing panels people can read

Red, yellow and green are the three colours most affected by the commonest colour-vision deficiencies, and indicator lamps are small, bright and often seen against a dark panel. LED indicators can also look very different from the incandescent lamps the scheme grew up with: a narrow-band amber LED and a red LED can be closer in appearance than their filament predecessors. Good practice therefore pairs colour with position (a consistent order in stack lights), text or symbols on buttons, and distinct lamp shapes. Nothing on this page replaces the standards or a machinery risk assessment.

The data

What goes wrong, and what to do

How to check it yourself

1. Find the machine's documentation to see what each indicator colour is defined to mean.
2. Check that only emergency functions use red actuators.
3. View the panel through a colour-vision-deficiency simulation to see which lamps rely on colour alone.

What the evidence says

Each statement is labelled by kind — established fact, a standard’s requirement, observed market data, a convention, or Colourwise’s own interpretation or analysis — with the strength of the evidence behind it.

• FactStrong evidence

  IEC 60204-1, the general standard for the electrical equipment of machines, is current in its 2016 edition with Amendment 1 of 2021, and IEC 60073 on coding principles for indicators and actuators is current in its 2002 edition.

  Source: International Electrotechnical Commission (IEC) webstore and catalogue; European Standards online catalogue (EN, ISO, IEC, BSI, ASTM listings)

• ConventionModerate evidence

  Common machine-status colour codes use red for failure or emergency-stop conditions, amber for warnings such as over-temperature, green for normal operation, blue for a request for external help or operator action, and white for user-defined conditions, following IEC 60073.

  Caveat: Summarised from a secondary source and not yet checked against the standard itself; confirm with the standard before relying on it.

  Source: Stack light (Wikipedia)

• StandardStrong evidence

  US OSHA requires red for emergency stop bars, buttons or switches on hazardous machines.

  Source: 29 CFR 1910.144 — Safety color code for marking physical hazards

• Colourwise interpretationModerate evidence

  Using red for routine stop or reset controls as well as the emergency stop weakens the emergency stop's visual distinctiveness on a panel.

  Based on: Follows from the purpose of reserving a single salient colour for the emergency function, as expressed across the cited machinery conventions and OSHA's colour rule.

Related questions

Why is blue used on machine indicators?

Blue marks a mandatory operator action, echoing the blue of mandatory safety signs. It tells the operator that something specific must be done, rather than describing a hazard level.

Does a green indicator mean a machine is safe to touch?

No. Green means the process is in its normal state. A machine running normally can still be dangerous; safe access depends on isolation procedures, not indicator colour.

What colour should a stack light's top segment be?

By common practice red sits at the top, with amber and green below, so position reinforces colour. Exact order and meanings should follow the machine's documentation.

Related topics

Go further

Sources

• International Electrotechnical Commission (IEC) webstore and catalogue — IEC (Standards body)
• European Standards online catalogue (EN, ISO, IEC, BSI, ASTM listings) — European Standards s.r.o. (Reference work)
• Stack light (Wikipedia) — Wikipedia (Reference work)
• 29 CFR 1910.144 — Safety color code for marking physical hazards — US Occupational Safety and Health Administration (Official standard or government)

Reviewed 29 September 2026. Colourwise summarises its sources in its own words and does not reproduce standards text or proprietary colour data. Spotted an error? Tell us.