Complete Andon / Stack Light Color Code Guide
While color meanings can be customized to fit specific workflows, the following definitions represent the most widely adopted industry standards.
🔴 Red — Stop / Fault / Emergency
Red is the universal signal for a serious problem. When the red light is on, production has stopped or must stop immediately.
Red is triggered by conditions such as:
- Machine fault or breakdown
- Safety hazard detected
- Equipment alarm or error code
- Emergency stop (E-stop) activation
A solid red light typically indicates a confirmed fault that requires direct intervention. A flashing red may signal an alarm condition that is escalating or has not yet been acknowledged. In either case, a red andon signal demands immediate attention from maintenance, a supervisor, or a safety officer.
🟡 Yellow — Caution / Warning / Attention Needed
Yellow — sometimes referred to as amber — signals a condition that isn't yet causing a stoppage but requires attention before it becomes one.
Common yellow-light triggers include:
- Raw material or component running low
- Scheduled maintenance is coming due
- A minor deviation from the standard process
- Quality check required
- Operator needs assistance
Yellow is your early warning system. It gives your team the opportunity to address an issue proactively — replenishing materials, scheduling a maintenance window, or sending a team leader to investigate — before the red light turns on and production halts
🟢 Green — Running / Normal Operation
Green is the light you want to see. It confirms that a machine or workstation is operating normally, within parameters, and producing at the expected rate.
In many facilities, green simply means "all clear" — no action is needed, and operators can focus on their standard work. Some operations also use a flashing green to indicate that production is running but at reduced capacity.
Green is a powerful signal in a lean environment because it creates a baseline. When you walk a production floor and see green lights everywhere, you know operations are stable. When one turns yellow or red, it stands out immediately — which is exactly the point.
🔵 Blue — Quality / Work-in-Progress / Special Condition
Blue is less universally standardized than the other colors, which gives facilities flexibility in how they use it. The most common application is to signal a quality issue or a part ready for inspection.
Typical blue-light scenarios include:
- A quality defect has been detected, and the part is being held for review
- A specific work instruction or special process is being followed
- A part changeover is in progress
- Material handling or a logistics call is needed
Some facilities use blue to indicate a "call for parts," signaling to material handlers or tuggers that a workstation needs resupply. In others, blue alerts quality engineers that an inspection checkpoint has been reached.
⚪ White — Production Count / General Information / Custom Use
White is the most flexible color in the stack light palette. Because it isn't loaded with a pre-existing association the way red or green are, white can be assigned to almost any custom signal a facility needs.
Common uses for white include:
- Production cycle complete (machine has finished a part)
- The operator is on break or the station is temporarily unmanned
- The system is in setup or changeover mode
- A general informational alert that doesn't fall into another category
Some digital andon systems use white to display cycle time information or to indicate that a process is running within a defined tolerance window, distinct from the full "all clear" of green.
Our stack lights also support audible buzzers or sirens as an additional output layer, which is especially useful in high-noise environments where visual signals alone may be missed.
We carry a large variety of Andon Lights and Stack Lights. These are in stock and ready to ship.
Designing an Effective Andon System for Your Facility
Knowing what the colors mean is only half the battle. To make your andon system truly effective, keep these principles in mind:
Standardize across your facility. If blue means "quality hold" in one area and "call for parts" in another, you've introduced confusion. Define your color code once and apply it consistently.
Post the color legend prominently. New operators, visitors, and temporary workers should be able to look up the meaning of each color without having to ask. Laminated reference cards at each station and large-format charts in common areas go a long way.
Respond, don't just observe. An andon system only adds value if your team responds to signals quickly and consistently. Define response time targets for each signal type and hold the process accountable.
Track your andon data. With our Stack-Light Commander software, you can track data. Every time a light turns red or yellow, that's a data point. Tracking andon calls over time reveals patterns — recurring faults, chronic material shortages, quality escapes — that point directly to opportunities for process improvement.
Looking for stack lights and andon solutions for your facility? Explore our product line at stack-light.com. Give us a call. We love to help. (678) 288-9678
