Walk through almost any factory, warehouse, or production facility, and you'll see them. They are the tall, cylindrical status lights mounted on machines, workstations, and assembly lines. They are red, green, amber, or blue. They tell you at a glance exactly what's happening on your shop floor.
They go by a few different names depending on who you ask. The terms Andon lights, stack lights, and tower lights are used interchangeably across the industry.
How They Work
A stack light is mounted to a workstation or on a machine. It's wired, or wirelessly connected to a PLC, a control panel or a button. When a condition changes, the corresponding color lights up.
The entire floor can see it instantly. No radio calls, no walking to find a supervisor. Just immediate, visible communication across the factory floor.
Modern stack lights use LED technology. They are bright, long-lasting, and energy-efficient. Most come with a built-in buzzer for audio alerts, which is especially useful in noisy plant environments where a visual signal alone might be missed.
What the Colors Mean
Color conventions for stack lights and tower lights are fairly standardized across industry. While you can configure colors to mean whatever works for your facility, most operations follow these common standards:
Red means stop. It signals a machine fault, a line stoppage, a safety issue, or any condition that requires immediate attention. When a red light is on, production is not running, and someone needs to respond.
Amber is a heads-up. The machine is still running, but something needs attention soon: a material level getting low, a maintenance window coming up, a quality check due, or a process starting to drift. Amber gives your team time to get ahead of the problem before it turns into a red.
Green means the machine or station is running normally. No faults, no stoppages, nothing needed. It's the color every supervisor wants to see when they walk the floor. A row of
Blue is the operator call light. When an operator needs help, whether it's a question for a supervisor, a part shortage, a tool swap, or anything short of a full stop, they trigger blue.
White is the most flexible color in the stack. Facilities use it for a wide range of custom signals: production target reached, end-of-shift notification, changeover in progress, or any status that doesn't fit neatly into the other four. You define what white means for your operation.
How Andon Lights Are Used in Industry
Stack lights and Andon systems show up in virtually every sector of industrial operations. Here are the most common applications:
Manufacturing & Assembly
The original home of the Andon system. Operators use a button or pull cord to signal machine faults, quality problems, or material shortages. Supervisors and maintenance can respond immediately without waiting to be found. This is the core use case for lean manufacturing and continuous improvement programs.
Warehousing & Distribution
Stack lights indicate pick station status, conveyor faults, and packing line conditions. In busy distribution centers, lights at each station tell supervisors at a glance which stations are active, idle, or need attention.
Food & Beverage Processing
Sanitary environments require quick, clear communication without paper or radio noise. Stack lights signal line stoppages, cleaning cycles, and equipment status on processing lines. IP-rated light can be used in washdown and humid environments.
Medical Device & Pharma
In clean room environments where verbal communication is limited, stack lights signal process status, equipment readiness, and quality holds. Every operator knows exactly what's happening at their station without anyone saying a word.
Automotive
Andon systems originated on automotive assembly lines. They remain a standard fixture in automotive manufacturing, signaling everything from part shortages to line-stop conditions. Every station on a modern automotive line typically has a stack light.
Facilities & Utilities
Pump stations, HVAC systems, and utility rooms use stack lights to show equipment status without anyone needing to enter the room. A green light outside the door means everything is running. A red light means help is needed.
Wired vs. Wireless Andon Lights
Traditional stack lights are hardwired to a machine or control panel. They are reliable and simple, but running conduit and wire across a facility can be expensive and time-consuming, especially in older buildings or when adding lights after the fact.
Wireless Andon systems have changed this. A wireless stack light connects via a radio mesh network. You mount it where you need it, configure it through software, and you're up and running with no electrician required. You can add, move, or reconfigure lights as your operation changes.
- No conduit or wiring runs required
- Install in an afternoon, not a week
- Easily moved or reconfigured as your layout changes
- Andon dashboard shows every light's status in real time
- Every button press is timestamped, giving you data, not just signals
At Stack-Light.com, we carry a full range of stack lights, Andon lights, and wireless Andon systems for industrial applications.